Despite a favorable outcome for most patients with WHO Grade I meningiomas, a subset of these patients will have recurrent or progressive disease that advances to a higher grade and requires increasingly aggressive therapy. The goal of this study was to identify clinical characteristics associated with the recurrence of benign meningiomas and their acceleration to atypical and malignant histological types.

Records of 216 patients with WHO Grade I, II, or III meningioma that were initially treated between 1965 and 2001 were retrospectively reviewed. Median follow-up was 7.2 years.

Patients with non-skull base cranial meningiomas (82 of 105 [78%]) were more likely to have undergone a gross-total resection than patients with skull base meningiomas (32 of 78 [41%]; p < 0.001). Consequently, patients with Grade I non-skull base cranial meningiomas had better 5-year recurrence-free survival (69%) than patients with Grade I skull base meningiomas (56%) or Grade II or III tumors at any site (50%; p = 0.005). Unexpectedly, patients with non-skull base tumors who experienced a recurrence (8 of 22 [36%]) were more likely than patients with skull base tumors (1 of 19 [5%]) to have a higher grade tumor at recurrence (p = 0.024). Furthermore, the median MIB-1 labeling index of Grade I non-skull base cranial meningiomas (2.60%) was significantly higher than that of Grade I skull base tumors (1.35%; p = 0.016).

Cranial meningiomas that occur outside of the skull base are more likely to have a higher MIB-1 labeling index and recur with a higher grade than those within the skull base, suggesting that non-skull base cranial tumors may have a more aggressive biology than skull base tumors.