Fig. 5.1
Drawings of different types and subtypes of ONSMs according to their location. For more description of each type, please refer to the text. Upper: Type I, purely intraorbital lesions. Type Ia is a flat tumor extension around the optic nerve (one patient, left). Type Ib is widespread; it presents as a large bulbiform mass around the optic nerve (center). Type Ic is an exophytic tumor on the optic nerve (right). Center: Type II, intraorbital ONSMs with extension through the optic canal or superior orbital fissure. Type IIa represents an intraorbital tumor with growth through the optic canal (left), and Type IIb represents tumors of the apex, superior orbital fissure, or cavernous sinus (right). Lower: Type III, intraorbital lesions with widespread intracranial tumor extension. Type IIIa ONSMs are intraorbital with intracranial extension to the chiasm (left), and Type IIIb lesions are intraorbital with widespread intracranial extension to the chiasm, contralateral optic nerve, and planum sphenoidale (right) (Schick et al. [1] with permission)
Type I is located purely intraorbitally. Type Ia is restricted to a flat extension around the optic nerve. Type Ib is manifested as a large bulbiform mass, growing concentrically around the optic nerve with marked proptosis. Type Ic shows exophytic tumor growth upon the optic nerve (◘ Fig. 5.2).
Fig. 5.2
Preoperative imaging of the right-sided ONSM Type Ic. a Preoperative axial CT scan, b T1 axial MRI without contrast, c T1 axial with contrast, d T1 sagittal with contrast, e T1 coronal fat suppressed. The surgical approach for this tumor would be lateral orbitotomy (see ◘ Fig. 5.3)
Type II is located intraorbitally with extension through the optic canal or superior orbital fissure. Type IIa manifests as an intraorbital tumor with tumor growth through the optic canal. Type IIb involves the orbital apex and the superior orbital fissure and sometimes even infiltrates the cavernous sinus.
Type III is located intraorbitally along the whole length of the optic nerve to the globe (not only within the apex) with large intracranial tumor extension (more than 1 cm). Type IIIa extends to the chiasm. Type IIIb involves the chiasm up to the contralateral optic nerve and planum sphenoidale.
Therapeutic Options
The loss of vision in ONSMs is a question of time. Treatment options can be radiotherapy, surgery, and observation. If the visual function is good, observation alone can be employed in intraorbital ONSMs until progression is apparent. The role of radiotherapy has to be reevaluated and should be offered to adults once mild vision loss develops in intraorbital ONSMs.
Surgery with decompression of the optic canal and intracranial tumor resection is still favored for tumors with intracanalicular and intracranial extension [2].
Tumors with exophytic intraorbital mass are amenable to be excised via a lateral orbitotomy (◘ Figs. 5.2 and 5.3).
Fig. 5.3
Area of removing the lateral orbital rim for lateral orbitotomy. a Schematic view, b intraoperative view
Prechiasmatic transection of the optic nerve might offer a surgical treatment option to control tumor growth (see Surgical Technique).
In cases of residual or recurrent tumor growth, surgery should be followed by stereotactic fractionated radiotherapy (SFRT).
Surgical Technique
In the last years, we changed our technique of decompression, performing extradural pterional decompression of the optic canal in the first stage of the surgery. This extradural drilling is much easier, more extensive, and safer for the optic nerve, avoiding any damage to the optic nerve. The second step remained intradural with tumor removal (◘ Fig. 5.4).
Fig. 5.4
a T1 axial MRI scan with contrast of the left-sided ONSM Type II. b Intraoperative view before tumor removal, c after opening the arachnoid layer, d after extradural optic nerve decompression and intradural removal of the intracranial tumor, e covering the drilled optic canal with autologous fat (OSM optic sheath meningioma, II optic nerve, ICA internal carotid artery)
In tumors without intracranial extension, an extradural pterional approach was favored with sphenoid ridge drilling, posterior orbitotomy, decompression of the superior orbital fissure, and unroofing of the optic canal.
As we have explained above, for tumors with exophytic laterally located intraorbital mass, we prefer the lateral orbitotomy approach (◘ Figs. 5.2 and 5.3).
In blind patients with disfiguring painful proptosis, a prechiasmatic transection of the optic nerve was performed intradurally, and the intraorbital part of the tumor was removed as well [3]. The intraorbital optic nerve was transected just behind the globe and deep in the apex and also intradurally 2–3 mm anterior to the chiasm. Tumor freedom of chiasm in preoperative magnetic resonance imaging (MRI) with contrast is the most important criterion for this surgical method (◘ Fig. 5.5).
Fig. 5.5
T1-weighted MRI scan showing a homogenously contrast-enhancing ONSM (right) growing from the orbit through the optic canal to the chiasm. The chiasm itself is still tumor-free. a Axial view, b sagittal view
Summary
Our classification system differentiates the intraorbital, intracanalicular or intrafissural, and intraorbital and intracranial types of ONSMs.
Surgery with decompression of the optic canal and intracranial tumor resection is favored for tumors with intracanalicular and intracranial extension.
5.1.2 Tuberculum Sellae and Planum Sphenoidale Meningioma
General Information
Approximately 25% of the anterior skull base meningiomas originated from tuberculum sellae and planum sphenoidale . Women are affected three times more often than men. The disease is diagnosed in the fourth or fifth decade. The tumor originates from the tuberculum sellae, chiasmatic sulcus, limbus sphenoidale, and diaphragma sellae. Tuberculum sellae meningiomas very commonly extend into both optic canals—a problem that is underestimated in published reports. The new classification system introduced recently by Sekhar et al. has considered also the extension of the tumor into optic canals [4] (◘ Fig. 5.6a–c). These tumors tend to displace the optic chiasm posteriorly and the optic nerves laterally and superiorly.
Fig. 5.6
Illustrations showing the new classification system for planum sphenoidale and tuberculum sellae meningiomas. a (Class I): Showing a <2 cm tumor, with no extension into the optic canal and no ICA or ACA encasement. b (Class II): Showing a >4 cm tumor, with >5 mm extension into the right optic canal, and >180° encasement of the right ICA. c (Class III): Showing a >4 cm tumor, with >5 mm extension into both optic canals, >180° encasement of bilateral ICAs or ACAs, and bone invasion with extension into the sphenoid (Mortazavi et al. [4] with permission)
Clinical Signs and Symptoms
Visual loss in one eye with optic atrophy is the initial and most common symptom. In most patients, visual loss has an insidious onset, and the course is progressive. It may, however, be acute or fluctuating. Monocular blindness may be present in half of the patients before surgery. Incongruity and asymmetry of the visual field defect are common findings.
Diagnostics
Preoperative ophthalmological examination should consist of testing the patients’ visual acuity, fundoscopy, and Goldmann perimetry for visual field defects.
Oculomotor function should be evaluated preoperatively along with other neurological functions. Endocrinological tests (adrenal, thyroid, and gonadal axes, specific gravity of the urine, and fluid balance) should be done preoperatively and at 1 week and 3 months postoperatively.
All patients should be evaluated by computed tomography (CT) and MRI with and without contrast (◘ Fig. 5.7). In many cases, high-resolution CT shows the hyperostosis of the planum sphenoidale and tuberculum sellae or calcification within the tumor. Both T1- and T2-weighted MRI should be done in three planes to analyze the relation to vascular and neighboring structures and the evaluation of tumor extension to both optic canals. The enlargement of the optic canal should be evaluated in preoperative CT scan with bone window.
Fig. 5.7
Post-contrast T1-weighted magnetic resonance imaging showing a tuberculum sellae meningioma. a Sagittal view, b coronal view
Therapeutic Options
For the time being, we believe that the role of microsurgical decompression is still the best choice of treatment providing optimal tumor management and visual recovery.
The indications for endoscopic approaches are tumors smaller than 2 cm situated on the midline with no extension into the optic canal and no vessels encased in tumor.
This method has the major drawback of having very high rates of cerebrospinal fluid (CSF) fistulas (up to 30% depends on the center’s experience).
Surgical Technique
We prefer the approach to these tumors through a unilateral frontotemporal, on the side of visual deterioration. In bilateral involvement, the right side is preferred [5].
In some special cases with asymmetric ipsilateral tumor growth under the optic chiasm, we prefer to approach the tumor from the contralateral side for better visualization of the tumor.
The drainage of CSF is done by opening the basal cisterns. Sylvian fissure is routinely opened, and the M1 segment of the middle cerebral artery is exposed (◘ Fig. 5.8, Step 1). The internal carotid artery (ICA) is identified (Step 2), and this leads to the exposure of the ipsilateral optic nerve (Step 3), which might be covered by the tumor. The anterior tumor capsule is opened, and the basal blood supply is interrupted by lifting the tumor and coagulating the feeding arteries (Step 4).
Fig. 5.8
a Schematic drawing of the target areas visible through a pterional approach (intradural structures left sided and bony structures right sided). b Anatomical sketch of the tuberculum sellae meningioma with adjacent structures (the brain stem and its vessels are retracted). Surgical steps: (1) identification of the M1 segment, (2) internal carotid artery bifurcation, (3) ipsilateral optic nerve and optic canal, (4) interruption of the blood supply and debulking, (5) contralateral optic nerve, (6) dissection from the skull base along the interoptic fold, (7) dissection of the arachnoidal plane from the ipsilateral optic nerve, (8) dissection from the A1 segment and (9) from the chiasm (see also the detailed description of steps in the text) (Schick et al. [5] with permission)
The tumor is further debulked to reduce its volume until the contralateral optic nerve became visible (Step 5). The tumor located medial to the ipsilateral optic nerve is then removed from the skull base (Step 6).
This step was followed by the dissection of the arachnoidal plane from the ipsilateral optic nerve (Step 7). After interruption of the basal blood supply, the tumor became soft and thus could easily be detached from the arachnoid plane of the gyrus rectus, the A1 segment of the anterior cerebral artery (ACA), or the anterior communicating artery. Finally, the tumor is removed from the A1 segment (Step 8) and the chiasm (Step 9) (◘ Figs. 5.8 and 5.9). The protection of the optic and chiasmatic blood supply is extremely important to preserve vision.
Fig. 5.9
Intraoperative view of the tumor presented in ◘ Fig. 5.2. a Tumor exposure, b complete tumor removal with exposure of the ACOM, A1 and A2. c Changing the microscope view and patient’s position to expose both the optic nerve and ICA (pay attention that with 30° head rotation in pterional approach, the contralateral ICA seems to be medial to the contralateral optic nerve) (ACOM anterior communicating artery, ICA internal carotid artery, II optic nerve)
Particularly, the small vessels from the carotid artery to the optic nerve have to remain in their arachnoidal layer and should not be occluded. In cases of hyperostotic planum sphenoidale, the basal dura was excised, and the bone was drilled away. The defect was covered with fat, TachoSil (absorbable fibrin sealant patch), and fibrin glue.
In optic canal involvement, the first 3–5 mm of the optic canal, which is fibrous, is opened. The bony roof is drilled away if there is further tumor extension. The ophthalmic artery below the optic nerve is exposed and preserved. If necessary, the optic nerve sheath is opened until the annulus of Zinn is reached and the tumor around the optic nerve is carefully removed. In contrast to ONSMs, the tumor mass in the optic canal in tuberculum sellae meningiomas can easily be dissected from the optic nerve.
Summary
In the majority of patients with tuberculum sellae meningiomas, total resection may be achieved through a unilateral pterional approach with minimal complications.
5.1.3 Sphenoid Wing, Clinoidal, and Tentorial Fold (TF) Meningiomas
General Information
Sphenoid wing meningiomas account for more than 20% of all intracranial meningiomas. Sphenoid wing and clinoidal meningiomas are classified based on their origin along the sphenoid wing as clinoidal, middle, and lateral sphenoid wing lesions. The more medially located clinoidal meningiomas represent a distinct clinicoanatomic entity, and historically, the resection of these lesions has been associated with significant morbidity and mortality and advances in cranial base surgery.
Al-Mefty classified clinoidal meningiomas into three categories based on the anatomic site of origin and degree of surgical difficulty: Type I, with severe adherence to the carotid; Type II, with the presence of an interfacing arachnoid plane between the tumor and the carotid artery; and Type III, originate at the optic foramen and extend into the optic canal and at the tip of the anterior clinoid process.
Clinical Signs and Symptoms
Visual disturbance is present in the majority of patients, ranging from slight decrease of vision and partial field defect to complete loss of vision. Other symptoms, in the order of frequency, included seizure, headache, anosmia, cognitive deficit, diplopia, dizziness, proptosis, and gait disturbance. Anosmia and cognitive defects are mainly present in tumors of giant sizes, extending into multiple regions.
Diagnostics
Preoperative MRI with and without contrast and magnetic resonance angiogram (with time-of-flight sequence) is used to determine the tumor location, size, and involvement of surrounding structures. These structures mainly included the ICA, ACA, optic canal and nerves, and the surrounding brain tissue.
Preoperative CT scan with thin slices (1 mm, multislice CT) is very useful to clarify the bone involvement (hyperostosis) and also the involvement of the optic canal and planning the surgical strategy.
Surgical Procedure and Technique
Nowadays, we do not recommend the cranio-orbital zygomatic approach for the resection of clinoidal or any type of sphenoid wing meningiomas. Although this provides the surgeon with a low-based approach, multiple avenues of dissection and minimal brain retraction are, however, very destructive and time consuming. We believe that a pterional approach with wide opening of the dura toward the basis provides a suitable corridor to remove different types of clinoidal and sphenoid wing meningiomas. Intraoperative visual-evoked potential (VEP) is the new routine monitoring technique that we use during the operation around the optic nerve (◘ Fig. 5.10).
Fig. 5.10
Intraoperative use of VEP during microsurgery of meningioma around the optic nerve
To achieve the optimal visual outcome in microsurgically resected meningiomas involving the optic nerve, wide bony extradural decompression of the optic canal with or without anterior clinoidectomy [6] (180–270° optic nerve decompression depends on the clinoid process anatomy and involvement) might be advocated (◘ Fig. 5.11, ◘ Video 5.1).
Fig. 5.11
a Illustrative anatomy centered on the anterior clinoid process and surroundings; intracranial view from dorsolateral to anteromedial. The angle between anterior and middle cranial fossae has been flattened to allow a drawing of the neurovascular structures rather side by side and not, as in reality, hidden by each other. The dura mater of the skull base resected: OC optic canal, ACP anterior clinoid process, SOF superior orbital fissure, LSW lesser sphenoid wing, OTPF orbitotemporal periosteal fold, FD frontal dura, TD temporal dura. b Illustrative anatomy after resection of ACP and opening of the SOF, as well as transection of OTPF. This drawing shows the amount of bone that is drilled during the stepwise procedures as described. This technique not only affords access to the distal dural ring of the ICA near the optic strut but also facilitates a wide decompression of the SOF and the OC. OS optic strut (right side) (Lehmberg et al. [6], Springer)
It can be performed in different stages of operation depending on the tumor size and intraoperative bleeding from the tumor.
This procedure increases the maneuverability of the optic nerve and carotid artery at their intradural entries. Moreover, it reduces dramatically the intradural bleeding from the tumor during removal (extradural devascularization).
◘ Figure 5.12 shows the preoperative MRI of the patient with large left-sided medial sphenoid wing meningioma with extension to the TF (◘ Fig. 5.12a–c).
Fig. 5.12
Preoperative MRI of the patient with large left-sided medial sphenoid wing meningioma with extension to the tentorial fold. a, b Axial view, c coronal view
We prefer to do the surgical approach via a unilateral frontotemporal craniotomy .
Craniotomy is extended to the middle of the orbital rim and 1 cm above the margin.
After opening the dura, the Sylvian fissure is frequently split by the tumor.
The first step (plane) is the coagulation of the tumor origin on the dura of the medial sphenoid wing (dura of the skull base). This step is very important, as it results in tumor devascularization and softness.
