[Preserving hearing function after Gamma Knife radiosurgery for unilateral vestibular schwannoma]. / Préservation de l'audition dans le traitement par radiochirurgie Gamma Knife des schwannomes vestibulaires unilatéraux.

OBJECTIVE: The majority of the patients still lose hearing function in spite of the technical advances in microsurgery. We wanted to evaluate preservation of hearing function potential after Gamma Knife Surgery. MATERIAL AND METHOD: In Marseille, we performed 1000 Gamma-Knife procedures for vestibular schwannomas between July 1992 and January 2002. This population included 175 patients undergoing first intention surgery for a unilateral schwannoma with functional preoperative hearing (Gardner and Robertson 1 or 2) who were studied with a follow-up longer than 3 Years. Univariate and multivariate analysis was performed. RESULTS: Numerous parameters significantly influenced the probability of functional hearing preservation at 3 years. The overall rate of preservation was 60%. The main parameters of predictability were limited hearing loss (Gardner and Robertson stage 1 versus 2) before radiosurgery, presence of tinnitus as the initial symptom, young age and the small tumor size. Preservation of functional hearing at 3 years was 77.8% when the patient was initially in stage I, 80% when the patient's first symptom was tinnitus, and 95% when the patient had both. In these patients, the probability of functional preservation at 5 years was 84%. CONCLUSION: We report a large population of patients treated by radiosurgery with initial functional hearing. These results demonstrate that a large percentage of selected patients can preserve functional hearing after Gamma Knife Surgery, their chances of functional preservation being greater than after microsurgery or simple surveillance.