Isolated Cochlear Nerve Hypoplasia with Various Internal Auditory Meatus Deformities in Children

Abstract

We report neuro-otological findings in isolated congenital cochlear nerve hypoplasia with various bony deformities and evaluate relationships between functional impairment and the radiologic dimensions of the internal auditory meatus (IAM). We performed imaging and functional analyses on consecutive juvenile or adolescent patients between 2001 and 2005 with "isolated" unilateral hypoplasia of the cochlear nerve, without inner ear anomaly or other deformities. Among 20 patients with unilateral profound deafness who underwent imaging studies, 10 (50%) passed the inclusion criteria. In all affected ears, auditory brain stem responses were absent and the speech discrimination score was very poor (0% to 5%). Distortion product otoacoustic emissions were good in 2 ears, fair in 1 ear, and poor in 7 ears. Caloric responses were absent in 2 ears, reduced in 3 ears, and normal in 5 ears. Inferior vestibular nerve function and facial nerve function were normal in all ears. Distortion product otoacoustic emissions and caloric responses tended to be better in ears with less severe narrowing of the IAM. The risk of co-involvement of the inner ear and superior vestibular nerve functions is higher in the presence of a narrower bony IAM. Cochlear nerve hypoplasia is proposed as one of the most important causes of juvenile unilateral deafness because of its unexpectedly high incidence.