ANN ARBOR, MI - Christine Warner had never heard the sound of her youngest granddaughter's laugh. Fifteen-month-old Michelle was born around the time her grandmother lost her hearing due to a rare condition, known as neurofibromatosis type II. This hereditary disorder causes non-cancerous tumors to grow on the hearing and balance nerves.

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Numerous surgeries to remove these "acoustic neuromas" on both sides of her head had left the 42-year-old completely deaf. Faced with a life of silence, Warner opted instead to undergo a complex surgical procedure at the University of Michigan Health System that would give her the chance for a new kind hearing with a "bionic ear."

"Christine was faced with very few options because her latest tumor was continuing to grow, she had no hearing at this point and there was no way to restore her hearing," explains Alexander Arts, M.D., a neurotologist in the U-M’s Department of Otolaryngology. "We felt that an auditory brain implant - or ABI - would give her a good chance at hearing again."

"I was very excited to be part of something so new, to be the first patient at the University of Michigan to have the ABI," says Warner. "I had dreaded going deaf all along and then suddenly there was an open door back into hearing," she says.

Surgery to remove acoustic neuromas is extremely delicate. Typically the neuromas grow right next to the facial nerve, pushing it aside and causing some degree of scarring. Surgeons must tread lightly to separate the tumor from the nerve without damaging it.

The second phase of surgery, to insert the ABI, is also highly specialized and invasive. Surgeons operate through a microscope on the brain stem, which acts as a funnel for virtually all of the functions of the brain, including bodily movement, coordination and sensation, as well as facial movement and the senses of sight, smell, taste and hearing.

"Everything, with respect to one’s consciousness, goes through the brain stem," says U-M neurosurgeon Gregory Thompson, M.D. "Because it’s such an important area, it has to be operated on very carefully with great, meticulous technique."

To create a new brain stem-based connection for hearing, surgeons implant an electrode array onto the surface of the brain stem directly over the hearing nerve, called the cochlear nucleus. This array is then connected to a package of electrodes implanted underneath the skin behind the ear. An antenna in this package allows the implanted device to communicate with the external hardware, which consists of a microphone and batteries.

"After the device is implanted, while the patient is still asleep in the operating room, we stimulate it and then electronically trace the brain stem auditory response to determine if the patient is hearing sound," explains Thompson. "We move it around, and once the best position is found, we pack the device into place and close the wound."

About 80 percent of patients who receive an auditory brain implant are able to hear sound again. "Most of them hear sound that enables them to be aware of their environment, and it improves lip reading," says Arts.

When doctors first activated Warner's implant, it failed. Arts says the device likely shifted during healing. After a tough decision to undergo a second surgery to reposition the device, Warner was ecstatic when it worked, and she was finally able to hear again. "It was very emotional for me when I realized that it really did work for me, and it was amazing to know that I was hearing with my brain and not my ears," says Warner.

Over time, Warner has come to understand the hard work that’s involved with learning how to hear with a bionic ear. "People's voices and ordinary noises sound a little bit different. I still have to lip read, but I think that eventually I'll be able to understand speech better and won't have to rely on that as much."

But for now, Warner is just happy to be able to hear the voices of the people she loves. "Because I was losing my hearing at the time my youngest granddaughter was born, I had never heard her voice," she says. "It’s so wonderful now to be able to hear her say ‘mama’ and listen to her giggle when we play together."

Not everyone who undergoes this surgery is as fortunate as Warner. According to Arts, one in five patients do not develop hearing with an ABI.

"Unlike with a cochlear implant, a more common and reliable implant used in patients whose hearing nerve is still intact, a significant number of patients who have an auditory brain implant don’t have any benefit," he says. "There are a number of factors which we don't fully understand yet, but we do know that the electrode array can be difficult to place and it can move post-operatively, as in Christine’s case."

Despite its limitations, both Arts and Thompson see real promise with this device and others like it.

"It's the beginning of a real expansion of what we call neural prostheses - devices with which we’ll be able to artificially stimulate the nervous system, possibly in the areas of sight or even sensation and movement after spinal cord injuries," says Arts.

"Now, with ever improving computer technology, we can begin to think about restoring the nervous system piece by piece," says Thompson. "As a neurosurgeon, this is particularly exciting because it allows me to take a patient who’s lost a function and try to restore it for her - there's nothing to compare to that."

Facts about acoustic neuromas

• Acoustic neuromas are benign tumors that grow on the cochleovestibular nerve.
  
• About one per 100,000 people are diagnosed with acoustic neuromas

For additional information

National Institute of Neurological Disorders and Stroke (NINDS): Neurofibromatosis
www.ninds.nih.gov/health_and_medical/disorders/neurofibro.htm

Written by Maria White

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