Microsurgical anatomy of the superior petrosal venous complex: new classifications and implications for subtemporal transtentorial and retrosigmoid suprameatal approaches

OBJECT: The purpose of this study was to define the patterns of drainage of the superior petrosal venous complex (SPVC) along the petrous ridge in relation to the Meckel cave and internal acoustic meatus (IAM) and to delineate its effect on the surgical exposures obtained in subtemporal transtentorial and retrosigmoid suprameatal approaches. METHODS: The patterns of drainage of the SPVC along the petrous ridge were characterized according to their relation to the Meckel cave and the IAM based on an examination of 30 hemispheres. Subtemporal transtentorial and retrosigmoid suprameatal approaches were performed in three additional cadavers to demonstrate the effect of the drainage pattern on the surgical exposures. CONCLUSIONS: The SPVC emptied into the superior petrosal sinus (SPS) within a distance of 1 cm from the midpoint of the Meckel cave. The patterns of drainage of the SPVC were classified into three groups. Type I emptied into the SPS above and lateral to the boundaries of the IAM. The most common type, Type II, emptied between the lateral limit of the trigeminal nerve at the Meckel cave and the medial limit of the facial nerve at the IAM, within an area of approximately 13 mm. Type III emptied into the SPS above or medial to the Meckel cave. The ideal SPVC for a subtemporal transtentorial approach (with or without anterior extradural petrosectomy) seems to be a Type I. In SPVC Type III and those Type II cases in which the SPVC is located near the Meckel cave, the amount of working space is significantly limited in a subtemporal transtentorial approach. In contrast, the ideal type of SPVC for a retrosigmoid suprameatal approach would be a Type III, and the SPVC must be divided in the majority of Type I and II cases for a satisfactory surgical exposure along the Meckel cave and middle fossa dura. The proposed modified classification system and its effect on the surgical exposure may aid in planning the approach directed along the petrous apex and may reduce the probability of venous complications.     

Anatomy of the superior petrosal veins and their exposure and management during petrous apex meningioma surgery using the lateral suboccipital retrosigmoid approach

During surgeries in the upper cerebellopontine angle (CPA), the superior petrosal veins (SPVs) often act as obstacles; and their sectioning sometimes causes serious complications. In this study, we introduced a classification system for the SPVs wherein their tributaries were classified into four groups on the basis of their courses and draining areas. We furthermore explained the detailed anatomy of the vein of the cerebellopontine fissure, which is the largest tributary. In surgeries of petrous apex meningioma, the knowledge of the displacement pattern of the vein is very helpful for avoiding major venous complications. Therefore, we elucidated its anatomical situation in relation to the original portion of the meningioma and the natural draining point of the vein into the superior petrosal sinus (SPS) in each patient. In addition, we described the methods and techniques used to expose and manage the vein of the cerebellopontine fissure during surgery using the lateral suboccipital retrosigmoid approach. Presenting two illustrative cases, we recommend that the initial exposure of the tumor should be performed through the infratentorial lateral supracerebellar route and that the suprafloccular cistern is the best area to find the vein of the cerebellopontine fissure. We emphasized the importance of the preservation of the vein of the cerebellopontine fissure and also proposed the order for exposure of SPV tributaries during upper CPA surgery using the retrosigmoid approach.     

Retrosigmoid intradural suprameatal approach to Meckel's cave and the middle fossa: surgical technique and outcome

OBJECT: The goal of this study was to determine whether some petroclival tumors can be safely and efficiently treated using a modified retrosigmoid petrosal approach that is called the retrosigmoid intradural suprameatal approach (RISA). METHODS: The RISA was introduced in 1983, and since that time 12 patients harboring petroclival meningiomas have been treated using this technique. The RISA includes a retrosigmoid craniotomy and drilling of the suprameatus petrous bone, which is located above and anterior to the internal auditory meatus, thus providing access to Meckel's cave and the middle fossa. Radical tumor resection (Simpson Grade I or II) was achieved in nine (75%) of the 12 patients. Two patients underwent subtotal resection (Simpson Grade III). and one patient underwent complete resection of tumor at the posterior fossa with subtotal resection at the middle fossa. There were no deaths or severe complications in this series; all patients did well postoperatively, being independent at the time of their last follow-up examinations (mean 5.6 years). Neurological deficits included facial paresis in one patient and worsening of hearing in two patients. CONCLUSIONS: The approach described here is a useful modification of the retrosigmoid approach, which allows resection of large petroclival tumors without the need for supratentorial craniotomies. Although technically meticulous, this approach is not time-consuming; it is safe and can produce good results. This is the first report on the use of this approach for petroclival meningiomas.     

