Endoscopic Anatomy of the Skull Base.

Presently, endoscopic skull base surgery has undergone significant advancements since its inception over two decades ago. Nevertheless, it is imperative to underscore that the fundamental basis of all surgical procedures lies in the meticulous understanding of anatomy, with particular emphasis on the ventral anatomy. This facet has recently garnered increased attention.Following the advancements in endoscopic skull base surgery techniques, this chapter will concentrate on the pertinent anatomical considerations that serve as key foundations for successful procedures. These considerations are categorized into two planes: the sagittal plane and the coronal plane.The sagittal plane is further subdivided into five distinct approaches, namely,(1) the transcribriform approach, (2) the transplanum approach, (3) the transsellar approach, (4) the transclival approach, and (5) the transodontoid approach.On the other hand, the coronal plane is delineated into seven specific zones to facilitate comprehension and potential applications: (1) the petrous apex approach, (2) the intrapetrous approach, (3) the suprapetrous approach, (4) the cavernous sinus approach, (5) the infratemporal approach, (6) the medial condyle approach, and (7) the jugular foramen approach.By organizing the anatomical aspects in this systematic manner, the information provided becomes more accessible, fostering a comprehensive understanding of the subject matter for potential future application.

Customized ventral bony and dural opening in the transplanum/transtuberculum and transclival variants of extended endoscopic endonasal approach to suprasellar craniopharyngiomas: an approach-based stepwise cadaveric dissection and clinical applicability.

BACKGROUND: Optimal initial exposure through an extended endoscopic endonasal approach (EEA) for suprasellar craniopharyngiomas ensures safe and unrestricted surgical access while avoiding overexposure, which may prolong the procedure and increase neurovascular adverse events. METHOD: Here, the authors outline the surgical nuances of a customized bony and dural opening through the transplanum/transtuberculum and transclival variants of the extended EEA to suprasellar craniopharyngiomas based on the tumor-pituitary stalk relationship. A stepwise cadaveric dissection and intraoperative photographs relevant to the approaches are also provided. CONCLUSION: Safe maximal resection of suprasellar craniopharyngiomas through extended EEAs can be feasibly and safely achieved by implementing of tailored ventral exposure.

How I do it: the endoscopic endonasal transclival approach for clipping of the ruptured vertebral artery aneurysm.

BACKGROUND: Vertebral artery aneurysms account for less than 5% of all cerebral aneurysms. They have a high risk of rupture and are associated with threatening clinical outcomes compared with anterior circulation aneurysms. METHOD: The endoscopic endonasal transclival approach (EETA) was used. During the temporary clipping, the neck of the aneurysm was dissected, and a permanent clip was applied. The repair of the skull base defect was carried out with the nasoseptal mucoperiosteal flap on the vascular pedicle. CONCLUSION: The EETA is a feasible alternative for the clipping of the medially located ruptured vertebral artery aneurysm. EETA can be recommended for centers with a large volume of cerebrovascular and endoscopic neurosurgical procedures.

The feasibility of three port endonasal, transorbital, and sublabial approach to the petroclival region: neurosurgical audit and multiportal anatomic quantitative investigation.

PURPOSE: The petroclival region represents the "Achille's heel" for the neurosurgeons. Many ventral endoscopic routes to this region, mainly performed as isolated, have been described. The aim of the present study is to verify the feasibility of a modular, combined, multiportal approach to the petroclival region to overcome the limits of a single approach, in terms of exposure and working areas, brain retraction and manipulation of neurovascular structures. METHODS: Four cadaver heads (8 sides) underwent endoscopic endonasal transclival, transorbital superior eyelid and contralateral sublabial transmaxillary-Caldwell-Luc approaches, to the petroclival region. CT scans were obtained before and after each approach to rigorously separate the contribution of each osteotomy and subsequentially to build a comprehensive 3D model of the progressively enlarged working area after each step. RESULTS: The addition of the contralateral transmaxillary and transorbital corridors to the extended endoscopic endonasal transclival in a combined multiportal approach provides complementary paramedian trajectories to overcome the natural barrier represented by the parasellar and paraclival segments of the internal carotid artery, resulting in significantly greater area of exposure than a pure endonasal midline route (8,77 cm2 and 11,14 cm2 vs 4,68 cm2 and 5,83cm2, extradural and intradural, respectively). CONCLUSION: The use of different endoscopic "head-on" trajectories can be combined in a wider multiportal extended approach to improve the ventral route to the most inaccessible petroclival regions. Finally, by combining these approaches and reiterating the importance of multiportal strategy, we quantitatively demonstrate the possibility to reach "far away" paramedian petroclival targets while preserving the neurovascular structures.

