Differences in the Diameter of Facial Nerve and Facial Canal in Bell’s Palsy—A 3-Dimensional Temporal Bone Study

Abstract

Bell's palsy is hypothesized to result from virally mediated neural edema. Ischemia occurs as the nerve swells in its bony canal, blocking neural blood supply. Because viral infection is relatively common and Bell's palsy relatively uncommon, it is reasonable to hypothesize that there are anatomic differences in facial canal (FC) that predispose the development of paralysis. Measurements of facial nerve (FN) and FC as it follows its tortuous course through the temporal bone are difficult without a 3D view. In this study, 3D reconstruction was used to compare temporal bones of patients with and without history of Bell's palsy. Twenty-two temporal bones (HTBs) were included in the study, 12 HTBs from patients with history of Bell's palsy and 10 healthy controls. Three-dimensional models were generated from HTB histopathologic slides with reconstruction software (Amira), diameters of the FC and FN were measured at the midpoint of each segment. The mean diameter of the FC and FN was significantly smaller in the tympanic and mastoid segments (p = 0.01) in the BP group than in the controls. The FN to FC diameter ratio (FN/FC) was significantly bigger in the mastoid segment of BP group, when compared with the controls. When comparing the BP and control groups, the narrowest part of FC was the labyrinthine segment in control group and the tympanic segment in the BP. This study suggests an anatomic difference in the diameter of FC in the tympanic and mastoid segments but not in the labyrinthine segment in patients with Bell's palsy.