The middle fossa transpetrous approach for petroclival meningiomas

Seventeen patients with petroclival meningioma were operated on through a middle fossa transpetrous approach. This approach exposes the anterior cerebellopontine angle through a middle fossa craniotomy with removal of the petrous apex medial to the cochlea and petrous carotid artery. This approach may be enlarged by transection of the superior petrosal sinus and tentorium. The surgical technique and application of the middle fossa transpetrous approach for petroclival meningiomas is presented.     

The Middle Fossa Transpetrous Approach for Petroclival Meningiomas

Seventeen patients with petroclival meningioma were operated on through a middle fossa transpetrous approach. This approach exposes the anterior cerebellopontine angle through a middle fossa craniotomy with removal of the petrous apex medial to the cochlea and petrous carotid artery. This approach may be enlarged by transection of the superior petrosal sinus and tentorium. The surgical technique and application of the middle fossa transpetrous approach for petroclival meningiomas is presented.     

Drainage Pathway of the Superior Petrosal Vein Evaluated by CT Venography in Petroclival Meningioma Surgery

Objectives This study aimed to clarify the drainage location of the superior petrosal vein (SPV) in relation to Meckel''s cave and the internal acoustic meatus (IAM) and to discuss its significance in petroclival meningioma surgery.Design Prospective clinical study.Setting Hospital-based.Participants Five patients with petroclival meningioma and 50 patients (primarily unruptured supratentorial aneurysm patients, with a few hemifacial spasm patients) with no posterior fossa lesions.Main Outcome Measures On computed tomography venography (CTV), the drainage site was classified into three patterns based on its relationship to Meckel''s cave and the IAM: Meckel''s cave type, Intermediate type, and Meatal type.Results In all patients, the SPV was patent and emptied into the superior petrosal sinus (SPS). In patients without posterior fossa lesions, 35% had Meckel''s cave type, 54% had Intermediate type, and 11% had Meatal type. Of the five patients with petroclival meningioma, three had Intermediate type, and two had Meckel''s cave type.Conclusion The SPV is a significant vein that should be preserved to prevent venous complications. Preoperative knowledge of the SPV drainage site is helpful for planning the approach and preserving the SPV in petroclival meningioma surgery.     

Clinical and neurophysiological observations after superior petrosal vein obstruction during surgery of the cerebellopontine angle: case report

IMPORTANCE: Preservation of venous drainage during surgery of the cerebellopontine angle has received little attention. CLINICAL PRESENTATION: We describe changes in brainstem auditory evoked potentials after temporary obstruction of the superior petrosal vein during surgical resection of a small meningioma at the petrous apex via a standard suboccipital-lateral approach. Temporary clipping of the petrosal vein resulted in deterioration of the brainstem auditory evoked potentials. The tumor was removed with preservation of the superior petrosal vein. CONCLUSION: A transient postoperative cochlear nerve deficit emphasizes the importance of venous drainage and its preservation during surgery for small lesions of the cerebellopontine angle that do not distort normal anatomic structures.     

Combined petrosal approach to petroclival meningiomas

OBJECTIVE: To study the use and advantages of combining the posterior petrosal approach with the anterior petrosal approach to petroclival meningiomas. METHODS: Seven cases of petroclival meningiomas operated on via the combined petrosal approach were retrospectively analyzed. The basis on which this approach was selected was assessed, as were its benefits and risks. RESULTS: Gross total resection was achieved in five of the seven patients. No mortality or decrease in Karnofsky performance score was observed at the time of the last follow-up examination. Six of the seven patients had serviceable hearing before the operation. Only one patient lost hearing after the operation, and this hearing loss occurred in only one ear. Before the operation, six patients were House-Brackmann facial nerve function Grade I, and one patient was Grade II to III. At the last follow-up examination, facial nerve function was Grade I in five patients, Grade II in one patient, and Grade V in one patient. Tumors in all patients involved the cavernous sinus, Meckel's cave, petroclival junction, and middle clivus. All patients possessed a large posterior fossa component of tumor measuring an average of 3.6 x 3.5 x 4.2 cm. In four patients, the tumor was attached for the entire width of the clivus to the contralateral petroclival junction. Four patients displayed central brainstem compression. Four patients displayed bony changes at the petrous apex. All patients displayed total or partial encasement of the vertebrobasilar artery and its major branches. CONCLUSION: The combined petrosal approach should be considered for patients who have a large petroclival meningioma and serviceable hearing. This approach enhances petroclival exposure and the degree of tumor resection, especially in the area of the petroclival junction, middle clivus, apical petrous bone, posterior cavernous sinus, and Meckel's cave. The combined petrosal approach also allows better visualization of the contralateral side and the ventral brainstem, which facilitates safe dissection of the tumor from the brainstem, the basilar artery, and the perforators. If a patient has an early draining bridging vein to the tentorial sinus (before it reaches the transverse-sigmoid junction) or a prominent sigmoid sinus and jugular bulb, the combined petrosal approach provides significant working space.     