Transclival approaches for intradural pathologies: historical overview and present scenario.

Recently, endoscopic transsphenoidal transclival approaches have been developed and their role is widely accepted for extradural pathologies. Their application to intradural pathologies is still debated, but is undoubtedly increasing. In the past five decades, different authors have reported various extracranial, anterior transclival approaches for intradural pathologies. The aim of this review is to provide a historical overview of transclival approaches applied to intradural pathologies. PubMed was searched in October 2018 using the terms transcliv*, cliv* intradural, transsphenoidal transcliv*, transoral transcliv*, transcervical transcliv*, transsphenoidal brainstem, and transoral brainstem. Exclusion criteria included not reporting reconstruction technique, anatomical studies, reviews without new data, and transcranial approaches. Ninety-one studies were included in the systematic review. Since 1966, transcervical, transoral, transsphenoidal microsurgical, and, recently, endoscopic routes have been used as a corridor for transclival approaches to treat intradural pathologies. Each approach presents a curve that follows Scott's parabola, with evident phases of enthusiasm that quickly faded, possibly due to high post-operative CSF leak rates and other complications. It is evident that the introduction of the endoscope has led to a significant increase in reports of transclival approaches for intradural pathologies. Various reconstruction techniques and materials have been used, although rates of CSF leak remain relatively high. Transclival approaches for intradural pathologies have a long history. We are now in a new era of interest, but achieving effective dural and skull base reconstruction must still be definitively addressed, possibly with the use of newly available technologies.

Endoscopic transsphenoidal drainage of a petrous apex cholesterol granuloma using a frontal sinus nasal stent: a case report with long term follow up.

BACKGROUND: Cholesterol granulomas of the petrous apex are benign cysts affecting 0.6 patients per 1 million. The pathophysiology involves cholesterol crystals and lipids that are surrounded by giant cells. The cholesterol deposits induce an inflammatory response likely from acute hemorrhage leading to the formation of a fibrous capsule. The capsule expands over time compressing nearby cranial nerves (VI-VIII), which can cause worsening symptoms. Surgical resection has been shown to provide excellent improvement in symptoms. Historically, open approaches such as the infracochlear, infralabyrinthine, and middle fossa have been used. Herein we present a case showing the feasibility and clinical utility of using an endoscopic endonasal transclival approach for treatment of these tumors. CASE: A 44-year-old female presented with history of intermittent double vision, dizziness, nausea, and headaches for 3 years. She developed a partial left CN6 palsy with significant diplopia and episodes of left facial weakness. The worsening symptoms prompted presentation to the ED where MRI and CT scan revealed a left petrous apex lesion (1.8 × 1.7 cm) with hyperintensity on T1 and T2 imaging, suggestive of cholesterol granuloma. She underwent an endoscopic transclival resection of the lesion: drainage of left petrous apex cholesterol granuloma and stent placement from left petrous apex into sphenoid sinus (novel technique). This was done to allow continued communication and drainage of the tumor bed from the petrous apex into the sphenoid sinus with the intent to minimize the risk of recurrence. At the postop visit both 6th nerve palsy and diplopia had resolved. Imaging is stable 2 years after the surgery. DISCUSSION: The placement of the stent in this case was done to prevent symptom recurrence. 11% of patients that do not receive a stent will have symptom recurrence within one year. From the historical literature, only 4% of patients who had stent placement developed cyst recurrence or expansion on follow-up imaging. Stent placement has been shown to prevent cyst enlargement within the first few months after surgery. We demonstrate that the endoscopic endonasal transclival approach provided good visualization of the tumor, allowed for an adequate working window for resection, and provided a sufficient approach for stent placement.

