The patient went on to have a craniectomy and cranioplasty. 

Histology: 

 BLOCK DESIGNATION: Fibrous dura 40x30x5mm and skull bone 95x80x up to 20mm in thickness. Sectioning the bone shows a solid pale white lesion 15mm in diameter. 

MICROSCOPIC DESCRIPTION: The sections show a moderately cellular meningioma with infiltration into the attached dura. The tumor forms whorls. No sheeting arrangement is seen. The tumor cells have ovoid nuclei with no nuclear pleomorphism. Mitoses are inconspicuous. There is no necrosis. No brain parenchyma is seen. No evidence of atypical or malignant change is identified. 

Bony sections show tumor invading into about 95% of the thickness of the skull bone. The outer bony margin is clear.

FINAL DIAGNOSIS: En plaque meningothelial meningioma (WHO Grade I).

 Discussion:

En plaque meningiomas are often associated with the most florid bony hypertrophy, and can, as in this case, be associated with bony invasion. In some cases, the dura appears normal and the tumor is then considered to be a primary intraosseous meningioma.