Solitary fibrous tumor (hemangiopericytoma)
This patient went on to have a resection which confirmed the diagnosis.
Sections show a highly cellular vascular neoplasm which appears to be adherent to dura matter. Numerous large thin-walled vascular channels are seen and there is a complex network of delicate small vascular sinusoids. In some areas, the tumor cells are separated by a collagenous stroma but in other regions they form more solid sheets.
Cellular morphology varies from one region to another. In some areas, the tumor cells have plumped oval nuclei and a relatively delicate chromatin resembling meningioma. In other regions, the nuclei are smaller, angulated and hyperchromatic and the cells have a spindle-cell morphology.
Cells with clear vacuolated cytoplasm are present and there are focal collections of multinucleate giant cells. The tumor cells have prominent nucleoli and mitotic activity is easily identified. Many areas of the tumor show abundant reticulin deposition which often forms delicate deposits outlining individual tumor cells. There is strong immunoreactivity for vimentin but no reaction for cytokeratin and EMA.
Final diagnosis: solitary fibrous tumor (previously hemangiopericytoma)
Note: Due to molecular/genetic similarities hemangiopericytomas are no longer recognized as distinct entities. Instead, they represent cellular higher-grade solitary fibrous tumors. In the 2016 revised 4th Edition of the WHO classification of CNS tumors, they were grouped together under one diagnosis (solitary fibrous tumor/hemangiopericytoma), and in the 2021 5th edition the term hemangiopericytoma was dropped entirely.