Radiosurgery for Atypical and Anaplastic Meningiomas: Histopathological Predictors of Local Tumor Control

OBJECTIVES: We investigated the radiosurgical outcomes of patients with nonbenign meningiomas retrospectively and sought to identify prognostic factors for local tumor control after radiosurgery with an emphasis on histopathology. METHODS: Between 1998 and 2010, 35 patients with 49 atypical or anaplastic meningiomas were treated with radiosurgery. The mean tumor volume and marginal irradiation dose were 3.5 cm3 (range 0.3-25.3) and 16 Gy (range 12-21), respectively. RESULTS: The actuarial local tumor control rates for patients with atypical meningiomas at 1, 2 and 3 years after radiosurgery were 78, 53 and 36%, respectively, whereas those for anaplastic meningiomas were 35% at 1 year and 10% at 2 years. Multivariate analysis revealed that the mitotic count (≤8 per 10 high-power fields; HPF) and the MIB-1 proliferation marker labeling index (LI; ≤8%) were significant favorable prognostic factors for the radiosurgical outcomes of patients with nonbenign meningiomas (p = 0.014 and p = 0.012, respectively). CONCLUSIONS: Radiosurgery could be a treatment option for patients with atypical meningiomas, but more aggressive treatments are needed for those with anaplastic meningiomas. Histopathological factors such as mitotic count and MIB-1 LI are significant prognostic factors for the radiosurgical outcomes of patients with nonbenign meningiomas and should be considered before radiosurgery.