Auditory Brainstem Implant (ABI)

What is an auditory brainstem implant (ABI)?

An auditory brainstem implant (ABI) is a surgically implanted device that delivers the sensation of sound to people with severe hearing loss. An ABI can improve the ability to lip read, sound awareness and sound recognition.

AN ABI device has two parts:

• Processor: Contains a microphone which picks up sounds, converts them to an electrical signal and sends it to the implant. The processor is worn on the side of the head or on top of the ear.
• Implant: Surgically implanted, this consists of a receiver-stimulator, which is placed under the skin on the side of head. This has an electrode paddle at the end, which is placed on the cochlear nucleus complex, the part of the brainstem surface responsible for hearing. This activates neurons in the brainstem and creates sound sensations.

How does an ABI work?

Our hearing nerve passes sound between the inner ear and the brain. If it is damaged, sound can’t reach the brain. An ABI acts as a bridge to bypass the nerve and directly stimulates the brainstem, passing sound to the brain.

An ABI is similar to cochlear implants, but instead of stimulating the auditory nerve, it bypasses it to stimulate your brainstem. Cochlear implants are more common and can help people with hearing loss arising from the cochlea but whose auditory nerve still works. An ABI helps people with hearing loss due to nonfunctioning or missing cochlea and/or auditory nerve.

Who is a candidate for an ABI?

ABI may be suitable for people with profound hearing loss due to a nonfunctioning or missing cochlea or hearing nerve, or because they have the rare genetic disorder neurofibromatosis 2 (NF2).

NF2 causes acoustic neuromas (a type of tumor) to form along the auditory nerve and damage it. The surgery to remove these tumors can also damage the nerve, and cochlear implants and hearing aids can’t restore hearing.

An ABI can help people who are deaf due to:

• An atypically shaped inner ear (cochlea)
• An incomplete inner ear (cochlear hypoplasia)
• Bone overgrowth (cochlear otosclerosis)
• Improper bone development in the inner ear (cochlear ossification)
• Missing inner ear structures (cochlea aplasia)An ABI can also help people who:
• Were born with an auditory nerve that wasn’t properly formed (hypoplasia)
• Were born without a functioning auditory nerve (aplasia)
• Have an injured auditory nerve, due to fractures to the skull near the temporal bone on both sides
• Are deaf due to other causes that can’t be improved with a hearing aid or cochlear implant

What happens during an ABI procedure?

Before an auditory brainstem implant, your doctor will perform a thorough physical examination as well as a number of tests and evaluations, which may include:

• Behavioral testing, to measure hearing ability with and without hearing aids.
• Communication evaluation to assess language development and communication.
• Electrophysiologic testing to evaluate the location and extent of hearing loss.
• Imaging studies to examine the auditory nerve, cochlea and surrounding structures.
• Neuropsychological evaluation of brain function and capacity.

The implantation surgery will be performed by a team which may include a neurosurgeon, anesthesiologist, neurotologist (an otolaryngologist with special training in auditory nerve conditions) electrophysiologist and audiologist.

What happens after an ABI procedure?

The amount of time you spend in the hospital following ABI surgery will depend on the type of surgery and the specific condition but is typically a few days. You will return a few weeks later and the ABI device will be activated.

An ABI won’t restore ‘normal’ hearing, but can improve sound identification and awareness, and lip-reading ability. The results will vary from person to person and will be dependent on factors such as the degree and length of deafness.

Are there risks associated with ABI surgery?

An ABI procedure is a complex neurosurgery, and as with all brain surgery, is associated with some degree of risk. When performed by an experienced team, the risk of complications from ABI surgery is low.