Cochlear Implantation: An Overview

Abstract

A cochlear implant (CI) is a surgically implanted device for the treatment of severe to profound sensorineural hearing loss in children and adults. It works by transducing acoustic energy into an electrical signal, which is used to stimulate surviving spiral ganglion cells of the auditory nerve. The past 2 decades have witnessed an exponential rise in the number of CI surgeries performed. Continual developments in programming strategies, device design, and minimally traumatic surgical technique have demonstrated the safety and efficacy of CI surgery. As a result, candidacy guidelines have expanded to include both pre and postlingually deaf children as young as 1 year of age, and those with greater degrees of residual hearing. A growing proportion of patients are undergoing CI for off-label or nontraditional indications including single-sided deafness, retrocochlear hearing loss, asymmetrical sensorineural hearing loss (SNHL) in adults and children with at least 1 ear that is better than performance cut-off for age, and children less than 12 months of age. Herein, we review CI design, clinical evaluation, indications, operative technique, and outcomes. We also discuss the expanding indications for CI surgery as it relates to lateral skull base pathology, comparing CI to auditory brainstem implants, and address the concerns with obtaining magnetic resonance imaging (MRI) in CI recipients.

Keywords: auditory brainstem implant; auditory nerve; auditory prosthesis; cochlear implantation; electric stimulation; hearing loss.

Fig. 1

Components of the cochlear implant system.

Fig. 2

( A ) A mastoidectomy has been performed. ( B ) The short process of the incus can be seen which identifies the level of the facial recess (outlined in black). ( C ) The facial recess is opened and the stapedial tendon can be appreciated (arrow). ( D ) The receiver-stimulator is inserted within a tight subperiosteal pocket. ( E ) The round window membrane is fully exposed by drilling away the ledge of bone over the round window niche. A slit is then made in the round window. ( F ) The electrode is inserted through the round window in a slow and controlled fashion and ultimately resides in the scala tympani of the cochlea.

Fig. 3

Comparison of MRI artifact with ( A–C ) and without ( D–F ) the internal magnet in place. ( A and D ), Contrast-enhanced T1-weighted axial images at the level of maximum image distortion demonstrate less ferromagnetic artifact with the internal magnet removed. Contrast-enhanced T1-weighted axial ( B and E ) and coronal ( C and F ) images demonstrate adequate visualization of the ipsilateral internal auditory canal (arrows) in both cases despite adjacent ferromagnetic artifact from the cochlear implant. B and E are both far enough from the magnet that neither demonstrate significant artifact. (Reprinted with permission from Carlson et al. 26 )