The patient went on to have a resection. 

Histology

Sections through the "scalp tumor" show fibroadipose tissue diffusely infiltrated by a tumor with the typical histologic appearance of meningioma. The tumor cells are arranged in sheets with focal formation of meningeal whorls. There is no cellular atypia, mitotic activity or necrosis. Rare psammoma bodies are seen in some of the sections.

Sections through "dura" show dura with attached tumor, which displays similar histologic appearance with the scalp tumor; a dural based tumor with the histologic features of well-differentiated meningioma. The tumor shows frequent whorl formation and presence of psammoma bodies. There is focal full thickness infiltration of the dura by tumor. There is no cytologic atypia and no necrosis.

MIB-1 immunohistochemistry, shows only a small number of positive staining scattered tumor cells. Minute fragments of cortical brain tissue are present adjacent to the tumor, but there is no apparent brain invasion. This is confirmed by the GFAP staining.

Final Diagnosis:

Diffuse infiltration of subcutaneous tissue by well-differentiated meningioma. ​

It is important to realize that except for invasion into brain parenchyma (which is by definition designated at least a WHO grade II tumor) invasion into adjacent structures does not preclude the diagnosis of a WHO grade I meningioma.