Apparent cochlear nerve aplasia: To implant or not to implant?

Objective: To describe the imaging findings and clinical outcomes of children with apparent cochlear nerve aplasia undergoing cochlear implantation. Study Design: Retrospective case review. Setting: Tertiary care center. Patients: Three patients with imaging findings consistent with absent cochlear nerve canal on diagnostic imaging and questionable audiometric responses on testing who underwent promontory stimulation and subsequent cochlear implantation. Intervention(S): Magnetic resonance imaging and computed tomography, audiologic assessment, and cochlear implantation. Main Outcome Measure(S): Audiologic performance after cochlear implantation. RESULTS: Three patients were identified to have hearing loss on newborn hearing screening and underwent auditory brainstem response testing revealing absent brainstem responses. ASSR testing was inconclusive when performed. Imaging in all cases identified 1 ear with a small internal auditory canal with 2 nerves present, one of which seems to enter the vestibule in each case and the other is assumed to be the functioning facial nerve. There was a bony plate present over the entrance to the cochlea in 2 of the 3 patients. Over time, 2 of the families reported responses to auditory stimuli with amplification. Promontory stimulation testing showed reproducible responses to electrical stimuli in the ears in question. After cochlear implantation, all 3 patients have shown responses to auditory stimuli. Conclusion: The absence of a visible cochlear nerve or cochlear nerve canal on radiologic imaging does not preclude auditory innervation of the cochlea. Cochlear implantation can be a viable option for patients with apparent cochlear nerve aplasia who have undergone appropriate testing. Electronically evoked auditory brainstem response is critical in the evaluation of this patient group.