Accepted Manuscript Which routes for petroclival tumors? A comparison between the anterior expanded endoscopic endonasal approach and lateral or posterior routes Timothée Jacquesson, M.D., M.Sc., Moncef Berhouma, M.D., M.Sc., Stéphane Tringali, M.D.,Ph.D., Emile Simon, M.D., M.Sc., Emmanuel Jouanneau, M.D.,Ph.D. PII:

S1878-8750(15)00080-7

DOI:

10.1016/j.wneu.2015.02.003

Reference:

WNEU 2712

To appear in:

World Neurosurgery

Received Date: 3 September 2014 Revised Date:

30 January 2015

Accepted Date: 2 February 2015

Please cite this article as: Jacquesson T, Berhouma M, Tringali S, Simon E, Jouanneau E, Which routes for petroclival tumors? A comparison between the anterior expanded endoscopic endonasal approach and lateral or posterior routes, World Neurosurgery (2015), doi: 10.1016/j.wneu.2015.02.003. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Which routes for petroclival tumors? A comparison between the anterior expanded endoscopic endonasal approach and lateral or posterior routes. Authors: 1,2

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Timothée JACQUESSON, M.D., M.Sc. , Moncef BERHOUMA M.D., M.Sc. , Stéphane TRINGALI 1,3 2 1 M.D.,Ph.D. , Emile SIMON, M.D., M.Sc. , Emmanuel JOUANNEAU M.D.,Ph.D. 1

Skull Base Multidisciplinary Unit, Department of Neurosurgery, Neurological Hospital Pierre Wertheimer, 59 Bd Pinel, 69677 Lyon Cedex - France 2 Department of Anatomy, University of Lyon 1, 8 Avenue Rockefeller, 69003 Lyon - France 3 Department of Otorhinolaryngology, Jules Courmont Hospital– Lyon Sud, 165 Chemin du Grand Revoyet, 69310 Pierre Benite - France

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Corresponding Author:

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Timothée JACQUESSON Skull Base Multidisciplinary Unit, Department of Neurosurgery, Neurological Hospital Pierre Wertheimer, 59 Bd Pinel, 69677 Lyon Cedex. Phone Number: +33 472357820 [email protected]

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ACCEPTED MANUSCRIPT ABSTRACT

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Objective. Petroclival tumors still remain a surgical challenge. Classically, the Retrosigmoid Approach (RSA) has long been used to reach such tumors while the Anterior Petrosectomy (AP) has been then proposed to avoid crossing cranial nerves. More Recently, the Endoscopic Endonasal Approach has been “expanded” (EEEA) to the petroclival region. We aim to compare these three approaches and to help petroclival tumors surgical management. Methods. Petroclival approaches were performed on five specimens after formaldehyde preparation and colored latex injection. Results. The EEEA provides a simple straightforward route to the clivus but reaching the petrous apex requires to circumvent the Internal Carotid Artery either via a medial transclival, an inferior transpterygoid or a lateral variant through the Meckel’s Cave. In contrast, the AP offers a narrow direct superolateral access to the petroclival region crossed by the trigeminal nerve. Finally, the RSA provides a wide simple and quick exposure of the cerebellopontine angle, but access to the petroclival region requires to deal with the Vth to XIth cranial nerves. Discussion-Conclusion. The EEEA should be preferred for extradural midline tumors (chordomas, chondrosarcomas) or for cystic lesions when drainage is essential. The AP could be optimal for the radical removal of intradural vascularized tumors (meningiomas) with intrapetrous or supratentorial extensions. The RSA retains advantage for small or cystic tumors near the IAM. The skull base surgeon has to master all of these routes to choose the more appropriate according to the surgical objective, the tumor characteristics and the patient’s medical status.

