World Health Organization Grade II Meningiomas: The Role of Adjuvant/Salvage Gamma Knife Surgery After Initial Surgery and Prognostic Factor Assessment. 
This study was performed to evaluate the efficiency of Gamma Knife surgery (GKS) on reducing recurrence of World Health Organization (WHO) grade II meningiomas after surgery and to define the risk factors associated with tumor recurrence/progression and patient's death.  This retrospective study included 75 patients who were diagnosed with WHO grade II meningiomas after initial surgery.  The Kaplan-Meier method with a log-rank test was used to calculate the survival curves.  Univariate and multivariate Cox proportional hazards model were used to identify the risk factors associated with tumor recurrence/progression and patient's death.  The median follow-up period was 70 months.  The overall survival (OS) was 97.2% at 2 years and 89.8% at 5 years.  The progression-free survival (PFS) at 1, 3, and 5 years was 89.3%, 72.6%, and 59.3%, respectively.  Comparing the effects on PFS and OS between different groups, there were no statistically significant differences between the surgery-alone group and the surgery with adjuvant/salvage GKS group (P = 0.512; P = 0.949).  In multivariate Cox proportional hazards model analysis, extent of resection (P = 0.001) and tumor location (P = 0.015) were associated with tumor recurrence; only histologic subtypes (P = 0.005) were associated with patient's death.  There was no significant PFS or OS benefit for patients with WHO grade II meningiomas treated with adjuvant/salvage GKS postoperatively.  Convexity meningiomas with gross total resection tended to benefit PFS.  We suggest trying to achieve maximum safe gross total resection for patients with WHO grade II meningiomas, then following up closely.