Peer-Review Reports
The Retrosigmoid Endoscopic Approach for Cerebellopontine-Angle Tumors and Microvascular Decompression Marcos S. Tatagiba, Florian Roser, Bernhard Hirt, Florian H. Ebner
Key words CPA - Endoscopy - MVD - Retrosigmoid approach - Vestibular schwannoma -
Abbreviations and Acronyms CPA: Cerebellopontine angle IAC: Inner auditory canal Department of Neurosurgery, University Hospital of Tuebingen, Tuebingen, Germany To whom correspondence should be addressed: Marcos S. Tatagiba, M.D., Ph.D. [E-mail: [email protected]] Citation: World Neurosurg. (2014) 82, 6S:S171-S176. http://dx.doi.org/10.1016/j.wneu.2014.08.001 Supplementary digital content available online. Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2014 Elsevier Inc. All rights reserved.
INTRODUCTION The seventies and eighties were marked by large, combined approaches in skull base surgery. After the initial enthusiasm for the wide exposure and gained resectability of lesions, the disillusioning perception of approach-related morbidity and mortality followed (3). Hence customized, tailored approaches were established and more favored for the removal of skull base tumors (23, 24, 29). The gist is rendering the procedure as safe and simple and thus effective as possible. This development particularly applies to surgery of cerebellopontine-angle (CPA) lesions (29). Therefore, in our Department, we operate on all lesions of the CPA and the vast majority of lesions related to the CPA via the retrosigmoid approach. An important element in this evolving concept of minimally invasive neurosurgery is implementation of the endoscope. Here, we discuss the microsurgical, endoscopeassisted technique for maximal tumor removal with minimal procedure-related morbidity.
BASIC PRINCIPLES OF CPA ANATOMY FOR ENDOSCOPIC SURGERY Anatomically, the CPA is delimited ventrally by the dura mater of the petrous bone, cranially by pons and middle cerebellar peduncle, caudally by lobulus biventer and olive, dorsally by the cerebellum (18). Detailed knowledge of the topography of this region and its cisternal organization is essential for successful surgery. From a surgical point of view, the CPA comprises the cerebellopontine and the cerebellomedullary cisterns. The herein crossing neurovascular structures delimit the anatomical workingspaces. The trigeminal nerve runs along the cranial border of the cerebellopontine cistern from the pons to Meckel’s cave. The inner auditory canal (IAC) with facial and vestibulocochlear nerves is localized 7.04 mm (3.5e10.5 mm) posteriorly and inferiorly to the posterior border of Meckel’s cave (28). The distance from the upper border of the IAC to the petrous ridge measures 4.18 mm (2.5e6.5 mm) (28). The inferior border of the IAC and upper limit of the jugular foramen are 4.52 mm (2.5e6.5 mm) apart. In this segment, the horizontal lateral pontomedullary membrane separates cerebellopontine and cerebellomedullary cisterns (26). Medially, the anterior pontine membrane delimits the cerebellopontine cistern. The left and right anterior pontine membranes delimit the pontomedullary cistern with the abducens nerves running from the pontomedullary sulcus towards Dorello’s canal. The superior cerebellar artery (level of trigeminal nerve), anterior inferior cerebellar artery with the labyrinthine branch (level of vestibulocochlear nerve), and posterior inferior cerebellar artery (level of caudal cranial nerves) further divide the spaces. The cisterns create natural cavities for introduction of the endoscope (Figure 1). However, under physiologic conditions, the working corridors between tentorium and trigeminal nerve, trigeminal nerve and
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vestibulocochlear nerve, and vestibulocochlear nerve and caudal cranial nerves (glossopharyngeal nerve) are very narrow (18, 28). SURGICAL CONCEPT OF CPA SURGERY VIA THE RETROSIGMOID APPROACH AND TECHNICAL PRINCIPLES In the presence of an extra-axial lesion in the CPA, the physiologic corridors are widened. We can take advantage from this fact and use the enlarged spaces for tumor removal. A tailored retrosigmoid craniectomy extending from the lower border of the transverse sinus and the medial border of the sigmoid sinus to the horizontal part of the occipital bone offers a wide window of entrance to the CPA. The crossing neurovascular structures might be significantly distorted. Hence, a detailed topographical knowledge in combination with a meticulous evaluation of the growth pattern on preoperative magnetic resonance imaging scans is essential for planning the surgical strategy. The dura is incised in semilunar fashion parallel to sinus knee and sigmoid sinus. This pattern of dura opening offers both a good exposure and facilitates watertight closure at the end of the procedure. In case of large tumors, the next step consists in opening the cerebellomedullary cistern for CSF drainage. The cerebellum will relax and give access to the CPA. Arachnoid dissection is a crucial step in CPA surgery and helps exposing cranial nerves, arteries, veins, and interposed lesions. At this stage, the required view is a straight one on the situs. Therefore, we perform this part of surgery under the microscope with variable zoom, under stereopsis and in bimanual technique. The same applies to removal of the tumour portions located in the straight optical path. However, as soon as the hidden corners of the complex CPA anatomy have to be inspected, the endoscope comes into operation. The size of the craniotomy is not smaller when using an endoscope-assisted technique instead of operating only with the microscope.
