Three-Dimensional Anatomic Analysis of Surgical Landmarks for Middle Fossa Approach

Abstract

Objectives:

The middle fossa approach needs the surgeon to have a 3-dimensional anatomic knowledge of internal auditory meatus (IAM), which is located underneath the middle fossa bony plate. Our purpose was to describe microsurgical anatomy of the middle fossa approach using temporal bone computed tomography (CT) 3-dimensional (3D) reconstruction.

Methods:

Thirty CT images of the temporal bone from patients aged between 20 and 60 years were selected. The inclusion criterion was a radiologically normal temporal bone CT scan. 3D-reconstructed images were obtained using high-resolution axial temporal bone CT scans. IAM, semicircular canal (SCC), cochlea, tympanic segment of the facial nerve (FN), geniculate ganglion (GG), and malleus were reconstructed. The length and angle among these structures was measured.

Results:

The mean lengths between the center of IAM and bony surface of middle cranial fossa at the Porus level was 7.7 mm (±1.0). The mean length between the superior of point of IAM of porus and GG was 15.4 mm (±1.5). The mean length between superior of point of IAM of porus and medial end of cochlear basal turn 9.9 mm (±0.9). Angle between the axis of SCC and the axis of tympanic segments of FN was 105.9° (±5.4). The mean angle between the axis of SCC and axis of IAM was 47.2° (±6.5) The mean angle between the axis of IAM and axis of tympanic segments of FN 59.6° (±10.9), The mean angle of 3-point malleus handle, GG, superior point of IAM of porus level was 113.8° (±9.8).

Conclusions:

The understanding of the 3D relationship in the microsurgical structure will help decide the drilling point for the IAM in case of lack of bony landmarks.