Cochlear Implantation: Patient Evaluation and Device Selection
Cochlear implants (CIs) are auditory prostheses designed to link an internal device interfaced with the auditory nerve to an external device using a specific sound-coding strategy to translate acoustic information into electrical stimulation. For the majority of causes of deafness, the auditory hair cells are lost or dysfunctional. The neurons of the bipolar spiral ganglion and their primary afferent dendrites remain intact and are available for direct electrical stimulation by the CI. The tonotopic organization of the cochlea is emulated by orienting the electrode contacts toward the modiolus within the scala tympani and assigning frequencies to specific electrodes along the length of the electrode array such that electrical stimulation corresponding to the highest pitches are delivered to the basal region of the cochlea and those of the lowest pitches are delivered to the apical region. The electrical impulses bypass the dysfunctional hair cells and directly depolarize the primary afferent neurons. In this chapter, medical, imaging, and candidacy criteria are addressed. Factors important for device selection are reviewed. The development of shorter electrodes for use in individuals with significant residual hearing has allowed complementary electrical and acoustic hearing in the same ear. In addition, cochlear implantation for tinnitus suppression and restoration of binaural benefit in patients with single-sided deafness has been well accepted in Europe with CE Mark approval, and it is emerging as an off-label treatment in the United States.