We usually start the coagulation of the tumor origin from the temporal skull base. The coagulation of the tumor from the dura at the base should be continued until encased carotid artery and optic nerve appear. The direction of bipolar coagulation should be toward the tumor and away from the vital structures. Water irrigation is very important to avoid heat injury to these structures. If it is not easy to find the optic nerve, it is useful to follow the olfactory nerve backward until it crosses the optic nerve.
Intraoperative Doppler sonography is very useful in many difficult cases to find the encased carotid artery. After the identification of the optic nerve and carotid artery, oculomotor nerve should be identified at its entrance to the cavernous sinus (oculomotor cistern, ◘ Fig. 5.13a).
Fig. 5.13
Intraoperative view of the tumor presented in ◘ Fig. 5.12: a After coagulation of the tumor origin and partial removal (Step 1 in text). b After total tumor removal with identification of cranial nerves II–IV and ICA bifurcation (Step 4 in text). The course of cranial nerve IV should be identified before removal of the tumor extension into the tentorial fold
The second step (plane) is the coagulation and shrinkage of the tumor capsule. The M2 segment of the medial cerebral artery should be also identified. Following this segment (M2) to the proximal is very helpful in the final identification of the M1 segment and carotid bifurcation. Now, the tumor should be debulked with the CUSA (cavitron ultrasonic surgical aspirator ). In this step, the following maneuvers should be continued over and over: coagulation and shrinkage of tumor capsule, pushing the capsule to the tumor cavity, and debulking with CUSA.
The third step (plane) is the tumor removal around the carotid artery and optic nerve and finally carotid bifurcation and A1 (◘ Fig. 5.13b).
If the tumor extended to the tentorial notch (see the discussion in the following part), the fourth step should be the identification of the trochlear nerve toward tentorial notch and the removal of the tumor in this part (◘ Fig. 5.13c).
In clinoid process meningioma or small medial sphenoid wing meningioma with the involvement of the optic canal, we prefer to perform extradural pterional decompression of the optic nerve in the first stage of operation before opening the dura.
TFM (Tentorial Fold Meningioma): A Unique Entity
From a surgical perspective, TFM or medial sphenoid wing meningiomas with extension to the TF are a unique entity of tumors. They involve the supratentorial and infratentorial space and often are in close contact to the cavernous sinus, cranial nerves, and mesencephalon. Complete resection is challenging and can be hazardous. Surgical outcome is related to a topographical classification.
We classified this tumor according to tumor extension in three different types: Type I (TFMs with compression of the brain stem), Type II (with extension into the anterior portion of middle fossa), and Type III (a combination of Types I and II; ◘ Fig. 5.14).
Fig. 5.14
TFM (tentorial fold meningioma) classification: Type I, TF meningiomas with origin in the dorsal portion of TF; Type II, with extension into the anterior portion of the middle fossa; and Type III, a combination of Types I and II (II optic nerve, III oculomotor nerve, IV trochlear nerve) (Hashemi et al. [7], Springer)
Surgical Technique
In the majority of patients with TFMs, total resection can be achieved through a pterional (for Type II), subtemporal (for Type I), or combined (for Type III) approaches but with a high rate of permanent morbidity.
In the first step, the trochlear nerve that is usually covered by the tumor should be identified and preserved below the tentorial edge. In some cases, elevation of the tentorium with a suture is very helpful to identify the trochlear nerve below the TF.
In cases in which it is difficult to find the oculomotor nerve, following the fourth nerve to the anterior is useful to find it. In cases with tumor extension below the tentorium (Type III), after the identification of the trochlear nerve, the tentorial dura behind the dural entrance of the trochlear nerve is divided in the direction to the petrous apex to remove the infratentorial part of the tumor. After complete tumor removal, the abducens nerve can be identified at the entrance of Dorello’s canal.
Summary
Due to the close proximity to important neurovascular structures, sphenoid wing meningiomas, especially medial sphenoid wing meningioma, with the involvement of the clinoid process and optic nerve require special surgical attention and technique to achieve the highest level of safety with maximal extent of resection.
We should always keep in mind that the primary surgical goals and principles include at first the preservation of the quality of life followed by the preservation of neurological functions. Nevertheless, the resection should be performed as radical as possible to gain a good tumor control. Radiotherapy should be offered as an effective alternative treatment in recurrent tumors.
5.1.4 Sphenoorbital en Plaque Meningiomas
General Information
Meningiomas en plaque (sphenoorbital meningiomas) constitute approximately 4% of all meningiomas. These are complex tumors involving the sphenoid wing, orbit, and cavernous sinus, which make their complete resection difficult or impossible. Sphenoidal hyperostosis that results in incomplete resection makes these tumors prone to high rates of recurrence postoperatively.
We believe that the surgical treatment of sphenoorbital en plaque meningiomas is safe and effective: in our series of more than 100 patients, a low morbidity rate was recorded and visual function improved in approximately two-thirds of the patients.
Clinical Findings
The duration of symptoms is usually long because of the minimal discomfort that is produced. Proptosis is the initial and most common symptom followed by cosmetic deformity with no neurological deficits. Finally, marked hyperostosis of the sphenoid bone and diffuse tumor invasion lead to cranial neuropathies caused by foraminal encroachment. The most common cranial nerve deficit is optic neuropathy.
Surgical Technique
For this type of meningioma, pterional approach has been well described in the literature.
For the use of CT scan-guided cranioplasty (CAD implant), we use always a special gauge as a guide for pterional craniotomy (◘ Fig. 5.15).
Fig. 5.15
Reconstruction of the sphenoid wing, lateral orbital wall, and orbital roof using individual preordered CT scan-guided cranioplasty (CAD implant, Biomet)
The first step of the tumor surgery is purely extradural bony decompression. The hyperostotic bone is drilled away until the normal shape of the bone (compared with the contralateral side) is remodeled. Craniotomy is usually extended to the middle of the orbital rim, and the dura mater is dissected from the sphenoid bone. The first steps of the operation are entirely extradural and involve drilling the lesser wing of the sphenoid bone down to the superior orbital fissure and the bone of the lateral orbital wall down to the foramen rotundum until the beginning of the inferior orbital fissure is exposed.
Then, a partial anterior clinoidectomy is performed (◘ Fig. 5.16a, b), and the optic canal is unroofed extradurally whenever tumor involvement is present. Do not open the periorbita at this stage.
Fig. 5.16
a Preoperative CT scan of a patient with right-sided huge sphenoorbital meningioma with involvement of the right optic canal. b Postoperative CT scan (axial view) after extradural tumor drilling and anterior clinoidectomy (arrow shows a removed part of clinoid process) followed by intradural tumor removal and reconstruction of the orbital roof. c Coronal view
The second step is the resection of the tumor intradurally, and it is somehow easy. The basal dura is excised as far as possible up to the superior orbital fissure and the optic canal. A small portion of the dura should be remained to be used for duraplasty later.
The third step is the reconstruction of the dura. The dura is tightly closed with audiomesh (collagen bioimplant), TachoSil (fibrin sealant patch) inside and outside, and autologous fat.
The fourth step is opening the periorbita in the case of tumor infiltration of intraorbital structures. After opening the periorbita, the lateral periorbital tumor is dissected from the beginning of the superior orbital fissure and intraorbitally to the superior rectus and levator muscles or the lateral rectus muscle. In cases in which there is an infiltration of the ocular muscles, only the exophytic tumor is removed and the muscles are not resected. The periorbita is closed only with the insertion of audiomesh upon the opened part (it should not be closed tightly to let the exophthalmus come back to the normal position postoperatively) [8].
Summary
The goals of surgery are acceptable cosmetic and functional results with tumor control and minimal morbidity.
The aggressive resection of tumor-invaded structures in the cavernous sinus, superior orbital fissure, or orbital apex is not recommended because of the attendant serious risk of morbidity. In case of tumor progression in this part, radiation should be considered. Surgery should be performed as early and as radically as possible to obviate future recurrence. Radiotherapy remains an alternative for recurrences or subtotal resections.
5.1.5 Petroclival Meningiomas
General Information
Basal posterior fossa meningiomas can be classified into the clival, petroclival, sphenopetroclival, foramen magnum, and cerebellopontine (CP) angle types depending on the zone of adherence. The tumors known as petroclival meningiomas can be broadly defined as those attached to the lateral sites along the petroclival borderline where the sphenoid, petrous, and occipital bones meet.
Petroclival tumors are located in an anatomically complicated area containing the dural folds, venous sinuses, and cranial nerves III–VIII. Therefore, a small anatomical variation in the zone of origin presents different clinical features and choice of surgical approaches that can influence the outcome [9, 14].
Kawase et al. preliminarily classified petroclival meningiomas into four subtypes based on MRI and surgical observations (◘ Fig. 5.17). This classification is useful to predict the relation between the tumor and the cranial nerves based on symptoms and images.
Fig. 5.17
Four subtypes of petroclival meningioma: upper left, the upper clivus (UC) type; upper right, the cavernous sinus (CS) type; lower left, the tentorium (TE) type; lower right, the petrous apex (PA) type. The shaded regions indicate tumors. The numbers indicate cranial nerves. PCP posterior clinoid process, PCS posterior cavernous sinus, IAM internal auditory meatus, BS brain stem, MC Meckel’s cave (Ichimura et al. [10])
Clinical Manifestations
As we discussed above, petroclival meningiomas can be classified into four subtypes (UC, CS, TE, and PA; for abbreviations, see the description of ◘ Fig. 5.17) based on their origin. The clinical signs of petroclival meningiomas are cranial nerve III–VIII deficits and signs associated with the brain stem and cerebellar compression.
The characteristic symptom of the UC type is ataxia caused by the direct compression of the brain stem or cerebellar peduncle. The primary goal of surgery is brain stem decompression in lifesaving situations.
Extraocular paresis was significantly noted in the CS type. This is because the abducens nerve is fixed intradurally in the inferomedial triangle of the cavernous sinus from the point of dural penetration to Dorello’s canal.
The TE type did not have any characteristic clinical symptoms other than trigeminal neuropathy. Regarding the PA type, many patients complained of trigeminal neuralgia, but the tumor rarely extends into Meckel’s cave.
Based on the literature, up to 70% of petroclival meningiomas show extension to the Meckel’s cave. The rate of extension differs based on the tumor type, as explained above.
Controversies in Approach Selection
In the literature, there is a great deal of discussion about the merits of using Kawase’s approach (anterior petrosal approach) vis-à-vis the retrosigmoid (RS) approach with suprameatal extension (RISA: retrosigmoid intradural suprameatal approach) for tumors involving both the middle and posterior fossa.
Although there are potential benefits and limitations with each approach, the specific characters of the tumor and the individual functional status of the patient should reflect the goals of the surgery and the proposed surgical approach. The RS approach is a powerful approach to lesions of the CP angle and ventral brain stem.
Lesions involving the trigeminal porus and Meckel’s cave can be approached through Kawase’s approach or a suprameatal extension of the RS approach [11]. Kawase’s approach is best suited for accessing middle fossa lesions with smaller petroclival components located above the internal auditory canal (IAC; ◘ Fig. 5.18).
Fig. 5.18
Schematic representation of calculated areas for the RS/RISA (blue) and Kawase’s (green) approaches (Chang et al. [11])
Surgical Technique
Extended RS Approach
Under general anesthesia and with intraoperative electrophysiological neuromonitoring (somatosensory evoked potential, electromyography of cranial nerves VI–XII) and using intraoperative transesophageal echocardiography (TEE) for the early detection of the air emboli, the patient is positioned in a semisitting position (with the head rotated away from the surgical site). An area approximately two fingerbreadths posterior to the mastoid is identified for the incision.
After standard RS craniotomy, the dura is opened parallel to the sinuses. After drainage of CSF from the cisterna magna, the CP angle with the IAC and its cranial nerves VII–VIII, the suprameatal tubercle, the petrosal vein, cranial nerve V, and the lower cranial nerves are identified and exposed.
Depending on the origin, petroclival meningiomas can change the normal anatomy of the cranial nerves.
These tumors’ origins are mostly anterior to the V–IX cranial nerves. There are three corridors to access the tumor ventral to the cranial nerves.
The first corridor is above the V cranial nerve. We use always this corridor as a first window to attack the tumor because of the resistance of the trigeminal nerve to manipulation. Here, if the suprameatal tubercle is large and on the way to the tumor, it will be drilled away (◘ Fig. 5.19). In this stage, the tumor should be internally debulked, reduced in its petroclival component, and bimanually dissected from the surrounding neurovascular structures to obtain brain stem decompression.
Fig. 5.19
a Photograph showing a large suprameatal tubercle (*) seen through the RS approach. b The tubercle has been removed via the RISA approach. In this exposure, Dandy’s vein (superior petrosal vein Type III which emptied into the superior petrosal sinus) was sacrificed (arrowhead) (Chang et al. [11])
The second corridor is the window between cranial nerve V and VII–VIII complex. Special attention should be given to the facial nerve because it is the most common nerve in danger during the RS approach. In some cases, the basilar artery is encased by the tumor, and it is not easy to dissect the tumor from its perforators. Finally, after tumor resection in this corridor, abducens nerve will be identified ventrally at the entrance of Dorello’s canal.
In cases with caudal extension, the third corridor will be the window between cranial nerve VII–VIII complex and the caudal cranial nerves. In tumor removal ventral to the cranial nerves, our invented-angle microbipolar forceps are very helpful as a multipurpose instrument because the forceps could be used for cutting, coagulation, and grasping of the tumor ventral to and also between cranial nerves V and IX [9, 12, 14].
In the case of supratentorial tumor components (middle fossa extension), the tentorium could be cut at the lower part (1–2 cm) toward the petrous ridge under the visualization and protection of cranial nerve IV to remove the tumor portion in the middle fossa. The removal of the tumor in the middle fossa opens a corridor up to the oculomotor nerve at the entrance of the cavernous sinus.
Nevertheless, in most of the cases, the tumor opens a way from posterior fossa to the middle fossa, and there is no need to open the tentorium.
In all of the cases, superior petrosal vein and other bridging veins should be identified and protected to prevent venous infarction [13].
As we have discussed above, in meningiomas with extension to Meckel’s cave, we prefer to remove the tumor via middle fossa extradural anterior petrosectomy (Kawase’s approach).
In cases with the involvement of the brain stem (edematous brain stem in MRI T2 sequence), a small part of the tumor should remain on the brain stem. It can guarantee a more suitable functional outcome for the patient.
Anterior Petrosal Approach
To access the posterior fossa from middle fossa in Kawase’s approach, the dura of the middle fossa should be peeled from the skull base until the petrous ridge is identified. The middle meningeal artery should be interrupted after coagulation to allow the manipulation beside the foramen spinosum. The greater superficial petrosal nerve (GSPN) is the most reliable superficial landmark on the middle cranial fossa for drilling of the petrous apex (Kawase’s triangle) in the extradural anterior transpetrosal approach (ATPA). It is the lateral border of Kawase’s triangle [9, 14].
The GSPN should be clearly recognized before drilling at Kawase’s triangle to avoid the risk of injury to the facial nerve and ICA (◘ Fig. 5.20).
Fig. 5.20
Schema of the standard ATPA (anterior transpetrosal approach). The standard ATPA is a fundamentally epidural procedure to expose the petrous apex. The middle meningeal artery is coagulated and cut. The GPN (greater petrosal nerve) is dissected in the interdural layer. AE arcuate eminence, GPN greater petrosal nerve, MMA middle meningeal artery, PA petrous apex, V1 ophthalmic nerve, V2 maxillary nerve, V3 mandibular nerve. Dotted line is the lateral border of anterior petrosectomy (Ichimura et al. [10], Springer)
The eminencia arcuata is the posterior border of Kawase’s triangle, and it must be preserved if hearing is to be preserved. The anterior border of Kawase’s triangle is trigeminal impression (bony impression of Gasserian ganglion).
