An auditory brainstem implant converts sound into an electrical signal and sends it to the brainstem, so your brain can create the sense of sound.

An auditory brainstem implant (ABI) is a treatment option for some people with sensorineural hearing loss.

An ABI completely bypasses your inner ear, unlike a cochlear implant, which stimulates the hearing nerve. An ABI may be an option for people who aren’t candidates for cochlear implants, such as people whose auditory nerve doesn’t work as it should.

The procedure is most often recommended for people with neurofibromatosis type 2 (NF2) who have noncancerous tumors on their auditory nerve. The ABI is sometimes also recommended for people with structural differences in the inner ear.

Read on to learn more about the potential benefits and risks of an ABI, who might be a candidate, and what happens during the procedure.

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Illustration by Alyssa Kiefer.

An ABI has two separate parts: the speech processor that you can see from the outside and the internal implant in your brainstem.

The processor receives sound, changes the sound waves into electrical signals, and then sends the signals to a receiver under your skin and to the implant in your brainstem. Your brain turns these signals into sound.

The results of an ABI vary widely between recipients. There are a few potential benefits of the procedure.

Sensory awareness of sounds in the environment

Most people with an ABI have near-to-complete or complete hearing loss. An ABI may help them with perception of environmental sounds.

Improvement in lipreading

People who lipread may find they’re better able to perceive speech when they also use an ABI. The combination of lipreading and an ABI can improve their comprehension.

Understanding of speech

Even without lipreading, the ABI may help with speech perception. Specifically, it may help people follow the rhythm of speech and the rise and fall of vocalizations.

The ABI doesn’t work for everyone. Some people who have an ABI are unable to hear any sounds.

Research from 2019 summarized the results of the more than 1,000 ABI procedures that had been performed worldwide as “mixed.” Still, the researchers noted that without the ABI, the candidates would have had no other option to gain some hearing.

A 2020 health technology assessment reviewed clinical evidence in the existing literature of the effectiveness of an ABI.

The assessment graded the quality of the evidence for those with NF2 and those with severe inner ear abnormalities. According to the assessment, for people with NF2, an ABI may:

  • improve sound recognition (high quality evidence)
  • improve speech perception together with lip reading (high quality evidence)
  • provide subjective hearing benefits (high quality evidence)
  • improve speech perception when used without lip reading (moderate quality evidence)
  • improve quality of life (low quality evidence)

The assessment also found that an ABI may offer these improvements for people with severe inner ear abnormalities, but there was only moderate to low quality evidence for this.

A cochlear implant relays signals to the cochlea in your inner ear. It then stimulates the auditory nerve that sends sound signals to your brain. In contrast, an ABI bypasses your inner ear entirely.

People with a cochlear implant often have open set speech recognition after receiving the surgery. This is the ability to understand speech without visual cues. People who get an ABI rarely achieve open set speech recognition.

There’s a risk that the ABI won’t provide any sound perception.

Possible side effects of the surgery include:

  • leak of cerebral spinal fluid
  • movement of the device
  • nonauditory stimuli

There are also some uncommon side effects, such as:

A doctor will first determine whether you’re eligible for an ABI. This usually means you have NF2 and have lost, or will lose, your auditory nerves. You may also be eligible if you’re unable to use a cochlear implant.

Getting an ABI involves preparation before the surgery and extensive follow-up and rehabilitation after. Here’s an overview of the steps.

Before the procedure

You’ll have extensive consultations before the procedure. This includes setting expectations for the ABI. Sound awareness may be a reasonable goal, but open set speech recognition is unlikely. You’ll very likely have to continue to rely on visual cues to understand speech.

You’ll also have to commit to an auditory or speech rehabilitation program after the surgery in order to get the most benefit from the ABI.

During the procedure

You’ll be under general anesthesia. You shouldn’t be aware of the surgery as it happens.

The surgeon will make an incision in your head behind your ear. They’ll drill a well into your skull to place the ABI receiver. They’ll place the device into the well and close the pocket to stop the device from moving. Then they’ll guide the electrode into the right position and secure it with a piece of Teflon felt.

After the procedure

You’ll spend 24 hours in intensive care. After that, you’ll move to a recovery unit in the hospital. You should be able to go home 3 days after surgery.

The ABI is turned on 6 weeks after the surgery. When the ABI is activated, you’ll be monitored for side effects such as throat tightening, slow heart rate, and losing consciousness.

An ABI may be an option for people who aren’t candidates for a cochlear implant. People who have damage to the auditory nerve, or who face removal of the auditory nerve, are also potential candidates.

If you live with NF2, you may experience a tumor on your auditory nerve. In the process of removing these tumors, a surgeon may have to cut through or remove the auditory nerve. They may put in an ABI during the same surgery or at a later time.

Rarely, an ABI may be an option for someone who:

  • was born with no functioning auditory nerve in either ear
  • lives with total hearing loss due to an unusually shaped cochlea
  • has a damaged cochlea due to meningitis

An ABI requires neurosurgery. It’s rarely performed on anyone who doesn’t have hearing loss as the result of NF2. In 2000, the Food and Drug Administration (FDA) approved the ABI for people with NF2.

Research from 2019 stated that the ABI had been placed in more than 1,000 people across the globe. It also indicated that the largest clinical population that might benefit from an ABI are those who live with NF2. It’s rarely an option for other types of hearing loss.

The ABI may be covered by Medicaid. Private insurers may also cover the procedure under certain circumstances depending on policy wording. For example, they may limit coverage to people over the age of 12 who are getting an ABI because of NF2-related tumor removal.

A private insurance policy may also cover the speech therapy necessary to benefit from the ABI. That coverage is also subject to conditions depending on your policy.

You may want to contact a doctor about potential hearing loss if you:

  • often ask people to repeat themselves
  • can’t hear high-pitched musical instruments like the violin or piano or dripping water
  • turn the television up louder than other people
  • think people mumble

If you live with NF2 or total hearing loss, an audiologist or primary care doctor may be able to help you determine if you may be a candidate for a cochlear implant or ABI.

An auditory brainstem implant is an option for people with hearing loss due to damaged or nonfunctioning auditory nerve. It sends a signal from an outside sound receiver directly to their brainstem, bypassing the inner ear. It can provide some sound perception. To reach the maximum benefit of an ABI, it’s best to participate in speech therapy afterward.