Microscopic diagnosis:

Solitary fibrous tumor (previously known as hemangiopericytoma) with foci of high mitotic activity and necrosis compatible with anaplastic transformation. WHO grade III.

Bone invasion is noted.

IHC result:

• EMA: Negative
• CD34: Positive in endothelial cells
• CD 99: Weakly positive
• Ki-67: Positive in up to 4% of tumor cells

Findings are consistent with hemangiopericytoma with focal anaplastic transformation, WHO grade III.

Note: at the time of diagnosis/case contribution this tumor was known as a hemangiopericytoma. Under the 5th Edition (2021) of the WHO classification of CNS tumors, it is now considered a solitary fibrous tumor of the dura.