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Keyword

Skull base, Petroclival, Petrosectomy, Petrous apex, Endoscopy, Endonasal. Acknowledgements

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We thank the technical staff of the Department of Anatomy for their preparation of specimens. We thank K. Erwin for english correction and editing

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ACCEPTED MANUSCRIPT INTRODUCTION The petroclival region is a « surgical » space limited anteriorly by the clivus, laterally by the petrous apex, medially by the brainstem and posteriorly by the Internal Acoustic Meatus (IAM). It extends from the dorsum sellae to the foramen jugulars. It’s crossed by cranial nerves IVth to VIIIth and by the basilar artery with its branches (1). Because of their critical neurovascular relationships and their deep-seated location, the surgical removal of petroclival tumors remains a fascinating challenge. Thereby, these tumors have long been considered as inoperable since the resection was often incomplete with a high morbidity(2).

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Advances in microsurgical technique, operative microscope, anesthesia and neuroradiology have allowed to move forward with the surgical strategy of petroclival tumors. Through a few series from leading neurosurgeons, some surgical approaches turning around the petrous bone to the petroclival region have been reported with hopeful results, but still frequent cranial nerves deficits (3–8),.

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One century ago, the posterior Retrosigmoid Approach (RSA) has been described to reach the petroclival region with a main disadvantage working through the cranial nerves (9). Then, the lateral approaches as the Anterior Petrosectomy (AP) have been proposed despite a “tricky” drilling around the intrapetrous otologic structures (10,11). More Recently, an anterior corridor has been developed with the Expanded Endoscopic Endonasal Approach (EEEA) which provides a broad exposure, vertically from the cribriform plate to the craniovertebral junction and laterally toward the middle cranial or infratemporal fossas (12–14).

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From the literature (15–18), the experience of our surgical team and anatomic dissections, we compare this anterior endoscopic endonasal approach to classical posterior and lateral ones and propose decisional criteria for the management of petroclival tumors. METHODS Anatomical study

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Five fresh cadaveric heads were harvested at the Anatomy laboratory of University Lyon 1 (Lyon, France), prepared with 10% formaldehyde and then injected with colored latex (Phocéenne de chimie – Marseille/France; Aérographe Colorex Technics, Magenta et Cyan).

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Five EEEA were performed according to the technique described by Kassam (14). A 180 millimeters (mm) length and 4 mm diameter endoscope was used with a 0 or 30° lenses (Karl STORZ Endoskope GmbH, Tuttlingen, Germany). A bi-nostril path was necessary and a self-retaining endoscope holder allowed a twohands technique by a single operator. After an anterior classic transphenoidal approach (19) with a head positioned as for pituitary surgery, the intrasphenoidal landmarks were identified: the paracavernous and paraclival segments of the Internal Carotid Artery (ICA), the optic canals, the lateral and medial optic-carotid recesses, the sella turcica, the paraclival recess and the planum sphenoidale. Access to the clivus was straightforward, but access to the petrous apex required to circumvent the ICA. Three variants were described: medial, lateral and below the ICA (Fig. 1).

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The first medial and easier one was transsphenoidal transclival, needed a continuous irrigated high speed drilling (Integrated Power Console and Handpieces, Medtronic, Louisville, USA) of the clivus and reached the tip of the petrous pyramid medially to the ICA. The second lateral variant was transsphenoidal trans-Meckel’s cave, involved a skeletonization of the vertical paraclival ICA segment and extended laterally to expose the orbital apex, the cavernous sinus and the Meckel’s cave. In addition to the sphenoidotomy, a middle turbinectomy and posterior ethmoidectomy were mandatory to enlarge enough the corridor laterally. The inferior third variant was transphenoidal transpterygoid. It required a maxillary sinus as well as a pterygopalatine fossa aperture, a section of the sphenopalatine artery. After outward putting the pterygopalatine fossa content, the medial pterygoid plate was long drilled. Thus, the vidian canal led to the foramen lacerum (20) and inferiorly to the inferior petrous apex (21). Five controlateral microsurgical AP were performed according to the technique described by Kawase (10). After the patient’s head was fixed at 45° to the floor, a curvilinear incision was made anterior to the tragus extending from the zygomatic arch to the temporal line and behind the External Acoustic meatus (EAM). The temporalis muscle was cut vertically and retracted anteriorly. Then, a classical temporal craniotomy was performed as low as possible, one third posterior and two thirds anterior to the EAM. The dura mater was elevated at the superior part of the petrous bone in a posterior to anterior way. The rhomboid construct (22) was gradualy discovered: the