Suprameatal extension of the retrosigmoid approach: microsurgical anatomy

OBJECTIVE: This study was conducted to determine whether removing the bony prominence located above the porus of the internal acoustic meatus, called the suprameatal tubercle, and surrounding bone using the retrosigmoid approach would aid in the exposure of tumors that are located predominantly in the cerebellopontine angle but that also extend into the middle cranial fossa in the region of Meckel's cave and thus avoid the need for a supratentorial craniotomy. METHODS: Thirty cerebellopontine angles from 15 cadaveric heads examined using 3 to 40x magnification provided the material for this study. A retrosigmoid craniotomy was completed and the exposure obtained before and after removing the suprameatal tubercle, and the surrounding bone was examined. In some cases, Meckel's cave and the tentorium lateral to the porus of Meckel's cave was opened to aid in the exposure. RESULTS: Removing the suprameatal tubercle and surrounding bone increased the exposure an average of 10.3 mm (range, 8.0-13.0 mm) forward of the exposure, which could be obtained without suprameatal drilling. The extent of bone removal was limited on the lateral side by the posterior and superior semicircular canals and their common crus. CONCLUSION: The suprameatal extension of the retrosigmoid approach will permit removal of some tumors that are located mainly in the posterior fossa but that extend into the middle fossa in the region of Meckel's cave. The exposure can be increased by opening the superior petrosal sinus as it crosses in the upper margin of the porus of Meckel's cave and by opening the tentorium lateral to Meckel's cave.     

Clinicopathological study of meningiomas of the tentorium and its surrounding structures

We report the clinical features, radiological studies, operative procedures and results, and follow-up data in 29 patients with meningiomas of the tentorium and its surrounding structures. The cases represented 22.5% of all the intracranial meningiomas operated on in a 15 year period and were divided into three groups, depending on their main attachments, tentorial, cerebellopontine angle (dorsal aspect of the petrous ridge) and others. Tumor size was generally large and 13 cases were larger than 5 cm. The most common tumor site was along or near the superior petrosal sinus and transverse-sigmoid junction in cases involving the tentorium, and medial to the porus acousticus in cases involving the cerebellopontine angle. Different operative approaches to these tumors were carried out, depending on their location. The tumors in the lateral or medial petrous ridge were approached mainly with a suboccipital craniectomy using a retromastoid incision. Total removal was carried out in 80% of the tentorial cases, in 46.2% of cerebellopontine angle cases, and in the 83.3% in the others. Total operative mortality rate was zero. Follow-up periods ranged up to 5 years 5 months in the tentorial cases, 4 years 6 months in cerebellopontine angle cases, and 7 years 1 month in the others. Long-term results were good in 21 cases (72.4%), fair in 3 cases (10.3%) and poor in 2 (6.9%). Three patients died due to tumor recurrence. One of them suffered lung metastasis, and two of them suffered extensive local recurrences. We recommend the retromastoid approach combined with the petrosal approach, if the CPA tumor is large enough and extends to the retroclival region.     

Partial labyrinthectomy petrous apicectomy approach to the petroclival region: an anatomic and technical study

