Clival, petroclival, and foramen magnum meningiomas are challenging lesions to manage independently of the selected surgical approach. The expanded endoscopic endonasal approach (EEA) provided a safe alternative on the armamentarium of skull base approaches. There is a paucity of literature regarding endoscopic management of meningiomas because of certain limiting factors, including rarity of the pathologic condition, technical challenges, expertise of the surgical team, and available resources. The surgical technique, possible complications, and postoperative care are described in detail. This article highlights the important aspects in choosing this surgical approach and managing ventral posterior fossa meningiomas through the EEA.
Key points
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Clival, petroclival, and foramen magnum meningiomas are challenging lesions to manage independently of the selected surgical approach.
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Current literature involving the endoscopic management of ventral posterior fossa meningioma is scant mainly because of rarity of the pathologic condition, limited indications, and technical difficulties in tumor resection and skull base reconstruction.
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The main challenge in the management of ventral posterior fossa meningioma is the surgical approach selection.
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Careful anatomoradiologic evaluation, patient’s clinical condition, and surgical team’s expertise must guide the surgical route selection.
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Nuances of the endoscopic transclival approach and skull base reconstruction are highlighted.
Introduction
Clival, petroclival, and foramen magnum meningiomas are challenging lesions to manage independently of the selected surgical approach and represent approximately 5% of all intracranial meningiomas. Despite reports of radiation therapy in its management, surgical resection continues to be the first and best treatment method aiming permanent tumor eradication.
The advances in the microsurgical technique, intraoperative monitoring, and radiologic imaging drastically improved surgical outcomes of meningiomas treated through posterior skull base approaches; however, the morbidity associated with the surgical resection of these tumors is still significant. New cranial nerve (CN) palsies or persisting/worsening of preexisting palsies is the most common morbidity, and it has been reported to range from 39% to 76% of the patients.
Driven by the revolution of endoscopic pituitary surgery, the development of the expanded endoscopic endonasal approach (EEA) and the associated surgical tools have pushed the limits of transnasal access to the ventral skull base. The EEA rapidly became a safe alternative on the armamentarium of skull base approaches and has been increasingly used in the management of ventral intradural posterior fossa tumors. It provides the advantage of direct access to pathologies with near-field magnification while minimizing manipulation of neurovascular structures and avoiding brain retraction, ultimately decreasing morbidity.
Nevertheless, unlike the EEA to sellar pathology, there is a relative paucity of literature regarding endoscopic management of meningiomas, more specifically, the ventral posterior cranial fossa meningiomas. The probable reason is the combination of limiting factors, including rarity of the pathologic condition, limited indication of approaching it through an EEA, technical challenges in tumor resection and skull base reconstruction, expertise of the surgical team, and available resources.
The current literature involving the endoscopic management of these meningiomas consists in the collective experience of an approach rather than experience with the particular type of tumor. Based on clinical experience and literature review, the authors highlight important aspects in choosing a surgical approach and managing ventral posterior fossa meningiomas through the EEA.
Introduction
Clival, petroclival, and foramen magnum meningiomas are challenging lesions to manage independently of the selected surgical approach and represent approximately 5% of all intracranial meningiomas. Despite reports of radiation therapy in its management, surgical resection continues to be the first and best treatment method aiming permanent tumor eradication.
The advances in the microsurgical technique, intraoperative monitoring, and radiologic imaging drastically improved surgical outcomes of meningiomas treated through posterior skull base approaches; however, the morbidity associated with the surgical resection of these tumors is still significant. New cranial nerve (CN) palsies or persisting/worsening of preexisting palsies is the most common morbidity, and it has been reported to range from 39% to 76% of the patients.
Driven by the revolution of endoscopic pituitary surgery, the development of the expanded endoscopic endonasal approach (EEA) and the associated surgical tools have pushed the limits of transnasal access to the ventral skull base. The EEA rapidly became a safe alternative on the armamentarium of skull base approaches and has been increasingly used in the management of ventral intradural posterior fossa tumors. It provides the advantage of direct access to pathologies with near-field magnification while minimizing manipulation of neurovascular structures and avoiding brain retraction, ultimately decreasing morbidity.
