Stapedius muscle: Don't mistake it for a branch of the facial nerve in images.

OBJECTIVE: The relationship between the stapedius muscle and the vertical part of the facial nerve is important for surgery. The study aims to understand the spatial relationship between the stapedius muscle and the vertical part of the facial nerve in ultra-high-resolution computed tomography (U-HRCT) images.

METHODS: A total of 105 ears from the heads of 54 human cadavers were analyzed using U-HRCT. The location and direction of the stapedius muscle were evaluated with the facial nerve as the reference. The integrity of the bony septum between the two structures and the distance between the transverse sections were examined. Paired Student's t-test and the nonparametric Wilcoxon test were applied.

RESULTS: The lower end of the stapedius muscle emerged at the upper (45 ears), middle (40 ears), or lower (20 ears) level of the facial nerve and was positioned medial (32 ears), medial posterior (61 ears), posterior (11 ears), or lateral posterior (1 ear) to the facial nerve. The bony septum was not continuous in 99 ears. The distance between the midpoints of the two structures was 1.75 mm (IQR=1.55-2.16 mm).

CONCLUSION: The spatial relationship between the stapedius muscle and the facial nerve was varied. They were close to each other and in most cases the bony septum was not intact. Preoperative familiarity with the relationship between the two structures is helpful for avoiding unwanted injury to the facial nerve in surgery.