Endoscopic endonasal skull base surgery: Part 2--The cavernous sinus.

OBJECTIVE: An endoscopic endonasal approach to the cavernous sinus was developed with cadaver study and, subsequently, has been used in patient treatment. METHODS: The endoscopic anatomy, surgical approaches, and ideal head positioning were studied with six cadaver head specimens in order to develop endoscopic endonasal surgery of the cavernous sinus. Three illustrative patient cases are also reported. RESULTS: Horizontal placement of the forehead-chin line of head specimens provided the ideal head positioning for endoscopic endonasal cavernous sinus surgery. Three different surgical approaches were developed to access the cavernous sinus: the paraseptal, middle meatal and middle turbinectomy approaches. While the ipsilateral middle meatal approach provided straight anterior exposure, the contralateral paraseptal approach provided anteromedial exposure at the cavernous sinus. The middle turbinectomy approach rendered straight anterior exposure ipsilaterally and anteromedial exposure contralaterally. The sympathetic nerve climbed up on the surface of the carotid artery. When the dura mater was opened at the anterior wall of the cavernous sinus, the S-shaped carotid siphon was exposed. Cranial nerves III and IV were located inside the C-shaped carotid siphon. Cranial nerve VI was just lateral to the inferior arch of the carotid siphon. The ophthalmic branch of the trigeminal nerve was lateral to cranial nerve VI. When used in patient treatment, this technique was observed to be minimally invasive. CONCLUSION: Endonasal endoscopy for cavernous sinus surgery was studied in cadaver dissection, and subsequently, was used in patient treatment with satisfactory outcomes.     

The combined petrosal approach. Anatomical principles, surgical technique and indications

Management of large petroclival tumors requires the use of extensive surgical approaches that usually jeopardize the intrapetrous neuro-otologic structures. To confirm the interest of the combined petrosal approach in this indication, we describe the relevant anatomy and the surgical steps of this procedure. After making a periauricular skin incision and muscle elevation, an occipitotemporal bone flap is shaped. Then a retrolabyrinthine exposure is undertaken, with optimal skeletonization of the semicircular canals. Around the internal auditory canal, the retromeatal area and the petrous apex are resected. The retrosigmoid dura is opened followed by the incision of the subtemporal and posterior fossa dura along the superior petrosal sinus. The sinus is coagulated and divided. The tentorium is sectioned transversally toward its free edge behind the porus of the trochlear nerve. The combined petrosal approach is able to provide a wide multidirectional corridor toward the ventral surface of the pons, the basilary trunk and the ipislateral cranial nerves from the oculomotor to the lower cranial nerves. This study confirms that despite a significant extra time needed for proper achievement, the combined petrosal approach is a valuable conservative approach when the petroclival area, ventral brain stem and basilary trunk are targeted. This approach should be included in the panel of the transpetrous routes available by expert skull base teams.     

Zones of approach for craniofacial resection: minimizing facial incisions for resection of anterior cranial base and paranasal sinus tumors

OBJECTIVE: Anterior cranial base tumors are surgically resected with combined craniofacial approaches that frequently involve disfiguring facial incisions and facial osteotomies. The authors outline three operative zones of the anterior cranial base and paranasal sinuses in which tumors can be resected with three standard surgical approaches that minimize transfacial incisions and extensive facial osteotomies. METHODS: The zones were defined by performing dissections on 10 cadaveric heads and by evaluating radiographic images of patients with anterior cranial base tumors. The three approaches performed on each cadaver were transbasal, transmaxillary, and extended transsphenoidal. RESULTS: Three zones of approach were defined for accessing tumors of the anterior cranial base, nasal cavity, and paranasal sinuses. Zone 1 is exposed by the transbasal approach, which is limited anteriorly by the supraorbital rim, posteriorly by the optic chiasm and clivus, inferiorly by the palate, and laterally by the medial orbital walls. This approach allows access to the entire anterior cranial base, nasal cavity, and the majority of maxillary sinuses. The limitation imposed by the orbits results in a blind spot in the superolateral extent of the maxillary sinus. Zone 2 is exposed by a sublabial maxillotomy approach and accesses the entire maxillary sinus, including the superolateral blind spot and the ipsilateral anterior cavernous sinus. However, access to the anterior cranial base is limited. Zone 3 is exposed by the transsphenoidal approach. This approach accesses the midline structures but is limited by the lateral nasal walls and intracavernous carotid arteries. An extended transsphenoidal approach allows further exposure to the anterior cranial base, clivus, or cavernous sinuses. The use of the endoscope facilitates tumor resection in the nasal cavity and paranasal sinuses. CONCLUSION: The operative zones outlined offer minimally invasive craniofacial approaches to accessing lesions of the anterior cranial base and paranasal sinuses, obviating facial incisions and facial osteotomies. Case illustrations demonstrating the approach selection paradigm are presented.     

