Morphometric analysis of anatomical relationships of the facial nerve for mastoid surgery.

Surgical anatomical relationships of the facial nerve (FN) with several landmarks used in mastoid surgery were studied in temporal bone axial high resolution CT scans of 90 patients (180 ears). The shortest distances between the FN and external auditory canal (EAC), sigmoid sinus (SS), posterior fossa dural plate (PFD), and joint of the bony EAC with the lateral surface of the mastoid (M) were measured. These measurements were also analysed in respect of pneumatization and side differences. On average, it was found that FN-EAC was 2.9 mm, FN-SS was 10.5 mm, FN-PFD was 7.3 mm and FN-M was 15.3 mm. FN-EAC was found to be longer in poorly pneumatized bones whereas other distances were longer in pneumatized bones. FN-M was found to be longer on the right side.