The auditory brainstem implant (ABI) was developed to restore some hearing to people in the situation where cochlear implants cannot be used due to damage to the hearing nerves.
In most cases, these are people with neurofibromatosis type II (NF2) who have tumours in both ears. As a result of the tumours or their surgical removal, hearing is lost and the hearing nerves are destroyed. The ABI bypasses the damaged hearing nerves by placing electrodes on the next centre up the pathway to the brain, the cochlear nucleus complex in the brainstem.
The ABI is usually placed at the time of surgical removal of the acoustic neuroma tumour. It can be placed during the first tumour removal to give time to adjust to the sound before losing all of the hearing in the other ear. The tumour is removed using the translabyrinthine approach. After removal of the tumour, the ABI electrode array is placed on the cochlear nucleus, and tests for electrical auditory responses are performed. These tests are helpful in determining whether the patient will be able to hear sounds from the device.
The overall hearing ability of people who have received ABI’s is generally similar to that of people with earlier simple cochlear implants. Eighty-five percent of people who have received an ABI do have auditory sensations. Auditory Brainstem Implants may be used in children and adults without NF2 who have sensorineural hearing loss who are not candidates for cochlear implants (CI). Reasons for such hearing loss may include an absence of the cochlear nerve, absence of the cochlear itself, ossification from meningitis or trauma.