Lower Dose Radiosurgery Better Preserves Hearing and Facial Nerve Function in Acoustic Neuroma Patients

Newswise — Brain tumors at the base of the skull may be treated effectively with lower doses of radiosurgery to preserve both hearing and facial nerve function using Gamma Knife® radiosurgery, according to the findings being presented at the 77th Annual Meeting of the American Association of Neurological Surgeons in San Diego.

Vestibular schwannomas (frequently called acoustic neuromas) are common skull-base brain tumors that account for 57 percent of all nerve sheath tumors and 5 percent of all primary brain tumors. These tumors arise near nerves that control hearing and movements of the face. Typically, patients notice unilateral (one-sided) or asymmetrical hearing loss, but sometimes these tumors are found incidentally in patients with normal hearing. Other symptoms may include tinnitus (ringing in the ear), and dizziness/loss of balance. These tumors can impact facial nerves, causing facial numbness, weakness, or paralysis on one side of face. If the tumor grows large enough, it may press against nearby brain structures (such as the brainstem and the cerebellum), becoming life-threatening or even fatal.

Researchers at the University of California, San Francisco (UCSF), analyzed outcomes in thousands of patients who underwent Gamma Knife® radiosurgery treatment for vestibular schwannomas. The results of this study, A Systematic Analysis of Hearing and Facial Outcomes after Gamma Knife Radiosurgery for Vestibular Schwannoma, will be presented as the Leksell Radiosurgery Award winner by Isaac Yang, MD, 3:31 to 3:45 pm, on Monday, May 4, 2009. Co-authors are Michael Sughrue, MD, Seunggu J. Han, BS, Derrick Aranda, MD, and senior author, Andrew T. Parsa, MD, PhD.

Gamma Knife® radiosurgery uses sophisticated 3-D computerized imaging to precisely target a high concentrated dose of radiation to the area of interest. Gamma Knife® radiosurgery is one treatment modality that can be used for patients, in addition to observation or microsurgical resection.

"This systematic review of patients represents the largest, broadest analysis to date objectively assessing hearing and facial nerve outcomes in patients with vestibular schwannoma treated with Gamma Knife® radiosurgery," stated Dr. Yang, lead author of the study. In this analysis of 6,438 patients, when Gamma Knife® radiosurgery was used to treat vestibular schwannomas, there appeared to be a good outcome if facial nerve function and hearing was preserved prior to treatment. There was an overall facial nerve function of 96 percent and hearing preservation of 51 percent with an average follow up of almost 4 years.

Patients who had the best facial and hearing outcomes were those patients treated with lower doses of radiosurgery at 13 Gray (Gy) or less. Patients treated with 13 Gy or less had a higher rate of hearing preservation compared to patients treated with higher doses (61 percent versus 50 percent) and improved facial nerve function (98 percent versus 95 percent). Older patients (65 years and older) showed a trend towards improved hearing preservation with Gamma Knife® radiosurgery (71 percent versus 56 percent).

"There are inherent limitations associated with this retrospective analysis, and future prospective studies are needed to investigate the critical factors that contribute to hearing and facial nerve outcomes. Our results from a large sample size confirm what many investigators have shown previously with smaller single institution studies," concluded Dr. Parsa, senior author of the study. Currently, Gamma Knife® radiosurgery is being performed at many medical centers and academic neurosurgery centers, such as UCSF.

Founded in 1931 as the Harvey Cushing Society, the American Association of Neurological Surgeons (AANS) is a scientific and educational association with more than 7,400 members worldwide. The AANS is dedicated to advancing the specialty of neurological surgery in order to provide the highest quality of neurosurgical care to the public. All active members of the AANS are certified by the American Board of Neurological Surgery, the Royal College of Physicians and Surgeons (Neurosurgery) of Canada or the Mexican Council of Neurological Surgery, AC. Neurological surgery is the medical specialty concerned with the prevention, diagnosis, treatment and rehabilitation of disorders that affect the entire nervous system, including the spinal column, spinal cord, brain and peripheral nerves.

The author reports no conflicts of interest.

Media Representatives: If you would like to cover the meeting or interview a neurosurgeon " either on-site or via telephone " please contact the AANS Communications Department at (847) 378-0517 or call the Annual Meeting Press Room beginning Monday, May 4 at (619) 525-6252.