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Figure 1. Retrosigmoidal view of the left cerebellopontine angle showing the working corridors between the cranial nerves.
According to Hopf and Perneczky (9), the endoscope may be used during surgery just for inspection (“endoscopic inspection”), in combination with a microscope and microsurgical instruments (“endoscope-assisted surgery”), as the sole visualization tool with microsurgical instruments (“endoscope-controlled surgery”) or equipped with working-channels (“endoscopic neurosurgery”). Following this definition, our surgeries are performed via the endoscope-assisted technique. In some cases we need the endoscope just for inspection. The angled optics is introduced along the corridors beyond the cranial nerves under direct visual microscopic control to avoid harming the delicate surrounding structures. The space of time when the endoscope is applied might be short compared with the whole duration of surgery, but it is crucial for the final result. We believe in the combination of the 2 powerful visualization tools, the microscope and endoscope, for successful
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along cisterns and engulf neurovascular structures. Because surgery is the only valuable treatment option for epidermoids (4), complete removal has to be the primary goal of interventions (40). Because of the spreading growth pattern, this is not always possible, and in a significant percentage epidermoids recurre after microsurgically estimated complete resection (31). In part this is caused by the rambling anatomy of the CPA that cannot be completely depicted by the microscope alone. Because epidermoids are soft and avascular lesions, they are particular suitable for endoscopic surgery (7). The use of angled optics allows inspection of corners hidden to the straight optic pathway of the microscope. Remnants that adhere to vessels or nerves may be removed in endoscopic-assisted technique (Video 1). Excellent results may be achieved both in primary surgery (32) as well as in the case of recurrence (7) with the endoscopeassisted technique despite the demanding anatomic situation and the insidious growth pattern. However, particularly in case of epidermoid cysts, not everything seen has to or can be removed. Because of chronic inflammatory reactions to the cyst content or previous surgery, the capsule might be very adherent to neurovascular structures. Excessive surgical manipulation of minute remnants bears endangers the functional outcome and bears no relation to the benign histological and slow-growing biological behavior of the lesion.
surgery of CPA lesions and beyond. Their characteristics complement one another: straight view, stereopsis, and variable zoom on the one hand; and angled view, enlargement and illumination in the depth on the Meningiomas of the CPA other hand (13). The endoscope facilitates Meningiomas are the second most frequent detecting tumor remnants in hidden angles lesions in the CPA after vestibular schwanof the complex surgical field and thus ennomas. Because of their usually slow hances the grade of resection but progressive growth pattern with preservation of function. (27), meningiomas often Manipulation of neurovascular become relevant mass lesions structures and cerebellar that displace the surrounding retraction may be minimized. structures and thus enlarging Video available at The endoscope is applied both the aforementioned corridors. WORLDNEUROSURGERY.org in the simple retrosigmoid and In microsurgical technique in the extended retrosigmoid approach. and under continuous intraoperative monitoring, the tumor mass may be debulked, the meningioma mobilized within the enlarged surgical corridors, and ENDOSCOPIC-ASSISTED SURGERY VIA thus stepwise resected (30). Once the major THE SIMPLE RETROSIGMOID APPROACH part of the meningioma has been resected, Epidermoids of the CPA the jugular foramen, the IAC, Meckel’s Epidermoids are dysontogenetic, slowcave, the area behind vessels, or nerves, growing ectodermal lesions. They spread the ventral brainstem as well as the
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RETROSIGMOID ENDOSCOPIC APPROACH FOR CPA TUMORS AND MICROVASCULAR DECOMPRESSION
contralateral side may be inspected with angled endoscopes of various degrees. In a series of 46 patients operated on for skull base meningiomas (23 via a retrosigmoid approach) in endoscopeassisted technique Schroeder et al. (34) showed that extensive bone drilling could be avoided by using the endoscope. Further, in 13 of 23 patients operated via the retrosigmoid approach tumour remnants not visible under the straight view of the operating microscope could be detected (34). Currently, in our daily practice the majority of skull base meningioma surgeries is performed under the operating microscope; the endoscope-assisted technique in CPA meningioma surgery is applied only in well-selected cases to visualize blind spots or in extended approaches (Video 2). Microvascular Decompression Although early posterior fossa surgery caused significant morbidity and mortality rates because of the lack of magnification and illumination (22), thanks to the modern surgical setting today, the achieved results drastically improved (35). Both operating microscope and endoscope are at the surgeons’ disposal during microvascular decompression. The most critical step of the procedure is “turning the corner” for exposition of the CPA (22). Applying the adequate technique this step is managed with both visualization tools. However, in this context, the angled view of endoscopes offers a significant advantage compared with the straight microscopic perspective. The ecstatic arteries or prominent veins compressing the Obersteiner-Redlich zone of trigeminal, facial, or glossopharyngeal nerves have to be identified and the microvascular conflict solved. It seems that, compared with the microscope, the endoscope may be of valuable aid during that step, increasing significantly the accuracy of the procedure (2) (Figure 2 and corresponding Videos 3 and 4, comparing the microscopic and the endoscopic perspective). The microvascular conflict occurs in more than 50% of cases at the proximal third of trigeminal nerve (37). In this region the local neurovascular relationships may be much easier explored with an angled endoscope than with the microscope. The recurrence rate accounts for about 25% after an average
follow-up of 4 years with an overall failure rate of 6%e38% (21). The suggested reason is an insufficient identification of the real reason, number and extends of microvascular conflicts (17, 19). Over the last years reports about microvascular decompression evolved from microscopic (22) to endoscope- assisted (10) and finally full endoscopic technique (11, 12). The microscopic procedure is well established, but the results achieved with the endoscope-assisted and pure endoscopic technique seem to be promising (12) and might yield improved short- and longterm results.