The combined subtemporal-suboccipital approach: a modified surgical access to the clivus and petrous apex.

OBJECTIVE: The surgical access to the clivus and the petrous apex is still a challenge. A combined approach is best fitted to lesions located in the middle and posterior cranial fossa. The approach described is centered on the petrous bone and requires an extensive bone resection; nevertheless, no osteoplastic bone flap is necessary. METHODS: In contrast to approaches described before, the petrous bone is drilled away anterior to the sigmoid sinus more extensively, the sinus is unroofed. For exposure of the middle cranial fossa the petrous bone should be resected down to the roof of the external meatus, the total extent of the craniotomy is significantly smaller. RESULTS AND CONCLUSION: The surgical access as described above provides a wide operative field under preservation of important intracranial structures. This modified approach minimizes the cerebellar and temporal lobe retraction. The neural and vascular structures can be preserved under direct vision to the tumor. The blood supply is interrupted at the beginning of the operation.     

Surgical approach for jugular foramen neurinoma--combined suboccipital and infralabyrinthine approach using a rotatable head holder

A 36-year-old male with jugular foramen neurinoma was operated upon using a rotatable head holder, which enables the surgeon to rotate the patient's head at any time during the procedure and to gain access in multiple directions to the tumor. The tumor was situated primarily in the jugular foramen and showed partial extension into intracranial as well as into extracranial space. The patient was placed in the lateral position with a rotatable head holder, which allows rotation of the patient's head with the range of 10 degrees face up to 80 degrees face down from the horizontal plane. A linear skin incision was made, beginning behind the auricle and extending along the anterior margin of the sternocleidomastoid muscle, and the sternocleidomastoid muscle was divided just below the tip of the mastoid process. During mastoidectomy and suboccipital craniectomy, the patient's head was rotated 15 degrees face down and sigmoid sinus was exposed toward the jugular foramen, meanwhile the posterior fossa dura mater was opened and the intracranial portion of the tumor was removed with the head positioned 45 degrees-60 degrees face down. The patient's head is then turned 30 degrees face down and the facial canal was opened to displace the facial nerve forward. This oblique posterior approach minimized facial nerve displacement and provided excellent exposure of the large tumor rest which was situated mainly in the jugular foramen and partly extended extracranially. The rotatable head holder allows excellent access in multiple directions and is very helpful in approaching to jugular foramen neurinomas which grow primarily in the jugular foramen and extend both into intra- and extracranially.     

En bloc resection of the temporal bone by the lateral approach in carcinoma of the middle ear associated with skull base infiltration with reference to the resection of the petrous apex

En bloc resection of the temporal bone was performed by the lateral approach on two patients with carcinoma of the middle ear, which was associated with destruction in the temporal bone and tumor infiltration of the cranial base. In one of the patients, the petrous apex was resected along with the temporal bone.En bloc resection on the temporal bone with the petrous apex is believed to be difficult because the internal carotid artery (ICA), cavernous sinus, and the brainstem are adjacent to each other in the petrous apex. However, the intra- and extracranial surgical procedures by this approach allow resection of the temporal bone ranging from the anterior part including the petrous apex to the posterior part including the mastoid process, the dura of the middle and posterior cranial fossae, and the sigmoid sinus, without exposure of the tumor. Special attention should be paid to the procedural points of surgery, such as, exposure of the petrous ICA, bleeding from the petrous sinus, and dural suturing in the vicinity of the apex. With regard to surgical indication, it is important to determine whether tumor infiltration is confined to the temporal bone and the dura of the middle and posterior fossa. If tumor infiltration into the petrous ICA, the dominant side of sigmoid sinus and/or the inferior cranial nerve is observed, then indication for surgery should be determined in a more critical manner.     

