The frequency of Grade II meningiomas has shown an increasing trend to 18%, 26%, and 30% when the WHO 1993, 2000, and 2007 criteria were applied, respectively. 21 , 22) Grade III meningiomas have accounted for 1–3%. 2 , 22) Grades II and III meningiomas occur far less frequently in the skull base and spine, and the occurrence of tumors in the “non-skull base” is an independent risk factor for Grades II and III meningiomas. 23 , 24) Currently, histologic grade is the best predictive factor for local recurrence.
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