Endoscopic Approaches for Skull Base Chordomas

Chordomas are developmental tumors that arise from remnants of the notochordal tissue that is located at the center of the axial skeleton. Location at the skull base, the spine, and the sacrum are correlated with distinct clinicopathologic pictures, and although variation exists between clinical series, these three subtypes are seen at comparable frequencies.1,​2,​3,​4,​5,​6,​7 They can be encountered at any age but are most frequently seen in third to fifth decades of life.3,​5 Chordomas are extra-axial tumors that are located within the bony skeleton; they commonly invade the dura when they reach large sizes. Rare cases of pure intradural location or ectopic occurrence have been reported.8 Osseous invasion is the hallmark of these lesions.9 Cranial base chordomas account for less than 0.2% of all intracranial neoplasms, with an incidence of 0.08 per 100,000.2,​3,​5,​6


Three main histologic patterns of chordoma have been described: classic, chondroid, and dedifferentiated. The most frequently encountered classic pattern is made up of islands and cords of eosinophilic and clear vacuolated cells set in a basophilic myxoid/mucoid background.3,​10 Cytokeratin, epithelial membrane antigen, S100 protein, and vimentin are positive in chordomas by immunohistochemical staining. Also, carcinoembryonic antigen staining is positive for some chordomas. However, the most proven specific immunohistochemical marker for chordomas is brachyury—a nuclear transcription factor associated with fetal notochord. Chondrosarcomas are negative for cytokeratin and brachyury.3,​11,​12 Due to the almost identical site of presentation and very similar radiologic appearance, chondrosarcomas have traditionally been considered together with chordomas.13,​14 However, the biology of chordomas and chondrosarcomas are quite distinct, with chondrosarcomas being quite benign pathologies. Therefore, the two entities will be discussed separately.


Clinical presentation is related to localization and extension of the tumor. Borba and Al-Mefty reported diplopia as the most common finding in adults with skull base chordomas.15 Basisphenoid lesions arising in the superior clivus may affect the upper cranial nerves, pituitary gland, and hypothalamus. Basiocciput lesions arising in the inferior clivus affect the lower cranial nerves first,7 and increased size of the lesion may cause brainstem compression and various neurologic symptoms. Neuro-ophthalmologic dysfunction is the most common finding in patients with chordomas extending to the cavernous sinus.15 Extradural approaches are warranted due to the extradural and hypovascular nature of the lesions.8,​9,​16,​17,​18


The surgical approaches used for skull base chordomas can be classified as anterior midline, anterolateral, lateral, and posterior approaches. For chordomas that are located at the very heart of the central skull base, anterior approaches that address the tumor within the bony clivus from a corridor that is free of neurovascular structures are extremely well suited. There has been an enormous change in the surgical management of chordomas: the number of surgical approaches has increased considerably; traditional approaches have been refined; approaches that resulted in poor outcome have been abandoned; and newer techniques and technologies have been added. Traditional anterior midline approaches are well suited to approach clival chordomas directly; however, chordomas with extensive lateral components have been proven to be notoriously challenging, as traditional approaches are completely limited in their addressing lateral extension. Therefore, for cases with lateral extensions, anterolateral and lateral approaches or transfacial or transoral combinations have been used, especially for lateralized chordomas involving the internal carotid artery (ICA) or the cavernous sinus by the tumor or those tumors with intradural extensions.4,​5,​19,​20 Popularization of endoscopic endonasal approaches (EEAs) and technological advancements have enabled a return to pure midline approaches while making gross total resections possible.5 Jho and Ha21 published the earliest reports of patients with chordomas that were operated on by an endoscopic transclival approach. Cavallo et al22 illustrated the extensive view of the ventral brainstem through an endoscopic endonasal transclival approach in their anatomical study, and Kassam et al23 published case descriptions demonstrating these approaches for clival pathologies.24 In time, several reports demonstrating EEA to clival chordomas were reported ( ▶ Table 15.1). Sen et al20 and Koutourousiou et al 5 published the largest series for clival chordomas that were resected via an endoscopic transclival approach.







































































































