Auditory Brainstem Implant (ABI)

What is an auditory brainstem implant?

An auditory brainstem implant, or ABI, is a device that provides a sensation of sound to people with profound hearing loss due to a missing or nonfunctioning cochlea (inner ear) or hearing nerve. People can achieve better:

• Sound awareness.
• Lip-reading ability.
• Sound recognition, sometimes including word and sentence recognition.

What does an auditory brainstem implant look like?

The implant has two parts:

Processor: You wear this part on top of your ear or on the side of your head. The processor contains a microphone that picks up surrounding sounds. It converts the sounds to an electrical signal and sends the signal to the implant. You remove the processor while you sleep.

Internal implant: A surgeon implants this part, which includes:

• Receiver-stimulator, implanted under your skin on the side of your head, ending in an electrode paddle.
• Electrode paddle, placed on the cochlear nucleus complex, the hearing portion of the brainstem surface.

How does an ABI work?

The electrodes on the paddle activate neurons in your brainstem, creating sound sensations. The technology is similar to cochlear implant technology. But in the cochlear implant, the electrodes stimulate your auditory nerve. An ABI bypasses your auditory nerve to stimulate your brainstem.

Who is a candidate for an ABI?

You may be a candidate for an ABI if you have profound hearing loss because of a nonfunctioning or absent cochlea (inner ear) or auditory (hearing) nerve.

Researchers first developed ABI for people with neurofibromatosis 2 (NF2), a rare genetic disorder. In NF2, tumors called acoustic neuromas form along your auditory nerve. Both the tumors and treatment to remove them can cause permanent damage to your auditory nerve. People often end up with deafness in both ears. Hearing aids and cochlear implants can’t restore hearing in these situations.

Your hearing nerve is like a bridge between your inner ear and brain. When the bridge is out, sound can’t travel to your brain. An ABI bypasses the nerve and directly stimulates your brainstem, from which sound travels to your brain.

People with NF2 were the first to receive an ABI. Since then, these implants have helped other people with profound hearing loss due to nonfunctioning or missing hearing nerves or inner ears. ABI can help infants, children and adults, including those who:

• Are born without a working auditory nerve (aplasia) or with an improperly developed auditory nerve (hypoplasia).
• Are deaf because of an atypically shaped inner ear (cochlea), incomplete inner ear development (cochlear hypoplasia), missing inner ear structures (cochlea aplasia), bone overgrowth (cochlear otosclerosis) or improper bone development (cochlear ossification) in their inner ear.
• Have injured or severed an auditory nerve, possibly due to fractures of their temporal bone (the skull area above the ear) on both sides of their head.
• Have other causes of deafness that a hearing aid or cochlear implant can’t improve.

Is an auditory brainstem implant a type of cochlear implant?

No. Both an ABI and cochlear implant are implanted hearing devices that treat hearing loss, but the devices that are implanted are different.

Cochlear implant

• Used for: People whose hearing loss arises from the cochlea (inner ear) who still have a working auditory nerve. This is a much more commonly used device than an ABI.
• Works by: Bypassing your inner ear and directly stimulating your auditory nerve.
• Type of surgery: Usually outpatient. Most people go home the same day.

Note: Many people who refer to their hearing loss as “nerve deafness” really have hearing loss arising from the cochlea. Check with your audiologist or ear, nose and throat doctor (ENT) before assuming you wouldn’t be a candidate for a cochlear implant.

Auditory brainstem implant

• Used for: People with profound hearing loss due to missing or nonfunctioning cochlea and/or auditory nerve
• Works by: Bypassing your inner ear and auditory nerve to stimulate your brainstem’s hearing pathways directly.
• Type of surgery: Much more complex than a cochlear implant. Usually involves both a neurotologist (ear surgeon) and a neurosurgeon (brain surgeon). Usually requires inpatient stay.

What happens before an auditory brainstem implant?

Here’s what you can expect before an auditory brainstem implant:

• Behavioral testing: Audiologists will measure your hearing ability with and without hearing aids.
• Communication evaluation: A speech-language pathologist may assess your language development and communication style.
• Electrophysiologic testing: Audiologists will conduct tests to evaluate the extent and location of hearing loss.
• Imaging studies: You may have a CT scan and MRI to examine your cochlea, auditory nerve and surrounding structures.
• Medical history: Your healthcare provider will ask you about your medical history and hearing loss.
• Neuropsychological evaluation: Your provider will evaluate your level of brain function and capacity.