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ACCEPTED MANUSCRIPT IAM located at the bissectrix of the Superficial Petrosal Nerves (SPN) and the eminentia arcuata (23), the geniculate ganglion, the cochlea, the foramen rotondum, the foramen ovale and the horizontal petrous ICA segment. The Kawase’s triangle extending before the IAM up to the trigeminal print and from the upper petrous ridge to the petroclival fissure, was gently drilled. Care was taken to not damage ICA or SPN laterally and cochlea or acoustic facial bundle posteriorly (10,11,24,25). Finally, the posterior cranial and midle fossa dura mater was cautiously opened and the tentorium split after having checked the IVth nerve course. Thus, it offered a broad supra/infra -tentorial exposure of the petroclival area through the drilled petrous apex (Fig.2).

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RSA and posterior transpetrosal approches were already well described by previous anatomical or surgical studies (26–30). Clinical data

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Also, we used data and experience obtained in our recent petroclival tumors cases, who underwent various surgical approaches since 2010. There were 23 patients with different histological types of petroclival tumors: meningiomas (11 cases), schwannomas (1 case), chordomas (2 cases), chondrosarcomas (2 cases) and epidermoid cysts (7 cases). Eight EEEA, 5 AP, 5 RSA and 5 Combined Approches were all performed by a single senior neurosurgeon (E.J.). Literature data

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A systematic review of the literature was performed using dedicated databases (Pubmed, Scopus, Sciencedirect) with the following keywords : petroclival, tumors, approach, management, retrosigmoid, petrosectomy, endoscopic, endonasal, petrous apex. RESULTS Anterior approach

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The anterior EEEA provides a simple straightforward access to the entire clivus, but the petrous apex is hiden right behind the vertical paraclival segment of the ICA (Fig. 1). The medial transsphenoidal transclival route runs through the middle clivus to the medial petrous apex and is bounded: superiorly by the pituitary fossa, inferiorly by the sphenoid floor, posteriorly by the basilar artery with the brainstem and the cisternal segment of the VIth nerve and laterally by the ICA. The lateral transsphenoidal trans-Meckel’s cave route offers access to the petrous apex through the Meckel’s cave and is limited : superiorly by the the cavernous sinus and optic canal, inferiorly by the thick sphenoid bone, laterally by the orbital apex, medially by the ICA (31). Its bone aperture exposes the cranial nerves IInd to VIth but reaching the petrous apex through the meningeal layers needs a tumor growth that has already opened the way. The inferior transsphenoidal transpterygoid route requires a drilling of the sphenopterygoid complex which is limited: superiorly by the horizontal petrous ICA segment, inferiorly by the Eustachian tube, laterally by the petrous pyramid and medially by the sphenoid floor. The bone resection frees the foramen rotondum and foramen ovale - laterally - and can extend - posteriorly - near the IAM or the foramen jugularis. For all variants, tumor extensions behind the ICA or the IAM are not accessible contrary to the controlateral side (Fig. 3). Lateral approach

The lateral AP provides a narrow, direct superior access to the petroclival region (Fig. 2) limited: superiorly by the IVth nerve and the temporal lobe, inferiorly by the inferior petrosal sinus and the VIth nerve, anteriorly by the clivus, posteriorly by the IAM with the VIIth and VIIIth nerves, laterally by the horizontal petrous ICA portion and medially by the brainstem and the vertebrobasilar arterial network. This surgical corridor can be enlarged toward the middle cranial fossa to expose the Meckel's cave and the cavernous sinus as well as the retrochiasmatic area and the perimesencephalic cisterns. While the corridor passes anterior to the IAM, it still crosses the trigeminal nerve, which has to be mobilized forward and upward. Also, tumor extensions toward the jugular foramen, inside the clivus or behind the IAM cannot be controlled (Fig. 3). Posterior approaches The posterior Retrosigmoid approach (RSA) offers a wide access to the petroclival area around 292.4 mm2 without any bone resection (18). However, the route crosses the cranial nerves from Vth to XIth (15,16), and is limited: superiorly by the tentorium and the trigeminal nerve, inferiorly by the foramen magnum, anteriorly by