After drilling the anterior part of the petrous bone, the dura of the posterior fossa is exposed (◘ Fig. 5.21a, b). In this part of the approach, dural incisions are made above and below the superior petrosal sinus. At this point, a double Weck clip or ligature is applied to close the superior petrosal sinus, and cuts are made toward an edge of the TE, behind the entrance point of the trochlear nerve, to preserve it. The bilateral retraction of the tentorial leaflets with sutures allows for the visualization of the posterior fossa and anterior part of the pons. The dura incision of the middle fossa is then extended anteriorly to expose the lateral wall of the CS.
Fig. 5.21
a Exposure of the posterior fossa dura (PFD) after anterior petrosectomy. b Postoperative axial CT scan of the patient after removing a large right-sided petroclival meningioma via Kawase’s approach. The red arrow shows the corridor of access from the middle fossa to posterior fossa after anterior petrosectomy
Summary
Petroclival meningiomas are located in an anatomically complex area containing dural folds, venous sinuses, and cranial nerves IV–XII. Therefore, even very small anatomical variations in the zone of origin can influence the outcome and present drastically different clinical features and choices of surgical approach.
The conclusions about the appropriate surgical approach are thus the particular aspects of the case.
5.1.6 Foramen Magnum Meningiomas
General Information
Foramen magnum meningiomas are divided into two main types: craniospinal (originating intracranially and extending downward) and spinocranial (originating in the upper spinal canal and extending intracranially).
Ventral foramen magnum meningiomas originate from the basal groove in the lower third of the clivus, anterior to the medulla, and project inferiorly toward the foramen magnum (◘ Fig. 5.22a, b). Spinocranial meningiomas, which originate from the upper cervical area, are usually posterior or posterolateral to the spinal cord and project superiorly into the cerebellomedullary cistern.
Fig. 5.22
Preoperative MRI of the patient with right-sided ventral foramen magnum meningiomas. a Sagittal view, b axial view
Clinical Signs and Symptoms
Patients with lesions in this location may present with unusual symptoms and are often misdiagnosed. Cervical pain (usually unilateral), motor and sensory deficits (especially involving the upper extremities and, in later stages, progressing to spastic quadriplegia), and cold, clumsy hands with intrinsic hand atrophy constitute the well-documented clinical triad that identifies foramen magnum meningiomas.
Surgical Technique
Lateral or posterior foramen magnum meningiomas can be resected using a standard inferior suboccipital approach . However, in ventral foramen magnum meningiomas, because of the involvement of the lower cranial nerves and vertebrobasilar artery complex and significant brain stem compression, we prefer resection of these tumors using the transcondylar approach .
For the transcondylar approach, we prefer the semisitting position with intraoperative monitoring of the caudal cranial nerves and using intraoperative TEE for the early detection of the air emboli.
The incision that we prefer is the modified hockey stick, although the linear incision could be also another favorable option. The incision starts at the tip of the ipsilateral mastoid, continues above the superior nuchal line, and then curves to the midline and down to the level of C3 (◘ Fig. 5.23a). Such type of incision provides enough space for C1–C2 navigated transpedicular screw fixation if complete condylar resection happened during this approach.
Fig. 5.23
a Modified hockey stick incision for right transcondylar approach in semisitting position. b Partial condylectomy after removing the C1, before opening the dura (pay attention to oblique dural entrance of vertebral artery). c Exposure of a ventral foramen magnum anatomy (schematic view) through the right transcondylar approach after opening the dura
The skin flap is then elevated. The preservation of a muscle «cuff» at the level of the superior nuchal line is helpful for the correct approximation of the musculature at the end of the procedure and in the prevention of a CSF leak. After the exposure of the C1, the posterior arch of C1 is followed laterally to the sulcus arteriosus, which marks the medial limit of the vertebral artery. The skeletonization of the vertebral artery is not anymore recommended, and it should be enough to see or palpate the pulsation of the artery [15].
After the position of the sulcus arteriosus and the vertebral artery is identified, the ipsilateral posterior arch of the atlas is removed, either with the footplate of a high-speed drill or with rongeurs. In semisitting position, it is very crucial to use bone wax at the remained part of C1 to stop any bleeding from the spongy bone and to prevent air entrance to the venous plexus followed by air emboli.
The lip of the foramen magnum is then identified, and a small craniotomy is performed with the aid of a high-speed drill or craniotome. The next key step is the drilling of the condyle (◘ Fig. 5.23b). Although debate exists regarding how much condyle needs to be drilled, we usually let the lesion dictate how much removal of the condyle is necessary. In our opinion, after drilling more than half of the condyle, the C0–C2 fusion surgery should be mandatory.
We usually open the dura in a curvilinear fashion with special attention to the vertebral artery oblique entrance to the dura (◘ Fig. 5.23b). After the dura is opened, the exposure obtained encompasses the lower cranial nerves to C2 (◘ Fig. 5.23c). A superior extension of this basic approach allows the surgeon to follow lesions up to the internal auditory meatus.
There are two corridors of attack to the tumor in this approach. The first corridor is above the intradural part of vertebral artery, and the second corridor is below it. Special attention should be given to the loop of the hypoglossal nerve curving over the vertebral artery. ◘ Figure 5.24 shows the exposure of a ventral foramen magnum meningioma through the transcondylar approach.
Fig. 5.24
Intraoperative view of the far lateral approach to the left-sided ventral foramen magnum meningioma (VA vertebral artery, XI accessory nerve, XII hypoglossal nerve, C2 second cervical nerve)
In some situations, it is necessary to sacrifice the C1 nerve root to expand the exposure. We usually use local anesthetic for the accessory nerve to prevent the firing of the trapezius muscle during the gentle nerve’s manipulation.
Summary
Advances in microsurgical techniques, neurological anesthetic management, and skull base approaches have led to improved results of foramen magnum meningiomas. The far lateral approach allows a tangential, unobstructed view of the lateroventral cervicomedullary area and can be applied effectively to manage ventral foramen magnum meningiomas.
5.2 Optic Pathway and Hypothalamus Gliomas
5.2.1 General Information
Optic pathway (OPG) and hypothalamus gliomas encompass a spectrum of findings ranging from lesions confined to the optic nerve only, lesions affecting the optic chiasm and hypothalamus, and to lesions with diffuse involvement of a large part of the optic pathway and neighboring structures. The origin of globular tumors in a suprasellar location may be indistinguishable; they can originate from either the chiasm or the hypothalamus because there are no discernible anatomic borders between these two structures.
As a relatively uncommon cause of vision loss in children, they affect young children more than adolescents or adults.
The majority (59–70%) of patients with optic pathway gliomas present before age 10 and another 20–22% by age 20. These are relatively rare tumors, but they comprise 5% of all brain tumors in children and 25–30% of all brain tumors in children less than 5 years old.
The incidence of neurofibromatosis Type I (von Recklinghausen’s disease) among patients with optic gliomas is 10–70% (mean, 25%). Fifteen percent of patients with neurofibromatosis Type I have optic gliomas. OPGs associated with neurofibromatosis Type I (NF1) generally have an even more favorable course [16].
The majority of pediatric low-grade astrocytomas in the optic/chiasmatic region are typical pilocytic astrocytoma [17]. The rest of them (10%) may be other gliomas such as fibrillary pilomyxoid astrocytoma (grade 2 WHO).
Adult patients with OPG can be divided into two groups: adult patients with tumors diagnosed in childhood and adult patients diagnosed during adulthood [18].
Orbital optic glioma without involving the chiasm is a special entity in glioma surgery that can be cured with a suitable treatment plan.
5.2.2 Clinical Findings
The presentation of optic pathway glioma depends on the location of the tumor within the visual pathway. Generally, involvement of the optic tracts and other postchiasmal structures at tumor diagnosis is associated with a higher probability of visual acuity loss [19].
Optic nerve gliomas which comprise approximately 25% of optic gliomas typically present with slow, painless, unilateral visual loss, optic disc swelling or atrophy, proptosis, or strabismus. Rarely, patients with optic nerve gliomas may develop a central retinal vein occlusion, iris rubeosis with neovascular glaucoma, or ocular ischemic syndrome (◘ Fig. 5.25).
Fig. 5.25
a Preoperative axial MRI with contrast of the 6-month-old baby shows tumor growth from the orbit into the optic canal and further tumor extension into the intracranial space affecting the ipsilateral optic nerve, but not having infiltrated the chiasm. b Postoperative axial MRI with contrast of this case shows complete removal of the tumor and the optic nerve via prechiasmatic and extradural transection
Chiasmal gliomas typically present with slow bilateral visual loss, optic disc swelling or atrophy, strabismus, or variable visual field defects (◘ Fig. 5.26).
Fig. 5.26
Preoperative MRI of the 14-year-old patient with chiasmal glioma, axial a and coronal b. Postoperative 1-year follow-up MRI after tumor biopsy and radiotherapy, axial c, coronal d
Hypothalamic gliomas may be signified by precocious puberty and diencephalic syndrome (Russell’s syndrome) consisting of emaciation, euphoria, hyperkinesis, or hydrocephalus. It can also be manifested with obesity.
Tumors of hypothalamic origin may not cause visual symptoms. Suprasellar gliomas extending into the third ventricle often cause obstructive hydrocephalus (◘ Fig. 5.27).
Fig. 5.27
Preoperative coronal a, axial b, and sagittal c MRI of the 1-year-old baby with diffuse hypothalamic suprasellar glioma
The diagnosis of OPHG is often delayed, and these tumors can be quite large at discovery.
5.2.3 Investigations
Magnetic resonance imaging (MRI) is superior to computerized tomography in the evaluation of the canalicular, chiasmal, and optic tract/hypothalamic extent of the glioma. Cyst formation in or around the solid tumor may be present.
Optic nerve gliomas show bulb-shaped intraorbital enlargement of the optic nerve with extension of the tumor to the apex, which results in a tortuous course and often kinking appearance (◘ Fig. 5.25).
Chiasmal hypothalamic gliomas appear as an enlargement of the chiasm or as a suprasellar mass, occasionally with a cystic component. The lesions are isointense or hypointense on T1-weighted images and hyperintense on T2-weighted images and may be enhanced with gadolinium. The MRI appearance is almost pathognomonic (◘ Figs. 5.26 and 5.27).
The differential diagnosis of children with suprasellar gliomas includes craniopharyngioma, pituitary adenoma, germ cell tumor, and hypothalamic hamartoma.
Differentiating between optic nerve neoplasm and inflammation may be difficult.
5.2.4 Therapeutic Options
Treatment should be considered when there is documented clinical worsening manifested by visual loss or radiographic progression indicated by tumor enlargement.
When the patient has symptoms or the tumor is progressing, or both, treatment is necessary. Although radical tumor resection is ideal, because of the anatomic structures present around the tumor, aggressive surgery would compromise visual, neurological, and endocrine functions. Therefore, total resection is not possible without risk of complications [21].
Chemotherapy
Chemotherapy has been frequently the primary mode of treatment of symptomatic children over the past two decades as a result of the significant latent morbidity associated with RT. At present, many clinicians consider chemotherapy to be the first-line treatment in children because of fewer side effects compared to RT [20]. In children younger than 3 years, it is usually the only adjuvant treatment because intellectual and other functions are relatively well preserved.
The SIOP LGG 2004 study applied stringent criteria for diagnostic work-up, guidelines for surgical procedures, and clear indications to start nonsurgical therapy, offering an individualized sequence of treatment modalities according to established guidelines for subgroups defined by the tumor location and the presence or absence of neurofibromatosis NF1. The published protocol of this European study can be used as a guideline for chemotherapy of different children with optic LGG (siop-lgg.cineca.org).
5.2.5 Surgical Treatment
Optic Nerve Glioma Without Involvement of the Chiasm
As explained previously, orbital glioma without involvement of the chiasm and contralateral eye (◘ Fig. 5.25) is a special entity in optic glioma that can be cured with suitable planning. In the literature, only 5–10% of optic nerve gliomas recur in the chiasm after «complete» intraorbital excision. In blind patients with ipsilateral proptosis and who are in pain without involving the chiasm, gross total tumor removal with prechiasmatic transection of the optic nerve could be achieved.
No recurrence in our series emphasizes that performing prechiasmatic transection in highly selected cases of optic nerve glioma might offer a further treatment option to avoid tumor growth toward the chiasm without any adjuvant therapy.
Our selected approach is pterional intra- and extradural with the opportunity to resect the infiltrated optic nerve (◘ Fig. 5.28) and transection of the nerve 2–3 mm behind the globe extradurally and 2–3 mm prechiasmatic intradurally and complete removal of the affected intracanalicular part of the optic nerve in between (◘ Figs. 5.29 and 5.30—see also surgical approaches).
Fig. 5.28
Pathology of case in ◘ Fig. 5.25: Diffuse astrocytoma infiltrating the optic nerve (left) and meninges (right). Hematoxylin and eosin
Fig. 5.29
Intradural exposure of the left optic nerve and chiasm in ◘ Fig. 5.25 emphasize the freedom of chiasm (yellow star shows the chiasm, blue line shows the border of the tumor in prechiasmatic region, black arrow shows the exact place of transection anterior to the chiasm and posterior to the tumor border)
Chiasmal Hypothalamic Tumors
Although incomplete surgical resection has not been shown to affect survival, the benefits of surgery include histologic verification, cytoreduction to allow increased sensitivity to adjuvant therapy, and restoration of CSF circulation (◘ Figs. 5.26 and 5.27).
Injury to the hypothalamus may lead to hypothalamic obesity, memory loss, electrolyte imbalance, or behavioral changes. Manipulation of arterial vessels may lead to ischemic injury and result in a cerebrovascular event.
The suitable surgical approach for debulking depends on the direction of maximal tumor extension [23]. Adjuvant therapy should be used based on the above discussion.
Approximately 50% of patients with suprasellar astrocytoma have obstructive hydrocephalus, which can be treated with a shunt. Because of obstruction at the interventricular foramen or anterior third ventricle, fenestration of the septum pellucidum or bilateral shunts is needed.
Diffuse Optic Pathway Gliomas
Surgical resection is not feasible for gliomas diffusely involving the optic pathway, including the optic chiasm, tracts, and radiations and the brain stem. These structures are treated nonsurgically with chemotherapy or RT, or both.
Obstructive hydrocephalus should be treated with a shunt.
Surgical Approaches
Combined Pterional Intra- and Extradural Approach
To perform a combined intra- and extradural approach, following a pterional craniotomy , first, the superior orbital fissure is exposed extradurally, and a partial anterior clinoidectomy is performed.
As a next step, the optic canal and the orbit are opened by drilling carefully the lateral and medial sides of the optic canal as well as the roof and the lateral wall of the orbit itself, finally allowing exploration of the optic nerve and the periorbita.
In particular, with respect to cosmetic outcome, special attention is paid to leaving the supraorbital rim intact. By a midline incision, the periorbita is opened, and the intraorbital part of the tumor-infiltrated optic nerve could be displayed and finally resected.
To achieve a vast tumor resection, the optic nerve needs to be transected extradurally behind the bulb with 2–3 mm distance from the bulb to preserve the integrity of the eyeball.
After removing the tumor-infiltrated optic nerve inside the orbit (intraorbital–intraconal part), the intracanalicular part of the tumor should be removed.
The affected part of the optic nerve at the apex should not be transected directly because of the risk of injury to the superior branch of the oculomotor nerve. The tumor should be gently pulled out in the apex and the optic canal underneath the nerve.
Next, the dura should be opened. After gentle retraction of the frontal lobe, the tumor-infiltrated nerve could be exposed, and tumor masses are removed by preserving all adjacent vascular and nervous structures with special attention paid to the ophthalmic artery before nerve transection.
By performing a prechiasmatic transection of the optic nerve, a complete removal of the tumor-infiltrated nerve can be achieved (◘ Figs. 5.28, 5.29, and 5.30; ◘ Video 5.2).
The dura is later closed tightly. To prevent a cerebrospinal fluid (CSF) leak extradurally, the optic canal should be closed by fat, TachoSil, and fibrin glue.
Finally, the periorbita should be closed by fat, fibrin glue, audiomesh, and autologous resected bone of the orbital roof without using any foreign bodies such as small plate or screws in children.
