Atrophy of the cochlear aperture segment of the cochlear nerve in patients with severe-to-profound acquired sensorineural hearing loss: a 5-T MRI study

OBJECTIVES: Cochlear nerve (CN) atrophy is a prognostic marker for cochlear implantation outcomes in acquired sensorineural hearing loss (ASNHL). However, conventional MRI confines assessment to the nerve trunk. This 5-T MRI study aimed to assess the feasibility of visualizing the cochlear aperture segment and investigate its potential atrophy. MATERIALS AND METHODS: Consecutive ASNHL patients and healthy controls (HCs) who underwent 5-T MRI were prospectively enrolled. Visualization of the cochlear aperture segment was scored. The CN sizes at the cochlear aperture and the internal acoustic meatus segments were measured and compared between groups. Factors associated with cochlear aperture segment size were explored using within-subject correlation analyses. Inter- and intra-observer agreements were assessed. RESULTS: This study included 71 ASNHL patients and 50 matched HCs, wherein 121 affected ears in 66 patients and 98 control ears were measured. The cochlear aperture segment showed a good agreement of visualization and measurement. Affected ears had a lower visualization score of the cochlear aperture segment and smaller absolute CN sizes than controls. After facial nerve normalizing, affected ears had the lower CN size at the cochlear aperture segment but not at the internal acoustic meatus segment. The ratio of the cochlear aperture segment size to the internal acoustic meatus segment size was significantly lower in affected ears than in controls (0.66 ± 0.20 vs. 0.75 ± 0.35; p = 0.045). Interaural differences in hearing loss duration and pure-tone audiometry correlated with interaural differences in the cochlear aperture segment sizes (Rho = -0.247 to -0.356, p < 0.05). CONCLUSION: The cochlear aperture segment of CN can be reliably visualized and measured at 5-T MRI. CN atrophy is confirmed in ASNHL ears, notably at the cochlear aperture segment. Cochlear aperture segment size was associated with hearing loss duration and severity. KEY POINTS: Questions The secondary cochlear nerve atrophy was reported in acquired sensorineural hearing loss (SNHL) patients, but the cochlear nerve at the cochlear aperture segment has not been evaluated. Findings The cochlear aperture segment of the cochlear nerve shows atrophy in acquired SNHL patients using 5-T MRI. Its size is associated with duration and hearing loss severity. Clinical relevance 5-T MRI holds promise as the workhorse modality for imaging the cochlear nerve for SNHL patients. Cochlear aperture segment atrophy is noted in acquired SNHL ears. The comprehensive assessment of the cochlear nerve offers pathophysiological insights into the secondary nerve atrophy.