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ACCEPTED MANUSCRIPT the clivus and the posterior side of the petrous bone, medially by the cerebellonpontine angle and the basilar artery. The superior petrosal vein (Dandy’s vein) has to be carefully identified at the superior anterior ridge of the tentorium. A minimal invasive Supracerebellar variant, commonly used for neurovascular conflicts decompression (32), leads to the superior petrous apex along the trigeminal nerve. Also, drilling the Suprameatal tubercule above the IAM increases the surgical corridor at the trigeminal porus and the Meckel’s cave (15,33,34). At last, tumor extensions toward the controlateral side, at the anterior side of the brainstem, inside the petrous bone and superiorly through the tentorium cannot be reached (Fig. 3).

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The posterior transpetrosal approches have been thoroughly described and are divided into : retrolabyrinthine, translabyrinthine and transcochlear one. Each offers an wide acces to the petroclival area with similar limits to those of RSA. In addition to require a pneumatized mastoid with favorable location of the labyrinthe strcuctures, the retrolabyrinthine approach provides a 108 mm2 limited petroclival exposure (17). The translabyrinthine approach permtis a larger osteo-dural aperture including within the IAM and its petroclival area exposure is around 449 mm2 (17). Likewise, the transcochlear approach provides the widest exposure of the petroclival region from 514 to 755.6 mm2 (17,18). Each of these three approaches requires ENT surgical skills for drilling around the petrous otologic structures and the sigmoid sinus. Thereby, each differs by the extent of bone resection, which comes with potential complications as an increasing risk of facial palsy. Finally, their corridor posterior to the IAM has to dangerously deal with the acoustic facial bundle. DISCUSSION

Wait-and-see, radiotherapy or surgery ?

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Under the same patronymic, different petroclival tumors can be encountered ; some are extradural or intradural and others cystic or solid. Whatever their characteristics, these tumors still challenge the neurosurgeon and the recent development of the endoscopic endonasal surgery rises hope to overcome some difficulties. To the best of our knowledge, no study summarizes all the routes that could be used to reach the petroclival region while trying to find criteria to orient the surgical management depending on the tumor characteristics.

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With the development of the imaging and the modern radiotherapy, the discovery of a petroclival tumor does not lead to surgical attitude at first line. As many are slow growing tumors like meningiomas, a wait-and-see attitude can be proposed primarily until symptoms or proofs of growing. Radiotherapy alone without histological diagnosis when imaging is considered as specific like meningiomas may be proposed (35). However, to maximize its efficacy and minimize its associated risks, radiosurgery should be reserved for small tumors away from neurovascular structures or for small tumors remnants (36). If advantages of such a proposal are easily understood by patients (less morbidity), disadvantages (no tumor removal with possible delayed recurrence) should also be explained especially for young patients. Others auhors prefer a first aggressive surgical option rather than a simpe follow-up especially if tumor size exceeds 25 mm (37). Indeed, the surveillance will then demonstrate the growth of meningiomas but also an increase of operative morbidity or mortality. Evolution of the philosophy of surgery

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Today, after the multiplication of invasive approaches aiming to achieve complete tumor removal whatever the price, the management of large petroclival tumors seems to be headed in a new direction with more functional goals. The purpose of surgery is to remove the tumor as much as possible while preserving the quality of life of the patient. As it reduces the risk of neurovascular damage, a first “near total” removal tactic is becoming increasingly popular for petroclival lesions like meningiomas (39–41), possibly followed by stereotactic or fractioned radiotherapy for the residue. Furthermore, the idea that increasing bone removal minimizes effects on neural structures appears to no longer hold true for the petrous bone since risks for the intrapetrous otologic structures are increasingly taken into consideration (36). Thus, a two-times surgery could enable large petroclival tumors complete removal with less morbidity due to a long operative time. Finally, “tailored” combined petrosectomies (RSA-AP e.g.) are more advocated for a satisfactory control of infratentorial and supratentorial tumor portions (42–44). Which decisionnal criteria to choose the route and predict the surgical difficulties? First of all, the choice of the surgical approach will be determined by the characteristics of the petroclival tumor. The consistency of the tumor is a major decision-making element. Indeed, fibrous or adherent tumors are independently associated with increased postoperative morbidity (6). A large approach should be used for hard or fibrous tumors to insure safe dissection of neurovascular structures and sufficient margins around them. In