Techniques and challenges of the expanded endoscopic endonasal access to the ventrolateral skull base during the "far-medial" and "extreme medial" approaches.

BACKGROUND: Expanding the ventrolateral skull base corridor from the midline of lower clivus to the petroclival fissure is a challenging endonasal surgical task. Resection of lytic lesions like chondrosarcoma can cause cranial nerve morbidities and injury of ICA, necessitating accurate knowledge of correlative endoscopic anatomy with stereotactic landmarks. METHODS: We describe an extended endoscopic endonasal approach (EEA) for a right petroclival chondrosarcoma with the demonstration of ipsilateral surgical landmarks with contralateral normal correlates, using a stepwise comparative image-guided cadaveric dissection study. CONCLUSION: EEA for lytic lesions like chondrosarcomas needs to address brain shift and displacement of ICA, posing a chance for cranial nerve morbidities and ICA injury. Meticulous utilization of intraoperative stereotactic landmarks can help avoid and mitigate surgical complications.

Endoscopic endonasal resection of a medullary cavernoma: a novel case.

Brainstem cavernomas can present very challenging operative problems. Endoscopic endonasal approaches to these lesions in the mesencephalon and pons have been described. In this article the authors present the first case of a medullary cavernoma resected by an endoscopic transclival approach. A 26 year-old woman with a 1.5 cm medullary cavernoma presented with imbalance, swallowing difficulty, and right hemibody weakness. She was taken to the operating room for endoscopic endonasal transclival resection. Her pre-existing neurologic deficits worsened initially after surgery, but at three-month follow-up she had made a full neurologic recovery.

[Extended endoscopic endonasal posterior (transclival) approach to tumors of the clival region and ventral posterior cranial fossa. Part 3. Analysis of surgical treatment outcomes in 127 patients]. / Éndoskopicheskii éndonazal'nyi zadnii rasshirennyi (transklival'nyi) dostup k opukholiam oblasti skata cherepa i ventral'nykh otdelov zadnei cherepnoi iamki. Chast' 3. Analiz rezul'tatov khirurgicheskogo lecheniia 127 patsientov.

Until recently, tumors of the clival region and ventral posterior cranial fossa were considered hard-to-reach and often inoperable via standard transcranial approaches. The introduction of minimally invasive methods combined with the endoscopic technique into neurosurgical practice has enabled removal of hard-to-reach tumors, including midline tumors of the ventral posterior cranial fossa. OBJECTIVE: To improve and introduce the extended endoscopic endonasal posterior (transclival) approach into clinical practice and to analyze the results of its application in surgical treatment of midline skull base tumors extending into the ventral posterior cranial fossa. MATERIAL AND METHODS: During the period from 2008 to the present, we have operated 127 patients with various skull base tumors located in the clival region and ventral posterior cranial fossa (60 males and 67 females); the patients' age was 3 to 74 years. The distribution of tumors by histology was as follows: 96 (75.6%) chordomas, 9 (7.1%) pituitary adenomas, 8 (6.3%) meningiomas, 3 (2.33%) cholesteatomas, 2 (1.6%) craniopharyngiomas, 3 (2.33%) fibrotic dysplasia, and 6 (4.7%) other tumors (giant cell tumor, glioma of the neurohypophysis, osteoma, plasmacytoma, carcinoid tumors, chondroma). The tumor size was as follows: 36 (28.35%) giant (more than 60 mm) tumors, 71 (55.9%) large (35-59 mm) tumors, 19 (14.96%) medium (21-35 mm) tumors, and 1 (0.79%) small (less than 20 mm) tumor. Intraoperative monitoring of the cranial nerves was performed (20 cranial nerves were identified) in 10 cases. RESULTS: The extent of chordoma resection was as follows: total removal - 63 (65.62%) cases, subtotal removal - 23 (23.96%) cases, and partial removal - 10 (10.42%) cases. Pituitary adenomas were resected totally in 6 cases, subtotally in 1 case, and partially in 2 cases. Meningioma was removed subtotally in 4 cases, partially in 3 cases, and less than 50% in 1 case. Other tumors (cholesteatoma, craniopharyngioma, fibrous dysplasia, giant cell tumor, glioma of the neurohypophysis, osteoma, plasmacytoma, carcinoid tumors, chondroma) were removed totally in 7 cases and subtotally in 7 cases. Postoperative cerebrospinal fluid leakage occurred in 9 (7.2%) cases, and meningitis developed in 12 (9.4%) cases. Oculomotor disorders occurred in 17 (13.4%) patients; in 10 of these patients, the disorders regressed within 4 to 38 days after surgery; in 7 patients the oculomotor disorders did not regress. A lethal outcome occurred in 2 (1.57%) cases. CONCLUSION: The extended endoscopic endonasal posterior (transclival) approach, being minimally invasive, enables removal of various midline skull base tumors with/without involvement of the clivus with high radicalness, low risk of postoperative complications, and low lethality. Until recently, these tumors were considered almost inoperable.