OBJECTIVE: The petroclival region generally is thought to be an inaccessible area in the intracranial compartment. A number of ways of reaching this area during surgery have been described, including the presigmoid petrosal approach. The partial labyrinthectomy petrous apicectomy approach is a relatively new approach to this region and is a variant of the presigmoid petrosal approach. This study aims to demonstrate the technique and the microsurgical anatomy of the partial labyrinthectomy petrous apicectomy approach and to provide a quantitative study of its exposure to compare it with other common approaches to this region, particularly the presigmoid petrosal approach. METHODS: Bilateral stepwise dissections were performed on 15 formalin-fixed and dye-injected cadaveric heads (30 sides) under x3 to x40 magnification. A temporal craniotomy was performed after a complete mastoidectomy. A partial labyrinthectomy and petrous apicectomy were performed next. The amount of dura exposed was measured before and after the partial labyrinthectomy and the petrous apicectomy. By measuring the angles of exposure, the approach was examined to analyze how much increased access was gained. RESULTS: This approach provided wide exposure to the petroclival region, the cerebellopontine angle, Meckel's cave, the cavernous sinus, and the prepontine region. On average, there was an increase of 10.8 mm in horizontal exposure as compared with the retrolabyrinthine approach. The average angle of vision achieved with the clival pit as the target was 58.9 degrees. In most of the specimens, an area from the IIIrd to the IXth cranial nerves was easily visible without any significant brain retraction. A high jugular bulb did not reduce the exposure. CONCLUSION: The partial labyrinthectomy petrous apicectomy approach converts two narrow tunnels into a wide corridor. It increases the angle of exposure markedly, providing easy and excellent exposure of the otherwise difficult-to-access petroclival region, and it may also preserve hearing.     

Microsurgical anatomy of the veins of the posterior fossa

The microsurgical anatomy of the veins of the posterior fossa was defined in 25 cadavers. These veins are divided into four groups: superficial, deep, brain-stem, and bridging veins. The superficial veins are divided on the basis of which of the three cortical surfaces they drain: the tentorial surface, which faces the tentorium and is exposed in a supracerebellar approach, is drained by the superior hemispheric and vermian veins; the suboccipital surface, which is below and between the lateral and sigmoid sinuses and is exposed in a wide suboccipital craniectomy, is drained by the inferior hemispheric and inferior vermian veins; and the petrosal surface, which faces forward toward the posterior surface of the petrous bone and is retracted to expose the cerebellopontine angle, is drained by the anterior hemispheric veins. The deep veins course in the three fissures between the cerebellum and the brain stem, and on the three cerebellar peduncles. The major deep veins in the fissures between the cerebellum and brain stem are the veins of the cerebellomesencephalic, cerebellomedullary, and cerebellopontine fissures, and those on the cerebellar peduncles are the veins of the superior, middle, and inferior cerebellar peduncles. The veins of the brain stem are named on the basis of whether they drain the midbrain, pons, or medulla. The veins of the posterior fossa terminate as bridging veins, which collect into three groups: a galenic group which drains into the vein of Galen; a petrosal group which drains into the petrosal sinuses; and a tentorial group which drains into the tentorial sinuses near the torcula.     

Combined subtemporal and retrosigmoid keyhole approach for extensive petroclival meningioma surgery: report of experience with 7 cases.

OBJECTIVE: Resection of petroclival meningiomas offers great challenges to the neurosurgeons. Our experience of 7 cases using a combined subtemporal and retrosigmoid keyhole approach surgery was evaluated for the treatment of extensive petroclival meningiomas. METHODS: From July 2002 to July 2005, resections of 7 petroclival meningiomas, which involved both supra- and infratentorial regions, were performed via a combined subtemporal and retrosigmoid keyhole approach. The extent of tumor resection was evaluated by MRI 3 months after surgery, and postoperative complications were investigated. RESULTS: The maximum diameter of the tumors ranged from 3.4 to 6.0 cm (mean: 4.4 cm). Gross total resection (GTR) was achieved in 3 cases, giving a GTR rate of 43%. Subtotal resection (STR) was carried out in 4 cases. Neurological status remained intact in one case, while others presented with cranial nerve deficits (VII, VI, V, III and lower CN). No death was reported in the cases during the postoperative period. CONCLUSION: The combined keyhole approach is suitable for the treatment of extensive petroclival meningiomas. It provides easy and quick access to the supra- and infratentorial juxtaclival region without any petrous bone drilling. Complications related to the approach can be minimized.     

Combined subtemporal and retrosigmoid keyhole approach for extensive petroclival meningiomas surgery: report of experience with 7 cases.

