Neurofibromatosis type 2–associated meningiomas: an international multicenter study of outcomes after Gamma Knife stereotactic radiosurgery

OBJECTIVE The management of neurofibromatosis type 2 (NF2)–associated meningiomas is challenging. The role of Gamma Knife radiosurgery (GKRS) in the treatment of these tumors remains to be fully defined. In this study, the authors aimed to examine the role of GKRS in the treatment of NF2-associated meningiomas and to evaluate the outcomes and complications after treatment. METHODS Seven international medical centers contributed data for this retrospective cohort. Tumor progression was defined as a ≥ 20% increase from the baseline value. The clinical features, treatment details, outcomes, and complications were studied. The median follow-up was 8.5 years (range 0.6–25.5 years) from the time of initial GKRS. Shared frailty Cox regression was used for analysis. RESULTS A total of 204 meningiomas in 39 patients treated with GKRS were analyzed. Cox regression analysis showed that increasing the maximum dose (p = 0.02; HR 12.2, 95% CI 1.287–116.7) and a lower number of meningiomas at presentation (p = 0.03; HR 0.9, 95% CI 0.821–0.990) were predictive of better tumor control in both univariable and multivariable settings. Age at onset, sex, margin dose, location, and presence of neurological deficit were not predictive of tumor progression. The cumulative 10-year progression-free survival was 94.8%. Radiation-induced adverse effects were noted in 4 patients (10%); these were transient and managed medically. No post-GKRS malignant transformation was noted in 287 person-years of follow-up. CONCLUSIONS GKRS achieved effective tumor control with a low and generally acceptable rate of complications in NF2-associated meningiomas. There did not appear to be an appreciable risk of post–GKRS-induced malignancy in patients with NF2-treated meningiomas.