[Extended endoscopic endonasal posterior (transclival) approach to tumors of the clival region and ventral posterior cranial fossa. Part 1. Topographic and anatomical features of the clivus and adjacent structures]. / Éndoskopicheskii éndonazal'nyi zadnii rasshirennyi (transklival'nyi) dostup k opukholiam oblasti skata i ventral'nykh otdelov zadnei cherepnoi iamki. Chast' 1. Topografo-anatomicheskie osobennosti skata i pogranichnykh s nim obrazovanii.

OBJECTIVE: to describe the main topographic and anatomical features of the clival region and its adjacent structures for improvement and optimization of the extended endoscopic endonasal posterior (transclival) approach for resection of tumors of the clival region and ventral posterior cranial fossa. MATERIAL AND METHODS: We performed a craniometric study of 125 human skulls and a topographic anatomical study of heads of 25 cadavers, the arterial and venous bed of which was stained with colored silicone (the staining technique was developed by the authors) to visualize bed features and individual variability. Currently, we have clinical material from more than 120 surgical patients with various skull base tumors of the clival region and ventral posterior cranial fossa (chordomas, pituitary adenomas, meningiomas, cholesteatomas, etc.) who were operated on using the endoscopic transclival approach. RESULTS: We present the main anatomical landmarks and parameters of some anatomical structures that are required for performing the endoscopic endonasal posterior approach. The anatomical landmarks, such as the intradural openings of the abducens and glossopharyngeal nerves, may be used to arbitrarily divide the clival region into the superior, middle, and inferior thirds. The anatomical landmarks important for the surgeon, which are detected during a topographic anatomical study of the skull base, facilitate identification of the boundaries between the different clival portions and the C1 segments of the internal carotid arteries. The superior, middle, and inferior transclival approaches provide an access to the ventral surface of the upper, middle, and lower neurovascular complexes in the posterior cranial fossa. CONCLUSION: The endoscopic transclival approach may be used to access midline tumors of the posterior cranial fossa. The approach is an alternative to transcranial approaches in surgical treatment of clival region lesions. This approach provides results comparable (and sometimes better) to those of the transcranial and transfacial approaches.

[Extended endoscopic endonasal posterior (transclival) approach to tumors of the clival region and ventral posterior cranial fossa. Part 2. Topographic and anatomical aspects and surgical technique]. / Éndoskopicheskii éndonazal'nyi zadnii rasshirennyi (transklival'nyi) dostup k opukholiam oblasti skata cherepa i ventral'nykh otdelov zadnei cherepnoi iamki. Chast' 2. Topografo-anatomicheskie aspekty i operativnaia tekhnika.

