Gamma knife radiosurgery of skull base meningiomas

Despite all advances and refinements in microneurosurgical techniques skull base meningiomas still have to be considered as inoperable tumors concerning radicality without putting the patient at high risk for severe or even life-threatening sequelae. As an adjuvant or alternative modality between April 1992 and November 1996 in 128 patients with skull base meningiomas 135 Gamma Knife radiosurgical procedures were performed. The age of these patients ranged from 10-80 years. Radiosurgery was performed as a primary treatment in 64 patients. The same number had primary open surgery for partial removal or recurrency and subsequent radiosurgical treatment. The mean tumor volume was 8.4 ccm (range: 0.5-69 ccm). These tumor volumes were covered by mean isodose volumes of 45% (range: 20-80%) and treated by a mean dose of 13 Gy (range: 7-25 Gy) at the tumor border. Five patients underwent radiosurgery with a staged treatment protocol with a 4.6-39 month interval. In 88 patients, a total of 270 follow-up scans were available. The mean interval between radiosurgery and the last scan was 19 months with a range from 6-57 months. Follow-up imaging revealed a decreased volume of the tumor in 43 cases (49%). Also in 43 patients (49%) tumor progression was stopped, and only in 2 cases (2%) a slight increase of tumor volume was observed. In those two cases as well as in 12 other cases (16%) marked central tumor necrosis was seen. Neurological follow-ups showed a stable status in 65%, amelioration in 29% and slight worsening in 6% (5 cases) of the patients. Although complete surgical resection should be the goal of treatment, this might not be the strategy in skull base meningiomas to avoid unacceptable risk. The results of radiosurgery either with primary treatment or after partial resection or recurrency prove Gamma Knife radiosurgery to be now a well established additional and alternative treatment in many of these lesions.