Subtemporal Approach and Its Infratentorial Extension: Review and a Comparative Analysis of Different Techniques

Introduction Surgical resection of lesions occupying the incisural space is challenging. In a comparative fashion, we aimed to describe the anatomy and surgical approaches to the tentorial incisura and to the rostral brainstem via the intradural subtemporal approach and its infratentorial extensions. Methods Six fresh human head specimens (12 sides) were prepared for the microscopic dissection of the tentorial incisura using the intradural subtemporal approach and its infratentorial extensions. Endoscope was used to examine the anatomy of the region inadequately exposed with the microscope. Image-guided navigation was used to confirm bony structures visualized around the petrous apex. Results Standard subtemporal approach provides surgical access to the supratentorial brainstem above the pontomesencephalic sulcus and to the lateral surface of the cerebral peduncle. The linear or triangular tentorial divisions can provide access to the infratentorial space below the pontomesencephalic sulcus. The triangular tentorial flap in comparison with the linear incision obstructs the exposure of anterior incisural space and of the prepontine cistern. Visualization of the brainstem below the trigeminal nerve can be achieved by the anterior petrosectomy. Conclusion Infratentorial extension of the intradural subtemporal approach is technically demanding due to critical neurovascular structures and a relatively narrow corridor. In-depth anatomical knowledge is essential for the selection of the appropriate operative approach and safe surgical resections of lesions.

Combined subtemporal and pterional approach for clipping of multiple aneurysms

Background: Despite ongoing improvements in endovascular techniques, open surgical management of basilar apex aneurysms is occasionally necessary.[2] Critical dissection of perforating vessels from the aneurysm is facilitated by the lateral trajectory of the subtemporal approach.[1] Incorporation of additional trajectories can facilitate treatment of multiple aneurysms within the same procedure. Case Description: A 48-year-old woman presented with a Hunt and Hess 1 and Fisher Grade 3 subarachnoid hemorrhage from a small and broad-necked basilar apex aneurysm that was not amenable to endovascular management. An unruptured left A1-A2 anterior cerebral artery aneurysm was also noted on vascular imaging. The patient underwent a combined right subtemporal and pterional approach for sequential clipping of the basilar and anterior communicating artery aneurysms. The third nerve, running between the posterior cerebral artery and the superior cerebellar artery, guided dissection to the basilar artery in the subtemporal approach. A temporary clip was placed on a vessel-free zone of the basilar trunk during dissection of perforators off the posterior aspect of the aneurysm dome. A fenestrated clip around the right P1 segment was used to ensure complete occlusion of the aneurysm. Indocyanine green angiography was used to confirm successful clipping and patency of parent and perforating vessels. The unruptured A1-A2 aneurysm was clipped without difficulty from the pterional trajectory. The patient had an uneventful postoperative recovery with the exception of transient right third nerve palsy. Conclusion: As highlighted by this case, maintenance of open surgical skills for the treatment of complex aneurysms unamenable to endovascular therapies is critical.

Microsurgical Management of Blister-Type Basilar Artery Apex Region Aneurysms: Companion Cases Demonstrate Technical Nuances of the Subtemporal Approach: 2-Dimensional Operative Video

The proportion of intracranial aneurysms treated by microsurgical clip ligation has drastically decreased in the endovascular era. However, some aneurysms cannot be treated by current endovascular techniques. Therefore, trainees and young vascular neurosurgeons must develop and maintain microsurgical skills to safely treat aneurysms that require surgery. Ruptured, basilar artery apex, blister-type aneurysms are particularly treacherous and require a high degree of skill to safely manage them surgically. In this video, 2 companion cases are exhibited to demonstrate the nuances of the subtemporal, skull base, approach to the basilar apex region. In each case, the patient consented to surgery and anonymized recording. The subtemporal approach is favored over the trans-sylvian for posteriorly directed basilar apex region aneurysms as the former affords a complete view of the relevant anatomy. Points for consideration include variations on the standard subtemporal approach, use of retractors vs lumbar drainage to mobilize the temporal lobe, and splitting the tentorium vs a suture-retraction technique for visualization of the basilar artery apex region. Techniques for successful navigation of intraoperative rupture are demonstrated. As the number of intracranial aneurysms treated by microsurgery continues to ebb, high-quality educational videos that supplement surgeon experience will become increasingly critical to ensure that a cohort of capable microvascular neurosurgeons is prepared to tackle challenging, but manageable aneurysms, such as the blister-type basilar apex variety. Video (c) Emory University School of Medicine, 2021. Used with permission.