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contrast, soft or cystic tumors can be accessed via a smaller approach and removed using aspiration or fenestration. This parameter would be imperfectly supposed using minium apparent diffusion coefficient or hypointense signal on T2 MRI and calcifications on CT-scan. Thereafter, the tumor volume, seat of the implantation zone (39), any encasement of nerves or vessels (4) and the presence of an arachnoid cleavage plane (36) will all play a role in surgical decision (2,5,6). Tumoral extensions are also crucial: extension to the sphenoid sinus creates an opportunity for an anterior transsphenoidal transclival approach (18); supra tentorial extension suggests an AP or an associated pterional approach with or without orbitozygomatic craniotomy (45,46); extension within or behind the IAM may lead to propose a combined petrosectomy including a posterior transpetrosal approach as translabyrinthine (2). Besides, an invasion of the Meckel's cave or the cavernous sinus has to be predicted to enlarge the route (39,45,46) or to prefer a subtotal resection. Eventually, the anatomic distortions caused by the tumor should favor the chosen approach (15).

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Second, the general medical status of the patient is determinant to orient the anesthesia and the aggressiveness of the surgery. A less invasive approach should be preferred in elderly, heavy comorbidities or altered general condition. Invalidating symptoms and rapid evolution may hasten the surgery (47). The results of preoperative examinations, particularly hearing status, will further lead the surgical choice (2). Moreover, knowledge of the anatomy of the petrous bone, surgical skills, and the availability of specific surgical equipment are obviously critical in the surgeon’s preference. To the end, the best decision of treatment must result of a multidisciplinary meeting with a neurosurgeon, an ENT surgeon, a radio-therapist and a radiologist.

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Which approaches for which petroclival tumors

Although bone resection and working areas have already been well studied (15,17,18,21,48), these assessments do not precisely fit with the final surgical exposure. Despite a little-sized bone drilling, the AP involves tentorium splitting, cerebrospinal fluid draining and V3 displacement that substantially enlarge the surgical corridor. The EEEA involves a widest bone opening but its access is still constrained by the ICA or the cavernous sinus. This may overcome by moving the endoscope around. Thus, the choice of the optimal route to the petroclival region will be more relevant depending on neurovascular structures endangered, extension possibilities and expected operative difficulties (Fig. 4).

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The EEEA provides a broad access to the clivus and nonesuch inferior lateral exposure toward the cavernous sinus, the pterygopalatine or the infratemporal fossas (Fig. 3). In addition to its corner vision, it allows a close-up panoramic view of the operative field without risks for intra petrous structures. However, the endoscopy requires a long learning curve and specific dedicated materiel. Also, the petrous apex is far posterior to the ICA which has to be dangerously circumvent. The three variants has their own pitfalls : the transclival variant deals with the veinous basilar plexus and barely exposes the medial tip of the petrous apex ; the trans-Meckel’s cave variant bares the ICA and the cavernous sinus with a high vascular and nerve risks and it remains a virtual space while a tumor hasn’t opened it ; the transpterygoid variant involves a time consuming drilling of the pterygoid plate and a damage of the vidian nerve or the eustachian tube. (Fig. 4). Moreover, the palatine nerve would be difficultly preserved. Furthermore, a potential CSF leak has always be kept in mind for such large skull base endoscopic endonasal approach, especially in case of extensive osteo-dural aperture. That’s why it should be reserved for extradural midline tumors like chondrosarcomes or chordomas, extradural lateral tumors such as neurinomas and soft tumors like cholesterol granulomas or epidermoid cysts which can be treated by fenestration and external drainage (Fig. 5 and 6). Finally, this is also a smart route for tumor biopsy as for simple pituitary surgery (19). The AP provides a short wide access to the upper clivus, the petrous apex, the trigeminal porus and the anterior lateral side of the brainsteam (1). Also, it eases the control of tumor vascular supply, bone invasion and supratentorial tumor extension. Despite the corridor runs before the acoustic facial bundle, it still deals with the pathetic and trigeminal nerves (Fig. 4 and 5). Likewise, it requires a long learning curve whereas drilling jeopardizes the horizontal ICA and the intrapetrous otologic structures. Moreover, the temporal lobe retraction and veinous drainage system injury have to be considered depending upon the hemipshere’s dominance (2). That’s why it should be reserved for medium-sized, intradural, vascularized, petroclival tumors like meningiomas (36). These last have to stay anterior to the IAM without cranial posterior fossa extension. In case of giant tumors, a combination of AP with a posterior infratentorial or transpetrosal approach could allowed a statisfactory surgical removal (Fig. 6). The RSA appears simple, safe and well-known. It offers a wider corridor along the posterior side of the petrous bone without hearing loss. It requires a short surgical training and controls easily a tumor extension behind the

