For potential candidates, an ABI offers a choice, one that they dId not have prior to the FDA approval of the devIce.
The Food and Drug Administration (FDA) has recently approved the clinical use of an auditory brainstem (ABI) implant. This type of implant is different from a cochlear implant in which an electrode is inserted within the cochlea. The cochlear implant depends upon an intact auditory nerve to transmit the electrical signals from the cochlea to the auditory centers in the brain. Since its clinical introduction a generation ago, this device has evolved into a routine clinical procedure of great benefit for people with severe-to-profound hearing losses, both children and adults.
The ABI, on the other hand, is designed for people whose auditory nerves have been severed or partially cut during surgery or are completely non-functional for other reasons. These people are completely and profoundly deaf. For the most part, they exhibit a condition known as neurofibromatosis Type II (NF2), a genetic problem that affects one in 40,000 people. Individuals with NF2 have tumors that frequently grow on both auditory nerves. When these tumors are removed, it is often necessary to also cut through auditory nerves as well. This precludes the use of a traditional cochlear implant. With an ABI, however, the electrodes are placed at a higher stage in the auditory system, in the cochlear nucleus located in the brainstem. This is the point at which the auditory nerves terminate as they leave the cochlea.
As far as I know, only one company makes auditory brain stem implants, the Cochlear Corporation. In addition to the processor itself, and the implanted portion that fits behind the ear, the unique portion of the Nucleus 24 ABI consists of 21 platinum disk electrodes arranged on a flat backing that is placed on the surface of the brain stem. These electrodes are designed to stimulate multiple sites on the cochlear nucleus, using any of the three coding strategies now employed with cochlear implants.
While the auditory benefits of the ABI are much less than that obtainable with a cochlear implant, these benefits can still be substantial from the viewpoint of patients. They no longer feel isolated in a completely soundless world. They are able to detect all types of environmental sounds and identify many of them. They can hear themselves when they talk and thus monitor their own speech productions. While they would be unable to understand speech through the ABI alone, the sound that they receive can improve their speechreading ability, much like the single channel cochlear implants of a generation ago.
Ongoing research, at the House Ear Institute and other research institutions, is aimed at the development of a new generation of sophisticated penetrating electrode array designed to improve frequency discrimination and sound quality The goal is to provide some speech perception capabilities. For potential candidates an ABI offers a choice, one they did not have prior to the FDA approval of the device.
From Hearing Loss, November/December, 2001.
Acknowledgement: This column is supported, in part, by GRANT #133E980010 from the U.S. Department of Education, NIDRR, to the Lexington Center.
Mention of products or companies by the author does not Indicate SHHH endorsement, nor should exclusion suggest disapproval. Since everyone's communication problems and needs vary, SHHH suggests consulting with your hearing health professional.