Hearing aids have gotten so small and so powerful, they are now barely noticeable. Advances in technology are not just helping external aids to improve hearing, though. New internal implants have been developed to replace damaged or missing auditory nerves.
Dr. Ravi N. Samy is a Neurotology at the University of Cincinnati Gardner Neuroscience Institute and the Program Director of the Neurotology Fellowship at the UC College of Medicine. His research focuses on neurofibromatosis type 2: tumors which develop along the nerve that carries information from the inner ear to the brain. Dr. Samy shares his findings and experience in this edition of Write Advice.
HealthScene Ohio: What is the difference between hearing aids, cochlear implants and auditory brainstem implants?
Dr. Ravi Samy: When we hear, sound travels into the ear, through the cochlea, along with the cochlear nerve to the brainstem and then to the higher centers of thinking, learning, and language. A hearing aid is an external device that amplifies sound before it goes into the ear. The cochlear implant is an electrode that goes into the inner ear (cochlea) and directly stimulates the auditory nerve. An auditory brainstem implant (ABI) is like a cochlear implant, the difference is that it goes into the brainstem.
HSO: What determines if a patient needs a cochlear implant verse an auditory brainstem implant?
RS: If the cochlear nerve is gone or the cochlea is unusable, then I can’t put in a cochlear implant, so I do a brainstem implant. An ABI acts as the nerve for hearing. A microphone and processor sit behind the ear to pick up sound. This sound is sent to a decoding chip under the skin and the electrodes attached to the brainstem alert the brain to sounds. It is most often used on patients with destroyed auditory nerves, like neurofibromatosis type 2 (NF2) patients, a disease that causes tumors in the ears.
HSO: Which procedure is more common, cochlear implant or brainstem implant?
RS: Worldwide, there are about 300,000 cochlear implants that have been done. Cochlear implants were FDA approved in 1984 for adults and 1989 for children. ABI was approved in 2000. Worldwide there are only about 600 to 900 ABIs. It tells you just the magnitude of difference; ABI is such a rare thing. The majority of patients that know about ABI will have NF2.
HSO: Why isn’t ABI done more often?
RS: For patients who still have an auditory nerve, cochlear implants are a better option. ABI is a challenge because it not only has to be the right surgical team, it also has to be the right patient with the right level of motivation and family support. The patient has got to understand that this is a device that has the ability to improve lip-reading skills and has the ability to improve sound awareness, but it’s never going to be complete and normal hearing.
HSO: You stated that ABI is most often performed on people who develop a tumor that damages the auditory nerve, but are there other patients who may benefit from this same procedure?
RS: We’re now trying to put more into pediatric patients because some kids are born without cochlear nerves. We’re starting to see success in younger kids. If they don’t have cochlear nerves, maybe the brainstem implant can get them to hear again.
Most adults that are candidates for ABI are NF2 patients, but we also have patients with meningitis. We try to get cochlear implants in as soon as possible but sometimes meningitis has a reaction that causes bone and scar formation within the cochleae. If you wait too long, you can’t get the cochlear implants in at all, so we must use a brainstem implant instead.
HSO: What are some of the risks of this surgery?
RS: Anything you are putting around the brain or the brainstem has a rare (1%) risk of stroke, seizures, or meningitis. You have to be careful that the patients understand the risk-benefit ratio, and if it’s worth it. They are not guaranteed to hear perfectly with implants. I think the data in the pediatric population is better than the adult population because the brain of a child is still growing and responding.
HSO: How long is the recovery time for patients?
RS: Usually, the hospital stay is about three days, one day in the ICU, but we technically activate the device with our audiologists about a month post-op. We will also tell the patients ‘no heavy lifting, no straining, no nose-blowing’ for a solid month after surgery.
A lot of the recovery is up to the patient. Implants are not like putting on a hearing aid or putting on glasses. Patients need to follow up with their audiologist and do the training and auditory therapy. The more time patients spend learning to work with these new devices, the better they will do.
HSO: What’s the next research frontier for hearing implants?
RS: I think that there are still areas fruitful for research. Even though ABIs started in 1979, it’s still not a result that is comparable or near as good as cochlear implants. For example, an adult with a cochlear implant can typically talk on the phone again, but very few adults with an ABI can do that. However, we’re seeing better results with the kids: some children may be able to talk on the phone over time.
We’re understanding that a lot of the battle is lost or won at the brain and its neuroplasticity (the brain's ability to reorganize itself by forming new neural connections). That’s probably why kids are doing better than adults. We are trying to see if different neurosurgical approaches to placing the ABI are helpful and impact the neuroplasticity.
Maria Lubanovic is a contributing writer. Feedback welcome at feedback@cityscenemediagroup.com.
About the Expert
Dr. Ravi N. Samy has been a Neurotologist at the University of Cincinnati Gardner Neuroscience Institute and the Program Director of the Neurotology Fellowship at the UC College of Medicine since 2005. He is also the director of the Adult Cochlear Implantation Program at the University of Cincinnati Medical Center (UCMC), as well as an associate professor of Otolaryngology at the College. After graduating from Duke University magna cum laude with a bachelor’s degree in zoology, Dr. Samy attended the Duke University School of Medicine until his graduation in 1995. He completed his residency training at Stanford University School of Medicine and spent two years at the University of Iowa as a Neurotology fellow.
