Recurrence and regrowth of benign meningiomas.

The World Health Organization (WHO) grading system for meningioma is helpful for predicting aggressive subtypes. However, even benign meningiomas sometimes show relatively rapid growth and may recur after total removal. We attempted to find histopathological features that would be valuable for predicting recurrence or regrowth of WHO grade I meningiomas. We investigated 135 benign meningiomas, of which 120 were totally removed (Simpson's grade I-III). The median follow-up period was 9.7 years (1-21 years). The recurrence rate in the patients with total removal was 7.5% at 10 years and 9.3% at 20 years. The univariate analysis revealed that MIB-1 index (>or=2%), existence of mitosis, absence of calcification, and paucity of fibrosis significantly correlated with recurrence. On the other hand, the histological features of sheet-like growth, prominent nucleoli, and necrosis did not correlate with recurrence, because they were relatively rare in grade I tumors. Multivariate analysis revealed that high MIB-1 index and absence of calcification significantly correlated with recurrence. The patients with recurrent or residual tumors did not always receive adjuvant treatment. Including subtotally treated tumors, the retreatment rate was 9.8% at 10 years and 25.6% at 20 years. MIB-1 index and Simpson's grade significantly correlated with retreatment in both univariate and multivariate analyses.