Expanding the Endoscopic Transpterygoid Corridor to the Petroclival Region: Anatomical Study and Volumetric Comparative Analysis

Object: The endoscopic endonasal transmaxillary transpterygoid (TMTP) approach has been the gateway for lateral skull base exposure. Removal of the cartilaginous Eustachian tube (ET) and lateral mobilization of the internal carotid artery (ICA) are technically demanding adjunctive steps to access the petroclival region. The gained expansion of the deep working corridor provided by these maneuvers has yet to be quantified.

Methods: The TMTP approach with cartilaginous ET removal and ICA mobilization was performed in five adult cadaver heads (10 sides). Accessible portions of the petrous apex were drilled in three stages: (1) before ET removal, (2) after ET removal but before ICA mobilization, and (3) after ET removal and ICA repositioning. Resection volumes were calculated using 3-D reconstructions generated from thin-slice CT scans performed before and after each step of the dissection.

Results: Average petrous temporal bone resection volumes at each stage were 0.21, 0.71, and 1.32 cm³, respectively (p < 0.05 by paired t-tests). Without ET removal inferior and superior access to the petrous apex was limited. Furthermore, without carotid mobilization, drilling was confined to the inferior two-thirds of the petrous apex. After mobilization, resection was extended superiorly through the upper extent of the petrous apex.

Conclusion: The transpterygoid corridor to the petroclival region is maximally expanded by the resection of the cartilaginous ET and mobilizing the paraclival ICA. These added maneuvers expanded the deep window almost six times and provided more lateral access to the petroclival region with a maximum volume of 1.5 cm³. This may result in the ability to resect small to moderate size intradural petroclival lesions up to that volume. Larger lesions may better be approached through an open transcranial approach.