PURPOSE: to present the main topographic and anatomical features of the clivus and adjacent structures for improving and optimizing the extended endoscopic transnasal posterior (transclival) approach in removal of clival and ventral posterior cranial fossa lesions. MATERIAL AND METHODS: We performed a topographic and anatomical study of 25 cadaver heads, the vascular bed of which was filled with colored silicone using the original technique for visualizing the bed features and individual variability. RESULTS: We present the main anatomical landmarks necessary for performing the extended endoscopic endonasal posterior approach. Superior, medial, and inferior transclival approaches provide access to the anterior surface of the upper, middle, and lower neurovascular complexes of the posterior cranial fossa. CONCLUSION: The endoscopic transclival approach can be used to reach ventral posterior cranial fossa lesions. The endoscopic transnasal transclival approach is an alternative to transcranial approaches to clival lesions.

Endoscopic transnasal skull base surgery: pushing the boundaries.

The endoscopic endonasal approach (EEA) has significantly evolved since its initial uses in pituitary and sinonasal surgery. The literature is filled with reports and case series demonstrating efficacy and advantages for the entire ventral skull base. With competence in 'minimally invasive' parasellar approaches, larger and more complex approaches were developed to utilize the endonasal corridor to create maximally invasive endoscopic skull base procedures. The challenges of these more complex endoscopic procedures include a long learning curve and navigating in a narrow corridor; reconstruction of defects presented new challenges and early experience revealed a significantly higher risk of cerebrospinal fluid leak. Despite these challenges, there are many benefits to the EEA including avoidance of brain and neurovascular retraction, improved visualization, a direct corridor onto many tumors and the two-surgeon approach. Most importantly, the EEA provides a midline corridor to directly access tumors, which displace critical neurovascular structures laterally, giving it an inherent advantage of minimizing any manipulation of these structures and thus decreasing their potential injury.

Full endoscopic endonasal transsellar-transclival approach: the modularity concept.

BACKGROUND: Endoscopic endonasal approaches (EEAs) constitute a reasonable option for the treatment of lesions that involve the sellar and clival regions. METHODS: We describe, step by step, the full EEA expanded to the middle and lower clivus for the treatment of perisellar lesions. Delimiting different modules around the sellar region is useful in establishing the best endoscopic approach for each tumor. A craniopharyngioma (CP) with clival extension will be used as an illustrative example of the modularity concept of these approaches. CONCLUSIONS: Transsellar-transclival EEA allows complete resection of lesions located in the sellar and infrasellar region with a low rate of complications.

Endoscopic endonasal transclival transodontoid approach for ventral decompression of the craniovertebral junction: operative technique and nuances.

The transoral approach is considered the gold-standard surgical route for performing anterior odontoidectomy and ventral decompression of the craniovertebral junction for pathological conditions that result in symptomatic cervicomedullary compression, including basilar invagination, rheumatoid pannus, platybasia with retroflexed odontoid processes, and neoplasms. Extended modifications to increase the operative corridor and exposure include the transmaxillary, extended "open-door" maxillotomy, transpalatal, and transmandibular approaches. With the advent of extended endoscopic endonasal skull base techniques, there has been increased interest in the last decade in the endoscopic endonasal transclival transodontoid approach to the craniovertebral junction. The endonasal route represents an attractive minimally invasive surgical alternative, especially in cases of irreducible basilar invagination in which the pathology is situated well above the palatine line. Angled endoscopes and instrumentation can also be used for lower-lying pathology. By avoiding the oral cavity and subsequently using a transoral retractor, the endonasal route has the advantages of avoiding complications related to tongue swelling, tracheal swelling, prolonged intubation, velopharyngeal insufficiency, dysphagia, and dysphonia. Postoperative recovery is quicker, and hospital stays are shorter. In this report, the authors describe and illustrate their method of purely endoscopic endonasal transclival odonotoidectomy for anterior decompression of the craniovertebral junction and describe various operative pearls and nuances of the technique for avoiding complications.

Extended endoscopic endonasal transclival clipping of posterior circulation aneurysms--an alternative to the transcranial approach.