Nevertheless, unlike the EEA to sellar pathology, there is a relative paucity of literature regarding endoscopic management of meningiomas, more specifically, the ventral posterior cranial fossa meningiomas. The probable reason is the combination of limiting factors, including rarity of the pathologic condition, limited indication of approaching it through an EEA, technical challenges in tumor resection and skull base reconstruction, expertise of the surgical team, and available resources.
The current literature involving the endoscopic management of these meningiomas consists in the collective experience of an approach rather than experience with the particular type of tumor. Based on clinical experience and literature review, the authors highlight important aspects in choosing a surgical approach and managing ventral posterior fossa meningiomas through the EEA.
Indications/contraindications
Independent of the surgical route, there are prerequisites that must be met before surgery. Patient, disease, and surgeon factors must be considered, as described in Box 1 .
Patient factors include
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A suitable candidate for prolonged general anesthesia
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A patient with no significant comorbidities (eg, coagulopathy)
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An informed patient who is accepting of potential complications and resulting morbidity
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A patient who is motivated and compliant
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Disease factors include
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Ability to surgically resect or decompress the disease
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Favorable anatomy
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Surgeon factors include
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Appropriate experience and expertise
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Availability of equipment
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Intensive care or high-dependency neurosurgical postoperative care
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The difficulty in the management of ventral posterior fossa meningiomas is not deciding when to surgically treat it, but weighting the risks and benefits when selecting the surgical approach. Thus, appropriate case selection is vital to a successful outcome.
Indications
The indications for the surgical treatment of posterior fossa meningiomas are symptomatic lesions, asymptomatic lesion with a large volume, and tumor growth on radiologic follow-up. Among these cases, in ventral posterior fossa meningiomas, the main indication for an expanded EEA is the midline location of the dural base. The more medial the dural attachment, posterior the brainstem dislocation, and lateral the CN displacement, the better is the indication of approaching the tumor through an anterior route. In these cases, the transclival approach is the direct route to the tumor without the need of any brainstem retraction or crossing the plane of the CNs ( Fig. 1 ).
Clival meningiomas
Clival meningiomas have their primary base at the midline. They tend to displace CN V laterally and superiorly; CN VI laterally and posteriorly; CNs VII, VIII, IX, X, and XI posteriorly; CN XII posteriorly and inferiorly; and the brainstem posteriorly. The primary base and pattern of displacement makes clival meningiomas ideal for the EEA.
Petroclival meningiomas
Petroclival meningiomas have their primary base at the petroclival fissure and have a particular displacement pattern of surrounding structures. They tend to dislocate the CNs V, VII, VIII, IX, X, XI posteriorly; the CN VI medially; and the brainstem medially and posteriorly. The main advantage of approaching these tumors through an anterior route is the posterior displacement of most of the CNs. However, the medial displacement of CN VI may pose a significant surgical difficulty, and its injury risk must be weighted in the case selection. The midline component of these tumors is prone for an EEA resection. Nevertheless, petroclival meningiomas are unlikely to be completely removed through an endoscopic transclival approach because of their paramedian origin. It should be considered in combination with a posterior or lateral surgical route or when the surgical goal is brainstem decompression.
Foramen magnum meningiomas
Foramen magnum meningiomas may be cranial or spinocranial lesions. The spinocranial tumors have their origin below the foramen magnum and thereby displace the CNs and the vertebral arteries to the superior pole of the tumor. On the other hand, the cranial lesions may have its origin anywhere at the foramen magnum with different patterns of structures dislocation. The anterior cranial lesions originating at the anterior border of the foramen magnum are suited for the EEA. Their origin is medial to the hypoglossal and jugular foramen, so all the CNs are displaced posteriorly and laterally. However, the cervical extension of these tumors may pose a limitation for the EEA because of the craniocervical instability associated with the removal of the anterior arch of the C1, C2 odontoid process and its ligamentous complex. Therefore, a posterior approach is usually the choice for a single or first-stage surgery for ventral foramen magnum meningiomas that extend inferiorly to C1 and C2 levels.
