April 2018 Newswise
Patients with rare brain tumours on the auditory nerve now have an option to prevent complete deafness at UC San Diego Health. The device called an auditory brainstem implant or ABI, fits behind the ear and connects directly to the brainstem. The device enables patients with neurofibromatosis type 2 (NF2) who develop bilateral hearing nerve tumours to be aware of environmental sounds, such as a door opening, a phone ringing or a car approaching.
“An auditory brainstem implant can have a profoundly positive impact on a patient’s quality of life,” said Marc Schwartz, MD, a neurosurgeon at UC San Diego Health. “The device helps patients to perceive sound and communicate more effectively through lip reading. It was designed for patients with NF2 who may not benefit from traditional hearing devices. The highest performing patients with ABIs may develop the ability to understand some speech.”
NF2 is an inherited disorder. There are two forms of the disease. In one form, patients develop growths called acoustic neuromas in both ears, which usually leads to complete deafness. A more aggressive form of the disease results in tumours throughout the brain and spine.
“Auditory brainstem implants can help restore sound perception to patients with NF2. This is critically important as a matter of safety and the ability to communicate with the world,” said Rick Friedman, MD, PhD, neurotologist. “These implants are appropriate for NF2 cases where the hearing is already lost or when the tumours have become so large that surgery is indicated and hearing preservation is not possible.”
Friedman and Schwartz make every attempt to preserve hearing in their patients. When NF2 is diagnosed with small tumours, and hearing is intact, the team will delicately remove the tumours. The team’s hearing preservation rates with the middle fossa approach are close to 80 percent. Early detection and treatment of these tumours can eliminate the need for an ABI.
The ABI procedure is normally performed simultaneously with the removal of the auditory nerve tumour. An ABI has two parts: a sound processor, worn behind the ear, and an implant that connects below the skin. A microphone on the processor picks up noises that are converted into electrical signals that are delivered to the brain. The implant bypasses both the cochlea and the hearing nerve, taking a shortcut to the brainstem. Patients over the age of 12 are eligible for this implant surgery.
After healing of the incision, the first sound processor fitting takes place. This initial stimulation session or “switch-on” is the first opportunity for the audiologist to determine if the ABI is providing hearing sensations. Using a computer, the audiologist will work with the patient to determine the most comfortable sound levels. Because the brain takes time to adapt to the electrical signals and to learn how to interpret these new sounds, several appointments are initially required. Over time, the number of visits decreases.