OBJECTIVE: The resection of petroclival meningiomas offers great challenges to the neurosurgeon. Surgery via a combined subtemporal and retrosigmoid keyhole approach surgery was evaluated for the treatment of extensive petroclival meningiomas on the basis of our experience with 7 cases. METHODS: From July 2002 to July 2005, the resections of 7 petroclival meningiomas, which involved both supra- and infra-tentorial regions, were performed via a combined subtemporal and retrosigmoid keyhole approach. The extent of tumor resection was evaluated by MRI 3 months after surgery, and postoperative complications were investigated. RESULTS: The maximum diameter of tumors ranged from 3.4 to 6.0 cm (mean: 4.4 cm). Gross total resection (GTR) was achieved in 3 cases, giving a GTR rate of 43%. Subtotal resection (STR) was carried out in 4 cases. Neurological status remained intact in one case, while the others presented with cranial nerve deficits (VII, VI, V, III and lower CN). No death was reported during the postoperative period. CONCLUSION: This combined keyhole approach is suitable for the treatment of extensive petroclival meningiomas. It provides easy and quick access to the supra- and infratentorial juxta-clival regions without any petrous bone drilling. Complications related to the approach can be minimized.     

Lateral Suboccipital Retrosigmoid Approach with Tentorial Incision for Petroclival Meningiomas: Technical Note

Introduction The resection of petroclival meningiomas presents great neurosurgical challenges. Although multiple surgical approaches have been developed, the retrosigmoid route tends to be used to address tumors that are predominantly located in the posterior fossa. Our modification of the lateral suboccipital retrosigmoid approach with the placement of a tentorial incision yields good visualization of the supratentorial part of the tumor around the midbrain. Methods We treated four patients, one with primary and three with recurrent petroclival meningioma, by our modified approach. After lateral suboccipital craniotomy, the infratentorial part of the tumor was removed after detaching it from the tentorial surface. The cerebellar tentorium was then carefully incised from the supracerebellar angle, taking care not to damage the superior cerebellar artery and trochlear nerve. Results The operative field surrounding the midbrain was widened by this procedure, and safe dissection of the tumor from the brainstem and other neurovascular structures was performed with direct observation of the interface. Conclusions Our approach is a useful modification of the retrosigmoid approach to petroclival meningiomas. It facilitates the safe resection of the supratentorial part of the tumor in the ambient cistern behind the tentorium.     

Conventional posterior fossa approach for surgery on petroclival meningiomas: a report on an experience with 28 cases

BACKGROUND: This is a report of our experience with 28 cases of select petroclival meningiomas operated by a posterior fossa route encompassing the lateral supracerebellar-infratentorial and retrosigmoid avenues. METHODS: Twenty-eight cases of petroclival meningiomas treated during the period 1991 to 2002 by conventional posterior cranial fossa route are analyzed. The average length of follow-up is 48 months. RESULTS: The maximum diameter of the tumors ranged from 1.8 to 6.8 cm (mean, 4.0 cm). Five tumors extended up to or beyond the contralateral petroclival junction. Basilar artery was at least partially encased in 9 cases. Gross total tumor resection was achieved in 21 cases and a partial tumor resection was achieved in the remaining 7 cases. Two patients died in the postoperative phase. CONCLUSIONS: Conventional posterior cranial fossa surgery can be suitable for a select group of petroclival meningioma. Apart from other advantages, it provides easy and quick exposure of the tumor without any petrous bone drilling. It also provides a direct and early exposure of the tumor-cranial nerve-brainstem interface facilitating the dissection. The lateral and inferior tumor extensions in relationship to the clivus can be more easily accessed. The site of attachment of the tumor to the dura overlying the posterior face of the petrous apex can be seen directly.     

Peduncular hallucinosis after sacrifice of veins of the petrosal venous complex for trigeminal neuralgia

Summary  Peduncular hallucinosis is characterized by striking visual images, highly colored and mobile, which are recognized by the patient as imaginary. A 50-year-old-man underwent microvascular decompression for a classical right sided trigeminal neuralgia. During the procedure, the petrosal vein and a transverse pontine vein were sacrificed for trigeminal decompression. On the second postoperative day, the patient developed peduncular hallucinosis that disappeared on the forth postoperative day. This is the third case in the literature of peduncular hallucinosis after obliteration of veins of the petrosal venous complex for trigeminal neuralgia. The best policy in cerebellopontine angle surgery is to preserve the petrosal vein whenever possible to avoid complications related to venous congestion.     

Selection of surgical approaches based on semi-quantifying the skull-base invasion by petroclival meningiomas: a review of 66 cases

Background

Petroclival meningiomas are still challenging for neurosurgeons. In the present study, we reviewed 66 petroclival meningiomas that underwent craniotomy to assess the surgical approaches for petroclival meningiomas based on semi-quantifying tumor extension to skull base and to evaluate the outcomes.