Table 15.1 Results of published endoscopic series

Authors


No. of chordomas


GTR


(n) %


Recurrence


(n) %


CSF leak


%


Complications (n)


Follow-up


(months)


Jho and Ha 200421


3


(3) 100


(1) 33.3


33.3


(4)


AF, stroke, PE, VI nerve palsy


20–28



Solares et al 200525


3


(2) 66.7


(0) 0


0


(0)


8–24


Frank et al 200626


9


(3) 33.3


(0) 0


11.1


(1)


ICA injury


10–69


Hwang and Ho 200727


3


(0) 0


NA


0


(1)


Hematoma


30–40


Dehdashti et al 200828


12


(7) 58.3


(0) 0


33.3


(3)


Hydrocephalus, hematoma, hemiparesis


4–26


Hong Jiang et al 200829


9


(6) 66.7


(0) 0


0


(0)


6–30


Zhang et al 200849


7


(6) 85.7


(0) 0


NA


(1)


SAH


3–37


Ceylan et al 200930


3


(2) 66.7


(0) 0


0



50–65


Fraser et al 201024


7


(5) 71.4


(1) 20




0.2–51


Koutourousiou et al 20125



60


(40) 66.7


(8) 20


20


(9)


CN palsy (4), ICA injury (2), pontine hematoma, hematoma, sinus infection


1–71


Abbreviations: AF, atrial fibrillation; CN, cranial Nerve; GTR, gross total resection; ICA, internal carotid artery; PE, pulmonary embolism; SAH, subarachnoid hemorrhage.


15.2 Endoscopic Anatomy


The anatomy of the clivus from the endoscopic surgical point of view differs from the microsurgical anatomy. Therefore, before discussing the “EEA” technique in further detail, the endoscopic anatomy deserves special consideration.3 The clivus is formed by the sphenoid and the basilar part of the occipital bones, which are fused at the spheno-occipital synchondrosis to form the very center of the skull base. The spheno-occipital synchondrosis ossifies between the 18th and 25th years of life. Clivus separates the nasopharynx from the posterior cranial fossa. In the endoscopy practice, the clivus is divided into superior, middle, and inferior “parts.”31 The superior part of the clivus is bound superiorly by the posterior clinoids/dorsum sella and inferiorly by the level of the Dorello’s canal.3 It spans from sphenoid plane back to the dorsum sella. The lateral borders of this superior segment are formed by both cavernous sinuses. Both petroclival fissures are located posteroventrally. The middle part, which is also called the sphenoidal clivus, extends from the level of the Dorello’s canal (which also corresponds to the level of the sellar floor) down to the pars nervosa of the jugular foramen. This segment is bordered laterally by the petrous and lacerum segments of the ICA as well as the petroclival fissure and inferolaterally the foramen lacerum. The portion caudal to the pars nervosa of the jugular foramen down to the foramen magnum is considered the lower part. This segment is bordered laterally by the eustachian tubes and laterally to the medial pterygoid plate3 ( ▶ Fig. 15.1). The lateral diameter at the midlevel is 28 mm. The thickness of the clivus ranges from 9 to 18 mm.31



978-1-62623-160-3_c015_f001.tif


Fig. 15.1 Cadaveric view of clival segments. CS, carotid siphon; LC, lateral corridor; MC, medial corridor; BA, basilar artery; PA, petrous apex; PeCA, petrous carotid artery; PCD, paraclival carotid artery; S, sella; PB, posterior band; *, cavernous sinus lateral wall; MCl, middle clivus; ET, eustachian tube; ICl, inferior clivus; OC, optic chiasm; SCl, superior clivus.


