Neurofibromatosis type 2. Preliminary results of gamma knife radiosurgery of vestibular schwannomas

Background and purpose. - The aim of this study was to assess tolerance and efficacy of gamma knife radiosurgery on vestibular schwannomas for patient s affected with neurofibromatosis type 2. Methods. - Between July 1992 and December 1997, a gamma knife procedure was performed on 35 vestibular schwannomas affecting 27 patients (12 females a nd 15 males, mean age = 27 years-old, range: 14-65). Fifteen of the patient s were included in the Wishart subtype (severe form) and 12 patients in the Gardner subtype (mild form). This group of 27 patients represented 8,2 % o f the total group of vestibular schwannomas radiosurgically treated by our team. The mean tumor volume was 4 000 mm(3) (range : 400-14 400 mm(3)) and staging according to Koos classification was 9 stade 2 tumors (extension in the cerebellopontine angle), 19 stade 3 tumors (in contact with the brain stem or cerebellum) and 7 stade 4 tumors (compression of axial structures). The delivered mean marginal dose (50 % isodose) was 13 Gy (range: 10-18 Gy ). After the treatment, the mean clinical and radiological follow-up was 32 months (range: 6-70). Results. - Twenty six (74 %) of the treated tumors were controlled by the t reatment (15 stabilisations and II regressions of the tumor volume) at last follow-lip. One microsurgical removal was required in a growing stade 4 tu mor and in 2 cases of growing stade 3 tumors. Three post-radiosurgical faci al nerve deficits (9 %) were observed, 2 of them were transient. According to the Gardner and Robertson classification, classes I (good) and II (servi ceable) hearing were preserved at last follow-rip in 57 % of the patients h aving the same hearing level prior to the gamma knife. Conclusions. - Our experience confirms that tolerance of gamma knife radios urgery compares favorably with microsurgery of bilateral vestibular schwann omas. This treatment should be restricted to small and medium growing tumor s. Treatment strategy of neurofibromatosis type 2 patients should be planne d by multidisciplinary experienced teams disposing of the whole armamentari um A longer follow-lip study is required to confirm the current results reg arding the tumor control rate.