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ACCEPTED MANUSCRIPT IAM. However, it raises problems of working through cranial nerves, cerebellum retraction, long distance to the target and late access to the vascular supply (Fig. 4). In fact, it should be reserved to little-size less vascularized or large cystic petroclival tumors. Furthermore, Meckle’s cave tumor extension could be achieved after suprameatal drilling but it endangers the acoustic facial bundle. Small upper petrous ridge tumors could benefit from minimal invasive supracerebellar route (Fig. 6). Finally, isolated posterior transpetrosal variants wouldn’t sufficient by their own for petroclival tumors resection. Coming from behind the IAM, they jeopardize the acousticofacial bundle wihout additional advantage for small tumors exposition as the RSA. They would play a role for giant tumors in combination with others approches like AP or any pterional variants.

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CONCLUSION

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From anatomical dissection, surgical experience and literature, it appears to us that each of these approaches has its own indications for petroclival tumors. There are different approaches for different petroclival tumors, not opposed but complementary. The choice of the optimal approach will have to fit the assumed histological diagnosis, the tumor characteristics, the patient’s status and the surgical goal. Thus, extradural tumors extended to the clivus and cysts are more candidates for an anterior EEEA. In contrast, AP will be preferred for intradural tumors necessitating radical removal with early vascular control and supratentorial tumor extensions. Smallsized intradural tumors seated on the petrous apex or extending around the IAM will be accessible by a RSA. Definitively, the skull base surgeon has to include these different routes in his armamentarium to choose the best surgical approach for each petroclival tumors.

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ACCEPTED MANUSCRIPT FIGURES

Figure 1 2: Endoscopic view of the final exposure after an Expanded Endoscopic Endonasal Approach.

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Despite the clivus straightforward, reaching the petrous apex needs to circumvent the Internal Carotid Artery (ICA). Three variants are described : a medial transsphenoidal transclival route (●) toward the pit of the petrous pyramid, a lateral transsphenoidal trans-Meckel’s cave route (■) including a ICA skeletonization then a cavernous sinus and Meckel’s cave opening, an inferior transpterygoid route (▲) which passes below the ICA to the low petrous apex after a time-consuming drilling of the sphenopterygoid complex along the vidian nerve. The Cavernous sinus is recognized as a dural bag th th lateral to the paraclival-paracavernous ICA junction ; containing the cranial nerves III , IV V.1 and th VI . The Meckel’s cave is an inferior dural bag to the cavernous sinus containing the cranial nerve V.1 rd th and V.2 and fat tissue. III to VIII: cranial nerves III to VIII , AICA: Anterior Inferior Cerebellar Artery, BA: Basilar Artery, ET :Eustachian tube, FL :Foramen Lacerum, OA :Orbital apex, OC: Optic canal, PG: Pituitary Gland. Figure 2 3: Operative view of the final exposure of the Anterior Petrosectomy.

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After drilling the Kawase’s triangle before the Internal Acoustic Meatus (IAM) until the trigeminal print, the dura mater is opened in the posterior cranial and temporal fossas, then the tentorium is split. This broad aperture extends : superiorly to the temporal lobe, inferiorly to the inferior petrosal sinus and the th VI nerve, anteriorly to the clivus, posteriorly to the IAM, medially to the brainsteam and laterally to the Internal Carotid Artery. The trigeminal nerve crosses the corridor and has to be moved forward and th upward. IV to VI: cranial nerves IV to VI , AICA: Anterior Inferior Cerebellar Artery, EA: Eminentia Arcuata, ICA: Internal Cerebral Artery, REZ: Root Entry Zone. Figure 3: Skull base view after right anterior petrosectomy and left expanded endoscopic endonasal approach.

