Atypical meningioma (WHO grade II)
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Selected images from an MRI of the brain of an adult demonstrates a mass arising in the inferomedial aspect of the anterior cranial fossa. It is of heterogeneous signal intensity, but largely isointense to grey matter on T1 and hyperintense to brain on T2, and demonstrates homogeneous intense contrast enhancement. The mass appears to be extra-axial (note the CSF cleft seen on T2 weighted images) and is associated with marked cerebral vasogenic edema.
The most likely diagnosis is that of an atypical meningioma, although a hemangiopericytoma or dural metastasis should also be considered.
The patient went on to have a craniotomy and excision.
Sections show meningioma, focally associated with thin rims of fibrous tissue and neutrophil. The pattern is predominantly meningothelial. Focal infiltration by meningioma into brain tissue is identified. Mitotic activity is not elevated.
Final diagnosis: atypical meningioma (WHO grade II).
Comment: This meningioma was designated as being atypical because of the focal infiltration into brain tissue, which is now sufficient to denote WHO grade II even with all other histological features consistent with a lower grade.