Three-dimensional Anatomical Analysis of Surgical Landmarks for the Middle Cranial Fossa Approach

This study describes the microsurgical anatomy of the middle cranial fossa approach using temporal bone three-dimensional (3D) computed tomography (CT) reconstruction, which should contribute to determining the drilling point for the internal auditory meatus (IAM) when bony landmarks are absent. Thirty temporal bone CT scans were reviewed retrospectively. We measured the shortest and longest distances to IAM from the petrous ridge, and measured the angle between the facial nerve and various labyrinth structures. Three-dimensional reconstructed images were obtained using high-resolution axial temporal bone CT (0.7-mm-thick slices, FOV 90 × 90, KVp 120, 305 mA, width 2,800, and level 800). The mean shortest and longest distances to IAM from the petrous ridge were 5.22 and 10.1 mm, respectively. The mean distance to the IAM from the cochlea was 9.91 mm. The mean angle between the IAM and superior semicircular canal was 47.21°, which was more acute than previously reported. The mean angle between the IAM and geniculate ganglion (GG) and external auditory canal was 113.8°, and the mean distance from the GG to the IAM was 15.44 mm. Understanding the 3D relationships among the microsurgical structures will help to decide the drilling point for the IAM when bony landmarks are absent. A preoperative evaluation might be useful for preserving important neurovascular structures while approaching the middle fossa.