Lateral Orbitotomy
Lateral orbitotomy provides excellent exposure of the lateral compartment of the orbit and can be used for well-defined periorbital and intraconal tumors located lateral, dorsal, and basal to the optic nerve. The skin incision begins superiorly and laterally in the eyebrow and is carried posteriorly along the zygomatic bone. Then the temporalis fascia is incised, beginning at the midportion of the frontozygomatic bone. Transection of the optic nerve in the apex is also possible by this approach.
Supraorbital Approach
Supraorbital craniotomy can be carried out using a keyhole-sized burr hole plus a small craniotomy. The tumor can be removed after decompression of the optic nerve via removal of the optic canal roof and anterior clinoid process and then intradurally.
Anterior Interhemispheric Transcallosal Approach
For resection of tumors with suprasellar extension or intraventricular tumors, an anterior interhemispheric transcallosal approach is used to gain direct access to the third ventricle. The fornix needs to be protected on both sides. One can separate the upper portion of the hypothalamic glioma from the lateral wall (thalamus), but the inferior portion below the hypothalamic sulcus tends to blend into the hypothalamus. Only the exophytic portion and central core of the tumor are amenable to removal (◘ Fig. 5.31).
Fig. 5.31
Postoperative MRI of the patient presented in ◘ Fig. 5.29 after tumor debulking via interhemispheric transcallosal approach, coronal a and sagittal b
5.3 Acoustic Neuromas
Acoustic neuroma (AN) aka vestibular schwannoma or acoustic neuroma is a benign sporadic tumor or a manifestation of neurofibromatosis Type 2 (NF2) with bilateral ANs. After pituitary adenoma, it is by far the most common skull base tumor with a current incidence in Denmark of more than 22 per million per year [71]. The current management modalities for AN are watchful waiting, microsurgery, stereotactic irradiation, or biological therapy.
The development of acoustic neuroma surgery has paved the way for posterolateral skull base surgery in general, and AN constitutes a separate entity in the skull base surgery specialty. A patient with an AN often presents with minor symptoms, making treatment prophylactic to a more severe deterioration of health, which may or may not happen after an uncertain period of time. Surgical treatment of AN is a complex undertaking with a potential for added severe and lasting disability, and the importance of a centralized team-based approach in order to deploy adequate advantage of experience cannot be overstated [35]. The present text will focus on the practical aspects of AN surgery, from preoperative work-up to surgery.
5.3.1 Classification of AN
AN is classified according to size, location, mass effect, structure, histology, and degree of removal. In 2003 it was agreed that the size of an AN should be reported as the largest extrameatal diameter [46]. A subdivision into intracanalicular (no extension beyond porus), small, medium-sized, large, and giant AN is often used, but there is unfortunately no consensus about the size distribution for each class. Others have suggested various classifications, of which the Koos grading according to mass effect [48] has been used frequently before the consensus paper in 2003. AN can be lateral or less frequently medial [77]. The structure of an AN can be described as cystic or solid. The grade of removal of AN has been suggested (Kanzaki) to be reported as either total, near total (less than 2% left), partial (less than 5% left), or subtotal (more than 5% left). AN is benign and contains various amounts of histologically distinct areas (Antoni A/Antoni B), but primary malignant AN (◘ Fig. 5.42, [34]) and malignant transformation of AN [27] have been reported. Malignant AN is classified as malignant peripheral nerve sheath tumor (MPNST) and belongs in the sarcoma group.
5.3.2 Strategy for Management of AN
Sporadic AN
◘ Figure 5.32 suggests pathways to select patients for surgery. The management strategies have been changing toward a more conservative management during the past decades [33]. There is limited evidence base for optimal choice of management, and it seems that all patients with small to medium tumors experience high rates of tumor control and excellent facial nerve outcomes regardless of treatment modality and that patient-related factors are the drivers of quality of life, rather than treatment modality [32]. Treatment of AN is not only influenced by medical evidence and preferences of doctors and patients but also by local tradition, health economy, and infrastructure. Hence, the best management option for a specific patient, given the individual circumstances, may be outside the outlined pathways in ◘ Fig. 5.32, where the assumption is unlimited and safe access to all treatment modalities.
Fig. 5.32
Suggested patient selection shown as a flowchart. Full lines show likely pathways; dotted lines show unusual pathways. Few patients with AN >25 mm are followed with wait and scan, but this is still the exception and is not shown
AN Associated with NF2
In terms of decision-making and surgical technique, the bilateral and sometimes multiple ANs in NF2 patients represent a difficult and more complex challenge compared to sporadic AN. Radiation therapy is less effective in NF2 [62], whereas biological therapy (bevacizumab) represents a further alternative to surgery [59]. There is a high lifetime risk of complete deafness regardless of management strategy. NF2 patients often have other benign tumors, such as schwannomas arising from other cranial nerves, meningiomas, and peripheral schwannomas, contributing to the burden of the disease. Due to the complexity of the disease, multidisciplinary centralized care has been introduced in some countries [39]. The strategy regarding surgery is more conservative than with sporadic AN, and when surgery is performed, it may be less aggressive and always balanced against the chance of hearing preservation. Surgery may have decompression of the meatus or tumor with possible release of the cochlear nerve as the only goal (◘ Fig. 5.33). Severe brain stem compression is a typical absolute indication for surgery, but any chance of hearing preservation should still be pursued, and cochlear implant [50, 75] or brain stem implant [52] is an option to be considered for hearing restoration. Patients under the age of 30 with unilateral symptomatic AN should be genetically tested for NF2 mutations prior to the choice of treatment strategy as they have a significant risk of NF2 and development of a contralateral AN [40].
Fig. 5.33
T2 axial MRI of an NF2 patient with a small AN on the right side (white arrow) and a large partly cystic (CP), partly solid (SP) AN on the left side. This patient had normal hearing on both sides but enlargement of the cystic AN on serial imaging. A selective decompression of the cystic AN was carried out with a retrosigmoid approach without any loss of hearing
Hydrocephalus Associated with AN
More than 10% of patients with AN have associated hydrocephalus at presentation. In the vast majority of AN patients presenting with hydrocephalus, this condition is relieved by surgical removal of the AN, and this should therefore be performed before any treatment of the hydrocephalus, unless the hydrocephalus is presenting as an emergency [41]. In cases where surgery is not the optimal management strategy, treatment should follow current general guidelines for treatment of hydrocephalus. If indicated, a ventricular–peritoneal shunt should be placed on the contralateral side.
5.3.3 Preoperative Management
Outpatient Assessment and Counsel ing
Imaging will invariably be available at the time of referral to the AN surgeon. After assessing the MRI, the history and neurological examination are the next important steps toward the pretreatment evaluation. Individual counseling is mandatory and rightly expected by patients at the first encounter. Factors such as AN size, age, overall hearing status, comorbidity, occupation, and life philosophy should be recorded and integrated in the decision-making toward informed consent for the chosen treatment strategy. If surgery is chosen as the preferred treatment strategy (◘ Fig. 5.32), there is still a decision to make regarding the approach (◘ Fig. 5.34).
Fig. 5.34
Surgical approaches for the resection of acoustic neuromas
Neuroradiological Investigations
MRI is the standard imaging modality for preoperative assessment of AN. Ideally, the MRI includes axial T1, axial T2, and axial, coronal, and sagittal T1 with intravenous contrast, as well as a 3D CISS/FIESTA axial sequence (◘ Fig. 5.35). This selection of sequences is far from always provided by the referring doctor. With an optimal high Tesla MRI and a 3D CISS/FIESTA axial sequence, nerves and vessels are seen in the meatus (◘ Fig. 5.35), and it is sometimes possible to assess the likely course of the cranial nerves around a small- or medium-sized AN. Recently, MRI tractography has been employed with some success to track the course of the meatal nerves in relation to large ANs [74].
Fig. 5.35
FIESTA T2 axial MRI of the normal meatus on the right side with vestibulocochlear nerve (vcn), facial nerve (fn), loop of anterior inferior cerebellar artery (aica), and intermedius nerve (in). Loop of anterior inferior cerebellar artery (white arrow) deep in the right meatus, as an incidental finding
The appearance of an extrameatal AN on MRI is typical (◘ Fig. 5.36), and the diagnosis is fairly easy to the trained eye. An AN appears as a rounded solid or cystic contrast-enhancing process with the «center of gravity» corresponding to the meatus, and usually involvement of this. Very small intrameatal ANs appear as enhancing nodules (◘ Fig. 5.37) in sharp contrast to the appearance of a giant AN (◘ Fig. 5.38). Before growing extrameatal, the intrameatal AN often fills the meatus (◘ Fig. 5.33, right meatus). Extrameatal ANs have a mushroomlike appearance on axial and coronal images due to the involvement of the meatus and frequently a significant meatal expansion compared to the contralateral side.
Fig. 5.36
Axial T1 MRI with gadolinium showing a typical extrameatal AN (an) without cystic elements. The small areas without contrast enhancement may represent degenerative change corresponding to the histological Antoni B areas. This should not be confused with cystic elements
Fig. 5.37
Axial T1 MRI with gadolinium showing a small enhancement (white arrow) representing a small AN in the fundus of the right meatus. This type of enhancement can also represent a loop of the anterior inferior cerebellar artery (◘ Fig. 5.35) or an inflammatory lesion of one of the nerves in the meatus
Fig. 5.38
Axial T1 MRI with gadolinium showing a giant AN (an) on the left side with a large expansion of the meatus. This patient had a marginal facial palsy preoperatively, and it was not possible to preserve the facial nerve or find the proximal end on the brain stem (bs). The patient had a facial–hypoglossal end-to-side anastomosis (► Chap. 20) and ended up with House–Brackmann grade 3 function
A computer tomography (CT) scan will rarely be available at the time of referral. A thin slice CT scan of the skull base provides a detailed information about the bony anatomy and is still a standard preoperative investigation in some practices. It is true that the position of semicircular canals, jugular bulb, and emissary veins may influence the choice of surgical approach, but this can also be assessed on a state-of-the-art MRI scan (see above). As a CT scan provides little additional information to MRI, involves a large dose of radiation, and may delay assessment and treatment, this investigation is no longer a standard in the preoperative work-up but may be added depending on the available resources and the AN surgeon’s preference.
Angiography is not needed for differential diagnosis or preoperative assessment. Angiography is used for assessment and embolization of glomus tumors, but these tumors share few characteristics with AN on MRI. Angiography and possible endovascular embolization should as an exception be considered in the rare event of AN in children, where the rich vascularization may pose a significant and even life-threatening surgical risk [60].
Differential Diagnosis
Few patients are diagnosed with AN by the AN surgeon. The first assessment of an AN patient is therefore that of the clinical information, and MRI images are included in the referral. It is at this stage that suspicion of a possible differential pathology should be raised, as additional imaging and information may be needed to increase diagnostic accuracy before seeing the patient. With the benefit of combined clinical and MRI information available after assessment of the patient, the diagnosis of AN is so characteristic that radiotherapy is routinely offered as treatment for a growing AN, without biopsy. Having noted that, even experienced skull base surgeons and neuroradiologists can sometimes be surprised by the pathology.
All the lesions mimicking AN on MRI may cause cochlear, facial, and/or vestibular nerve dysfunction. It is noteworthy that AN on a rare occasion can originate distal to the meatus, from the cochlea or vestibule [72]. Differential diagnoses include other benign tumors, malignant tumors, infectious disease, inflammatory disease, or a vascular lesion. Meningioma arising from the petrous meninges (◘ Fig. 5.39) can mimic AN and is often referred to as AN. Wide contact with the petrous bone, frequent hyperostosis at the insertion point, and a dural «tail» usually distinguish this pathology from AN. Large schwannomas arising from the lower cranial nerves (◘ Fig. 5.40) do not involve the meatus, but the jugular foramen, and will have a lower center of gravity. Often the patient has symptoms or signs of lower cranial nerve deficits. Moreover, even giant ANs rarely invade the jugular foramen. Schwannomas of the facial nerve (◘ Fig. 5.41) are sometimes intrameatal, but arising near the geniculate ganglion, and cause bony erosion. Facial palsy is the typical presentation, as opposed to AN, where complaints of facial weakness are the exception. Very infrequently tumors arising from the medial structures, such as the cerebellum or the choroid plexus, involve the meatus, and hence hemangioblastoma, plexus papilloma, or even pilocytic astrocytoma may masquerade as AN. Small spots of enhancement in the meatus (◘ Fig. 5.37) may represent inflammatory or infectious lesions, especially in the presence of cranial nerve deficits disproportionate to the size of the lesion, and will often disappear on serial imaging. Enhancing lesions representing a malignant disease and involving the meatus may be primary (◘ Fig. 5.42) or secondary (◘ Fig. 5.43). The pattern and time course of cranial nerve involvement should raise the suspicion of an aggressive disease. The anterior inferior cerebellar artery sometimes forms a loop into the meatus (◘ Fig. 5.35), and this also causes meatal enhancement on MRI. Vascular pathology is otherwise rare but an anterior inferior cerebellar artery aneurysm in the meatus can be an unpleasant surprise when operating for an AN [42, 58].
Fig. 5.39
Axial T1 MRI with gadolinium showing typical meningioma (m) centered on the left meatus and growing into this. Enhancement of the adjacent dura (white arrow) forming a dural «tail» is typical for a meningioma, but not for an AN. The same meningioma (m) as in AN but with T2 axial MRI showing a hyperostosis (h) of the petrous bone around the porus and a narrowing of the meatus. Hyperostosis is typical for meningioma, especially at the point of insertion, but it is not seen with AN. Axial T1 with gadolinium showing a nodular meningioma at the left meatus (m). There is no tumor in the meatus (mt), which can also be the case with AN, and there is only a vague dural «tail» (white arrow)
Fig. 5.40
Axial T1 MRI with gadolinium showing a large left-sided lower cranial nerve schwannoma (lcns) which may at a quick glance be confused with an AN. In this case, the tumor is not entering the meatus (m), which should raise the suspicion that it is not an AN
Fig. 5.41
FIESTA T2 axial MRI showing a space-occupying lesion in the left meatus. This is a facial schwannoma. Axial T1 MRI with gadolinium showing that the same facial schwannoma has a much larger component coming from the geniculate ganglion and growing above the petrous bone. This is not seen with an AN
Fig. 5.42
Axial T1 MRI with gadolinium showing a primary malignant schwannoma (PMS) or malignant peripheral nerve sheath tumor on the right side. The tumor is filling the meatus (m), and the anterior part has the configuration of a regular AN, whereas the posterior part seems to have broken through the capsule and is expanding all the way back to the sigmoid sinus (ss). This young patient had two operations, radiotherapy and chemotherapy, but sadly died a few years after presentation despite aggressive therapy
Fig. 5.43
Axial T1 MRI with gadolinium showing B-cell lymphoma (ly) in the left meatus. He presented with hearing loss and facial palsy. It turned out that there was bilateral meatal involvement, as indicated by the faint enhancement (white arrow) on the right side. A biopsy was obtained via left retrosigmoid approach, and the patient was cured by hematological treatment. Axial T1 MRI with gadolinium showing a left-sided meatal metastasis (me) from a known breast carcinoma. The patient had a left retrosigmoid approach for biopsy and radiotherapy and did well for some years. She died from multiple metastases
Audiological and Vestibular Tests
Hearing status on both sides should be assessed by pure-tone audiogram and speech discrimination test. Which combination the hearing level and speech discrimination is serviceable is a matter of constant debate among AN surgeons, but patients quite often have a sensible opinion as well, if they are asked. Hearing is important, not only for the choice of treatment modality but also for the choice of surgical approach. Vestibular function tests will help to predict the immediate postoperative course in terms of nausea, vomiting, and vertigo. Postoperatively the patient must rely on the opposite vestibular apparatus, and the status of this may help predict the degree of vertigo and balance problems in the long term, something which is more important to AN patients than previously acknowledged [32].