Anterior Petrosal Approach for Enlarging Previously Radiated Recurrent Trigeminal Schwannoma: 2-Dimensional Operative Video

Trigeminal nerve schwannomas (TNSs) are rare lesions that typically present with symptoms of trigeminal neuropathy or other cranial nerve palsies. These lesions classically have a dumbbell shape, with an anterior component within Meckel's cave and posterior component extending into the posterior fossa through the porus trigeminus. Surgical resection of TNSs can often be achieved via an extradural subtemporal approach to Meckel's cave without an anterior petrousectomy, even for tumors with a significant posterior fossa component, as the tumor often erodes a portion of the petrous apex.1 We present the case of a 53-yr-old female presenting to our institution with complete trigeminal neuropathy secondary to a right-sided, previously resected and radiated TNS. Serial imaging demonstrated an interval growth of significant residual tumor despite multiple adjuvant therapies, and, thus, the patient was recommended to undergo additional surgical resection. The lesion was approached through a right-sided subtemporal approach to Meckel's cave,2 with a plan to utilize an anterior petrousectomy only if difficulty resecting the posterior fossa component of the tumor was encountered. Intraoperatively, the posterior fossa component was found to be densely adherent to the adjacent brainstem, likely secondary to prior surgery and radiation therapy, and, thus, an anterior petrousectomy was performed. Postoperatively, the patient had stable trigeminal neuropathy without any new neurological deficits and a magnetic resonance imaging (MRI) confirmed a gross total resection. In the accompanying video, we hope to demonstrate the steps and nuances of both the subtemporal approach to accessing Meckel's cave and anterior petrousectomy when employed for the resection of TNSs. The patient in question provided formal consent for the making of this video.

Elective inferior temporal lobe resection as an adjunct to subtemporal approach for a case of tentorial meningioma arising from the middle part of the free edge of the tentorium: A case report

Background: Tentorial meningiomas attached to the inner edge of the tentorium are difficult to excise due to their deep location. Sufficient space may not be always available through a subtemporal approach. Thus, the aim of not retracting the brain is not fulfilled. Methods: To gain surgical corridor, we electively resected the inferior temporal lobe. This helped in greater working space, better visualization, and less chances of venous damage. Results: Employing this technique of elective temporal lobe resection helped us in complete tumor removal without compromising on vision or surgical corridor. Conclusion: A limited inferior temporal lobectomy greatly enhances the working space and vision in cases of difficult tentorial meningiomas. This translates into ease of tumor excision without compromising the patient safety.

Using the Arcuate Eminence–Trigeminal Notch Line to Localize the Anterior Wall of the Internal Auditory Canal in a Subtemporal Approach: An Anatomical Study

Background This article aims to describe the regional anatomy of the anterior end of the arcuate eminence, the lateral end of the trigeminal notch, and the line connecting the two (i.e., the arcuate eminence–trigeminal notch line [ATL]) and to determine whether the ATL could be used as a landmark for localizing the internal auditory canal (IAC). Methods Twenty sides of the middle cranial fossae were examined. The anterior end of the arcuate eminence, the lateral end of the trigeminal notch, the ATL, and other crucial structures were exposed. The relevant distance and angle of related structures in the anterior wall of the petrosal bone were measured. Results The anterior end of the arcuate eminence and the lateral end of the trigeminal notch could be identified in all specimens. The anterior end of the arcuate eminence lay over the geniculate ganglia and the vestibule area, and could be visualized directly or determined from the intersection of the long axes of the greater superficial petrosal nerve and arcuate eminence. On the petrous ridge, the lateral end of the trigeminal notch was also the transitional point of the suprameatal tubercle and trigeminal notch. The ATL corresponded to the projection of the anterior wall of the IAC on the anterior surface of the petrous bone. Conclusion The ATL corresponded to the projection of the anterior wall of the IAC on the anterior petrous surface and could be used as an alternative landmark for localizing the anterior wall of the IAC.