Aplasia of the Cochlear Nerve: A Temporal Bone Study

OBJECTIVE: The purpose of this study was to evaluate the temporal bone findings in individuals with cochlear nerve aplasia. STUDY DESIGN: Retrospective case review. METHODS: Two individuals with unilateral profound deafness caused by aplasia of the cochlear nerve were identified. The temporal bones were processed, and the cochlear elements were quantified. RESULTS: Histopathologic study of the temporal bones from these individuals demonstrate that a fully formed cochlea and normal-appearing organ of Corti can occur in the absence of the spiral ganglion and cochlear nerve. Cochlear nerve aplasia can occur in both a narrow or a normal-sized internal auditory canal. CONCLUSION: These findings suggest that the development of the cochlea and organ of Corti are not dependent on the presence of the cochlear nerve and spiral ganglion. The entity of cochlear nerve aplasia in the presence of a normally formed cochlea must be considered when evaluating individuals as candidates for cochlear implantation.