Jugular tubercle meningiomas
The jugular tubercle meningiomas have their primary base at lateral location and tend to dislocate the CNs of the jugular foramen posteriorly and CN VI superiorly. In rare cases, the medial extension to the clivus makes the endonasal resection a possibility.
Contraindications
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Patient comorbidities precluding them from prolonged general anesthesia
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Lateral dural base of the meningioma
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Vascular encasement
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Unfavorable anatomy for transsphenoidal surgery
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No multidisciplinary service
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Lack of specialized equipment/instruments
Surgical technique/procedure
Preoperative Planning
Radiologic investigation
The evolution of imaging studies improved the preoperative information on the pathologic anatomy of the tumors, enabling surgeons to plan the intraoperative setting in greater detail. The radiologic preoperative investigation for a meningioma should always include computed tomography (CT) and MRI for bone and soft-tissue assessment, respectively.
Primary base of the tumor
Identifying the primary base of the meningioma is essential to understand the growth pattern of the tumor and its relationship to surrounding neurovascular structures, which may help predict intraoperative difficulties due to pathologic anatomy.
The T1-weighted with gadolinium-enhanced contrast imaging is the best MRI sequence to define the dural attachment site (dural tail) of the meningioma. Although MRI provides superior soft-tissue assessment, the CT scan with bone window remains the tool of choice for identifying calcification, hyperostosis, and osseous anatomy. Frequently, a hyperostotic bone is found at the primary base of the tumor. In addition, the CT scan bone assessment provides a better idea of the surgical corridor available and allows planning of the extent of bone removal necessary for tumor resection.
Vascular relationship
Angiographic studies (CT, MRI, or conventional) are also important to understand the vascular relationship in and around the tumor, including arterial encasement, blood supply, and venous drainage.
The presence of arterial encasement must be assessed before surgery so the internal debulking of the tumor can proceed safely ( Fig. 2 ). Arterial narrowing is highly suggestive of adventitia invasion, which hinders a total resection when the encased artery cannot be sacrificed.
Conventional angiography may also help to define whether sacrifice of the encased artery is possible by defining collateral flow and the patient’s tolerance to balloon test occlusion.
Regarding venous assessment, the patency of a venous sinus should be known if the posterior fossa meningioma is near one of them. Preoperative diagnosis of venous sinus occlusion makes the sacrifice of the involved segment a possibility.
Cranial nerve relationship
As mentioned previously, the primary base of the meningioma determines the pattern of CN displacement, hence the surgical corridors available for tumor resection. The evolution of MRI (steady-state free precession imaging/fast imaging employing steady-state acquisition) permitted clear identification of the CNs, instead of assuming their position based on the origin of the tumor.
Hydrocephalus
Posterior fossa meningiomas may cause obstructive hydrocephalus. In the presence of significant ventricular dilation and signs of elevated intracranial pressure, a temporary or permanent cerebrospinal fluid (CSF) diversion may be necessary before the surgical management of the tumor. In these cases, the insertion of CSF shunt immediately before addressing the meningioma may facilitate the intraoperative management of the posterior fossa tumor and may help prevent postoperative CSF leakage.
Nasosinusal assessment
Once the choice for EEA is made, the preoperative radiologic assessment of the nasosinusal region is imperative ( Box 2 ). A CT scan with slice thickness of no more than 3 mm (and preferably less) and coronal, axial, and parasagittal images of the paranasal sinuses and skull base are essential before surgery.