The retrolabyrinthine approach. Its value in the treatment of lesions of the lateral sinus

The Authors conceive the petrous bone as made of four segments bounded by two vertical plans, one passing through the anterior wall of the internal auditory canal and the posterior wall of the external auditory canal, the other passing through the inner aspect of the tympanic cavity and the outer aspect of the labyrinthe. Drilling away one or several segments realizes a trans-petrous approach which always begins by drilling away the posterior-external segment, the retro-labyrinthine segment. Drilling away only the retro-labyrinthine segment realizes retro-labyrinthine approach which entirely put into sight the circumference of the bending of the lateral sinus. Thus, it is possible to perfectly and more easily deal with lesions localized in this region. The skin incision is made two fingerbreadths above and behind the external ear. The scalp uncovers the mastoid as far as the posterior ring of the external auditory canal. The superficial drilling uncovers the temporal dura, the lateral sinus and the occipital dura and between them the sinuso-dural angle. Then the mastoid is drilled away as far as the antrum is opened. Its aditus internally sided by the loop of the external semi-circular canal serves to localize the external surface of the labyrinthe. Finally, the retro-labyrinthine approach is bounded by the posterior wall of the external auditory canal anteriorly, by the external surface of the labyrinthe internally, by the dura of the superior surface of the petrous bone superiorly and by the bended part of the lateral sinus and the dura of the posterior surface of the petrous bone posteriorly. The closure is made with a dural graft then with bony dust mixed with biologic glue, then the petrectomy is plugged with under-skin fat and then the superficial planes are carefully stitched. The authors report 5 cases of meningiomas of the lateral sinus, 1 case of hemangiopericytoma and 2 dural arteriovenous fistulas which demonstrate the interest of this approach to lesions developed on this part of the lateral sinus.     

En Bloc Resection of the Temporal Bone by the Lateral Approach in Carcinoma of the Middle Ear Associated with Skull Base Infiltration with Reference to the Resection of the Petrous Apex

En bloc resection of the temporal bone was performed by the lateral approach on two patients with carcinoma of the middle ear, which was associated with destruction in the temporal bone and tumor infiltration of the cranial base. In one of the patients, the petrous apex was resected along with the temporal bone.

En bloc resection on the temporal bone with the petrous apex is believed to be difficult because the internal carotid artery (ICA), cavernous sinus, and the brainstem are adjacent to each other in the petrous apex. However, the intra- and extracranial surgical procedures by this approach allow resection of the temporal bone ranging from the anterior part including the petrous apex to the posterior part including the mastoid process, the dura of the middle and posterior cranial fossae, and the sigmoid sinus, without exposure of the tumor. Special attention should be paid to the procedural points of surgery, such as, exposure of the petrous ICA, bleeding from the petrous sinus, and dural suturing in the vicinity of the apex. With regard to surgical indication, it is important to determine whether tumor infiltration is confined to the temporal bone and the dura of the middle and posterior fossa. If tumor infiltration into the petrous ICA, the dominant side of sigmoid sinus and/or the inferior cranial nerve is observed, then indication for surgery should be determined in a more critical manner.

     

Surgical approaches to the cavernous sinus: a microsurgical study

The surgical approaches to the cavernous sinus were examined in 50 adult cadaveric cavernous sinuses using magnification of X3 to X40. The following approaches were examined: 1) the superior intradural approach directed through a frontotemporal craniotomy and the roof of the cavernous sinus; 2) the superior intradural approach combined with an extradural approach for removing the anterior clinoid process and unroofing the optic canal and orbit; 3) the superomedial approach directed through a supraorbital craniotomy and subfrontal exposure to the wall of the sinus adjacent to the pituitary gland; 4) the lateral intradural approach directed below the temporal lobe to the lateral wall of the sinus; 5) the lateral extradural approach for exposure of the internal carotid artery in the floor of the middle cranial fossa proximal to the sinus; 6) the combined lateral and inferolateral approach, in which the infratemporal fossa was opened and the full course of the petrous carotid artery and the lateral wall of the sinus were exposed and; 7) the inferomedial approach, in which the medial wall of the sinus was exposed by the transnasal-transsphenoidal route. It was clear that a single approach was not capable of providing access to all parts of the sinus. The intracavernous structures best exposed by each route are reviewed. The osseous relationships in the region were examined in dry skulls. Anatomic variants important in exposing the cavernous sinus are reviewed.     

Analysis of different surgical approaches for the treatment of cerebrospinal fluid rhinorrhea.