ENDOSCOPIC-ASSISTED SURGERY VIA THE EXTENDED RETROSIGMOID APPROACH Transmeatal Extension Vestibular schwannomas, CPA or petroclival meningiomas as well as epidermoids may extend inside the IAC. When the patient has a good hearing function preoperatively, the aim of surgery is complete tumor removal with preservation hearing achieved. This implies anatomical preservation of the inner ear structures and in particular of the posterior semicircular canal (38). Therefore, the meatus cannot be opened completely to expose the fundus. The pure microsurgical option is working blind around the corner with fine hooklets relying upon the distinct tactile sense. The endoscope-assisted option is looking around the corner towards the fundus and removing the most lateral part of the tumor under visual control (39) (Figure 3). In demanding situations like adherent tumors or a very soft tumor consistency, the combination of visual and tactile control facilitates removal of the most lateral part of the vestibular schwannoma under continuous intraoperative monitoring. Both 30 and 70 optics come into operation. Suprameatal Extension Tumors growing from the posterior fossa through Meckel’s cave into middle fossa and parasellar area may be microsurgically resected via a retrosigmoid approach with suprameatal extension (30). Exact knowledge of the anatomy is essential (36). The extra-axial lesion—in most of the cases petroclival meningioma or trigeminal
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schwannoma type C—already displaced the neurovascular structures. Debulking the tumor, a corridor is created and the tumor is followed upward. When no considerable displacement of the neurovascular structures and the brain stem occurred, the use of an endoscope is essential for reaching the tumour parts within the middle fossa (5). The superior cerebellar artery (SCA) is an important landmark for the endoscopeassisted technique in this extended approach. Under microscopic control, an angled optic may be introduced from the CPA to the parasellar region through the space limited superiorly by the SCA, laterally by the oculomotor nerve, medially by the brainstem, and inferiorly by the upper boarder of the trigeminal nerve (5). The ambient cistern is entered and the posterior communicating artery followed towards carotid, crural, and chiasmatic cisterns, thus reaching and exploring the parasellar area. Extensive petrosectomies may be associated with a relevant, approach-related morbidity. Thus, the endoscope-assisted suprameatal extension (with opening of the tentorium) of the retrosigmoid approach became our standard approach for petroclival meningiomas, trigeminal schwannomas (Figure 4 and corresponding Video 5) and epidermoids predominately located in the posterior and extending to the middle fossa. Outlook: Technical Developments The technical progress is probably the major reason for the continuously growing role of endoscopy in neurosurgery over the last 2 decades (25). High-definition imaging, neuronavigation, development of new instruments, the interdisciplinary approach, and detailed anatomical studies led to the breakthrough of endoscopic endonasal extended approach in skull base surgery (14, 15, 33). As the result of advanced technologies, the field of endoscope-assisted surgery is continuously growing, and the advantages in treatment of CPA lesions are well acknowledged (7, 34). However, some major optic and ergonomic drawbacks exist. The aim of further innovation is to reduce technical limitations and render the procedure in this noble area safe and direct. A starting-point is the use of multivariable rigid endoscopes (1, 6, 8, 16,
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Figure 2. Case of a patient presenting with a recurrency of a left hemifacial spasm after previous microvascular decompression. (A, B) Axial constructive interference in steady state showing the microvascular conflict between the anterior inferior cerebellar artery (AICA) and facial nerve at the level of the root exit zone. (C, D, E) Intraoperative, microscopic view of the local anatomical situation. (F, G, H, I, J) The angled endoscope
20). Our group, among others, tested both the Endocameleon (Karl Storz, Tuttlingen, Germany) and the EndActive (Karl Storz) for application in the CPA (6, 8). The Endocameleon is a rigid, rod-lens endoscope, steerable in one plane from 10 to þ120 by a fine optomechanical mechanism. Testing in the anatomical lab revealed a superior usability and visualization potential compared with rigid fixed angle endoscopes (6). However, the ergonomics and the perspective, limited to one plane, could be improved. The EndActive overcomes these limitations. It is a rigid videoendoscope connected to a laptop (video data) and USB
port (control and power supply). The EndActive is lightweight and can be held in one hand like a microsurgical instrument. The field of view can be changed with a joystick mounted on the handle in a range of 160 in all 4 directions. An overview inset allows orientation and facilitates the insertion of instruments. A major drawback of the current prototype is the poor image resolution, but with the ongoing progress of chip technology, it is probably only a matter of time before limitation is addressed (8). Multivariable rigid endoscopes are inserted with a 0 view into the operative
Figure 3. Endoscopic inspection of the right internal acoustic canal after resection of a large vestibular schwannoma.
