Gamma Knife Radiosurgery for Postoperative Remnant Meningioma: Analysis of Recurrence Factors According to World Health Organization Grade

Objective: The effectiveness of tumor control after Gamma Knife radiosurgery (GKS) for intracranial meningioma is well established. Moreover, GKS is an alternative to reduce surgical-remnant meningioma recurrence. Nevertheless, the tumor can recur even after GKS and is associated with its histologic malignancy. We here investigated the risk factors associated with recurrence from remnant lesions after GKS, assessing recurrence patterns according to histological grades. Methods: From January 2007 to January 2017, 218 patients underwent GKS for surgical-remnant lesions. To evaluate post-GKS lesion recurrence, pre-GKS magnetic resonance images were compared with those at follow-up. We retrospectively analyzed the histologic classification of meningioma and patients' clinical characteristics (sex, age, tumor location, target volume, and prescription dose). Results: Of the 218 patients, 13 (5.9%) developed post-GKS recurrence within a mean follow-up period of 37.4 months. The recurrence patterns were as follows: adjacent to the 50% marginal-dose field (9 patients); within the 50% marginal-dose field (2 patients); and outside the field (2 patients). Six of 196 World Health Organization grade I meningioma cases, 6 of 20 grade II cases, and 1 of 2 grade III cases developed recurrence. Thus 32% of high-grade meningioma cases (grades II and III) developed recurrence during the follow-up period. Histologic grade was significantly associated (P < 0.001) with recurrence. Conclusions: The study findings indicate that the post-GKS meningioma recurrence likelihood is high when the meningioma has malignant histologic features. In addition, considering the recurrence patterns, it is important to define a precise target for GKS.