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Eighth Nerve Aplasia and Hypoplasia in Cochlear Implant Candidates: The Clinical Perspective

Objective To identify the clinical and radiologic characteristics of aplasia and hypoplasia of the eighth nerve. Study Design Retrospective case-note review. Setting Cochlear implant program. Patients All children at the authors' institution in whom the cochlear implant assessment failed because of absence or hypoplasia of the eighth nerve. Intervention Computed tomography of petrous bones and magnetic resonance imaging of the brain. Main Outcome Measures Presence or absence of eighth nerve and other radiologic factors contraindicating implantation. Results Of 143 cochlear implant candidates, 237 were judged ineligible for cochlear implantation. The preimplant assessment failed in 10 candidates of 143 because of bilateral aplasia or hypoplasia of the eighth nerve (7 cases) or unilateral aplasia or hypoplasia of the eighth nerve and a contraindication to operation on the other side (3 cases). The aplasia or hypoplasia of the eighth nerve was confirmed by magnetic resonance imaging in seven cases (5%): six were syndromic (3 CHARGE, 1 VATER-RAPADILLINO, 1 Möbius, 1 Okihiro), and one was nonsyndromic autosomal-recessive. All seven children had delayed motor milestones and absence of auditory brainstem responses. Conclusion Aplasia and hypoplasia of the eighth nerve are not uncommon in pediatric cochlear implant candidates, particularly in the presence of a syndrome such as CHARGE. Magnetic resonance imaging of the brain is mandatory before implantation because it can identify the presence or absence of the eighth nerve. Parents of children with profound hearing loss, delayed motor milestones, absence of auditory brainstem responses, and a syndromic diagnosis, should be made aware of this possible abnormality.