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(30 ) elucidates the topographical relationship and highlights the actual extend of microvascular decompression. The teflon introduced during the first surgery was scrunched (F). After displacement of the AICA (G), the facial nerve appears impressively compressed and even flattened at the level of the brain stem (H). Under endoscopic control a new and extended pillow of teflon is inserted (I, J).
situs beyond neurovascular structures. Once the final position is reached, the field of view is directed towards the region or structures of interest. The endoscope’s tip itself does not move. The gist is that this new category of endoscopes improves ergonomics and safety and thus has an enormous potential in CPA microsurgery.
CONCLUSION The characteristics of microscopes and endoscopes complement one another. The intraoperative combination of these 2 powerful visualization tools in sense of an endoscope-assisted technique expands the
CN VII, facial nerve; F, fundus; PB, petrous bone.
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RETROSIGMOID ENDOSCOPIC APPROACH FOR CPA TUMORS AND MICROVASCULAR DECOMPRESSION
Figure 4. Patient harboring a dumbell-shaped trigeminal schwannoma type D on the right side (AeD). Microscopic resection of the tumor through a retrosigmoid intradural suprameatal approach (GeK). The most lateral part of the schwannoma in the middle fossa is resected in the endoscopic
effectiveness of microsurgical procedures in the CPA and has the potential to further improve surgical results. REFERENCES 1. Aryan HE, Hoeg HD, Marshall LF, Levy ML: Multidirectional projectional rigid neuro-endoscopy: prototype and initial experience. Minim Invasive Neurosurg 48:293-296, 2005. 2. Badr-El-Dine M, El-Garem HF, Talaat AM, Magnan J: Endoscopically assisted minimally invasive microvascular decompression of hemifacial spasm. Otol Neurotol 23:122-128, 2002. 3. Bambakidis NC, Kakarla UK, Kim LJ, Nakaji P, Porter RW, Daspit CP, Spetzler RF: Evolution of surgical approaches in the treatment of petroclival meningiomas: a retrospective review. Neurosurgery 61:202-209, 2007. 4. Cobbs CS, Pitts LH, Wilson CB: Epidermoid and dermoid cysts of the posterior fossa. Clin Neurosurg 44:511-528, 1997. 5. Ebner FH, Koerbel A, Kirschniak A, Roser F, Kaminsky J, Tatagiba M: Endoscope-assisted retrosigmoid intradural suprameatal approach to the middle fossa: anatomical and surgical considerations. Eur J Surg Oncol 33:109-113, 2007.
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12. Kabil MS, Eby JB, Shahinian HK: Endoscopic vascular decompression versus microvascular decompression of the trigeminal nerve. Minim Invasive Neurosurg 48:207-212, 2005. 13. Kalavakonda C, Sekhar LN, Ramachandran P, Hechl P: Endoscope-assisted microsurgery for intracranial aneurysms. Neurosurgery 51:1119-1126, 2002. 14. Kassam A, Snyderman CH, Mintz A, Gardner P, Carrau RL: Expanded endonasal approach: the rostrocaudal axis. Part I. Crista galli to the sella turcica. Neurosurg Focus 19:E3, 2005. 15. Kassam A, Snyderman CH, Mintz A, Gardner P, Carrau RL: Expanded endonasal approach: the rostrocaudal axis. Part II. Posterior clinoids to the foramen magnum. Neurosurg Focus 19:E4, 2005. 16. Kim K, Kim D, Matsumiya K, Kobayashi E, Dohi T: Wide FOV wedge prism endoscope. Conf Proc IEEE Eng Med Biol Soc 6:5758-5761, 2005. 17. Kureshi SA, Wilkins RH: Posterior fossa reexploration for persistent or recurrent trigeminal neuralgia or hemifacial spasm: surgical findings and therapeutic implications. Neurosurgery 43: 1111-1117, 1998. 18. Lang J: Skull base and related structures. New York: Schattauer, Stuttgart; 2001.
