Evaluation of hearing function after Gamma Knife surgery of vestibular schwannomas

Due to technological advances in neuroradiology in recent years, incidental diagnoses of vestibular schwannomas (VSs) have increased. The aim of this study was to evaluate the hearing function after treatment with Gamma Knife surgery (GKS) for VSs in patients adequately selected with "good" or "useful" hearing before treatment and to assess the possible predictive factors for hearing function preservation.

Of all patients treated in the authors' hospital between 2001 and 2007, they retrospectively studied 50 patients with a unilateral VS in whom there was serviceable hearing (Gardner-Robertson [GR] Class I or II). Additional inclusion criteria were: no Type 2 neurofibromatosis, no previous treatment, and at least 6 months' follow-up of neuroradiological and audiological data. The median patient age was 54 years (range 24-78 years). The median tumor volume was 0.73 ml (range 0.03-6.6 ml), and the median radiation dose to the tumor margin was 13 Gy (range 12-16 Gy) with an isodose of 50%.

Patient age, tumor volume, and presenting symptoms were found to correlate with hearing function. At a median of 36 months after radiosurgery, tumor growth control was 96% and no patient required any other additional treatment. Serviceable hearing was preserved in 34 patients (68%): 21 (62%) with GR Class I hearing and 13 (38%) with GR Class II hearing. The remaining 16 patients had poor hearing function:15 with GR Class III and 1 with GR Class IV hearing function. In 19 (58%) of 33 patients with GR Class I function before GKS the same class was maintained posttreatment; 29 (88%) maintained functional hearing (GR Class I or II). In all patients with an intracanalicular lesion, functional hearing was maintained. Significant prognostic factors for maintaining serviceable hearing were GR Class I function before treatment, symptoms at presentation, patient age younger than 54 years, and Koos Stage T1 disease.

The results of the study show that the probability of preserving functional hearing in patients undergoing GKS treatment for unilateral VSs is very high. Patients with GR Class I, age younger than 54 years, with presenting symptoms other than hearing loss, and a Koos Stage T1 tumor have better prognosis. The prescribed dose of 13 Gy appears to represent an excellent compromise between controlling the disease and preserving auditory function.