Methods

According to invasion characteristics, skull base related to petroclival meningiomas was semi-quantitatively divided into five regions: upper, middle, and lower petroclival regions (region A, B, and C, respectively), cerebellopontine angle region (region D), and parasellar and cavernous sinus region (region E). Appropriate surgical approaches were adopted for petroclival meningiomas with varying degrees of invasion, including the subtemporal (11/66), retrosigmoid (15/66), presigmoid (32/66), combined retrosigmoid and far-lateral (2/66), supra-infratentorial (4/66), and extended middle cranial fossa (2/66) approaches.

Results

The results showed that involvement of region A, B, and C was in 64, 50, and eight patients, respectively. Invasion to region D and E occurred in 13 and 39 cases, respectively. The ratio of single region involvement was only 7.6 %, whereas most petroclival meningiomas tended to invade more regions (39.4 % for two, 37.9 % for three, 12.1 % for four, and 3.0 % for five regions, respectively). Gross total resection was achieved in 29 cases (43.9 %), near total resection in 27 cases (40.9 %), and subtotal resection in ten cases (15.2 %). After a mean follow-up period of 32.21 months, obvious cranial nerve deficits existed in seven patients, and recurrence occurred in eight patients.

Conclusions

We introduced a simple and practicable method for classification of petroclival meningiomas, which could semi-quantify tumor invasion and help to select surgical approaches. With careful preoperative evaluation, a cautiously selected approach would improve the prognosis.     

Guidelines for the Ligation of the Sigmoid or Transverse Sinus during Large Petroclival Meningioma Surgery

The authors present guidelines for the ligation of the transverse or sigmoid sinus during the surgical removal of petroclival meningiomas. The medical records and venograms of 14 patients with a petroclival meningioma requiring transverse or sigmoid sinus ligation treated in the Department of Neurosurgery, Seoul National University Hospital between 1986 and 1999 were reviewed. All patients successfully received a sinus trial clamping during the operation. The drainage pattern of the confluens of Herophili was classified into four types: Type A, confluens and equal on both transverse sinuses; Type B, confluens and nondominant transverse sinus on the tumor side; Type C, confluens and dominant transverse sinus on the tumor side; and Type D, unilateral transverse sinus only. Of the 14 cases, four were Type A, five were Type B, and two were Type C. There was no brain swelling after intraoperative test clamping of the sinus for more than 30 minutes. None of the cases developed postoperative complications related to the sinus ligation. Patients with Type A, B, or C drainage patterns were ideal candidates for sinus ligation, especially transverse sinus ligation, if the test clamping proved to be safe. The sinus was cut proximal to the superior petrosal sinus, distal to the vein of Labbé.     

An endoscopic-assisted technique for retrosellar access during the extended retrosigmoid approach: a cadaveric feasibility study and quantitative analysis of retrosellar working area

The retrosigmoid approach has been advocated for certain petroclival tumors but provides limited access to any retrosellar extension of tumor, necessitating a two-stage operation. Our purpose was to demonstrate preliminary feasibility of an endoscopic-assisted technique to provide retrosellar access during the extended retrosigmoid approach and compare microscopic and endoscopic retrosellar working area. Standard retrosigmoid craniectomy and partial petrosectomy respecting inner ear structures were performed on six embalmed cadaveric heads. Two balloons were inflated to simulate a 15 mm petroclival tumor. Retrosellar clival and brainstem working area and ipsilateral oculomotor nerve and posterior cerebral artery (PCA) working distance were measured using the endoscope and microscope. Artificial tumors were implanted and resected using the endoscopic-assisted technique to assess feasibility. The endoscope provided significantly greater mean working area/distance on the clivus (201.6 vs 114.8 mm², p?<?0.01), brainstem (223.5 vs 121.2 mm², p?<?0.01), ipsilateral oculomotor nerve (10.8 vs 6.4 mm, p?<?0.01), and ipsilateral PCA (13.7 vs 8.9 mm, p?=?0.01). Petrous dissection to create a 10?×?10 mm working channel and artificial tumor resection was feasible in all dissections. The superior petrosal vein required ligation in 9 (75 %) cases. Air cells were exposed in 1 (8 %) case. The described endoscopic-assisted technique can provide retrosellar access during the extended retrosigmoid approach to access petroclival tumors with retrosellar extension. Risks include superior petrosal vein sacrifice, bleeding that can impair visualization, injury to the trigeminal nerve during endoscopic insertion/manipulation or injury to the brainstem while working in the medial limits of exposure. Further work is necessary to determine clinical feasibility, safety, and efficacy.