BACKGROUND: Transcranial clipping of most posterior circulation aneurysms is one of the most difficult procedures, with high morbidity, and endovascular coiling is an alternative with less risk, but is not devoid of complications and not suitable for all aneurysms. Here we describe four cases of posterior circulation aneurysms clipped via the extended endoscopic endonasal transclival route. To the best of our knowledge, this is the first report of basilar top and posterior cerebral artery aneurysms being clipped endonasally. METHODS AND RESULTS: Four patients with posterior circulation aneurysms underwent extended endoscopic endonasal transclival clipping of the aneurysm. The age range was 35-70 years. There were two males and two females. Three of the four patients presented after the rupture of aneurysms, and the other patient presented with sudden-onset left hemiparesis probably due to thromboembolism from a large unruptured left posterior cerebral artery (PCA) aneurysm. On evaluation with four-vessel digital subtraction angiography (DSA), two patients had a basilar apex aneurysm, one had a basilar trunk aneurysm, and the other had a PCA (P1) aneurysm. Postoperatively, two patients had good recovery. One patient with a PCA aneurysm and another with a basilar apex aneurysm had fresh postoperative deficits. One patient developed postoperative CSF rhinorrhea. CONCLUSION: Endoscopic extended transnasal surgery is an expanding field in neurosurgery with a steep learning curve. With improvement in techniques and instrumentation the use of this approach for clipping posterior circulation aneurysms can become an effective alternative in the treatment of aneurysms.

Full endoscopic endonasal transclival approach: meningioma attached to the ventral surface of the brainstem.

BACKGROUND: Intracranial meningiomas without dural attachment (MWODA) are rare entities. We present the first case published, to the best of our knowledge, regarding a MWODA attached to the ventral surface of the brainstem. This location makes the patient subsidiary to treatment through an expanded endonasal transclival approach. CLINICAL PRESENTATION: A 16-year-old female with suspected diagnosis of recurrence of a clear cell meningioma (CCM) at a distance from the initial lesion, located on the premedullary cistern. The patient underwent a pure endoscopic low transclival approach. The attachment to the ventral surface of the brainstem was confirmed intraoperatively. Postoperative MRI confirmed gross total resection and treatment was complemented with adjuvant fractionated stereotactic radiotherapy. No complications related to the procedure were observed. CONCLUSION: MWODA may appear attached to the ventral brainstem. The expanded endonasal approach to the clivus provides a critical anatomical advantage in the treatment of medial lesions, even ventral meningiomas, to the lower cranial nerves. Reconstruction principles must be strictly respected to reduce complications.

Safety and efficacy of the endoscopic transsphenoidal transclival approach performed using direct cortical stimulation for pontine cavernous malformations.

OBJECTIVE: Surgical treatment of brainstem cavernous malformations (CMs) is challenging. Surgery using the endoscopic transsphenoidal transclival approach (eTSTCA) is reported as a useful alternative for ventral brainstem CMs. However, CMs located in the ventral midline of the brainstem are rare, and only a small number of case reports on these CMs treated with the eTSTCA exist. The efficacy and safety of the eTSTCA have not yet been fully examined. METHODS: A retrospective analysis was performed for 5 consecutive patients who underwent surgery via the eTSTCA for treating ventral pontine CMs. RESULTS: The average maximum CM diameter was 26.0 mm (18-38 mm). All patients underwent MR-diffusion tensor imaging, which confirmed that the corticospinal tract (CST) deviated posteriorly or laterally to the CM. Direct brainstem cortical stimulation was performed to localize the CST before making the cortical incision. After the excision of the CM, the cavity was filled with artificial CSF to make an aqueous surgical field (wet-field technique) for observing the tumor cavity and confirming complete hemostasis and resection. Total removal was achieved in all patients. The preoperative modified Rankin Scale score was 3 in 3 patients and 4 in 2 patients, whereas it was 1 in 2 patients and 0 in 3 patients 3 months after surgery. Postoperative CSF leakage was observed in 1 patient, and transient abducens nerve palsy was observed in 1 patient. No other intra- or postoperative complications were observed. CONCLUSIONS: MR-diffusion tensor imaging and direct brainstem cortical stimulation were useful to ascertain the proximity of the CST to the CM. The endoscope provides a clear view even underwater, and it was safe and effective to observe the entire CM cavity and confirm complete hemostasis without additional retraction of the brainstem parenchyma, including the CST. The eTSTCA provides a direct access point to the lesion and may be a safer alternative treatment for patients whose CST deviates laterally or posteriorly to the CM.

