Dysfunction of the cochlea contributing to hearing loss in acoustic neuromas: An underappreciated entity

Objective: Hearing loss is a common symptom in patients with cochleovestibular schwannoma. Clinical and histologic observations have suggested that the hearing loss may be caused by both retrocochlear and cochlear mechanisms. Our goal was to perform a detailed assessment of cochlear pathology in patients with vestibular schwannoma (VS). Study Design: Retrospective analysis of temporal bone histopathology. Setting: Multi-center study. Material: Temporal bones from 32 patients with unilateral, sporadic VS within the internal auditory canal. Main Outcome Measures: Sections through the cochleae on the VS side and opposite (control) ear were evaluated for loss of inner and outer hair cells, atrophy of the stria vascularis, loss of cochlear neurons, and presence of endolymphatic hydrops and precipitate within the endolymph or perilymph. Observed pathologies were correlated to nerve of origin, VS volume, and distance of VS from the cochlea. Hearing thresholds also were assessed. Results: VS caused significantly more inner and outer hair cell loss, cochlear neuronal loss, precipitate in endolymph and perilymph, and decreased pure tone average, when compared with the opposite ear. Tumor size, distance from the cochlea, and nerve of origin did not correlate with structural changes in the cochlea or the hearing threshold. Conclusion: There is significant degeneration of cochlear structures in ears with VS. Cochlear dysfunction may be an important contributor to the hearing loss caused by VS and can explain certain clinically observed phenomena in patients with VS.