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Nasal septum deviations
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Integrity and degree of aeration of the paranasal sinuses (particularly the sphenoid sinus)
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Location and presence of intersinus septae
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Presence of an Onodi cell
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Presence and extent of bone erosions, dehiscence, or hyperosteosis of the skull base
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Position of the internal carotid arteries (especially the paraclival segment)
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Thickness and incline of the clivus (basal angle)
Equipment and instrumentation
Adequate instrumentation is paramount for the endoscopic approach to the clivus and posterior fossa, and a lack of instrumentation is considered a contraindication to performing the procedure.
The equipment includes the following:
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High-quality endoscopes (0° and 45°)
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Video equipment (camera and monitor)
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Long endoscopic bipolar forceps
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Long and delicate drills
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Long dissection instruments
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Long ultrasonic surgical aspirator
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Hemostatic materials
Preparation and Patient Positioning
The surgery is performed under hypotensive general anesthesia with total intravenous anesthetic, using propofol and remifentanil.
The patient is placed in a supine position on the operating table, head elevated 30°, neck slightly flexed, and head extended and turned toward the surgeon.
Neurophysiologic monitoring is mandatory when approaching the posterior fossa through a transnasal route. As a rule, CN VI-, motor-, and somatosensory-evoked potentials are monitored. The remaining CNs are monitored according to the tumor size and location.
Neuropatties soaked in adrenaline 1:1000 are placed in the nasal cavity for 10 minutes before the surgical procedure begins. The septum is infiltrated with lidocaine with adrenaline 1:100,000.
Surgical Approach
The endoscopic transnasal access to the posterior fossa is through a transclival approach. The clivus separates the nasopharynx from the posterior cranial fossa. It is composed of the posterior portion of the sphenoid body (basisphenoid) and the basilar part of the occipital bone (basiocciput) and is further subdivided into upper, middle, and lower thirds:
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Upper clivus is at the level of the sphenoid sinus and is formed by the basisphenoid bone including the dorsum sella.
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Middle clivus corresponds to the rostral part of the basiocciput and is located above a line connecting the caudal ends of the petroclival fissures.
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Lower clivus is formed by the caudal part of the basiocciput.
Approaching the posterior fossa through the upper two-thirds of the clivus requires the opening of the sphenoid sinus. When the posterior fossa is approached at the lower clivus, bone removal may be done solely below the sphenoid rostrum.
The intracranial surface of the upper two-thirds of the clivus faces the pons and is concave from side to side. The extracranial surface of the clivus gives rise to the pharyngeal tubercle at the junction of the middle and lower clivus. The upper clivus faces the roof of the nasopharynx that extends downward in the midline to the level of the pharyngeal tubercle.
The upper and middle clivus are separated from the petrous portion of the temporal bone on each side by the petroclival fissure. The basilar venous plexus is situated between the 2 layers of the dura of the upper clivus and is related to the dorsum sella and the posterior wall of the sphenoid sinus. It forms interconnecting venous channels between the inferior petrosal sinuses laterally, the cavernous sinuses superiorly, and the marginal sinus and epidural venous plexus inferiorly. The basilar sinus is the largest communicating channel between the paired cavernous sinuses.
Surgical Procedure
Nasosinusal preparation
The access initiates with the combined transnasal/transseptal binostril approach :
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Using anterior septoplasty incision, mucoperichondrial/mucoperiosteal flaps are created bilaterally.
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Most of the septal cartilage and bone are removed, preserving an L-shaped cartilage strut to support the nasal dorsum and tip.
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The mucosal flaps are lifted until both natural sphenoid ostia are on view.
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Rectangular sphenopalatine artery–based nasal septal mucosal flaps are created.
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The resulting mucosal flaps can be rotated and placed on the nasal floor back toward the choana or safely placed into the maxillary sinus cavity through a large middle meatus antrostomy.
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A wide opening of the anterior sphenoid sinus wall is created with a micro-Kerrison punch, and a drill is used to lower the sphenoid rostrum.
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The sinus mucosa that lines the clival area is reflected carefully, exposing the clival bone.
