Auditory Brainstem Implants

Auditory brainstem implants (ABI) bypass the need for a functioning auditory nerve by directly stimulating the auditory processing centers of the brainstem. (In contrast, cochlear implants require a functioning auditory nerve to transmit impulses from the cochlea to the auditory processing centers of the brainstem.) This class of auditory prosthesis currently represents the best auditory prosthesis for individuals with absence, malformation, or destruction of the auditory nerve. This device is commonly used in people with neurofibromatosis type II. [Colletti: 2012]

Currently, the U.S. Food and Drug Administration has limited approval for ABIs, and children must be 12 years of age or older with certain severe types of hearing loss to be candidates for these implants. Other countries have different regulatory requirements. A number of current clinical trials are examining the use of ABIs in pediatric patients, including younger patients and in conditions other than NFII. For a listing, see Auditory Brainstem Implants in Children and Adolescents (ClinicalTrial.gov).

ABI components are similar to those found in cochlear implants and consist of an external speech processor and receiver that transmit sound waves in the form of electrical impulses to a microelectrode array. This array is inserted through an opening in the mastoid bone and is advanced to the lateral recess of the fourth ventricle, adjacent to the ventral cochlear nucleus. The first generation of auditory brainstem implants were designed to stimulate the surface of the ventral cochlear nucleus in the auditory brainstem. [Hitselberger: 1984] These surface-electrode ABIs rarely provided the range of frequency information and resolution required for speech understanding, although speech reception in combination with lip-reading was markedly improved.

A new generation of ABIs has been designed that incorporates penetrating microelectrodes. These implants provide significant benefit in terms of hearing, language, and cognitive development for children who are not candidates for cochlear implantation. [Colletti: 2007]