Brain invasion in otherwise benign meningiomas does not predict tumor recurrence

Excerpt

In the current edition of the WHO classification for CNS tumors, meningiomas are defined as WHO grade II by either displaying a distinct histological subtype (such as chordoid or clear cell meningioma) or by atypical histopathology. Atypical meningiomas are defined by (1) increased mitotic activity (>3 mitoses per 10 high power fields (HPF) but <20 mitoses), (2) brain invasion on histology or (3) a combination of 3 or more of the 5 following histomorphological features: sheet-like growth, increased cellularity, prominent nucleoli, foci of spontaneous necrosis, small cells with high nuclear-cytoplasmic ratio [4]. While histomorphological signs of atypia, increased mitotic activity and the aforementioned histological subtypes are widely accepted as criteria for grading a meningioma as WHO grade II, brain invasion as sole criterion for atypia is still a matter of debate and lacked clear association with tumor recurrence in several studies [3, 8, 11, 16, 18]. Furthermore, histologically benign meningiomas do not show genetic changes as seen in higher-grade meningiomas [9, 14, 19]. …