Compared with standard EEA for intrasellar pathologies, the clivus requires a lower anterior point of entry with a slightly more rostral trajectory. The vomer is removed to expose the part inferior to the sella. It should be kept in mind that the sphenopalatine artery and its branches lie inferolaterally to the sphenoid sinus. An approach to the clivus requires a wider nasal port of entry. Unilateral resection of the middle turbinate can be performed, and the posterior portion of the nasal septum can be removed. The mucosal incision is extended down to the caudal part of the nasal cavity. The vidian nerves form the lateral boundaries. Drilling of the clival bone can be as extensive as needed. Dorsum sella forms the cranial limit, and the arch of C1 (atlas) forms the caudal limit. At the superior part of the clivus, the basilar plexus as well as the abducens nerves are identified. Laterally, at the level of the medial part of the clivus, the resection can be extended to the lacerum segment of the ICA. The osseous prominences of the ICA are identified lateral to the sphenoid sinus. It is of crucial importance to remember that the ICA is not covered by bony structures as it passes from foramen lacerum to the cavernous sinus, and every measure should be taken for early identification and protection of the ICA. Dorsally, the meningohypophyseal trunk from the ICA is identified as well as the prepontine dura.


15.3 Surgical Treatment


Skull base chordomas are a surgical challenge due to the deep location, extensive local bony infiltration and destruction, and their proximity to vital neurovascular structures. Surgical removal, as extensive as possible while avoiding injury to important structures, remains the absolute aim of chordoma surgery. This holds true for most anatomical tumor locations, including the cavernous sinus. Surgery aimed at maximum resection is the most important step in the management of these lesions.8,​9,​16,​17 In patients with extensive or significantly invasive chordomas (whether primary or recurrent) or elderly and frail patients, a compromise is reached between the need for total resection and risk of complications for the eventual aim of patient well-being. Even in such cases, most surgeons prefer extensive decompressions rather than simple biopsies.5


Surgical techniques to expose and resect chordomas must be personalized according to the location and extent of the tumor and are accomplished by various techniques, including endoscopic approaches, as well as open craniotomies or transsphenoidal approach using the microsurgical technique.16,​18,​32,​33,​34 Open craniotomies include the subfrontal, transbasal, extended frontal, subtemporal–infratemporal, transpetrosal, and lateral transcondylar approaches and are utilized depending on the region targeted.4,​7,​35,​36,​37 Clival tumors often lie between the carotid arteries, ventral to the brainstem. The most direct approach to the center of these tumors is through a corridor that is formed by the natural sinuses that can be accessed easily through the natural orifice provided by the nostrils.24 Traditionally, these midline tumors are approached from a lateral or paramedian trajectory. However, many important neurovascular structures may be located in front of the tumor, and this may contribute to the potential morbidity of traditional skull base approaches.7 Strict midline approaches such as the modified transsphenoidal approaches provide the most direct route to clival chordomas, and the absence of neurovascular structures between the surgeon and the tumor makes them especially appealing. The transsphenoidal approach is not new; it has been used since the time of Cushing for approaching chordomas, and much experience exists in the use of microsurgical techniques for transsphenoidal surgeries. However, it was realized early on that the pure transsphenoidal approach is a pure anterior midline approach and is limited in addressing tumor extension beyond the sagittal plane. Therefore, many variations, making use of transfacial or transoral trajectories, have been devised, as well as combinations with anterolateral approaches.


