Optimizing Extradural Exposure in the Posterior Petrosal Approach: The Role of Endolymphatic Sac Peeling.

Background and objectives: The posterior petrosal approach is a technically challenging procedure used to treat complex, deep-seated lesions. The petrosal ridge, located between the middle and posterior fossae, can be anatomically compared with the sphenoid ridge, which separates the anterior and middle fossae. Analogous to the orbitotemporal periosteal fold, which connects the orbit to the middle fossa dura, the endolymphatic sac (ELS) acts as a fold connecting the vestibule to the posterior fossa dura. This fold presents an obstacle to further elevating the dura from the posterior surface of the petrous bone. The objective of this study is to provide anatomic details and key landmarks for the preservation and safe peeling of the ELS, thereby expanding the surgical field during posterior petrosectomy and combined petrosal approaches. Methods: Five formalin-fixed cadaveric heads were injected with colored silicone, and 10 sides were used for cadaveric dissections. Results: At the level of the superomedial margin of the operculum, the periosteal layer is incised to enter a surgical plane between the dura propria and the ELS. The dura is then peeled away from the posterior aspect of the ELS, and the periosteal layer is further incised along the ELS. A dural thickening continuing medially from the operculum, corresponding to the Tubingen line, allows access to the plane between the dural leaflets before reaching the full extent of the ELS. Conclusion: Analogous to the orbitotemporal periosteal fold in anterior approaches, the ELS can be safely peeled from the dura of the posterior fossa, thereby enhancing the extradural exposure in these approaches.