Prevalence of Radiographic Cochlear-Facial Nerve Dehiscence

Objective: To determine the prevalence of radiographic cochlear-facial nerve dehiscence (CFD). Study Design: Retrospective radiological study. Setting: Two tertiary-referral centers. Patients: Two hundred six temporal-bone computed tomography (CT) scans (405 total ears) of otology/neurotology patients from two academic institutions between the years 2014 and 2017. Intervention: Diagnostic. Main Outcome Measures: The cochlear-facial nerve partition width (CFPW) was measured on coronal CT sections and defined as the shortest distance between the cochlear basal turn and facial nerve (FN) labyrinthine segment. We used logistics regression analyses to determine positive predictors for radiographic evidence of CFD. Results: The overall prevalence of radiographic CFD was 5.4% (22/406 ears). 9.2% of patients (19/206) had CFD. Of these 19 patients, only one patient had mixed hearing loss that could not be explained by any other vestibular or auditory etiology. Three out of 206 patients had dehiscence in both ears (1.4%). The average CFPW was 0.6 +/- 0.2 mm, and fallopian canal width was 1.1 +/- 0.02 mm (n = 405). Older age, use of traditional CT scans, and thinner CT slice thickness were significant predictors for radiographic CFD. Conclusions: The radiographic prevalence of CFD is higher than what is reported in histologic studies, and may overestimate the true prevalence of CFD. The clinician should keep this in mind when considering this as potential cause for third-window symptoms.