Conclusion: Even if hearing loss is mild to moderate, the presence of cochlear nerve (CN) hypoplasia associated with retrocochlear disorders should be considered.
Objectives: CN hypoplasia is a term that refers to an absent cochlear nerve on high-resolution magnetic resonance imaging (MRI). Most cases of CN hypoplasia are associated with profound hearing loss. The present study reports six pediatric cases of unilateral CN hypoplasia with mild to moderate hearing loss.
Methods: Between May 2008 and April 2011, pure-tone hearing tests were performed in 17 patients who were diagnosed with CN hypoplasia on high resolution for evaluation of unilateral sensorineural hearing loss at the National Center for Child Health and Development. Of these, six patients had average hearing levels in the affected ears of < 60 dB and were therefore included in this study.
Results: All six ears with CN hypoplasia were associated with CN canal stenosis. DPOAEs were present in one (17%) of the six affected ears. The ABR thresholds of the ears with CN hypoplasia were significantly elevated compared with 1-4 kHz pure-tone hearing levels in one of three cases. In two of five cases, the maximum word recognition scores of the affected ears were poor compared with pure-tone hearing levels.