360 Degrees Around the Petrous Apex: An Anatomic and Quantitative Comparative Analysis of Surgical Approaches

BACKGROUND AND OBJECTIVES: The Petrous Apex (PA) is one of the most difficult areas to access within the skull base. This study qualitatively and quantitatively analyses the most common approaches to the PA, comparing the zero-degree endoscopic endonasal approach (EEA), contralateral transmaxillary approach (CTM), middle fossa approach (MFA), translabyrinthine transcochlear approach (TL), and rectosigmoid approach (RS). METHODS: Dissections were performed on 7 fresh frozen cadaveric specimens. Five landmarks were chosen as objectives: the petroclival synchondrosis, foramen lacerum, internal acoustic canal (IAC), carotid foramen, and jugular bulb. Predissection computed tomography scans and neuronavigation coordinates were obtained and uploaded to Slicer 3D. Working distances, angles of attack (AOA) to the landmarks, and area of surgical freedom were calculated. RESULTS: The shortest distance to the petroclival synchondrosis was achieved with the CTM. The shortest distance to the foramen lacerum was observed in the TL, along with the widest vertical and horizontal AOA. The IAC was reached with all approaches except the EEA. The CTM exhibited the longest distance, while the MFA had the shortest. The MFA offered the broadest horizontal AOA, whereas the TL provided the widest vertical angle. The carotid foramen was accessible through the CTM and TL. The latter exhibited the shortest distance and offered the widest vertical and horizontal AOAs. Both RS and TL reached the jugular bulb without a significant difference in length. The TL provided the largest area of surgical freedom. CONCLUSION: While the TL exposes most landmarks and offers the greatest surgical freedom, it is unfamiliar for neurosurgeons and usually involves sacrificing hearing. Contralateral approaches are viable structure-sparing alternatives but necessitate extensive endonasal manipulation with endoscopic. The EEA provides a simple and effective route for PA lesions extending medially. The RS and MFA enable access to the posterior-inferior and anterior-superior aspects of the IAC, respectively.