Petrous anatomy for middle fossa approach

Objective: The objective was to describe the relationship of anatomical landmarks required for the middle fossa approach to lesions of the petrous apex and internal auditory canal (IAC). Landmarks for safe identification of the IAC are defined, as are two zones (safe zones I and II) anterior and posterior to the IAC. Study Design: Temporal bone anatomical study. Methods: Ten temporal bones underwent high-resolution computed tomography followed by wet bench dissection. A set of 39 different distances between vital structures was measured, where possible, from both radiology films and under the microscope. Mean, median, minimum, and maximum measurements of all distances were determined. Angular measurements were made using a specially designed instrument. Results: Measurements were made in an anatomical position to mimic the middle fossa surgical technique. Measurements are presented for the superior surface of the temporal bone from the sigmoid sinus and inner table to vital structures, from the anterior and posterior petrous apex, and from the IAC. Conclusions: Petrous apex anatomical knowledge is required for the safe middle fossa approach to the IAC and petrous apex. Two safe zones are defined that should prevent damage to the cochlea and the superior semi-circular canal.