Blood Analyses
Surgery of large or giant ANs can from time to time lead to major blood loss and a need for blood transfusion. Therefore, the blood type should be determined prior to surgery. A match is rarely necessary, unless the patient has atypical antibodies. No further blood analysis is needed for otherwise healthy patients without history or clinical signs of coagulopathy. Patients on anticoagulation or antiplatelet therapy and patients who take dietary supplements with anticoagulative effect, such as fish oil, should pause this prior to surgery, except when there is an absolute indication, for example, due to a stent or a mechanical heart valve. In such cases, the anticoagulation treatment must be bridged with heparin around the time of surgery.
Other Preoperative Considerations
Once it has been decided to operate, there are still details that can help foreseeing problems during surgery.
It is of value to note the dominance of the ipsilateral sigmoid sinus, to know whether it can be sacrificed if accidentally damaged.
A well-pneumatized mastoid process (◘ Fig. 5.44) makes the mastoidectomy easy, but beware of the possible suspension of the fallopian canal and facial nerve in air cells.
Fig. 5.44
Bone window axial CT showing an almost fully pneumatized mastoid process with the labyrinth (la) standing out as a dense block of the bone. In this situation, the mastoidectomy is easy, but the facial nerve may be suspended in an air cell, making the opening of the fallopian canal and identification of the nerve dangerous, if this anatomical variant is not suspected
Extensive bony erosion of the meatus makes the last part of the bony exposure more challenging and predicts trouble during the facial nerve dissection, especially at the porus edge.
The position of the posterior semicircular canal can limit the access to the fundus in the retrosigmoid approach (◘ Fig. 5.45).
Fig. 5.45
FIESTA T2 axial MRI showing an AN (an) in a patient with an almost normal hearing and no tumor in the fundus (f). The anatomy is not favorable for a retrosigmoid or presigmoid approach, as the posterior semicircular canal (white arrow) is in the way. The dotted line shows the limited access to the fundus. FIESTA T2 axial MRI showing an AN (an) in another similar patient with an almost normal hearing and no tumor in the fundus (f). The anatomy here is favorable for a retrosigmoid or presigmoid approach, as the posterior semicircular canal (white arrow) is not in the way. The dotted line shows sufficient access to the fundus
High position of the jugular bulb may deter some surgeons from the translabyrinthine approach, but in reality, this may also be a problem when opening the meatus from the retrosigmoid approach . Although a high bulb can reduce access, it is possible to remove even large ANs via the translabyrinthine approach, when the bulb is «egg shelled» and pushed aside [61].
A very «tight» posterior fossa in a young patient may warrant a preoperative lumbar spinal drain for early and safe CSF release.
5.3.4 Operative Setup, Technique, Approaches, and Tumor Excision
Intraoperative Neuromonitoring
Facial nerve monitoring [38] by facial electromyography (EMG) has improved facial nerve outcome after AN surgery. It can be set up by the surgeon with little extra effort and cost, and no AN should be removed without facial nerve monitoring, if there is a functioning facial nerve. A two-channel EMG with free running recording from the orbicularis oris and orbicularis oculi muscles is sufficient in most cases, but in the rare case of a preoperative partial facial palsy, four-channel recording is useful to increase the sensitivity. Continuous monitoring by either facial motor evoked potentials [51] or facial nerve root exit zone-elicited compound muscle action potential (FREMAP) is a new method offering a possible additional protection of the facial nerve at the cost of extra equipment and specialist staff in theaters.
Cochlear nerve monitoring in hearing preservation surgery can be performed by auditory evoked potentials (AEP), but this is not very useful due to the long delay arising from the necessary 500–2000 times averaging of the potential. A much better feedback can be obtained from continuous, direct, auditory evoked dorsal cochlear nucleus action potentials (AEDNAP). At the cost of additional equipment and specialist staff, this method may well prove to increase the quality of intraoperative decision-making as well as the chance of hearing preservation.
For giant AN, additional monitoring of the lower cranial nerves, of the trigeminal motor nerve, and of the abducens nerve by EMG, and continuous motor/sensory evoked potentials, can be used. This is probably reducing the risk of postoperative cranial nerve and brain stem problems, although this has not been investigated thoroughly.
Microsurgical Technique in AN Sur gery
For centuries, craftsmen have traveled the world to pick up new inspiration and knowledge of their trade. In a similar way, each surgeon will develop his own preference regarding techniques, instruments, and equipment, and in this process, it is advisable to visit other skull base surgeons. Seeking inspiration from others and sharing experience are still important elements in the way the specialty is taken forward and developed.
The microsurgical technique used in AN surgery is similar to the technique used for other skull base tumors but perhaps with more uniform strategies and phases. There are clear similarities to mine clearing. With 100% attention to the task, quick advancement can be made through safe corridors, whereas the surgeon(s) must reduce the pace when hidden «mines» are anticipated close by. At the tumor removal stage of the operation, the nerve stimulator becomes a mine seeker. Without a sufficient experience and a detailed knowledge of the pathological anatomy, the operation will progress very slowly due to lack of confidence and unnecessary caution. Surgeons’ fatigue will then be inevitable, posing a further risk of complications. After a long operation and complete excision, the facial nerve is not safe until the wound is closed, as I was taught by Glenn Neil-Dwyer, my first AN master and mentor.
There are different opinions regarding the use of cutting burrs or diamond burrs. The truth is probably that you should use the instruments that you are familiar with and which are safe. Cutting burrs are very fast and produce little heat. Cutting burrs are more sensitive to unstable bearings in the attachment, which will make the burr jump. This is dangerous. Diamond burrs are slower and produce more heat, which is also dangerous. Diamond burrs are more accurate and do not jump. Many surgeons start out with cutting burrs and change to diamond burrs when close to the facial nerve or the meatus.
It is not possible to learn microsurgical technique or AN surgery by reading a book. The technique is best developed through a combination of studies of anatomy and surgery books (e.g., [57, 78]) and Internet-based anatomy/surgical video resources, work in the anatomy lab, microscope training, and most importantly surgical assistance to experienced AN surgeons.
Retraction
The need for retraction depends on the size of the AN, the CSF release, the approach, the age of the patient, the anatomical variations, and the surgical setup. Retractorless surgery should become the standard [49], and when using the four-hand technique (see below), fixed retraction is unnecessary for any of the approaches, perhaps with the exception of extradural retraction for the subtemporal approach. If fixed retraction is used, the risk of cerebellar ischemia and retraction-related cerebellar dysfunction is high [24].
Four-Hand Technique for AN Surgery
Acoustic neuroma surgery spans the classical territories of neurosurgical and otological surgery and is also known as neurotological surgery. Starting with House and Hitzelberger [44], a long tradition of collaboration between surgeons of the two specialties has evolved, especially for the translabyrinthine approach. For the larger tumors, the approach is typically performed in the morning by the otological surgeon and the tumor resection carried out in the afternoon by the neurosurgeon, although many variations of collaboration exist. For the retrosigmoid approach, the sequence could be the reverse, or the procedure may be done by one surgeon altogether. Instead of two senior surgeons working after each other in a serial fashion, the four-hand technique allows two senior surgeons to work in parallel (◘ Fig. 5.46). Such a concept has already been adopted for endoscopic surgery for some time and works equally well for skull base surgery in our setting. The technique requires a good and respectful relationship between the surgeons and a microscope allowing both surgeons to have equal access and visual depth.
Fig. 5.46
Schematic representation of the difference in organization and use of resources between serial and parallel (four-hand technique) collaboration between two senior skull base surgeons. Time axis (red arrow). The area of each square under the yellow bars represents the effort of one surgeon
Ideally each surgeon is able to book his own patients and remains responsible for the patient before and after surgery. The surgeon in charge of the patient takes the lead during the operation by performing the drilling, supported by the other surgeon. The advantages of the four-hand technique are that both surgeons are able to perform the entire procedure, that the operating time can be shortened significantly with less risk of surgeon fatigue and complications from prolonged unchanged position of the patient on the operating table, that fixed retraction can be avoided, that the intraoperative decision-making is improved, that there is a build-in continuous learning process, that both surgeons can deal effectively with the whole range of complications, and that the surgeons can replace each other as the surgeon in charge of the patient postoperatively, when needed. It is difficult to see any drawbacks of this method. The question of who is finally responsible for the care of the patient has to be clearly defined, and both surgeons have to be present on the operating day, but this is not different from other setups, where the two surgeons are involved in a serial rather than parallel fashion.
Intraoperative Decision-Making
A few decades ago, complete excision of an AN was the only acceptable result for some AN surgeons, regardless of functional outcome. Now, subtotal or near total excision with preservation of function may be the only acceptable result for the patient. Hence, the relentless pursue of complete tumor removal, continuing long into the night, has given way to a less rigid and more patient-oriented practice. How old is the patient? Is the cochlear nerve or the facial nerve preservation the real challenge in this case? When do we stop? These are among the questions considered or discussed intraoperatively. Tumor resection may be ended several times, and every time, after reconsideration, a small opening may allow further progress, on some occasions leading to a total excision and preservation of the facial nerve after all. Retrospective analysis shows that remnants of AN carry a low re-treatment risk [36, 43, 68] and that remnants are less likely to grow than untreated AN [76]. Acoustic neuroma remnants rarely transform into malignant tumors, whether irradiated or not [27]. Refinements of intraoperative monitoring are likely to allow the surgeon(s) to go closer to the edge and leave a smaller tumor remnant behind, when complete excision with preservation of function is not achievable. This is important as the re-treatment rate is related to the size of the tumor remnant [54, 76].
Approaches
The translabyrinthine and retrosigmoid approaches remain the workhorses for AN surgery (◘ Fig. 5.34). Very few AN surgeons use the other approaches routinely, and if they do, it is primarily for small ANs. The subtemporal approach is best for small ANs with intended hearing preservation, and as an increasing share of these small tumors are followed rather than removed, this approach is now used less than previously. No approaches have shown to be superior to the translabyrinthine or retrosigmoid approaches for larger tumors. The exact indication for the translabyrinthine versus the retrosigmoid approach varies between AN surgeons and is a subject for continuing discussions.
Translabyrinthine Approach (◘ Video 5.3)
The patient is in general anesthesia without paralysis and placed on the operating table in the supine position with the head rotated 60° toward the opposite side and fixed in 3- or 4-point fixation. Some surgeons prefer to have a lumbar spinal drain in place for CSF release and postoperative CSF drainage to avoid CSF fistula. Although this may reduce the CSF leak rate after translabyrinthine surgery to near zero (personal communication, Michael Gleeson), there is no published evidence for this [37]. The area behind the ear is shaved, and a curved incision is marked from the mastoid tip to 1 cm above the attachment of the pinna (◘ Fig. 5.34). The incision line is infiltrated with local anesthetic. The facial electrodes, ground electrode, and reference electrode are placed, and the monitoring system is tested. An incision for harvesting of the fat graft is marked and infiltrated with local anesthetic at the lower part of the abdomen lateral to the midline. The patient is strapped to the table across the chest to allow tilting of the table during surgery. For a large or giant AN, it may be wise to secure access to a sural nerve branch graft from the lateral aspect of the foot, just in case (► Sect. 5.3.6). Washing and draping is done in a standard fashion, and the microscope is adjusted and draped.
The translabyrinthine approach should be tailored to the size and position of the AN. Intracanalicular disease can often be managed without mobilization of the sigmoid sinus, whereas large or giant tumors require more mobilization of adjacent structures, sometimes including division of the superior petrosal sinus and the tentorium.
The skin incision is taken to the fascia/pericranium, and the skin flap is dissected separately and turned forward. About 5 mm inside the skin incision, the fascia/pericranium is incised and turned forward with exposure of the bone. ◘ Figure 5.47 shows the «mind map» (some would say «mine map») of the translabyrinthine approach. By memorizing the sequence of landmarks before surgery, the rather complex approach soon becomes familiar, as the landmarks become waypoints on the route to the meatus. The bony exposure stops where the spine of Henle (◘ Fig. 5.47a) marks the edge of the external meatus (◘ Fig. 5.47b). The fascia/pericranial flap is turned forward and retracted together with the skin flap.
Fig. 5.47
«Mind map» of landmark waypoints on the translabyrinthine route to the right meatus, depicted in a schematic fashion. Although not all surgeons progress in the same sequence, it is useful to memorize the landmarks. For the experienced AN surgeon, this becomes a subconscious routine, and the focus can then be on the individual anatomy of the patient. Letters: a external auditory meatus, b spine of Henle, c temporal dura, d sigmoid sinus, e retrosigmoid posterior fossa dura, f presigmoid posterior fossa dura, g superior petrosal sinus, h mastoid antrum, i lateral semicircular canal, j fallopian canal with descending facial nerve, k posterior semicircular canal, l jugular bulb, m superior semicircular canal, n endolymphatic duct, o internal acoustic meatus
The triangular area defined by the temporal dura (◘ Fig. 5.47c), the external meatus, and the sigmoid sinus (◘ Fig. 5.47d) is drilled away, and the temporal dura and the sigmoid sinus are exposed. The temporal dura can be quite vascular, and a postoperative extradural hematoma is a risk if this bleeding is arterial and not managed effectively. Pneumatization of the mastoid process (◘ Fig. 5.44) may make this part very easy and quick but can also pose a higher risk during facial nerve exposure as the fallopian canal and descending part of the facial nerve can then be suspended in an air cell. It is important to expose a few mm of the posterior fossa dura (◘ Fig. 5.47e) behind the sigmoid sinus to allow dynamic retraction during tumor excision. During the exposure of the sigmoid sinus, the emissary vein(s) may lead to profuse bleeding. The veins(s), large or small, can be pushed toward the sinus, backward out of their canal, with repeated application of bone wax on a thin dissector. The vein is then appearing as a small hose when the bone has been removed and can then be safely coagulated. Lesions of the sigmoid sinus are not unusual and can be dealt with by a piece of muscle or Spongostan and a 4-0 resorbable suture. The presigmoid dura (◘ Fig. 5.47f) and superior petrosal sinus (◘ Fig. 5.47g) can then be identified. The antrum (◘ Fig. 5.47h) is found at a vertical line directly underneath the spine of Henle. As a positive identification of the antrum, the short process of the incus is seen protruding from the middle ear cavity. Further bone is removed at the posterior aspect to identify the dense bone of the labyrinth (◘ Fig. 5.44), without getting near the fallopian canal. There is no need to identify the digastric groove for this approach.
The microscope is introduced, and the pace is now slowed down significantly. The lateral semicircular canal (◘ Figs. 5.47i and 5.48) is an important landmark for the descending facial nerve in the fallopian canal (◘ Fig. 5.47j). While exposing the labyrinth, either the posterior (◘ Fig. 5.47k) or lateral (◘ Fig. 5.47j) semicircular canal is encountered first. Careful drilling lateral to the lateral semicircular canal will show a white–gray color change and tiny blood vessels as a warning before the nerve is exposed (◘ Fig. 5.48). Even with a thin bony cover, the nerve can be identified with the nerve stimulator on a high stimulus current such as 0.3 mA. The canal is opened just enough to get a reliable EMG response, which is then used as a reference when needed during the rest of the procedure. A long latency, low amplitude, polyphasic response, already at this stage, is a warning of a very thin facial nerve on the tumor and a difficult high-risk nerve dissection. A sharp bone edge is shaped along the fallopian canal for a safe identification before further drilling is performed. The next structure to look for is the jugular bulb (◘ Fig. 5.47l), which will show as a rounded darkening of the bone at the lower aspect of the exposure. The superior semicircular canal (◘ Fig. 5.47m) is removed toward the temporal dura. The endolymphatic duct (◘ Fig. 5.47n) will appear at further dissection between the temporal bone and the posterior fossa dura anterior to the sigmoid sinus. The dural component of this can be pulled out of the bony canal or transected. It is now important to expose the meatus at the central part, not at the fundus, where the risk of facial nerve damage is higher. The bone is gradually removed above and below the meatus to get at least 180° opening of the meatus. Whether the fundus needs to be opened depends on the extension of the tumor. When the bony crest between the upper and lower vestibular nerves (Bill’s bar) can be identified with a blunt micro hook, sufficient fundus exposure has been achieved. It is the removal of the bone superior to the meatus that carries the highest risk of facial nerve damage.