This approach allows 2 surgeons to simultaneously manipulate surgical instruments using both nostrils, has a robust tissue pedicle to help in the closure of skull base defects, and preserves the nasal septal mucosa of one side, avoiding nasal septal perforation.
Multiple modifications regarding length and width are possible, and the flap should be created according to the size and shape of the planned defect.
Transclival approach
The clival bone is fully exposed, and its removal is initiated with a diamond burr drill and continued carefully with a micro-Kerrison punch if necessary. The extent of bone removal must be tailored to the size and location of the tumor, with the following limits:
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Superiorly: Floor of the sella
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Inferiorly: Foramen magnum
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Laterally: Internal carotid arteries, hypoglossal canal, and occipital condyles
The outer layer of the dura is first incised, and the basilar venous plexus is encountered. Bleeding in the plexus cannot be cauterized safely but is usually controlled with packing using hemostatic gelatin paste. Large lesions that infiltrate the dura mater often encroach on and obliterate much of the plexus, but if the lesion is not large or if the plexus is not completely compressed, profuse and intense bleeding can occur. Judicious packing, time, patience, and experience are required to control it. The interdural segment of CN VI is located laterally in this space, and lateral openings should be performed carefully with intraoperative monitoring and nerve stimulation.
The opening of the internal layer of the dura at the level of the middle and superior clivus must be accomplished with great care to avoid injury to the underlying basilar artery. Once the dura is opened, minor bleeding is stopped by bipolar coagulation, and it is finally possible to introduce the 0° endoscope carefully into the intradural space and to identify the following:
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Vertebral arteries
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Basilar artery and branches
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Anteroinferior cerebellar arteries
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Superior cerebellar arteries
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Posterior cerebral arteries
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Intradural course of CNs III, IV, V, and VI
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Brainstem
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Mamillary bodies
With angled endoscopes, it is also possible to visualize the following:
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Cerebellopontine angle
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CNs VII, VIII, IX, X, XI, and XII
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Retrosellar region
Once the anatomy is appreciated, meticulous dissection is required to remove the tumor. To optimize the surgeon’s view, persistent hemostasis of the tissues of the nasal cavity and sphenoid needs to be maintained to minimize soiling of the endoscopes. Frequent irrigation and suction with neurosurgical tip protected low suction is used to maintain good vision.
A 4-handed microsurgical technique is used to resect the tumor:
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Identification of the limits of the tumor and normal anatomy
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Debulking of the meningioma using microsurgical scissors and ultrasonic surgical aspirator
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Microsurgical dissection around the tumor preserving the arachnoid interface
Reconstruction
Dural repair in the region of the clivus is difficult and performed as follows:
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If the defect is large, it is first occluded with abdominal fat and then covered with grafts of fascia lata or a synthetic dural substitute.
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These grafts are covered by the sphenopalatine-based pedicled nasal septal flaps, as described previously. Fibrin glue is not typically necessary but may be used to hold the graft and flap in position.
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Spongostan powder (Ethicon, Somerville, NJ, USA) and Gelfoam (Pfizer, New York, NY, USA) are layered directly over the flap, followed by gauze packing soaked in antibiotic paste.
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A silastic splint is inserted into the nose on the side from which the graft was taken to promote reepithelialization.
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The packing is supported by a Rapid Rhino 900 (Arthrocare, Austin, TX, USA) or similar pack.
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Lumbar drain is not used routinely.
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Broad-spectrum antibiotics are used for 10 days or as long as necessary.
Nuances and Pitfalls of the Technique
Box 3 lists the nuances and pitfalls of the surgical technique.
Related posts:
Endoscopic Endonasal Skull Base Surgery
Endoscopic Endonasal Extended Approaches for the Management of Large Pituitary Adenomas
Endoscopic Endonasal Repair of Spontaneous and Traumatic Cerebrospinal Fluid Rhinorrhea
Surgical Techniques for Sinonasal Malignancies
Endoscopic Endonasal Odontoidectomy
Chordomas
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