The patient went on to have surgery.

Histology

Paraffin sections show a densely cellular, dural-based tumor. Tumor cells have pleomorphic round, oval and elongated nuclei with vesicular chromatin and a variable amount of cytoplasm and are arranged in solid sheets in a fibrous stroma. The formation of thin-walled "staghorn" vascular channels is noted in many areas. Five mitotic figures are identified in 20 high power fields. There are several foci of geographic necrosis. One of these is surrounded by a palisaded arrangement of tumor cells. No evidence of brain invasion is seen.

Immunohistochemistry results show tumor cells stain: STAT6+ (focal), Co99+, BCL2+, EMA-, PR-, SST R2- and Co34-. The Topoisomerase proliferation index is approximately 15%.

FINAL DIAGNOSIS: solitary fibrous tumor of the dura (previously hemangiopericytoma/solitary fibrous tumor) - WHO Grade II.

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.