Stereotactic radiosurgery of skull base meningiomas

Between April 1992 and March 1994, 48 patients with skull base meningiomas were treated at our department. The age of these patients ranged from 10 to 76 years. The male:female ratio was 1:3. Thirty-seven of these patients had primary open surgery for partial removal and subsequent radiosurgical treatment. In 1 patient a recurrent meningioma after so-called total microsurgical removal was treated radiosurgically. Radiosurgery was performed as a primary treatment in 11 patients. The mean tumor volume was 13.7 cm3 (range: 0.8-82 cm3). These tumor volumes could be covered by mean isodose volumes of 44% (range: 30-70%) and were treated by a mean dose of 15 Gy (range: 8-25 Gy) at the tumor border. One patient underwent radiosurgery with a staged treatment protocol with a 4.6-month interval. In 37 patients, a total of 102 follow-up scans were available. The remaining 11 patients have not been included in the postradiosurgical evaluation, since the observation time was either too short or the patients were lost to follow-up. The mean interval between Gamma Knife treatment and the last follow-up scan was 12 months, with a range from 2.3 to 22.7 months. Follow-up imaging (CT, MRI or both) revealed a decreased volume of the tumor in 9 cases (24%). In 25 cases (68%), tumor progression was stopped, and in 3 cases (8%) increased tumor volumes could be observed (2 patients with malignant meningiomas). In 3 cases marked central tumor necrosis was seen. Neurological follow-up examinations (n = 38 patients) showed a stable neurological status in 74%, ameliorated status in 13% and worsening in 13% of the patients.