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19. Lee SH, Levy EI, Scarrow AM, Kassam A, Jannetta PJ: Recurrent trigeminal neuralgia attributable to veins after microvascular decompression. Neurosurgery 46:356-361, 2000. 20. Levy ML, Nguyen A, Aryan H, Jandial R, Meltzer HS, Apuzzo ML: Robotic virtual endoscopy: development of a multidirectional rigid endoscope. Neurosurgery 59:134-141, 2006. 21. Lovely TJ, Jannetta PJ: Microvascular decompression for trigeminal neuralgia. Surgical technique and long-term results. Neurosurg Clin N Am 8: 11-29, 1997. 22. McLaughlin MR, Jannetta PJ, Clyde BL, Subach BR, Comey CH, Resnick DK: Microvascular decompression of cranial nerves: lessons learned after 4400 operations. J Neurosurg 90:1-8, 1999.
meningiomas in the elderly patient. J Clin Neurosci 14:224-228, 2007. 28. Samii M, Draf W: Surgery of The Skull Base—An Interdisciplinary Approach. Berlin, Heidelberg: Springer-Verlag; 1989. 29. Samii M, Tatagiba M, Carvalho GA: Resection of large petroclival meningiomas by the simple retrosigmoid route. J Clin Neurosci 6:27-30, 1999. 30. Samii M, Tatagiba M, Carvalho GA: Retrosigmoid intradural suprameatal approach to Meckel’s cave and the middle fossa: surgical technique and outcome. J Neurosurg 92:235-241, 2000. 31. Schiefer TK, Link MJ: Epidermoids of the cerebellopontine angle: a 20-year experience. Surgical Neurology 70:584-590, 2008.
23. Nakamura M, Roser F, Struck M, Vorkapic P, Samii M: Tuberculum sellae meningiomas: clinical outcome considering different surgical approaches. Neurosurgery 59:1019-1028, 2006.
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25. Prevedello DM, Doglietto F, Jane JA Jr, Jagannathan J, Han J, Laws ER Jr: History of endoscopic skull base surgery: its evolution and current reality. J Neurosurg 107:206-213, 2007. 26. Rhoton AL Jr: The posterior fossa cisterns. Neurosurgery 47:287-297, 2000. 27. Roser F, Ebner FH, Ritz R, Samii M, Tatagiba MS, Nakamura M: Management of skull based
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34. Schroeder HW, Hickmann AK, Baldauf J: Endoscope-assisted microsurgical resection of skull base meningiomas. Neurosurg Rev 34:441-455, 2011. 35. Sekula RF Jr, Frederickson AM, Jannetta PJ, Quigley MR, Aziz KM, Arnone GD: Microvascular decompression for elderly patients with trigeminal neuralgia: a prospective study and systematic review with meta-analysis. J Neurosurg 114:172-179, 2011.
36. Seoane E, Rhoton AL Jr: Suprameatal extension of the retrosigmoid approach: microsurgical anatomy. Neurosurgery 44:553-560, 1999. 37. Sindou M, Howeidy T, Acevedo G: Anatomical observations during microvascular decompression for idiopathic trigeminal neuralgia. Acta Neurochir 144:1-13, 2002. 38. Tatagiba M, Matthies C, Samii M: Microendoscopy of the internal auditory canal in vestibular schwannoma surgery. Neurosurgery 38: 737-740, 1996. 39. Tatagiba M, Samii M, Matthies C, el Azm M, Schönmayr R: The significance for postoperative hearing of preserving the labyrinth in acoustic neurinoma surgery. J Neurosurg 77:677-684, 1992. 40. Yasargil MG, Abernathey CD, Sarioglu AC: Microneurosurgical treatment of intracranial dermoid and epidermoid tumors. Neurosurgery 24: 561-567, 1989.
Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Received 23 July 2014; accepted 1 August 2014 Citation: World Neurosurg. (2014) 82, 6S:S171-S176. http://dx.doi.org/10.1016/j.wneu.2014.08.001 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2014 Elsevier Inc. All rights reserved.
WORLD NEUROSURGERY, http://dx.doi.org/10.1016/j.wneu.2014.08.001
The Retrosigmoid Endoscopic Approach for Cerebellopontine-Angle Tumors and Microvascular Decompression Marcos S. Tatagiba, Florian Roser, Bernhard Hirt, Florian H. Ebner
Key words CPA - Endoscopy - MVD - Retrosigmoid approach - Vestibular schwannoma -
Abbreviations and Acronyms CPA: Cerebellopontine angle IAC: Inner auditory canal Department of Neurosurgery, University Hospital of Tuebingen, Tuebingen, Germany To whom correspondence should be addressed: Marcos S. Tatagiba, M.D., Ph.D. [E-mail: [email protected]] Citation: World Neurosurg. (2014) 82, 6S:S171-S176. http://dx.doi.org/10.1016/j.wneu.2014.08.001 Supplementary digital content available online. Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2014 Elsevier Inc. All rights reserved.
INTRODUCTION The seventies and eighties were marked by large, combined approaches in skull base surgery. After the initial enthusiasm for the wide exposure and gained resectability of lesions, the disillusioning perception of approach-related morbidity and mortality followed (3). Hence customized, tailored approaches were established and more favored for the removal of skull base tumors (23, 24, 29). The gist is rendering the procedure as safe and simple and thus effective as possible. This development particularly applies to surgery of cerebellopontine-angle (CPA) lesions (29). Therefore, in our Department, we operate on all lesions of the CPA and the vast majority of lesions related to the CPA via the retrosigmoid approach. An important element in this evolving concept of minimally invasive neurosurgery is implementation of the endoscope. Here, we discuss the microsurgical, endoscopeassisted technique for maximal tumor removal with minimal procedure-related morbidity.
