Even when they're extremely small, tumors on the nerves that connect the brain to the ear can wreak havoc on a person's hearing and balance. But removing them is a delicate process that can, in some cases, cause further harm.
That's why a new study from the University of Michigan Medical School is encouraging. Researchers found high rates of success at preserving patients' hearing when a particular type of procedure was used to remove the tumors, which are known as acoustic neuromas or vestibular schwannomas.
The study, published in the latest issue of the journal Otology & Neurotology, examined the cases of 73 patients with acoustic neuromas who were operated on between 1999 and 2005 using a procedure known as the middle cranial fossa, or MCF, approach. Of the people in the study who had useful hearing before the surgery, about three-quarters retained a level of useful hearing after their tumors were removed.
"Hearing preservation rates have not always been high following the removal of acoustic neuromas," says H. Alexander Arts, M.D., professor of otolaryngology at the U-M Medical School. "The important message with this research is that if you present to us with a small acoustic neuroma, we have a very good chance of preserving your hearing."
The issue of how to preserve the hearing of patients with small acoustic neuromas has become increasingly significant in recent years, with the widespread use of magnetic resonance imaging resulting in the diagnosis of the tumors much earlier than in the past. When very small lesions are detected in people with excellent hearing, Arts notes, hearing conservation is a primary goal of the treatment.
There are several surgical approaches for removing acoustic neuromas. Only two, the MCF approach and the "suboccipital" approach, allow for the possibility of hearing preservation. The suboccipital approach comes from behind the ear, and the MCF approach is from above the ear. Smaller tumors usually can be removed much more easily and with less chance of injury to the hearing nerve using the MCF approach.
Hearing status in the study was classified as A, B, C or D, with Class A being the best. Sixty-two people had Class A or B hearing (referred to in the study as "useful hearing") before the procedure, and of those, 45 people (73 percent) remained in Class A or B afterward. Three people began with Class C, with two of them remaining at that level afterward; eight patients began with Class D hearing, and one of them improved to Class C.
One of the best gauges of success was that a large number of patients with the highest level of hearing did not deteriorate significantly after the procedure. Of the 34 patients who began with Class A hearing, 27 people (80 percent) maintained Class A or B hearing. Ninety-six percent of patients experienced excellent or satisfactory facial nerve outcomes.
Arts notes that previous analyses of hearing preservation have indicated about a 30 percent rate of hearing preservation when techniques other than MCF were used. Since the more widespread use of the MCF approach, and because tumors are now being diagnosed when they are smaller due to more improved MRI imaging techniques, hearing preservation rates have been improving. The results presented in this study represent the highest hearing preservation rates published to date.
In addition to Arts, who also has an appointment in the Department of Neurosurgery, the authors on the paper were Steven A. Telian, M.D., and Hussam El-Kashlan, M.D., of the Department of Otolaryngology at U-M, and B. Gregory Thompson, M.D., of the departments of Neurosurgery and Otolaryngology at U-M.
Reference: "Hearing Preservation and Facial Nerve Outcomes in Vestibular Schwannoma Surgery: Results Using the Middle Cranial Fossa Approach," Otology & Neurotology, 27(2):234-241, February 2006.
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