Endoscopic Endonasal Interdural Middle Fossa Approach to the Maxillary Nerve: Anatomic Considerations and Surgical Relevance.

BACKGROUND: The maxillary nerve (V2) can be approached via the open middle fossa approach. OBJECTIVE: To delineate the anatomy of V2 and its specific segments with respect to the endonasal landmarks. We present the endoscopic endonasal interdural middle fossa approach to V2 and its potential application for the treatment of perineural spread in sinonasal/skull base tumors. METHODS: Five human head silicon-injected specimens underwent bilateral endoscopic endonasal transpterygoid approaches. V2 prominence and the maxillary strut were identified in the lateral recess along with paraclival carotid protruberance. The regions superior and inferior to V2 corresponding to the anteromedial and anterolateral triangles of the middle fossa were exposed. RESULTS: V2 can be classified into 3 segments: interdural (from the Gasserian ganglion to the proximal part of the maxillary strut), intracanalicular (corresponding to the anteroposterior length of the maxillary strut), and pterygopalatine (distal to the maxillary strut and the site of its divisions). Endonasally, the average length of the interdural and the intracanalicular segments were approximately 9 and 4.4 mm, respectively. V2, following its division distal to the maxillary strut, was successfully dissected off the middle fossa dura and transected just distal to the Gasserian ganglion. CONCLUSION: Endonasally, the interdural segment can be safely mobilized between the periosteal and meningeal dural layers while ensuring the integrity of the middle fossa dura. This allows transection of infiltrated V2 to facilitate tumor resection without entering the intradural/arachnoidal space. Posteriorly, this is limited by the Gasserian ganglion and superomedially by the dural envelope surrounding the cavernous sinus and the paraclival carotid artery.