The current treatment method for cerebrospinal fluid (CSF) rhinorrhea is surgical repair of the fistula. The aim of this study was to analyse different surgical approaches used for the treatment of CSF rhinorrhea regarding several preoperative and postoperative variables to determine the optimal method in these patients. Patients' charts were retrospectively reviewed to get the required data. Twenty-six patients who underwent different types of surgical approach for the treatment of CSF rhinorrhea were included in the study. Patients who had extensive comminuted fractures of the anterior cranial base and additional brain injury besides CSF rhinorrhea, mostly as a result of gunshot injuries, underwent craniotomy (n = 14). Osteoplastic frontal sinusotomy was used in two patients with a dural defect located at the posterior wall of the frontal sinus. Uncomplicated CSF fistulas in ten patients, located at the anterior and posterior ethmoid roof and in the sphenoid sinus, were closed with an endonasal endoscopic approach. Postoperative success rate was higher (97 % for intracranial approach, 100 % for extracranial external and endonasal endoscopic approach) for all techniques. Anosmia was the most frequent permanent complication (n = 5), seen after craniotomy. In conclusion, endonasal endoscopic approach can be preferred for the closure of uncomplicated CSF fistula, located at the anterior or posterior ethmoid roof and in the sphenoid sinus, due to its minimal postoperative morbidity. Uncomplicated CSF fistula, located at the posterior wall of frontal sinuses can be repaired extradurally with osteoplastic frontal sinusotomy. Intracranial approaches should be reserved for more complicated CSF rhinorrhea which results from extensive comminuted fractures of the anterior cranial base and is accompanied with intracranial complications.     

Endoscopic Endonasal Approach to the Middle Cranial Fossa through the Cavernous Sinus Triangles: Anatomical Considerations

The lateral limit of endoscopic endonasal surgery has yet to be defined. The aim of this study was to investigate the lateral limit of endoscopic endonasal surgery at the level of the sphenoid sinus. Access from the sphenoid sinus to the middle cranial fossa through the cavernous sinus triangles was evaluated by cadaver dissection. Anatomical analysis demonstrated that the medial temporal dura mater was exposed through the anterior area of the clinoidal triangle, anteromedial triangle, and superior area of the anterolateral triangle, indicating potential corridors to the middle cranial fossa. This study suggests that the cavernous sinus triangles are applicable in selected cases to manage middle cranial fossa lesions by endoscopic endonasal surgery.     

A Combined Intradural Presigmoid-Transtransversarium-Transcondylar Approach to the Whole Clivus and Anterior Craniospinal Region: Anatomic Study

Surgical exposure of the clivus is difficult because of its proximity to vital neurovascular structures. The anatomic bases of a new surgical approach to this area are discussed. A supra-auricular skin incision is extended toward the posterior border of the sternocleidomastoid muscle. The vertebral artery is exposed from C2 to the occiput unroofing the foramen transversarium of C1. The bone removal consists of a posterior temporal craniotomy, a suboccipital craniectomy, including mastoidectomy with sigmoid sinus unroofing, removal of the lateral margin of the foramen magnum, of the medial third of the occipital condyle, and retrolabyrinthine petrous drilling. Posterior retraction of the vertebral artery facilitates occipital condyle drilling. Intradural exposure of the petroclival region is achieved by L-shaped cutting of the dura with the long branch placed infratentorially anterior to the sigmoid sinus. Intradural exposure of the craniospinal/upper cervical areas is achieved by cutting of the dura medial to the distal sigmoid sinus and by longitudinal cutting of the dura anterior to the vertebral artery. This approach allows multiple ports of entry to the clivus with full control of the vertebrobasilar system, and of the dural sinuses, and is anatomically suited for controlled removal of tumors located in these areas. This approach, or segments of it, has been used successfully in the treatment of large neoplasms of the craniovertebral junction.     

A combined intradural presigmoid-transtransversarium-transcondylar approach to the whole clivus and anterior craniospinal region: anatomic study

Surgical exposure of the clivus is difficult because of its proximity to vital neurovascular structures. The anatomic bases of a new surgical approach to this area are discussed. A supra-auricular skin incision is extended toward the posterior border of the sternocleidomastoid muscle. The vertebral artery is exposed from C2 to the occiput unroofing the foramen transversarium of C1. The bone removal consists of a posterior temporal craniotomy, a suboccipital craniectomy, including mastoidectomy with sigmoid sinus unroofing, removal of the lateral margin of the foramen magnum, of the medial third of the occipital condyle, and retrolabyrinthine petrous drilling. Posterior retraction of the vertebral artery facilitates occipital condyle drilling. Intradural exposure of the petroclival region is achieved by L-shaped cutting of the dura with the long branch placed infratentorially anterior to the sigmoid sinus. Intradural exposure of the craniospinal/upper cervical areas is achieved by cutting of the dura medial to the distal sigmoid sinus and by longitudinal cutting of the dura anterior to the vertebral artery. This approach allows multiple ports of entry to the clivus with full control of the vertebrobasilar system, and of the dural sinuses, and is anatomically suited for controlled removal of tumors located in these areas. This approach, or segments of it, has been used successfully in the treatment of large neoplasms of the craniovertebral junction.     

