Physicians at the University of Illinois Medical Center at Chicago performed a rare surgery this week to restore hearing to a deaf patient.
Marisela Leon, 44, has neurofibromatosis type 2 -- a rare genetic condition that causes tumors to grow on nerves in the brain or spinal cord, but most commonly on the auditory nerve. Leon lost her hearing more than four years ago when surgery to remove a tumor damaged her auditory nerve.
NF2 affects an estimated one-in-15,000 to one-in-35,000 in the United States. It is characterized by the growth of benign tumors on the auditory nerve, hearing impairment, ringing or fullness in the ear, imbalance, and facial numbness or twitching. Left untreated, an NF2 tumor may compress the brain with fatal results. While surgery may be life saving, it may also result in damage to the auditory nerve that can cause deafness.
Leon had another NF2 tumor requiring surgical removal. Dr. G. Michael Lemole, UIC assistant professor of neurosurgery, removed the tumor, and Dr. Thomas Haberkamp, professor of otolaryngology head and neck surgery, implanted an auditory brainstem implant (ABI) device during the procedure on Dec. 15.
The implant bypasses the damaged auditory nerve and can restore sound perception. An implanted electrode array stimulates the cochlear nuclei in the brainstem, delivering coded signals transmitted from sounds picked up by a small microphone placed behind the patient's ear.
The auditory brainstem implant surgery has only been performed approximately 600 times worldwide, says David Klodd, assistant director of audiology, otolaryngology head and neck surgery.
"We will be following her progress closely to learn from her experience," Klodd said. "Because this treatment is so rare, it's important to study each individual's performance."
This is the first auditory brainstem implant at the University of Illinois Medical Center at Chicago. Dr. William Hitzelberger of the House Ear Institute in Los Angeles, who was part of the team that developed the ABI, will join the UIC team to observe the surgery.
Leon has been waiting for this surgery for years, Haberkamp said.
"UIC's comprehensive center for hearing healthcare, including hearing implants through to rehabilitation, is the ideal setting for this complex treatment," he said. "We have a unique skull base surgery team that includes experts in neurosurgery, otolaryngology, audiology, neuropsychiatry, radiation therapy, radiology and plastic surgery able to treat a broad patient population from children to adults."
The ABI system consists of a receiver/stimulator that is implanted into the temporal bone, a speech processor worn on the body, and a microphone. The device is similar in concept to the cochlear implant, except that the electrode design and surgical placement are aimed at the cochlear nuclei deep in the brainstem. Patients who have had the auditory nerve severed are not candidates for hearing aids or cochlear implants.
After implantation, a long period of rehabilitation begins, during which the patient works with an audiologist who programs the device. Using a computer, the device is first set to an appropriate loudness, said Klodd, who will work with Leon following the surgery. The audiologist will then work to adjust the pitch, relying on Leon's memory of sound.
Klodd will keep an elaborate scorecard that allows him to track performance with each set of electrode pairs.
Although the auditory brainstem implant does not restore normal hearing, with lip-reading most patients can once again communicate easily with their family and friends.
"In most cases, we can expect the auditory brainstem implant to continue to work for the rest of the patient's life," Klodd said. "The patient with the very first ABI still has the original implant more than 29 years later."