BASIC PRINCIPLES OF CPA ANATOMY FOR ENDOSCOPIC SURGERY Anatomically, the CPA is delimited ventrally by the dura mater of the petrous bone, cranially by pons and middle cerebellar peduncle, caudally by lobulus biventer and olive, dorsally by the cerebellum (18). Detailed knowledge of the topography of this region and its cisternal organization is essential for successful surgery. From a surgical point of view, the CPA comprises the cerebellopontine and the cerebellomedullary cisterns. The herein crossing neurovascular structures delimit the anatomical workingspaces. The trigeminal nerve runs along the cranial border of the cerebellopontine cistern from the pons to Meckel’s cave. The inner auditory canal (IAC) with facial and vestibulocochlear nerves is localized 7.04 mm (3.5e10.5 mm) posteriorly and inferiorly to the posterior border of Meckel’s cave (28). The distance from the upper border of the IAC to the petrous ridge measures 4.18 mm (2.5e6.5 mm) (28). The inferior border of the IAC and upper limit of the jugular foramen are 4.52 mm (2.5e6.5 mm) apart. In this segment, the horizontal lateral pontomedullary membrane separates cerebellopontine and cerebellomedullary cisterns (26). Medially, the anterior pontine membrane delimits the cerebellopontine cistern. The left and right anterior pontine membranes delimit the pontomedullary cistern with the abducens nerves running from the pontomedullary sulcus towards Dorello’s canal. The superior cerebellar artery (level of trigeminal nerve), anterior inferior cerebellar artery with the labyrinthine branch (level of vestibulocochlear nerve), and posterior inferior cerebellar artery (level of caudal cranial nerves) further divide the spaces. The cisterns create natural cavities for introduction of the endoscope (Figure 1). However, under physiologic conditions, the working corridors between tentorium and trigeminal nerve, trigeminal nerve and
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vestibulocochlear nerve, and vestibulocochlear nerve and caudal cranial nerves (glossopharyngeal nerve) are very narrow (18, 28). SURGICAL CONCEPT OF CPA SURGERY VIA THE RETROSIGMOID APPROACH AND TECHNICAL PRINCIPLES In the presence of an extra-axial lesion in the CPA, the physiologic corridors are widened. We can take advantage from this fact and use the enlarged spaces for tumor removal. A tailored retrosigmoid craniectomy extending from the lower border of the transverse sinus and the medial border of the sigmoid sinus to the horizontal part of the occipital bone offers a wide window of entrance to the CPA. The crossing neurovascular structures might be significantly distorted. Hence, a detailed topographical knowledge in combination with a meticulous evaluation of the growth pattern on preoperative magnetic resonance imaging scans is essential for planning the surgical strategy. The dura is incised in semilunar fashion parallel to sinus knee and sigmoid sinus. This pattern of dura opening offers both a good exposure and facilitates watertight closure at the end of the procedure. In case of large tumors, the next step consists in opening the cerebellomedullary cistern for CSF drainage. The cerebellum will relax and give access to the CPA. Arachnoid dissection is a crucial step in CPA surgery and helps exposing cranial nerves, arteries, veins, and interposed lesions. At this stage, the required view is a straight one on the situs. Therefore, we perform this part of surgery under the microscope with variable zoom, under stereopsis and in bimanual technique. The same applies to removal of the tumour portions located in the straight optical path. However, as soon as the hidden corners of the complex CPA anatomy have to be inspected, the endoscope comes into operation. The size of the craniotomy is not smaller when using an endoscope-assisted technique instead of operating only with the microscope.
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Figure 1. Retrosigmoidal view of the left cerebellopontine angle showing the working corridors between the cranial nerves.
According to Hopf and Perneczky (9), the endoscope may be used during surgery just for inspection (“endoscopic inspection”), in combination with a microscope and microsurgical instruments (“endoscope-assisted surgery”), as the sole visualization tool with microsurgical instruments (“endoscope-controlled surgery”) or equipped with working-channels (“endoscopic neurosurgery”). Following this definition, our surgeries are performed via the endoscope-assisted technique. In some cases we need the endoscope just for inspection. The angled optics is introduced along the corridors beyond the cranial nerves under direct visual microscopic control to avoid harming the delicate surrounding structures. The space of time when the endoscope is applied might be short compared with the whole duration of surgery, but it is crucial for the final result. We believe in the combination of the 2 powerful visualization tools, the microscope and endoscope, for successful
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along cisterns and engulf neurovascular structures. Because surgery is the only valuable treatment option for epidermoids (4), complete removal has to be the primary goal of interventions (40). Because of the spreading growth pattern, this is not always possible, and in a significant percentage epidermoids recurre after microsurgically estimated complete resection (31). In part this is caused by the rambling anatomy of the CPA that cannot be completely depicted by the microscope alone. Because epidermoids are soft and avascular lesions, they are particular suitable for endoscopic surgery (7). The use of angled optics allows inspection of corners hidden to the straight optic pathway of the microscope. Remnants that adhere to vessels or nerves may be removed in endoscopic-assisted technique (Video 1). Excellent results may be achieved both in primary surgery (32) as well as in the case of recurrence (7) with the endoscopeassisted technique despite the demanding anatomic situation and the insidious growth pattern. However, particularly in case of epidermoid cysts, not everything seen has to or can be removed. Because of chronic inflammatory reactions to the cyst content or previous surgery, the capsule might be very adherent to neurovascular structures. Excessive surgical manipulation of minute remnants bears endangers the functional outcome and bears no relation to the benign histological and slow-growing biological behavior of the lesion.