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This view accurately shows the anatomical limits of each approach. The dura mater has bee removed on the half right skull base. The Expanded Endoscopic Endonasal Approach (EEEA) offers an anterior th corridor with a large osteodural opening bounded posteriorly by the basilar artery, the VI nerve and the brainstem, superiorly by the sella and the optic canal, inferiorly by the Eustachian tube and the sphenoid floor. Deeply, EEEA can reach the porus of the Internal Acoustic Meatus (IAM) and the th th foramen jugularis with the cranial nerves from VII to XI . Despite the dangerous circumvention around the ICA, it provides a large access to the clivus and multiple expansions to the pterygopalatine fossa, the cavernous sinus, the Meckel's cave, the contralateral side and the suprasellar area. The Anterior Petrosectomy (AP) provides a lateral narrow access bounded anteriorly by the clivus, th th posteriorly by the IAM, superiorly by IV and V nerve, inferiorly by the inferior petrosal sinus, laterally th by the horizontal portion of the ICA and medially by the brainstem, the VI nerve and the basilar artery. As a supratentorial skull base approach, AP allows access to the retrochiasmatic space or perimesencephalic cisterns. According to the bone flap, AP could also lead to the anterior cranial fossa, middle cranial fossa, superior orbital fissure, cavernous sinus and Meckel's cave with exposure nd th of cranial nerves from II to VI . The RSA, even simple and popular among neurosurgeon, involves a th th cerebellum retraction and a risky course through the V to XI nerves. Its wide corridor is bounded : th anteriorly by the clivus, superiorly by the tentorium and IV/V nerves, inferiorly by the foramen magnum, laterally by the petrous bone and medially by the cerebellopontine angle. Somes variants exist with specfic interest as the suprameatal, retrolabyrinthine or translabyrinthine approaches. All of these approaches are turning around the petrous bone to reach the petroclival region with more or st less danger and efficiency according to the bone resection. characteristics. I to XI: cranial nerves I to th XI , ACA: Anterior Cerebral Artery, AICA: Anterior Inferior Cerebellar Artery, BA: Basilar Artery, BT: Brainsteam, Ch: Chiasma, EA: Eminentia Arcuata, ICA: Internal Carotid Artery, LSW: Lesser Sphenoid Wing, MCA: Middle (Sylvian) Cerebral Artery, MMA: Middle Menigeal Artery, PCA: Posterior Cerebral Artery, PComA : Posterior Communicating Artery, PS: Pituitary Stalk, SCA: Superior Cerebellar Artery, SS: Sigmoid Sinus, UPR: Upper Petrous Ridge. Figure 4: Artistic draw of different approaches turning around the petrous bone to reach the petroclival region.

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Figure 5: Intraoperative views of petroclival tumors approaches

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The petroclival tumors (purple raspberry) are deep-seated with many neurovascular structures around that still makes a fascinating surgical challenge. The expanded endoscopic endonasal approach th (EEEA) jeopardizes successively the sphenopalatine artery, the Eustachian tube, the ICA, the VI nerve, the cavernous sinus, then the great palatine nerve and the vidian nerve. The Anterior Petrosectomy (AP) provides a lateral narrow access to the petroclival region anterior to the Internal Acoustic Meatus. It also successively endangers the temporal lobe, the inferior anastomotic vein of Labbé, the mandibular nerve, the supericial petrosal nerves, the otologic intrapetrous structures, the ICA, the superior and inferior petrosal sinuses and the cranial nerves IV and VI. The Retrosigmoid Approach (RSA) exposes the venous sigmoid sinus and the cerebellum. Although it courses through th th the VII to XI nerves, it provides a wide corridor with well-known limits. Finally, The posterior transpetrosal approaches (TPA) outline the venous sigmoid sinus and the otologic intra petrous structures and differ by an increasing bone resection which comes with potential complications as facial palsy.