Long-Term Outcomes after Multimodal Treatment for Clival Chordoma: Efficacy of the Endonasal Transclival Approach with Early Adjuvant Radiation Therapy.

This study investigates the long-term outcomes of clival chordoma patients treated with the endonasal transclival approach (ETCA) and early adjuvant radiation therapy. A retrospective review of 17 patients (2002-2013) showed a 10-year progression-free survival (PFS) rate of 67.4%, with the ETCA group showing fewer progressions and cranial neuropathies than those treated with combined approaches. The ETCA, a minimally invasive technique, provided a similar extent of resection compared to conventional skull-base approaches and enabled safe delivery of high-dose adjuvant radiotherapy. The findings suggest that ETCA is an effective treatment for centrally located clival chordomas.

Endoscopic endonasal transclival clipping of a cerebellar arteriovenous malformation feeding vessel and associated aneurysm; a 2D operative video.

Positioned along the ventral surface of the pons, proximal superior cerebellar artery (SCA) aneurysms account for only 1.7% of all intracranial aneurysms [1]. Unlike more commonly encountered basilar artery aneurysms, patients often experience good outcomes when treated via endovascular coiling or surgical clipping [1,2]. These lesions frequently have a lateral projection and paucity of perforator arteries [2]. With further development of endoscopic endonasal techniques, access to this region is possible via a direct frontal exposure to the ventral brainstem, basilar artery and branching vessels. To date, there are only a limited number of reports describing an endoscopic endonasal transclival (EETC) approach for surgical clipping [3-5]. In this operative video, we detail the surgical clipping of a cerebellar arteriovenous malformation feeding vessel and an associated aneurysm using the EETC approach in a 59-year-old woman who presented with sudden onset of a severe headache. The feeding vessel and aneurysm's midline location, just below the take-off of the SCA made it a good candidate for this surgery. Major steps included in this video include 1) transsphenoidal exposure of and subsequent drilling of the clivus, 2) dural opening into the pre-pontine cistern and dissection of the aneurysm, 3) clipping of the aneurysm, and 4) multi-layered closure of the skull base defect. Overall, the patient tolerated the procedure well and was found to have no residual filling of the aneurysm or the AVM feeding vessel at 2-year follow-up. EETC is a viable surgical option for the treatment of aneurysm located along the midline of the pre-pontine cistern.

Anatomical Description and Literature Review of the Endoscopic Endonasal Transclival Transodontoid Approach Combined with Endoscopic Transoral Decompression to the Anterior Craniovertebral Junction: A New Strategy.

OBJECTIVE: To describe and evaluate the steps required to perform a combined endoscopic endonasal/transoral transclival transodontoid approach for anterior decompression of the craniovertebral junction. METHODS: The endoscopic endonasal transclival transodontoid approach combined with endoscopic transoral decompression was performed on 4 cadaveric specimens. Evaluation of this combined technique; a review of the literature; and the nuances, advantages, and pitfalls are reported. RESULTS: Adequate wide anterior decompression was achieved in all specimens. This combined approach allowed the preservation of the anterior arch of C1 without injuring the eustachian tube anatomy and avoiding internal carotid artery manipulation. CONCLUSIONS: Mastery of both techniques allows for a safe and comfortable surgical corridor. The transoral and transnasal approaches should not be considered as either/or techniques, but rather as a complement to each other. However, as with all new or developing techniques, there is a steep learning curve, which requires ample training in the skull base laboratory.