Prevalence and characteristics of facial nerve bifurcation in the mastoid segment: a retrospective analysis using temporal bone CT scans

To investigate the prevalence and characteristics of bifurcation of the facial nerve (FN) in the mastoid segment using temporal bone CT scans.

A total of 970 cases (1931 ears) of temporal bone CT scans were reviewed, including 463 females and 498 males, aged 1 to 95 years (interquartile range: 20–69 years). CT imaging with multiplanar reconstruction (MPR) was used to identify and evaluate the bifurcation of the FN. Cases showing branching were confirmed by consensus among three physicians.

We identified 10 cases (10 ears) with facial nerve branching in the vertical segment, yielding an incidence rate of 0.52% (10/1931 ears). Every cases were unilateral, predominantly on the left side. Age analysis revealed 1 case (0.22%) in individuals under 20 years and 9 cases (0.61%) in those over 20 years. Bifurcation generally occurred near the middle to lower vertical segment, with the closest proximity to the second genu observed in a 15-year-old patient.

Bifurcation of the FN in the mastoid segment, though rare, can be encountered in otologic surgery. Detailed preoperative imaging evaluations are crucial for surgical planning to minimize the risk of nerve damage. Our findings emphasize the importance of recognizing anatomical variations in the FN for improving surgical outcomes and patient safety.