Meningioma (atypical) with extensive bony invasion


This case demonstrates the importance of accurate histological assessment, as the tumor shows atypical histologic features, such as mitotic activity averaging 5 mitotic figures/10 high-power fields, small-cell changes, prominence of nucleoli, and sometimes hypercellularity. 

Under the WHO classification this meningioma is classified as WHO grade 2,  which likely indicate a higher recurrence rate and more aggressive behavior than benign meningioma.

It is tempting to use the term intraosseous meningioma for tumors such as this, but infact finding involvement of the arachnoid layer and dura with tumor suggests that this is an intracranial meningioma (often of the en plaque morphology) with bony involvement. True 'primary intraosseous meningiomas' have no dural involvement.