Who performs auditory brainstem implant surgery?

The implantation surgery requires an expert surgical team working together. The team typically includes a(n):

• Neurosurgeon (brain surgeon).
• Anesthesiologist, who manages pain relief and keeps you from moving during surgery.
• Neurotologist, a board-certified otolaryngologist with special training in providing surgical care for people with auditory nerve conditions.
• Electrophysiologist and audiologist, who perform testing during the procedure to make sure the device functions well and help fine-tune the placement of the electrode paddle.

When is the auditory brainstem implant surgery performed?

If you have NF2 that causes an acoustic neuroma, the tumor removal surgery may result in hearing loss. Your surgical team will usually implant the ABI during the tumor removal surgery.

You may have a separate surgery to implant the ABI if you:

• Had a previous surgery or radiation therapy for NF2 or another condition.
• Have inner ear malformation, trauma or other causes of deafness, and a cochlear implant won’t help.

How long will I be in the hospital after surgery?

You’ll probably be in the hospital for two to four days after the surgery. The hospital stay may be longer depending on the specific condition and type of surgery. Your team programs the device during surgery and activates it a few weeks later.

What are the advantages of an auditory brainstem implant?

An ABI can’t restore typical hearing, but it can improve sound awareness and identification and lip-reading ability. Results vary widely.

Children who receive an ABI at a young age (after a short period of deafness) tend to have more word understanding compared to adults with NF2 (who’ve had a long period of deafness).

Other factors that can impact outcomes in addition to length of profound deafness can include participation in hearing therapy after surgery, the size and position of the tumor, and other medical factors.

Talk with your healthcare provider to carefully weigh the risks and benefits. Together, you can make an informed decision for your health.

What are the risks of this procedure?

An auditory brainstem implant is a complex neurosurgery. Any brain surgery comes with risks. It’s also difficult to predict how well an ABI will work for you. Your care team can help you decide if this surgery is right for you.

Are there complications of auditory implant surgery?

The complication rate for ABI surgery is low, especially if an experienced team performs your surgery.

Your surgical team will discuss possible complications of the surgery and how to treat or manage them. Complications include:

• Cerebrospinal fluid leaks.
• Implant failure (when the device doesn’t provide useful auditory sensations or electrodes move out of place).
• Non-auditory stimulation (when the device causes uncomfortable stimulation of structures other than the hearing centers).
• Incomplete tumor removal.
• Meningitis.
• Palsy of your facial nerve (nerve damage that causes loss of facial movement).
• Wound infection.

What is the recovery time after surgery?

You’ll likely be in the hospital for two to four days. If you have NF2 and had tumor removal at the same time, you may need a longer hospital stay. Your team will program the ABI in the PACU (Post Anesthesia Care Unit).

Activating the device happens about four to six weeks after surgery. Your care team adjusts the device programming over a few days, then monthly during the first year after surgery.

Does an ABI restore normal hearing?

No, an auditory brainstem implant can’t restore typical hearing. It does improve:

• Sound awareness.
• Ability to detect and distinguish sounds (a child voice vs. an adult voice).
• Ability to identify sounds in the environment (dog barking vs. phone ringing).
• Lip-reading ability, resulting in better face-to-face communication.

What are the results of ABI surgery?

Researchers have found that results differ by patient group. People without NF2 typically have better hearing outcomes than people with NF2.

Children, with or without NF2, can become aware of sounds around them and have better language development. Children’s hearing abilities continue improving in the years after the surgery.

When should I see my healthcare provider?

If you have fever or pain after ABI surgery, contact to your healthcare provider. Your team will monitor you carefully after surgery to prevent complications. You’ll also need to return to your audiologist after the surgery to adjust the programming on the device.

A note from Cleveland Clinic

An auditory brainstem implant (ABI) can bring sound to people with profound hearing loss. An ABI may help people who have a missing or nonfunctioning cochlea (inner ear) or auditory nerve from neurofibromatosis 2, an acoustic neuroma or other conditions. You may achieve better sound awareness and lip-reading ability with an ABI. Talk to your healthcare provider about whether an ABI might be right for you.