Fig. 5.48
Intraoperative photo showing the identification of the facial nerve (black arrows) in the fallopian canal on the right side. The lateral semicircular canal (lsc) is an important landmark found posteroinferiorly to the facial nerve at the same depth, as illustrated. The facial nerve is still covered by a thin window of the bone
The dura is opened in a linear fashion from the sigmoid sinus to the meatus. The facial nerve position in the medial part of the meatus is examined with the nerve stimulator. The CSF is released by a careful mobilization of the tumor capsule with a dissector at the inferior aspect toward the cisterna magna. It is now time for tumor excision (see below).
Retrosigmoid (Suboccipital) Approach (◘ Video 5.4)
The patient is in general anesthesia without paralysis and placed on the operating table in the prone position with the head rotated 30° toward the same side and fixed in 3- or 4-point fixation. Some surgeons prefer the sitting position or park-bench position for this approach. The area behind the ear is shaved, and a straight oblique incision is marked from 3 cm above the asterion (◘ Fig. 5.49a) to the spinous process of C2 (◘ Fig. 5.34). The incision line is infiltrated with local anesthetic. The facial electrodes, ground electrode, and reference electrode are placed, and the system is tested. If needed, electrodes and sound applicator for cochlear nerve monitoring are mounted and tested. Washing and draping is done in a standard fashion, and the microscope is adjusted and draped. The skin is incised straight to the bone starting above the asterion (◘ Fig. 5.49a), and the muscles are then divided to expose the posterior fossa bone toward the foramen magnum. Self-retaining retractors are placed. A groove is drilled along the sigmoid sinus to expose the dura just medial to the sinus. Exposed air cells are sealed with bone wax. The emissary vein(s) (◘ Fig. 5.49b) will be encountered at this stage and can be managed by pushing bone wax repeatedly into their bony canal. In this way, the vein is dissected backward out of the canal and can be coagulated on the sigmoid sinus (◘ Fig. 5.49c) when the bone is removed. The groove should go as far as the transition between the sigmoid and transverse sinuses (◘ Fig. 5.49d). From this point, a craniotomy can be performed with the craniotomy attachment, avoiding a lesion to the transverse sinus. The craniotomy should be 3–4 cm wide and reach close to the foramen magnum, to allow CSF release. It is important to expose the entire medial edge of the sigmoid sinus to reduce cerebellar retraction during tumor removal. From this point, the remaining part of the approach is intradural, and as large AN will be encountered before the meatus is opened, some preliminary tumor resection may be needed to allow a space for opening of the meatus. The dura (◘ Fig. 5.49e) is opened along the sigmoid sinus in a curved fashion with a distance of 5 mm to the sinus to allow watertight closure. Avoid cruciate or t-shaped incisions as these are very difficult to close watertight. The microscope is introduced. By carefully passing a brain retractor, sliding between the dura and cerebellum, toward the foramen magnum, it is possible to open the cisterna magna with a blunt hook and get CSF release. This is a critical step, and with larger tumors, further progress is almost impossible without this maneuver. When CSF is released, there may be tension and tear of a posterior bridging vein (◘ Fig. 5.49e) entering the tent, or tear of the petrosal vein (◘ Fig. 5.49f), situated with significant variations somewhat deeper in the angle between the tent and the petrosal dura. The vein passing from the cerebellum to the tent posteriorly can be identified and divided, whereas the petrosal vein should be preserved when possible [47]. The cerebellum (◘ Fig. 5.49h) is displaced posteriorly, and the brain stem (◘ Fig. 5.49i) comes into view. The jugular foramen (◘ Fig. 5.49j) is identified with the lower cranial nerves (◘ Fig. 5.49k). For hearing preservation, the meatus (◘ Fig. 5.49l) is now opened from behind, 180°. While drilling, the cerebellum is best protected by large pieces of Spongostan, which will not be caught in the drill. The posterior semicircular canal (◘ Fig. 5.45) will be the limitation of the meatal opening, and access to the fundus is not always possible. If this is the case, the fundus can be assessed with the aid of an endoscope at the end of tumor excision (see below).
Fig. 5.49
«Mind map» of landmark waypoints on the retrosigmoid (suboccipital) route to the right meatus, depicted in a schematic fashion. Letters: a asterion, b emissary vein, c sigmoid sinus, d transverse sinus, e posterior fossa dura after opening and retraction, f bridging the vein between the cerebellum and the tent, g petrosal sinus, h right cerebellar hemisphere, i brain stem, j jugular foramen, k lower cranial nerves, l internal acoustic meatus
Subtemporal (Middle Fossa) Approach
The patient is in general anesthesia without paralysis and placed on the operating table in the supine position with the head rotated 60° toward the opposite side and fixed in 3- or 4-point fixation. The area above the ear is shaved, and a curved incision is marked from the zygomatic arch to the top of the mastoid process, centered above the top of the pinna (◘ Figs. 5.34 and 5.50a). The incision line is infiltrated with local anesthetic. The facial electrodes, ground electrode, and reference electrode are placed, and the system is tested. If needed, electrodes and sound applicator for cochlear nerve monitoring are mounted and tested. Washing and draping is done in a standard fashion, and the microscope is adjusted and draped. The skin is opened and reflected downward as a separate flap. Then the temporal muscle fascia is incised, and the temporal muscle is reflected forward in order to preserve its nerve and blood supply. A small burr hole is placed at the root of the zygomatic process (◘ Fig. 5.50b) and a small craniotomy performed, with two-thirds anterior and one-third posterior to the external meatus. Opening of mastoid air should be avoided, if possible, as this increases the risk of postoperative CSF rhinorrhea. After leveling the inferior edge (◘ Fig. 5.50c) of the craniotomy with the anterior surface of the petrous bone, extradural dissection is started. Extradural retraction of the temporal dura (◘ Fig. 5.50d) is needed. As there is no direct temporal lobe contact, the impact of retraction is less, and gradual increase of the retraction will displace CSF and compensate for the lack of open CSF release. Custom-made retractor systems fixed on the craniotomy edge exist for the subtemporal approach, but retractors fixed to the head fixation system can also be used. Although fixed retraction should generally be avoided in skull base surgery, this may be the exception, even when using the four-hand technique. Landmarks on the petrous bone are the arcuate eminence (◘ Fig. 5.50e), hiatus facialis (◘ Fig. 5.50f), greater superior petrosal nerve (GSPN, ◘ Fig. 5.50g), foramen spinosum (◘ Fig. 5.50h) with the middle meningeal artery, and foramen ovale (◘ Fig. 5.50i). Watch out, as the facial nerve at the geniculate ganglion, the superior semicircular canal at the arcuate eminence, and the carotid artery (◘ Fig. 5.50j) at the GSPN may be dehiscent. If the superior semicircular canal is opened or dehiscent, keep the suction away from the opening and seal it with a small piece of fascia or pericranium. After the extradural dissection, the landmarks are as outlined in ◘ Fig. 5.50. The internal meatus (◘ Fig. 5.50j) is found at a line approximately 60° from the GSPN or, if measuring the angle between the arcuate eminence and the GSPN, at the junction between two-thirds and one-third measured from the GSPN. With the tip of a spatula locked at the petrous ridge, the inner part of the meatus should be identified and opened first. This part of the meatus is up to 10 mm below the surface of the bone, as opposed to the thin bone covering the fundus and geniculate ganglion at the lateral aspect. The meatus is then opened 180° backward toward the fundus. Due to the position right under the dura, the facial nerve is at high risk, especially from heat produced by the drill. Is it important not to open the cochlea just anterolateral to the fundus and posteromedial to the carotid artery and GSPN? The middle ear cavity is just lateral to the superior semicircular canal and should not be opened either, due to the risk of CSF leak. The dura is opened very carefully, as the facial nerve is not protected by the vestibular nerves, as it is in the posterior fossa approaches. The dissection and removal of the tumor in the meatus follow the same principles as with other approaches. The approach can be extended by transection of the superior petrosal sinus and the tentorium, but this will only give a slightly better exposure of the posterior fossa, and the subtemporal approach is not advisable for large ANs. Tumor excision then follows (see below).
Fig. 5.50
«Mind map» of landmark waypoints on the subtemporal (middle fossa) route to the right meatus, depicted in a schematic fashion. Letters: a top of the pinna, b theca externa of the temporal bone, c craniotomy edge, d temporal dura, retracted, e arcuate eminence covering the superior semicircular canal, f facial hiatus, g greater superficial petrosal nerve (GSPN), h foramen spinosum (with middle meningeal artery divided), i foramen ovale, j petrous segment of the internal carotid artery, k internal acoustic meatus
Retrolabyrinthine Presigmoid Approach
This approach is performed with the same steps as in the translabyrinthine approach but without the labyrinthectomy. The labyrinth is blue lined. Access is narrow, and good exposure of the retrosigmoid dura is required, allowing retraction of the sigmoid sinus. This technique can be used for small or intracanalicular AN not extending to the fundus. The technique has also been demonstrated for endoscope-assisted removal of large AN [45].
Retrosigmoid Fully Endoscopic Approach
While many surgeons have used the endoscope to assist AN surgery, this procedure is new and at the pioneering stage, with few publications of results [65–67]. The patient is in general anesthesia and placed in the supine semisitting position with the head rotated 60° to the opposite side. The approach corresponds to that used for microvascular decompression of the trigeminal nerve, and the landmarks correspond to those used for the retrosigmoid approach. The details of the endoscopic procedure are described in [65].
Tumor Excision
After dural opening, CSF release, and identification of the facial nerve in the meatus, stepwise central debulking followed by dissection of capsule is the standard way forward. For small tumors, the vestibulocochlear and facial nerve can be identified early at the brain stem, and tumor dissection is then fairly straight forward in terms of surgical anatomy but still sometimes time consuming. In large tumors, it is extremely important to find and keep the plane between the arachnoid membrane and tumor capsule. After stimulation of the capsule, the initial debulking at the dorsal aspect of the tumor may be done with rongeurs, followed by ultrasonic aspirator. Low suction on the aspirator reduces the risk of breaching the capsule with damage to nerves, vessels, and brain stem. If in doubt, the stimulator can be used at increasing stimulation strength to judge the thickness of capsule between aspirator and facial nerve. The cerebellum, lower cranial nerves, trigeminal nerve, and brain stem are successively dissected free and covered by cottonoids, and the petrous vein is preserved, if possible. The choroid plexus at the foramen of Luschka is a landmark for the vestibulocochlear root entry zone, and the facial root exit zone is found a few millimeters anterior to this. In between, the intermedius nerve can often be seen as a thin thread, but this nerve may also exit the brain stem with the facial or vestibulocochlear nerve. The course of the facial nerve is on the anterior tumor surface in 90% of the cases [63], although the position varies somewhat with tumor size [64]. An anterosuperior course is the most likely followed by anterior central and anterior inferior. One-third of medial acoustic neuromas [77] with little or no meatal tumor have a split facial nerve [73] compared to only 2% when the tumor is reaching the fundus [73]. More than 3% may have a dorsal course of the facial nerve over the tumor surface, and this variant is associated with less complete tumor removal and a higher re-treatment rate compared to anterior courses of the nerve [56]. The facial nerve can be trapped between cystic elements of an AN, but a true intratumoral location of the facial nerve is fortunately rare.
The steps and progression of the tumor removal vary between surgeons. Some prefer an early dissection at the meatus, whereas others find the facial nerve at the brain stem first. The facial nerve can make a significant loop on the anterior aspect of the tumor. The most difficult place to get the right plane between the facial nerve and the tumor is at the porus edge, and here, the best approach is from proximal to distal, if the space allows. When dissection is carried out from proximal to distal, the remaining tumor may end up being attached only to the facial nerve. This happens more often with medium-sized AN and carries a high risk of facial nerve damage by displacement. If the facial nerve is torn or transected and without continuity, the connection between the proximal and distal ends must be restored immediately in the same surgical session. There are very few good reasons to postpone this to a second stage surgery. The remaining AN is removed, and the ends are approximated directly or connected with a sural or greater auricular nerve graft (► Sect. 5.3.6).
If a nerve block occurs during tumor excision, this might disappear after a few minutes, and the EMG signal then comes back. If the nerve is structurally intact and nerve block remains despite technical integrity of the facial nerve monitor, additional «safe» tumor may be removed before stopping surgery. The process of facial nerve dissection requires dexterity, patience, and stamina, and it is sometimes utterly painstaking. Here it is worth remembering that «just a few more moments of your time may save a lifetime of misery for your patient» (said by Professor Ugo Fisch to his fellow Michael Gleeson in 1985).
Hemostasis
Intracranial postoperative hematoma is a life-threatening complication to AN surgery (◘ Fig. 5.51). It is easy to control bleeding when removing small- to medium-sized AN, whereas large and giant AN can have a rich blood supply in combination with involvement of «native» vessels on the tumor capsule and pose a much bigger challenge. The blood supply to the AN comes from the anterior inferior cerebellar artery, mainly from the porus edge, and as this is also a difficult location to oversee, angled bipolar forceps may be needed to obtain hemostasis here. To keep the progress during dissection of the tumor capsule, venous bleeding is sometimes best dealt with in a temporary fashion by a hemostatic agent such as Spongostan or Surgicel and cottonoids. After tumor removal, these sites then represent multiple «bombs,» with potential vigorous bleeding when the cottonoids are removed. The hemostasis’ work is often carried out at the end of a long operation, and the surgeon has to resist the temptation to accept a little oozing. At this point, application of further hemostatic agents such as Flowseal may help, if the exact location of the remaining bleed cannot be identified. Even when the rinsing water is crystal clear, a postoperative hematoma may form, for example, from a small artery, which has come out of spasm after closure. The risk of postoperative hematoma, and the sometimes sinister consequences of not identifying this at an early stage, warrants overnight recovery in an intensive care setting.
Fig. 5.51
Axial CT scan showing a postoperative hematoma (h) after translabyrinthine approach and total removal of a large AN on the right side. The hematoma was evacuated acutely and the patient recovered with some ataxia. Fat graft (f)
Closure
The dura cannot be closed in a watertight fashion in the translabyrinthine, presigmoid, and subtemporal approaches, whereas this is usually possible for retrosigmoid approach whether endoscopic or not. It is important to seal all air cells opened on the way in. There may not be obvious air cells when the meatus is drilled open in the retrosigmoid approach, but this should be checked, as this is a common site for CSF fistula. After suturing as much of the dural opening as possible, the abdominal fat is used to obliterate the dead space left in the translabyrinthine and presigmoid approaches. Fat, fascia, or muscle or a combination of this can be used to seal the antrum and middle ear. Care should be taken not to damage the chorda tympani, if the incus is removed. Fibrin or artificial sealant can be applied to reinforce the closure. Bone cement or bone chips collected during the mastoidectomy are also used to various extents for this purpose. The soft tissues should always be closed in two layers with the fascia acting as an internal compression of the fat graft, if this is used. Finally, a tight head bandage is applied.
5.3.5 Complications of AN Surgery
The mortality from AN surgery is less than 1%, and of the general surgical complications, postoperative hematoma is responsible for two-thirds of the mortality [70].
The risk of complications is related to tumor size. Facial palsy, CSF leak, trigeminal and lower cranial nerve deficits, wound infection/dehiscence, vertigo, and ataxia are other complications. The special management of facial nerve injuries is covered in the following chapter.
5.3.6 Management of Facial Nerve Complications in Skull Base Surgery
Characteristics and Time Course of Deficits After Facial Nerve Lesions in Skull Base Surgery
Facial nerve damage is a relatively common complication following lateral skull base surgery. Focus is usually on the weakness of the face, but a number of other complaints can be related to facial nerve lesions intracranially or in the base of the skull. In addition to facial weakness, patients may also complain of ipsilateral symptoms relating to tear production, salivation, taste, sensation in the outer ear canal as well as ear pain, dryness in the nose, and less often hyperacusis. ◘ Figures 5.52 and 5.53 show a schematic overview of the function of nerve fibers carried in the facial nerve and the likely deficits resulting from facial nerve lesions at different levels from the brain stem to the stylomastoid foramen. Surgical lesions distal to the stylomastoid foramen, related to skull base surgery, are primarily lesions to the frontal branch, which can be seen after an orbitozygomatic approach. These lesions can be avoided [69].