surgery of CPA lesions and beyond. Their characteristics complement one another: straight view, stereopsis, and variable zoom on the one hand; and angled view, enlargement and illumination in the depth on the Meningiomas of the CPA other hand (13). The endoscope facilitates Meningiomas are the second most frequent detecting tumor remnants in hidden angles lesions in the CPA after vestibular schwanof the complex surgical field and thus ennomas. Because of their usually slow hances the grade of resection but progressive growth pattern with preservation of function. (27), meningiomas often Manipulation of neurovascular become relevant mass lesions structures and cerebellar that displace the surrounding retraction may be minimized. structures and thus enlarging Video available at The endoscope is applied both the aforementioned corridors. WORLDNEUROSURGERY.org in the simple retrosigmoid and In microsurgical technique in the extended retrosigmoid approach. and under continuous intraoperative monitoring, the tumor mass may be debulked, the meningioma mobilized within the enlarged surgical corridors, and ENDOSCOPIC-ASSISTED SURGERY VIA thus stepwise resected (30). Once the major THE SIMPLE RETROSIGMOID APPROACH part of the meningioma has been resected, Epidermoids of the CPA the jugular foramen, the IAC, Meckel’s Epidermoids are dysontogenetic, slowcave, the area behind vessels, or nerves, growing ectodermal lesions. They spread the ventral brainstem as well as the
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contralateral side may be inspected with angled endoscopes of various degrees. In a series of 46 patients operated on for skull base meningiomas (23 via a retrosigmoid approach) in endoscopeassisted technique Schroeder et al. (34) showed that extensive bone drilling could be avoided by using the endoscope. Further, in 13 of 23 patients operated via the retrosigmoid approach tumour remnants not visible under the straight view of the operating microscope could be detected (34). Currently, in our daily practice the majority of skull base meningioma surgeries is performed under the operating microscope; the endoscope-assisted technique in CPA meningioma surgery is applied only in well-selected cases to visualize blind spots or in extended approaches (Video 2). Microvascular Decompression Although early posterior fossa surgery caused significant morbidity and mortality rates because of the lack of magnification and illumination (22), thanks to the modern surgical setting today, the achieved results drastically improved (35). Both operating microscope and endoscope are at the surgeons’ disposal during microvascular decompression. The most critical step of the procedure is “turning the corner” for exposition of the CPA (22). Applying the adequate technique this step is managed with both visualization tools. However, in this context, the angled view of endoscopes offers a significant advantage compared with the straight microscopic perspective. The ecstatic arteries or prominent veins compressing the Obersteiner-Redlich zone of trigeminal, facial, or glossopharyngeal nerves have to be identified and the microvascular conflict solved. It seems that, compared with the microscope, the endoscope may be of valuable aid during that step, increasing significantly the accuracy of the procedure (2) (Figure 2 and corresponding Videos 3 and 4, comparing the microscopic and the endoscopic perspective). The microvascular conflict occurs in more than 50% of cases at the proximal third of trigeminal nerve (37). In this region the local neurovascular relationships may be much easier explored with an angled endoscope than with the microscope. The recurrence rate accounts for about 25% after an average
follow-up of 4 years with an overall failure rate of 6%e38% (21). The suggested reason is an insufficient identification of the real reason, number and extends of microvascular conflicts (17, 19). Over the last years reports about microvascular decompression evolved from microscopic (22) to endoscope- assisted (10) and finally full endoscopic technique (11, 12). The microscopic procedure is well established, but the results achieved with the endoscope-assisted and pure endoscopic technique seem to be promising (12) and might yield improved short- and longterm results.