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The anterior petrosectomy (A) allows a satisfactory control of vascular supply and supra/infra tentorial tumor extensions. However, the trigeminal nerve dangerously crosses the surgical corridor. The expanded endoscopic endonasal approach (B) is advantageous in case of soft petroclival tumors which need to be drained. Nevertheless, such solid or large sized tumors cannot be assessed by this endoscopic anterior route. MCF :Middle Cranial Fossa, BT: Brainsteam, CS: Cavernous Sinus, V: Trigeminal nerve, T: Tentorium, TL: Temporal Lobe. ST: Sella Turcica. Figure 6: Pre and post-operative Cerebral MRI of petroclival tumors

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Yellow arrows show the surgical approaches for these petroclival tumors. Patient 1 presented a recurrent left cerebellopotine epidermoid cyst after multiples surgical approaches above and through the petrous bone. Smart fenestration and drainage were possible via an expanded endoscopic endonasal approach (A,B). Patient 2 presented a left medium size petrous apex tumor implanted just anterior to the cranial nerves, suggestive of a meningioma. A radical anterior petrosectomy was thus performed (C,D). Patient 3 presented a upper petrous ridge little size tumor discovered by a V2 trigeminal neuralgia which leads to choose an effective “tailored” supracerebellar retrosigmoid rpprocach. The intraoperative appearance and histological examination confirmed a meningioma (E,F). Patient 4 presented a large petroclival tumor extending from the foramen magnum to the sellar region and behind the right internal acoustic meatus. Diagnosis of meningioma was obtained by an initial retrosigmoid biopsy. A combined petrosectomy (translabyrinthine apparoach and AP during the same procedure) has allowed a subtotal resection. Adhesion between the tumor and the brainstem has led to keep in place the shell (G,H).

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ACCEPTED MANUSCRIPT REFERENCES Fournier H-D, Mercier P, Roche P-H: Surgical anatomy of the petrous apex and petroclival region. Adv Tech Stand Neurosurg 91–146, 2007.

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Which routes for petroclival tumors? A comparison between the anterior expanded endoscopic endonasal approach and lateral or posterior routes. Highlights

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We compare posterior, lateral and anterior approaches to the petroclival region. We try to find decisional criteria to help petroclival tumors surgical management. The new anterior endoscopic approach is relevant for extradural midline tumors or for cystic lesions. The lateral trans petrous approach is helpful for radical removal of intradural vascularized tumors with intrapetrous or supratentorial extensions. The posterior retrosigmoid approach retains interest for small tumors around the internal acoustic meatus.

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AP: Anterior petrosectomy CT: computed tomography CSF: Cerebrospinal Fluid EAM: External Acoustic Meatus EEEA: Expanded Endoscopic Endonasal Appraoch IAM: Internal acoustic meatus ICA: Internal carotid artery MRI: Magnetic resonance imaging RSA: Retrosigmoid approach SPN: Superficial Petrosal Nerve

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Which routes for petroclival tumors? A comparison between the anterior expanded endoscopic endonasal approach and lateral or posterior routes. DISCLOSURE OF FUNDING

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CONFLICT OF INTEREST

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We wish to draw the attention of the Editor to the following facts which may be considered as potential conflicts of interest and to significant financial contributions to this work. [OR] We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome. We confirm that the manuscript has been read and approved by all named authors and that there are no other persons who satisfied the criteria for authorship but are not listed. We further confirm that the order of authors listed in the manuscript has been approved by all of us.

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We confirm that we have given due consideration to the protection of intellectual property associated with this work and that there are no impediments to publication, including the timing of publication, with respect to intellectual property. In so doing we confirm that we have followed the regulations of our institutions concerning intellectual property. We understand that the Corresponding Author is the sole contact for the Editorial process (including Editorial Manager and direct communications with the office). He is responsible for communicating with the other authors about progress, submissions of revisions and final approval of proofs.

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Signed by all authors as follows: Timothée JACQUESSON Moncef BERHOUMA Stéphane TRINGALI Emile SIMON Emmanuel JOUANNEAU