Fig. 5.52
Schematic outline of the facial nerve and its branches at different anatomical levels. Note that the facial nerve carries fibers from the intermedius nerve. This nerve leaves the brain stem together with the eighth nerve or between the facial nerve proper and the eighth nerve. The Obersteiner–Redlich (O–R) zone is the zone of transition between central and peripheral myelin and hence the level from which regeneration of axons is possible. The capital letters A–H refer to ◘ Fig. 5.53
Fig. 5.53
Components and functions of the facial nerve. Typical complaints after damage and likely involvement (dark gray) after damage at different levels (A–H) depicted in ◘ Fig. 5.52. * The intermedius nerve is often damaged in its cisternal course if the facial nerve is damaged at the same level, for example, during removal of a large acoustic neuroma
When the facial nerve is transected at a certain level, immediate deficits will follow, but an acute facial paralysis will not present in the same fashion in all patients. Depending on the age of the patient and the status of the muscles, the resting tone in the face after complete denervation may be enough for sufficient eye closure, at least for some days after the lesion, and in some patients for much longer. In other patients, eye closure is a problem from the outset. With the facial nerve damaged, but in continuity, the clinical picture may range from paralysis to a discrete paresis with a variety of deficits related to the functions carried by the intermedius nerve (◘ Fig. 5.53). Function may then return over a period of weeks (no axonal loss) to months (axonal loss) depending on the nature of the lesion.
Even with a normal facial nerve function the day after surgery, some patients will experience a delayed reaction with a significant facial palsy. This usually occurs within the first weeks after surgery, and in the absence of postoperative infection or hematoma, the patient should be reassured that function will return to near normal. A short course of high-dose steroids has been suggested in this situation, but this is not based on a strong evidence.
Identification of Facial Nerve Problems During Surgery
The motor function of the facial nerve can be monitored intraoperatively (► Sect. 5.3), and this should be done in all lateral skull base surgery, where manipulation of the facial nerve is likely. Loss of the electromyography (EMG) response during surgery can happen due to physical damage to the nerve, due to heat from the bipolar coagulation or drill, or due to ischemia. If the nerve is not divided, a conduction block may only be temporary, and in that case, the EMG response may sometimes recover after a while [55]. There is currently no method of intraoperative monitoring of the functions carried via the intermedius nerve.
Intraoperative monitoring of brain stem function by auditory evoked potentials and sensory evoked potentials may reveal damage to the brain stem. Although there is some variation in the blood supply to the pons, lesions affecting the facial nucleus are most likely due to occlusion of the anterior inferior cerebellar artery or the pontine perforators from the basilar artery.
Same Stage Management of Intraoperative Facial Nerve Lesions
Loosing facial nerve continuity during a skull base procedure is unnerving, but failure to repair the nerve in the same procedure, if possible, is unreasonable. If a surgeon is skilled enough to perform complex lateral skull base surgery, he or she should also know the simple technique on how to repair a complete facial nerve lesion.
Direct End-to-End Anastomosis
In a situation where the continuity of the facial nerve is lost during surgery of a benign pathology, the best recovery of function will result from a direct end-to-end anastomosis. This is often possible in acoustic neuroma surgery, where the nerve may be elongated by the tumor, allowing the ends to reach after complete tumor resection. There is very little peri- or epineurium in the cisternal segment of the nerve, so suture is not a good option if the lesion is at this segment. Instead, the ends should be adapted on the dura or a piece of Gelfoam, and the position then is secured by fibrin glue, which is sufficient to resist the forces applied by change of the head position during postoperative mobilization. Postoperative function is likely to return to House–Brackmann grade (HB) 2–3, with a good resting tone. If the ends do not reach each other without tension, an interpositional nerve graft is needed.
Interpositional Nerve Graft
The donor nerve for an interpositional nerve graft should match the size of the facial nerve. The great auricular nerve runs superficial to the sternomastoid muscle and is easily available with a minor extension of the original incision in most lateral skull base approaches. Sensation over the parotid gland, over the mastoid process, and on the ear will be lost. A good alternative is one of the terminal branches of the sural nerve, which can be harvested with very little morbidity just distal to the lateral malleolus, and has a diameter similar to the cisternal segment of the facial nerve. If a longer graft is needed, the sural nerve is the best choice, as only 3–4 cm can be harvested from the great auricular nerve as opposed to 20 cm from the sural nerve. A third option is an allograft [31], which works well for shorter nerve gaps but is currently quite costly and not readily available in all parts of the world. After end-to-end adaptation, the anastomosis is secured with fibrin glue if the lesion is intracranial. If the distal anastomosis is extracranial, two 7-0 nylon sutures secure the anastomosis here. It is important to reverse the nerve graft distal to proximal to avoid that regenerating axons are misdirected by small nerve branches along the course of the graft.
Second Stage Management of Intraoperative Facial Nerve Lesions
In a few patients, the facial nerve function is permanently lost due to complications of a skull base procedure. This may, despite loss of the EMG response during surgery, not be clear from the outset, as some hope for facial nerve recovery will exist when the facial nerve is left in anatomical continuity. When the facial nerve is obviously lost during surgery and there is for some reason no possibility of the same stage repair, or when no facial nerve recovery has happened after 6 months, a nerve transfer is usually the best option for reanimation of the face. This is hopefully not a routine situation in a skull base practice, and it is therefore advisable to seek help from, for example, peripheral nerve surgeons or plastic and reconstructive surgeons. If more than 18 months have passed since the lesion, the facial nerve and muscles are atrophied and unlikely to allow any recovery from a nerve transfer. In that situation, a cross facial nerve transfer to a free vascularized gracilis muscle graft or static procedures are the only options to restore symmetry and alleviate some of the problems experienced with facial nerve paralysis [29].
Hypoglossal-Facial Anastomosis
In this procedure, motor fibers from the hypoglossal nerve are directed into the facial nerve by means of an extracranial anastomosis between the two nerves. A side-to-end technique with or without interpositional nerve graft preserves function of the tongue and is now the gold standard ([25, 53], ◘ Fig. 5.54). Restoration of the tone and symmetry at rest (HB 3) is the most significant result, whereas few patients regain any social function, such as a spontaneous smile, although this has been seen, especially in young patients.
Fig. 5.54
Schematic drawings showing the principles of facial reanimation by hypoglossal–facial and masseteric–facial nerve transfers. a Hypoglossal–facial transfer with interpositional graft (sural or auricular donor nerve) and end-to-side connection to hypoglossal nerve. b Intratemporal transposition and direct end-to-side connection to hypoglossal nerve. c Masseteric to facial transfer with interpositional graft (sural or auricular donor nerve) and end-to-end connection to the masseter nerve
Masseteric-Facial Anastomosis
This procedure is gaining popularity and is probably the gold standard of the future. Results are now reported from a large series of patients [28, 30]. In this procedure, the masseter nerve is transected as proximal as possible and connected end to end to the facial nerve by means of a nerve graft (◘ Fig. 5.54). To lose the function of the masseter muscle on one side is bearable. Resting tone in the face is restored after the hypoglossal–facial anastomosis, but it seems that activation of the face is easier by clinching the teeth than by moving the tongue, and more patients regain some social function.
Cross Facial Nerve Transfer to Free Vascularized Gracilis Muscle Graft
This procedure works best for younger patients and is usually carried out by plastic and reconstructive surgeons. A sural nerve graft is anastomosed to the zygomatic branch of the contralateral facial nerve and tunneled subcutaneously to the paralyzed side. Time is allowed for regeneration of axons through the sural nerve graft, and a free vascularized gracilis muscle graft is then placed and allowed to be innervated by the axons from the opposite side. This provides some improvement, but the results are inferior to hypoglossal or masseter nerve transfers to the facial nerve.
Static Procedures and Muscle Transfer
A range of static procedures can help restore passive symmetry and eye closure [29]. These techniques include implantation of fascial slings, implantation of a gold weight in the upper eyelid, and partial tarsorrhaphy. In some situations, a transfer of the temporal muscle may restore some function.
Postoperative Care of Patients with Facial Palsy
In case of a partial palsy, facial exercises may improve function to some degree, but time is the most important factor in recovery. A range of specific techniques for facial exercises has been described, but there is currently little evidence for the effect [26]. Active facial exercises in the absence of any facial muscle function on the affected side are only going to increase the difference between the two sides, which will if anything worsen the cosmetic appearance. Passive exercise and massage should be used until reinnervation takes place. There is currently no good evidence for or against transcutaneous muscle stimulation to avoid atrophy while waiting for reinnervation. As some patients with facial nerve palsy also have reduced tear production and in addition with anesthesia of the cornea (due to a concomitant trigeminal lesion), focus on postoperative eye care is important to avoid corneal abrasions and reduced vision. Patients should have neutral eye drops and will often need an occlusive bandage at night.
5.4 Chordomas
Chordomas involve the central skull base in 30% of cases. This rare and locally malignant tumor has challenged the standard of care and has fascinated the skull base surgeons for decades. Uncertainty remains about the biological behavior, prognosis factors, and better treatment. Still some tumors will be cured with a single-session surgical procedure, while other patients will experience multiple regrowth and untreatable chordomas whatever we do. The role of adjunctive radiation therapy (RT), the technique to use, and the timing of RT are still under debate. Recent advances in skull base surgical techniques and refinement of endoscopic practice have brought new tools to offer a better radical resection than in the past. The goal of this chapter is to describe the different subtypes of skull base chordomas (SBCs) and to clarify the role and results of the microsurgical resection in the management of SBCs. We will exclude from our purpose the chordomas arising from the craniocervical junction and upper cervical spine.
5.4.1 General Considerations
Chordomas arise from the rest of vestigial notochordal cells. They represent 1–4% of primary bone tumors. SBCs represent 0.2% of all intracranial tumors and 6% of skull base tumors. Their incidence rate is about 0.08 per 100,000 patient-years. This incidence is twofold greater in males and fivefold greater incidence in the Caucasian population [81]. Chordoma families are rare. The tumor is rare before the age of 40. Peak incidence is in the fourth to seventh decade, and median age at the time of diagnosis is 60 years (range 3–95 years). About one-third of chordomas involve the clivus and spheno-occipital region (spheno-occipital synchondrosis). Luschka was probably the first to identify a jellylike tumor mass at the level of the clivus in 1856, but the link with notochord was originally understood by Ribbert in 1894. Cushing was the first to report a case of SBCs successfully removed in 1909.
5.4.2 Clinical Presentation
The interval between the first symptom and diagnosis is comprised of a few days to 3 years. Since the tumors are mainly located extradurally and are of slow growth, the symptoms are usually minimal. Headaches are poorly localized or retro-orbital. Intermittent or persistent diplopia is frequently encountered. Swallowing problem and gait difficulties are also reported. The most common finding on examination is abducens palsy. Dysphagia, hoarseness, facial numbness (30%), and gait ataxia are less common, depending of tumor location. Normal examination is described in 20% of patients. In the recent series published by George [89] about 58 SBCs, the most frequent symptom was diplopia in 43 patients, followed by headaches in 19 patients and visual field or visual acuity deficit in 15 patients.
5.4.3 Neuroradiology
SBCs usually originate extradurally, while primary intradural origin is very unusual. Dural invasion occurs at the late stage of their course. SBCs invade local and regional structures widely in an irregular fashion. SBCs mostly arise at the spheno-occipital synchondrosis and grow within the clival bone in the majority of cases. Parasellar area is involved in 60%, foramen magnum in 25%, CPA in 25%, infratemporal fossa in 10%, and parapharyngeal and/or retropharyngeal space in 10%. SBCs may remain focal and well circumscribed but display usually an aggressive pattern with regional and multifocal invasion. Seeding in the operative route has been reported in up to 7% of cases and metastasis in 7–12% of cases, particularly to the lungs, lymph nodes, and bones.
A careful neuroradiological work-up is required before treatment (◘ Fig. 5.55). There is a lack of reliable radiological finding that makes the distinction between chordomas and chondrosarcomas on CT scan and MRI. CT scan shows a well-circumscribed but invasive, lytic soft tissue lesion. The mass usually contains large calcifications and bone sequestra. CT is very useful to evaluate the bony extension. MRI is the single best imaging modality. SBCs display a homogenous hypointense T1 and bright hyperintense T2 signal. They are enhanced moderately and heterogeneously after contrast injection. The mass is polylobulated, and major vascular structures are displaced or encased in up to 80% of cases. Abnormal vascularity is generally absent on angiography, but angiography can be done to assess the vascularization of the brain if an arterial bypass and balloon occlusion test are considered. Preoperative embolization is worthless in the management of SBCs. SBCs should be differentiated from the ecchordosis physaliphora first described by Luschka and from benign notochordal cell tumors. Both are slow-growing tumor mass and can be assimilated to notochordal hamartomas.
Fig. 5.55
Imaging of various presentations of skull base chordomas according to their origin. Chordomas usually originate extradurally a and b. Sagittal contrast-enhanced T1-weighted magnetic resonance imaging (MRI) shows a heterogeneous enhancement linked to a variable calcified content a. Non-enhanced CT scan b reveals a slightly hyperdense mass which contains large calcifications and bone sequestra. Dural invasion may occur at the late stage of tumor growth c. Remnants of the notochord may be found in the intradural clival area; thus, purely intradural chordomas can be described d—T2-weighted MRI
5.4.4 Pathology
SBCs are grayish tumors and firm to gelatinous in consistency. They include foci of calcification and bone sequestra. Histologically they contain physaliphorous cells, which are large, vacuolated, and mucus-containing cells organized in a lobular pattern [95]. These cells express an immunoreactivity for EMA, cytokeratin, and rarely S-100 proteins. Brachyury has been more recently described as a powerful marker of chordomas, and co-expression of cytokeratin and brachyury by tumor cells reaches 100% specificity. Three histopathological variants are recognized: classic, chondroid, and dedifferentiated chordomas [82]. The distinctive prognosis value of these variants is not established. About 10% of chordomas show histologic features of malignancy. Chromosome aberrations (hypodiploid or near-diploid karyotypes) are described in 62% of tumor cell karyotypes. Chromosome 1 monosomy and gain of chromosome 7 are frequent chromosomal abnormalities. Genome analysis indicates losses on 1p (50%), while most frequent gains are on 7q in 75%. Linkage analysis showed defect of 1p36.13 in 85% of cases. Candidate genes in this region are well-identified tumor suppressor genes. A p53 deregulation is frequently observed.
5.4.5 Treatment
Conservative management or simple biopsy is not an option [88]. Historical reports indicate that in the absence of treatment, the tumor growth leading to death was the rule within 6 months to 2 years. Current treatment options rest mostly on level-4 and very limited level-3 evidence. It is recommended to manage the patients in multidisciplinary teams.
Surgical Treatment
Aggressive surgical resection is the standard of care for SBCs . The first shot should be optimal. We learn from the results of major series that repeated surgery is associated with worst prognosis in terms of progression-free survival (PFS), overall survival (OS), and morbidity [99]. For the last decade, the trend is to select endoscopic approaches considering the midline location and the extradural growth for most of these tumors. However, each surgical strategy is associated with proper limitations and complications.