ENDOSCOPIC-ASSISTED SURGERY VIA THE EXTENDED RETROSIGMOID APPROACH Transmeatal Extension Vestibular schwannomas, CPA or petroclival meningiomas as well as epidermoids may extend inside the IAC. When the patient has a good hearing function preoperatively, the aim of surgery is complete tumor removal with preservation hearing achieved. This implies anatomical preservation of the inner ear structures and in particular of the posterior semicircular canal (38). Therefore, the meatus cannot be opened completely to expose the fundus. The pure microsurgical option is working blind around the corner with fine hooklets relying upon the distinct tactile sense. The endoscope-assisted option is looking around the corner towards the fundus and removing the most lateral part of the tumor under visual control (39) (Figure 3). In demanding situations like adherent tumors or a very soft tumor consistency, the combination of visual and tactile control facilitates removal of the most lateral part of the vestibular schwannoma under continuous intraoperative monitoring. Both 30 and 70 optics come into operation. Suprameatal Extension Tumors growing from the posterior fossa through Meckel’s cave into middle fossa and parasellar area may be microsurgically resected via a retrosigmoid approach with suprameatal extension (30). Exact knowledge of the anatomy is essential (36). The extra-axial lesion—in most of the cases petroclival meningioma or trigeminal
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schwannoma type C—already displaced the neurovascular structures. Debulking the tumor, a corridor is created and the tumor is followed upward. When no considerable displacement of the neurovascular structures and the brain stem occurred, the use of an endoscope is essential for reaching the tumour parts within the middle fossa (5). The superior cerebellar artery (SCA) is an important landmark for the endoscopeassisted technique in this extended approach. Under microscopic control, an angled optic may be introduced from the CPA to the parasellar region through the space limited superiorly by the SCA, laterally by the oculomotor nerve, medially by the brainstem, and inferiorly by the upper boarder of the trigeminal nerve (5). The ambient cistern is entered and the posterior communicating artery followed towards carotid, crural, and chiasmatic cisterns, thus reaching and exploring the parasellar area. Extensive petrosectomies may be associated with a relevant, approach-related morbidity. Thus, the endoscope-assisted suprameatal extension (with opening of the tentorium) of the retrosigmoid approach became our standard approach for petroclival meningiomas, trigeminal schwannomas (Figure 4 and corresponding Video 5) and epidermoids predominately located in the posterior and extending to the middle fossa. Outlook: Technical Developments The technical progress is probably the major reason for the continuously growing role of endoscopy in neurosurgery over the last 2 decades (25). High-definition imaging, neuronavigation, development of new instruments, the interdisciplinary approach, and detailed anatomical studies led to the breakthrough of endoscopic endonasal extended approach in skull base surgery (14, 15, 33). As the result of advanced technologies, the field of endoscope-assisted surgery is continuously growing, and the advantages in treatment of CPA lesions are well acknowledged (7, 34). However, some major optic and ergonomic drawbacks exist. The aim of further innovation is to reduce technical limitations and render the procedure in this noble area safe and direct. A starting-point is the use of multivariable rigid endoscopes (1, 6, 8, 16,
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Figure 2. Case of a patient presenting with a recurrency of a left hemifacial spasm after previous microvascular decompression. (A, B) Axial constructive interference in steady state showing the microvascular conflict between the anterior inferior cerebellar artery (AICA) and facial nerve at the level of the root exit zone. (C, D, E) Intraoperative, microscopic view of the local anatomical situation. (F, G, H, I, J) The angled endoscope
20). Our group, among others, tested both the Endocameleon (Karl Storz, Tuttlingen, Germany) and the EndActive (Karl Storz) for application in the CPA (6, 8). The Endocameleon is a rigid, rod-lens endoscope, steerable in one plane from 10 to þ120 by a fine optomechanical mechanism. Testing in the anatomical lab revealed a superior usability and visualization potential compared with rigid fixed angle endoscopes (6). However, the ergonomics and the perspective, limited to one plane, could be improved. The EndActive overcomes these limitations. It is a rigid videoendoscope connected to a laptop (video data) and USB
port (control and power supply). The EndActive is lightweight and can be held in one hand like a microsurgical instrument. The field of view can be changed with a joystick mounted on the handle in a range of 160 in all 4 directions. An overview inset allows orientation and facilitates the insertion of instruments. A major drawback of the current prototype is the poor image resolution, but with the ongoing progress of chip technology, it is probably only a matter of time before limitation is addressed (8). Multivariable rigid endoscopes are inserted with a 0 view into the operative
Figure 3. Endoscopic inspection of the right internal acoustic canal after resection of a large vestibular schwannoma.
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(30 ) elucidates the topographical relationship and highlights the actual extend of microvascular decompression. The teflon introduced during the first surgery was scrunched (F). After displacement of the AICA (G), the facial nerve appears impressively compressed and even flattened at the level of the brain stem (H). Under endoscopic control a new and extended pillow of teflon is inserted (I, J).
situs beyond neurovascular structures. Once the final position is reached, the field of view is directed towards the region or structures of interest. The endoscope’s tip itself does not move. The gist is that this new category of endoscopes improves ergonomics and safety and thus has an enormous potential in CPA microsurgery.
CONCLUSION The characteristics of microscopes and endoscopes complement one another. The intraoperative combination of these 2 powerful visualization tools in sense of an endoscope-assisted technique expands the
CN VII, facial nerve; F, fundus; PB, petrous bone.
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Figure 4. Patient harboring a dumbell-shaped trigeminal schwannoma type D on the right side (AeD). Microscopic resection of the tumor through a retrosigmoid intradural suprameatal approach (GeK). The most lateral part of the schwannoma in the middle fossa is resected in the endoscopic
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Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Received 23 July 2014; accepted 1 August 2014 Citation: World Neurosurg. (2014) 82, 6S:S171-S176. http://dx.doi.org/10.1016/j.wneu.2014.08.001 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2014 Elsevier Inc. All rights reserved.
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