Although both microsurgical and endoscopic techniques use the same entry trajectory, their fundamental strategies deviate from each other significantly. This derives in essence from differences in instrumentation as well as the surgical technique. Both microsurgical and endoscopic techniques can be applied to chordoma surgery. Microscopic transsphenoidal surgery is a well-accepted technique for the treatment of chordomas growing in the sella and upper clivus and confined to the midline.7,​38,​39 Microscopic transsphenoidal approach to clival chordomas was analyzed in several studies. Maira et al39 described their experience in 12 patients with clival chordomas treated with microsurgical transsphenoidal approaches. Total resection was achieved in 9 (75%). Couldwell et al32 reported results of extended microsurgical transsphenoidal approaches in 105 patients, 18 of whom had clival chordomas. Total resection was achieved in 12 (66.7%) of 18 chordomas.24 Sen and Triana40 demonstrated their outcomes for 71 chordomas treated with different surgical approaches. They compared anterior approaches with lateral approaches; they explained that anterior approaches had better postoperative cranial nerve function because lateral approaches often involved working through spaces between cranial nerves. In this study, a radical resection was achieved in 62% of the patients operated via a purely midline anterior approach, and in 57% of patients operated with a lateral skull base approach. Radical resection was achieved in 57% of the cases for patients in whom anterior and lateral approaches were combined.3,​40 Sekhar et al 41 described their experience in treating 42 patients with chordomas in their open surgical series. They achieved gross total resection (GTR) in 25 (59%) and subtotal resection in 12 (28%). Al-Mefty et al42 published a series of 38 patients with clival chordomas resected via an open midline anterior clivectomy approach. GTR was achieved in 29 (76.3%). In 4 patients with residual chordoma, a cranio-orbitozygomatic approach was used; in 3 a transcondylar approach was used, with 2 having occipitocervical fusion; and in 2 a transoral approach was used.42


15.4 Endoscopic Endonasal Approaches


Several groups in both clinical and cadaveric series have described the EEA to the clival chordomas in detail.7,​22,​24,​26,​30,​31,​34,​43,​44,​45 The usefulness is not debated, and this has also been addressed in numerous studies.21,​26,​30,​31,​34,​44,​45,​46,​47 Today, well-accepted and extended endoscopic endonasal approaches are being used as relatively less invasive routes to the midline and paramedian skull base region.7,​23,​24,​25,​26,​27,​29,​30,​31,​34,​44,​45,​46,​48,​49 The endoscopic endonasal transclival approach takes advantage of the nasopharynx as a natural corridor for the anterior midline cranial base tumors and provides a minimal access corridor with maximal visualization to the clival region.24 Advances in rigid endoscope technology and instrumentation combined with real-time neuronavigation and mini-Doppler probes facilitate the endoscopic endonasal skull base approaches.24 Koutourousiou et al5 reported a total resection rate of 66.7% in a review of 60 patients who underwent surgery using an EEA for cranial base chordomas. Nine of these patients (15%) required combination with an open approach.3,​5 Considering the anterior approaches, the literature on microsurgical transsphenoidal surgery provides a reference to comparing the far newer EEAs. But the EEAs are new and still have not maturated to their full potential. With further advances in intraoperative technique and technology, EEAs have a far bigger potential to achieve better surgical results.24


However, there are also limitations to anterior endoscopic approaches and they are not suited for all chordomas.24 Although traditional anterior midline EEAs provide direct access to the tumor, there is significant limitation for resection of lateral extending tumor portions.5 Currently, the most significant limitation is the relation between the ICAs and the chordoma mass. They suggested two alternatives to reach lateral to the carotid arteries through an endonasal approach: one is a lateral skull base approach and the other is combined or staged approaches by removing the midline tumor endonasally and the lateral tumor transcranially.24 Koutourousiou et al 5 also explained that extension of the tumor lateral to the optic nerves is one of the clear limitations of EEA. They offered orbitofrontal craniotomy for these lesions and combined with use of posterolateral open approach if there was an extension of the tumor lateral to the course of the horizontal petrous carotid artery and parapharyngeal carotid artery. They suggested that orbitozygomatic, subtemporal, retromastoid, or far lateral craniotomy may be utilized in cases with extreme lateralization of the tumor beyond the lateral wall of the cavernous sinus or lateral to the vertebral or posterior cerebral arteries.5


Endoscopic endonasal surgical approaches to the clivus vary according to the segments and extension of the clivus ( ▶ Table 15.2). The early phases of the operation are comparable: in the sphenoidal phase, wide bilateral sphenoidotomies extending to the lateral recess permit wide exposure to clivus. Tumors extending to the lateral or posterior plane of the paraclival and petrous ICA necessitate control of these segments. Use of navigation tools and a mini-Doppler probe are required in this phase of the operation.



