A variety of open skull base techniques have been developed through lateral transpetrosal corridors but also transfacially and subfrontally. These approaches mainly proceed with a lateral-to-medial or superior-to-inferior trajectory via an extensive amount of bone resection. They expose the patient to some degree of brain retraction before and after dura opening and cranial nerve manipulation. The most illustrative technique is the subtemporal–preauricular infratemporal fossa approach [98]. This procedure exposes the two upper thirds of the clivus and petrous apex, cavernous sinus, and infratemporal fossa through an extended corridor. Less invasive are a variety of transpetrosal routes named epidural anterior petrosectomy or combined petrosectomy which are more dedicated to petrous apex and intradural petroclival area with limited control of the clivus. During these lateral approaches, at risk structures are the neuro-otological content inside the petrous bone, the brain stem and temporal lobe, the intradural cranial nerves, and the basilar artery including its branches and perforators. In the situation of repeated surgery for recurrent chordomas, particularly the ones that have been already irradiated, the scar tissues and the adhesion of the tumor to critical structures may complicate seriously the resection. In these same patients, reconstructions and closure may be technically challenging with a high risk of CSF leaks and meningitis.
Extended endonasal approaches are ventral, midline approaches that pass through the ethmoid and sphenoid sinuses [87]. They are very logical to reach and to fully expose extradural midline chordomas, taking advantage of natural anatomic corridors (sinuses and nasal cavities). The endoscope offers an access to the parasellar extension of chordomas inside the cavernous sinus and Meckel’s cave. Here, there is a need to perform an ethmoidectomy and translocate the carotid siphon medially to reach the lateral compartment. Technical variants are also required to reach the infratemporal fossa. The petrous apex is also under control, but while the tumor spreads toward the internal auditory canal and cerebellopontine angle, manipulation of the tumor becomes hazardous. In this latter situation, planning an additional transpetrosal procedure should be anticipated. Another limitation is the access to the compartment of the tumor that involves the carotid artery bifurcation and even more laterally which means that a combined endoscopic and transcranial strategy should be considered.
From an endoscopic endonasal perspective, the clivus is divided into superior clivus, middle clivus, and inferior clivus :
Superior clivus also called sellar clivus and formed by the dorsum sellae is limited superolaterally by the posterior clinoid processes, inferomedially by the sellar floor, and inferolaterally by cranial nerve VI through Dorello’s canal just below the level of the floor of the sella and medial to the paraclival segment of the internal carotid artery (ICA) located laterally.
Middle clivus, also named the sphenoidal clivus, extends vertically, from the sellar floor superomedially and Dorello’s canal superolaterally at the uppermost aspect of the petroclival fissure and the level where the ICA enters the cavernous sinus to the floor of the sphenoid sinus corresponding to the roof of the choana. The middle clivus is limited laterally by the paraclival ICA and petroclival fissure and inferolaterally by the lacerum segment of the ICA, the foramen lacerum above the fibrous attachments of the Eustachian tube, and the parapharyngeal muscles. The Vidian nerve is a key landmark as it runs within the Vidian canal through the pterygoid body just below the sphenoid body toward the lateral portion of the foramen lacerum.
Inferior clivus extends from the roof of the choana corresponding to the floor of the sphenoid sinus to the foramen magnum and is termed the nasopharyngeal clivus. The inferior clivus is limited laterally by the Eustachian tubes and more laterally by the parapharyngeal segment of the ICA.
The binostril-expanded endoscopic four-hand (surgical team including ideally an otorhinolaryngologist and a neurosurgeon) transclival approach is the endoscopic endonasal approach required for skull base chordoma resection. For the purpose of this surgical procedure-dedicated tools as neuronavigation using MR and angioMR imaging with CT, monitoring of cranial nerves in addition to brain stem and somatosensory evoked potentials, high-speed and low-profile extendable drill, surgical Doppler ultrasonography with microprobe, endonasal bipolar forceps, and low-profile ultrasonic aspirator is substantial.
First of all, if dural penetration is suspected, before opening the anterior midline wide corridor to the clivus, a posterior mucosal nasoseptal flap pediculated on the sphenopalatine artery is realized and kept in place in the oropharynx through the choana, unilaterally or bilaterally depending on the predictable size of the oteo-dural skull base defect to be reconstructed.
The widened endoscopic endonasal transclival approach requires the following steps: removal of the middle turbinate in one chosen nostril, outfracturation and lateral luxation of the middle turbinate in the other side, resection of the posterior portion of the nasal septum, large anterior sphenoidotomy, and removal of all the septa within the sphenoid sinus to allow identification of all the bone landmarks. These septa resections have to be realized up to their attachments such as to the opticocarotid recess paying attention not to damage the optic nerve or the ICA.
At this stage, the sphenoidal clivus (middle clivus) is exposed from the level of the floor of the sella turcica down to that of the sphenoid sinus corresponding to the roof of the choana.
Surgical endoscopic endonasal access to the sellar clivus (superior transclival approach) may require a pituitary gland superior transposition, extradurally, interdurally, or intradurally, with preservation of the stalk, to reach the dorsum sellae and the posterior clinoid processes.
To gain access to the nasopharyngeal clivus (inferior clivus), one must strip the nasopharyngeal fascia and completely remove the vomer and the floor of the sphenoidal sinus until the Vidian nerves are identified laterally exposing inferiorly the clivus up to the level of the Eustachian tubes.
A critical technical point when removing chordomas localized at the junction of the superior and middle clivus is to avoid damaging the abducens nerve when passing through Dorello’s canal and crossing the inferior side of Grüber’s ligament. The method consists of removing the bone and periosteal dura surrounding the superomedial attachment of Grüber’s ligament to posterior clinoid process and upper clivus in the interdural space, following its course inferolaterally to petrous apex until identification of the abducens nerve at their intersection point.
Extension of SBCs in the suprasellar suprachiasmatic area and the anterior cranial fossa across the anterosuperior aspect of the pituitary fossa requires the transtuberculum–transplanum module, which is limited laterally, from posterior to anterior, by medial opto-carotid recesses which are landmarks of the optic nerves in the optic canals and paraclinoid segments of the ICA, optic nerve prominences, and lamina papyracea (medial wall of orbits). It consists of completing the anterior rostral exposure by performing a posterior ethmoidectomy until identification of the posterior ethmoidal arteries anteriorly and leaving the rostral attachments of the nasal septum to the ethmoid roof thus to minimize the risk of damaging the olfactory nerve endings. Once this has been done, the tuberculum sellae and the planum sphenoidale are removed in a posteroanterior direction.
In the midline, rostro-caudally, there is no limitation of the endoscopic endonasal transclival approach from the frontal sinuses to the craniovertebral junction.
When addressing extension of SBCs lateral to the parasellar and paraclival ICA (cavernous sinus, lateral recess of the sphenoid sinus, Meckel’s cave, middle cranial fossa) or at the level of petrous bone, above or under the horizontal ICA, the basic transpterygoid route is required using the maxillary sinus as a working corridor which can be widened if needed to get access to the most lateral aspect of the posterior wall of the maxillary sinus and the infratemporal fossa. This is performed in a stepwise manner, starting with a wide midmeatal antrostomy (uncinectomy added to the previously completed middle turbinectomy) followed by a medial maxillectomy and extending to an ipsilateral anteromedial maxillotomy. Once this wide nasomaxillary window is opened, the posterior wall of the maxillary sinus and the ascending process of the palatine bone are removed to expose the pterygopalatine fossa. The content of the pterygopalatine fossa is then mobilized laterally once the sphenopalatine artery and posterior nasal branch have been coagulated and transected. The Vidian canal is exposed just lateral to the junction of the sphenoid floor with the base of the medial pterygoid plate and drilled, following the Vidian artery posteriorly as an inferolateral landmark for the anterior genu of the ICA. Once the anterior genu has been isolated, then the bone surrounding the horizontal segment can be removed proceeding the drilling in a caudal to rostral trajectory from the inferior margin of the medial pterygoid plate to flush its plane to the middle cranial fossa and foramen rotundum. The bone around the maxillary nerve is removed until it disappears into the dura mater of the middle fossa drilling away the bone located between the foramen rotundum and the Vidian canal toward the junction of the horizontal petrous segment of the ICA and its anterior genu giving access under the ICA horizontal petrous segment to the petroclival synchondrosis. The ICA is then followed superiorly from the genu, and the bony carotid parasellar prominence is removed exposing the quadrangular space which is bounded by the parasellar ICA medially, the maxillary nerve laterally, the horizontal petrous ICA inferiorly, and the abducens nerve superiorly. Removing the bone surrounding the ICA allows lateralization to gain access to the medial petrous apex. The quadrangular space gives access to Meckel’s cave and middle cranial fossa. Passing above cranial nerve VI gives access to the superior portion of the cavernous sinus. Caudally the dissection can be pursued laterally identifying the lateral pterygoid plate which is drilled rostrally to flush its plane to the middle cranial fossa and foramen ovale opening the access to the posteromedial part of the infratemporal fossa.
Lateral spreading of the tumor from the inferior clivus and foramen magnum, to the level of hypoglossal canal within the occipital condyle, and to the jugular foramen may require in addition to the transpterygoid corridor a resection of the Eustachian tube enlarging the route laterally until the limit of the parapharyngeal ICA.
At the end of an endoscopic endonasal transclival procedure, when the dura has been violated, obtaining a watertight closure to prevent CSF leak is mandatory. The osteo-dural skull base defect repairing can be realized in five steps, first, filling the intradural dead space and reestablishing an arachnoidal tissue barrier using a thin layer of fibrin glue and then covering the dural aperture using a single layer of dural substitute positioned extradurally. Once this has been achieved, overlapping and embedding the extradural space with resorbable semirigid material shaped to conform to the bony defect and drag the dural substitute extradurally in an overlay mode, therefore, the vascularized pediculated nasoseptal mucosal flap is placed over the reconstruction of the clivus to support it and, finally, packing of the sphenoid cavity using abdominal fat to fill it and hold the reconstruction in place.
◘ Table 5.1 displays the results of a series that included 20 patients and more operated via selected transcranial skull base approaches or EEAs. It seems difficult to conclude for the superiority of one approach than the other. In a recent review done by Komotar et al. [91] about clival SBC, a higher rate of GTR in the EEA group than in the transcranial group, lesser cranial nerve deficits, and no difference in CSF leak percentages was shown. But an attempt to compare complication rates and oncological results in both groups looks inadequate: The retrospective design of reports, the lack of controlled studies, the interferences of redo surgery, and the heterogeneity of postoperative RT regimen are serious limitations. Moreover, the authors of this review stressed that approaches targeted different tumors in terms of location with more cavernous sinus invasion in the group of EEA and more petrosal and intradural invasion in the open group [91]. Shorter follow-up in the EEA group is another significant limitation.
Table 5.1
Operative outcomes and complications in open versus endoscopic resection of clival chordomas
Technique | Autors | Nb | Previous Surg (%) | Mean Age | Gross Tot. Resect. (%) | Near Tot. Resect. (%) | Partial. Resect, (%) | Mean FU | 1 yr PFS (%) | 5 yrs PFS (%) | lyr OS (%) | 5 yrs OS (%) | CSF Leak (%) | Meningiti dis (%) | CN palsy (%) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Transcranial approaches | Colli and Al-Mefty [85] | 53 | 28 | 41 | 45 | 28 | 26 | 46 | 80 | 51 | – | 86 | 5 | 1 | 22 |
Samii et al. [97] | 37 | – | 38 | 49 | 50 | 63 | 78 | 18 | – | 65 | 5 | 5 | 12 | ||
Takahashi et al. [101] | 32 | – | 41 | 15 | 17 | 36 | 50 | 29 | 92 | 92 | 7 | 7 | 20 | ||
Wu et al. [103] | 79 | 22 | 36 | 11 | 51 | 17 | 64 | 81 | 53 | 87 | 68 | – | – | 25 | |
Sen et al. [99] | 45 | 27 | 41 | 58 | 42 | 60 | – | 48 | – | 75 | 20 | 15 | 95 | ||
Di Maio et al. [86] | 95 | 55 | 42 | 71 | 29 | 38 | 80 | 56 | 90 | 74 | 6 | 25 | |||
Komotar et al. [91] Review | 639 | 33 | 43 | 48 | 48 | 4 | 59 | 66–80 | 69 | – | 66 | 7 | 6 | 24 | |
Endoscopic endonasal approach | Stippler et al. [100] | 20 | 40 | 45 | 20 | 35 | 13 | 65 during FU | 95 during FU | 25 | 0 | 5 | |||
Koutourousiou et al. [93] | 60 | 42 | 41 | 67 | 25 | 8 | 14 | 67 during FU | 90 during FU | 20 | 3 | 7 | |||
Chibbaro et al. [84] | 54 | 40 | 49 | 65 | 17 | 18 | 34 | 78 during FU | 96 during FU | 8 | 14 | 0 | |||
127 | 33 | 44 | 61 | 27 | 12 | 18 | 83 during FU | 95 during FU | 5 | 1 | 1 | ||||
Indications for the selection of approaches incorporate the following parameters: The origin and extension of the SBC, as shown on the initial radiological work-up, is of paramount importance. The general condition and neurological status of the patient and history of previous surgeries are also considered. Petrous apex and petroclival location without moderate invasion of the bony clivus deserves lateral skull base approaches, while midclivus tumors are eligible for extended endoscopic approaches particularly when the intradural extension is reduced or absent. There are tumors that require combined approaches and that should be individually discussed by an expert skull base team who is trained to the full panel of techniques.
5.4.6 Radiation Therapy
In SBCS , postoperative radiation therapy is quite uniformly adopted as an adjuvant treatment. There are radiobiological and topographic arguments to favor proton therapy or combined proton and photon therapy versus conventional radiation therapy in SBCs. Reported by [94], the 3-year local control rate was 69.2% (+/-6.0%) for SBCs. The majority of treatment failures are due to dose limitations. The most frequent complications are visual decline (5%) and endocrine abnormalities (20%). Temporal lobe or brain stem radiation injuries are also reported (10%). Radiosurgery gives promising results (60% of 3-year PFS) with low rates of complications [92]. Long-term results are expected. To be effective, the treatment should be delivered on a residual tumor volume that does not exceed 30 cm3. Carbon ion irradiation is another option still confidential with recently published results [102] in a large group of 155 SBC patients.
◘ Table 5.2 indicates the main published series that included at least 20 patients in different RT protocols. Five- and ten-year PFS and OS are shown. Complications are also reported. For the reasons that were expressed about the surgical series, there is no clue about the standard of care to adopt with RT. The theoretical advantage of Bragg peak effect for the use of protons is counterbalanced by the limitations of available machines. Radiosurgery takes benefit of its extremely targeted treatment and few side effects but is limited on focal tumors and the need to precisely identify the limits of what should be treated which is challenging for locoregional tumors like chordomas. New RT techniques are emerging and will be evaluated with substantial delay.
Table 5.2
Studies and patient characteristics in published series of patients with clival chordoma treated with radiation therapy
Autors | Technique | Nb | Mean age | Prior RT (%) | Prior surg (94) | Mean FU | Median target Vol. (cc) | Median margin dose (Gy/CGE) | 5 yrs PFS (%) | 5 yrs OS (%) | Complication (%) |
Amichetti et al. [79] Review | PBRT | 416 | 38 | – | – | 46 | – | 66–83 | 69 | 80 | 5–17 |
Yasuda et al. [104] | PBRT | 30 | 45 | 45 | 30 | 46 | – | 68, 9 | 70 | 83 | 3 |
Amichetti et al. [79] Review | Carbon | 206 | 46 | – | – | 38 | – | 48–30 | 64 | 80 | 20 |
Amichetti et al.[79] | RT | 191 | 44 | – | – | 65 | – | 52, 7 | 36 | 36 | 0–5 |
Amichetti et al. [79] Review | FSRT | 45 | 37 | – | – | 27 | 56 (17–215) | 66, 6 | 50 | 82 | 2 |
Amichetti et al. [79] Review | GKS | 109 | 37 | – | – | 56 | 21.1 (0.4–129) | 15.4 | 56 | 75 | 0–33 |
Kano et al. [90] | GKS | 71 | 45 | 20 | 58 | 62 | 7, 1 (0, 9–109) | 15 | 66 | 80 | 8 |
Sahgal et al. [96] | IMRT | 24 | 46 | 0 | 24 | 36 | 14.5 (1.70–85.60) | 76
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