A limited anterior petrosectomy with preoperative embolization of the inferior petrosal sinus for ventral brainstem tumor removal

BACKGROUND: The present study describes the use of a limited subtemporal extradural anterior petrosectomy with preoperative embolization of the inferior petrosal sinus for the management of tumors located behind the clivus and ventral to the brainstem. Details of the procedure and its application in five cases are presented. METHODS: This procedure consists of using the extradural route to approach the upper side of the petrosal pyramid so that it can be drilled medially, and to resect the apex to come out into the posterior fossa. This route gives a petrosectomy just medial to the horizontal segment of the petrous carotid artery in front of the cochlea. It goes around the labyrinthine mass and the internal auditory canal from above to expose the posterior fossa dura between the two petrosal sinuses. The dural opening exposes the ventral aspect of the pons from the trigeminal nerve to the origin of the abducens nerve, ventral to the facial nerve. Preoperative embolization of the inferior petrosal sinus allows its intraoperative section for a wider exposure along the lower clivus. This approach can easily be combined with an intradural approach to provide additional exposure above the trigeminal nerve. Patients who underwent this procedure had prepontine cisternal chordoma or epidermoid cyst of the petroclival region. RESULTS: One patient experienced a cranial nerve deficit as a direct result of the surgical procedure (VIth nerve palsy requiring surgery) but no other patient has had permanent neuromuscular compromise. Complications consisted of a wound infection in one case. Tumor removal was total in three cases and partial in two cases. CONCLUSION: Quite easy to master, the anterior petrosectomy with preoperative embolization of the inferior petrosal sinus is a time-conserving approach giving one of the best routes to reach the ventral brainstem while working in front of the cranial nerves and preserving hearing.     

Anatomical study of the orbitozygomatic transsellar-transcavernous-transclinoidal approach to the basilar artery bifurcation

OBJECT: An anatomical study in which measurements were obtained was undertaken to demonstrate that the orbitozygomatic transcavernous-transclinoidal approach provides excellent exposure of the trunk of the basilar artery (BA) and its bifurcation. METHODS: Bilateral stepwise dissections were performed on 10 fixed cadaver heads with the aid of x 3 to x 40 magnifications. A frontotemporal craniotomy was made, followed by an orbitozygomatic osteotomy. After the dura mater had been opened, the sylvian fissure was widely separated. The anteromedial triangle of the cavernous sinus was opened to mobilize the internal carotid artery medially. The sella turcica and the dorsum sellae were exposed. The posterior clinoid process and the dorsum sellae were drilled to expose a length of BA that included its bifurcation. Measurements were obtained following the frontotemporal craniotomy, orbitozygomatic osteotomy, and drilling of the posterior clinoid process to quantify the exposures provided by these procedures. Excellent exposure of the trunk of the BA and its bifurcation was achieved. The structures in the interpeduncular cistern and the prepontine cistern were also exposed. There was an average gain of a 13.4-mm-long segment of the BA, which in some surgeries can be invaluable. The angle of exposure that was achieved with the BA bifurcation located at the apex increased markedly. Moreover, this method widened the oculomotor nerve-carotid artery corridor for easier access to the BA bifurcation region. CONCLUSIONS: This approach combines the advantages granted by most conventional approaches to aneurysms of the BA bifurcation. The approach is suitable for aneurysms situated at a high, normal, or low position on the BA bifurcation. It exposes a sufficient length of the BA trunk to place a temporary clip.     

Vascularized omentum graft for the reconstruction of the skull base after removal of a nasoethmoidal tumor with intracranial extension: case report

A 16-year-old boy with rhabdomyosarcoma occupying the nasal cavities and the ethmoid sinus with intracranial extension underwent transcranial surgery. The intradural tumor was resected first with the affected dura of the anterior skull base, and the dural defect was repaired with fascia harvested from the sheath of the rectus abdominis muscle. The remaining tumor contiguous to the nasal cavities was completely extirpated. The cranial cavity was then exposed to the opened nasal cavities, where a revascularized omental graft was used to separate these compartments. Lyophilized dura was placed beforehand beneath the omental graft, as a roof to the nasal cavity, and was removed 3 weeks later through the nostril. A bony skull base repair was performed over the omentum using the inner table of the bone flap. Subcutaneous fat from the abdomen was placed on the bone graft for fixation and as an additional seal for the dural defect. Reconstruction of the anterior skull base with a vascularized omental transfer provides an efficient barrier to the nasal cavity. It also serves as an excellent supporting structure for regeneration of the mucosal epithelium of the nasal cavities.     