Table 15.2 Classification of the 20 chordoma patients in the authors’ series according to clival segments and invasion

Location


Invasion


N


Superior clivus


(N = 12)


Suprasellar


Cavernous sinus


Orbital


Frontal and temporal fossae


3


7


1


2


Middle clivus


(N = 14)


Cavernous sinus


Meckel’s cave


Pterygopalatine fossa


Petrous apex


2


1


2


1


Inferior clivus


(N = 11)


Odontoid


Petrous apex


Parapharyngeal area


Occipital condyle


Infratemporal fossa


1


1


2


1


2


Note: N, total number of patients.


15.4.1 Superior and Middle Clivus Approaches


Lesions located in the superior and middle parts of the clivus can be resected by transsellar endoscopic approach for the superior part and after removal of the sphenoid sinus floor, for both superior and middle clival lesions. Superior clival lesions may extend to the suprasellar region. Pituitary transposition maneuvers were described for these lesions.3 However, in our series, the infrachiasmatic corridor was described as an important surgical safety zone for inferior endoscopic approaches formed by the BAM, LM, DL and ML, extending from the optic canal and tuberculum sella to the corpus mammillare.50,​51 The borders of this area are made up of the optic chiasma, stalk, and tuber cinereum superiorly, the diaphragmatic sella–dorsum sella and interpeduncular cisterns inferiorly, the ICA, posterior communicating artery, and oculomotor nerve laterally, and the corpus mammillare posteriorly. The prepontine area represents the region between the clival dura, mesencephalic leaf, and prepontine membranes. The infrachiasmatic corridor contributes to the resection of both superior and middle clival lesions as well as access to the interpeduncular cistern and its contents, including the basilar artery bifurcation, mammillary bodies, and the floor of the third ventricle. A transclival approach is required for middle clival lesions. In these cases, after removal of the sphenoid floor, limited access can be achieved through the middle clivus. The paraclival ICA is uncovered from foramen lacerum to the proximal ring and then gently mobilized laterally to achieve complete removal of the tumor with lateral extensions behind the ICA. In our series, bleeding from the carotid artery was encountered during this maneuver in one case. Tumor resection was continued after the bleeding was under control ( ▶ Fig. 15.2). Lesions in the superior part of the clivus extending to the cavernous sinus require an extended approach laterally. Transsellar transcavernous and ethmoidopterygosphenoidal approaches were used in pituitary adenomas invading the cavernous sinus. Transmaxillary approach was preferred in cases where the lesions invaded the lateral corridor. Wide exposure was provided by using medial and lateral corridors that were described in cavernous sinus approaches.52,​53 Midclival tumors may extend from the posterior to the middle fossa through the Meckel’s cave. In these circumstances, the lateral wall of the sphenoid sinus should be exposed to access the middle fossa. Transmaxillary approach is also mandatory in cases extending to the pterygopalatine fossa and parapharyngeal area. Sphenoid sinus is located anteromedial to the pterygopalatine fossa. Middle turbinate and then medial wall of the maxillary sinus were removed to access the posterior wall of the maxillary sinus. The sphenopalatine artery runs to the nasal cavity through the sphenopalatine foramen and divides into two branches: “nasopalatine artery,” which is medial to the nasal septum, and the “posterior nasal artery,” which reaches the turbinates.31 After removal of the medial wall of the maxillary sinus, lesions located anterior to the pterygopalatine fossa were reached. Removal of the posterior wall of the maxillary sinus provides access to the pterygopalatine fossa. Internal maxillary artery ligation is needed before tumor removal is possible and avoids continuous bleeding during the lesion removal.



978-1-62623-160-3_c015_f002.tif


Fig. 15.2 (a, b) Preoperative MRI. (c, d) Postoperative MRI. (e) Bleeding from the carotid artery during the mobilizing paraclival ICA laterally to achieve complete removal of the tumor with lateral extensions behind the ICA. PCA, paraclival carotid artery; CD, clival dura; *, arterial bleeding.

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May 1, 2018 | Posted by in NEUROSURGERY | Comments Off on Endoscopic Approaches for Skull Base Chordomas
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