The patient went on to have a resection. 

Histology

Macroscopic description: A semi-circular piece of recognizable skull bone grossly involved on one surface by an infiltrating soft, tan, bosselated tumour in the centre of the piece. The skull bone measures 7 x 9 cm in the maximum two diameters, while it ranges in thickness from 0.6 up to 1.5 cm nearest the tumour involvement. The diameter of the tumour within the centre of the skull bone is 5 x 4 cm, and the tumour appears to involve the bone resection margin.

Microscopic description: Representative sections from the specimens received in four containers reveal classic features of meningioma with prominent whorling effects sometimes hyalinized whorls and occasional psammoma bodies. Some of the hyalinized whorls show peculiar radial arrangement of collagen fibers that stain green with the Masson trichrome stain. The tumour cells are arranged mostly in fibroblastic growth pattern admixed sometimes with a meningothelial pattern with indistinct cell borders. 

Cytologically, there is focal enlargement of the nuclei in association with prominent nucleoli and focal areas of small-cell change. Apoptotic bodies are readily identified and mitotic activity averages 5 mitotic figures/10 high-power field. There are no areas of micronecrosis. At the periphery of the tumour fragments there is extensive prominent transmural tumor invasion of blood vessels, but no luminal tumour emboli are identified. Sections including skeletal muscle tissue and bone trabeculae confirm invasion by meningioma. The tumor is noted to invade the dura on both sides. MIB-1 immunostaining shows a considerable number of cells in the mitotic cycle.

FINAL DIAGNOSIS:   Atypical meningioma with diffuse infiltration of dura, skeletal muscle and bone. 

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