Transzygomatic-Subtemporal Approach for Middle Meningeal-to-P2 Segment of the Posterior Cerebral Artery Bypass: An Anatomical and Technical Study.

We evaluated the use of a bypass between the middle meningeal artery (MMA) and P2 segment of the posterior cerebral artery (PCA) as an alternative to an external carotid artery (ECA-to-PCA) anastomosis. Five adult cadaveric heads (10 sides) were used. After a temporal craniotomy and zygomatic arch osteotomy were performed, the dura of the floor of the middle cranial fossa was separated and elevated. The MMA was dissected away from the dura until the foramen spinosum was reached. Intradurally, the carotid and sylvian cisterns were opened. After the temporal lobe was retracted, the interpeduncular and ambient cisterns were opened and the P2 segment of the PCA was exposed. The MMA trunk was transsected just before the bifurcation of its anterior and posterior branches where it passes inside the dura and over the foramen spinosum. It was anastomosed end to side with the P2 segment of the PCA. The mean caliber of the MMA trunk before its bifurcation was 2.1 +/- 0.25 mm, and the mean caliber of the P2 was 2.2 +/- 0.2 mm. The mean length of the MMA used to perform the bypass was 32 +/- 4.1 mm, and the mean length of the MMA trunk was 39.5 +/- 4.4 mm. This bypass procedure is simpler to perform than an ECA-to-P2 revascularization using long grafts. The caliber and length of the MMA trunk are suitable to provide sufficient blood flow. Furthermore, the course of the bypass is straight.     

A large AVM extensively involving the parietal region and posterior fossa

A 47-year-old male was concerned with a large AVM involved extensively in the parietal region and the posterior fossa. Radiological examinations showed multiple radiolucencies in the parietal and occipital bone and torturous vascular nets (nidus) in those bones on the angiograms. Nidus was found also in the dura mater in the posterior fossa. Therefore, this case seemed to be an extremely rare case of calvarial AVM in the parietal region with the mixed calvarial dural AVM in the posterior fossa. His symptoms were bruit, transient hemiparesis and Gerstmann's syndrome in addition to the symptoms due to raised intracranial pressure. Favorable results of therapies could be attained by extensive exfoliation of dura mater from the cranial bone and incision of proximal dura mater in the sinus.     

The jugular dural fold-a helpful skull base landmark to the cranial nerves

During a retrosigmoid (or combined retrolabyrinthine-retrosigmoid) approach to the posterior fossa for vestibular neurectomy or removal of small acoustic neuromas, a white dural fold is a consistent landmark to cranial nerves VII through XII. This fold of dura appears as a white linear structure extending from the foramen magnum across the sigmoid sinus, attaching to the posterior aspect of the temporal bone, anterior to the vestibular aqueduct. The name "jugular dural fold" is suggested for this landmark. The jugular dural fold overlies the junction of the sigmoid sinus and the jugular foramen. As measured in formalin-fixed cadaver heads, the overall length of the jugular dural fold is 20.8 mm (+/- 2.9 mm). The cochleovestibular nerve lies 9.9 mm (+/- 1.5 mm) anterior to the superior aspect of the jugular dural fold, the glossopharyngeal nerve lies 9.5 mm (+/- 1.6 mm) anterior to the midpoint of the jugular dural fold, and the operculum of the vestibular aqueduct lies 6.6 mm (+/- 0.7 mm) posterior to the jugular dural fold. Intraoperative measurements in patients undergoing combined retrolabyrinthine-retrosigmoid vestibular neurectomy show an overall length of the jugular dural fold of 16.3 mm (+/- 1.9 mm). The cochleovestibular nerve lies 8.6 mm (+/- 1.3 mm) anterior to the superior aspect of the jugular dural fold, the glossopharyngeal nerve lies 8.6 mm (+/- 1.3 mm) anterior to the midpoint of the jugular dural fold, and the operculum lies 7.5 mm (+/- 0.8 mm) posterior to the jugular dural fold. The jugular dural fold can be used as a reliable landmark for rapidly locating cranial nerves in the posterior fossa.