Cochlear Nerve Deficiency: Prevalence and Audiologic Features

Abstract

Objective: Cochlear nerve deficiency (CND) is increasingly being recognized as a cause of sensorineural hearing loss. Our objectives were to 1) determine the prevalence of CND in children with unilateral SNHL, and 2) explore the relationship between imaging and audiologic features. Method: In 115 consecutive children with unilateral SNHL who underwent high resolution MRI, diameter and image intensity of the CN were measured and normalized to the ipsilateral facial nerve (FN). Patients were divided into 2 groups, normal or CND, based on our published criteria (ie, a CN density < FN density, or CN area). Results: CND was present in 38 of 115 (33%) of patients with unilateral SNHL. In the CND group, a strong correlation was found between PTA and relative CN density ( r2 0.55, P < .0001) and area ( r2 0.50, P < .0001). Cochlear nerve aplasia was always accompanied by severe to profound SNHL. No progression was observed in any patient, except 1 with an ipsilateral EVA. All contralateral ears remained normal. In the normal group (ie, unilateral SNHL without CND), normal variations in nerve size did not correlate with hearing severity. Conclusion: CND, once thought rare, is actually a relatively common cause of pediatric unilateral SNHL. Diagnosis is easily made on MRI. A consistent hearing phenotype is observed, whereby hearing levels correlate with nerve size, and remain remarkably stable over years of follow-up.