The patient went on to have a resection.
Paraffin sections show a densely hypercellular tumour. Tumour cells have moderately pleomorphic round, oval and angulated vesicular nuclei. Cytoplasmic boundaries are poorly defined. Tumour cells are aggregated in solid sheets with no specific architectural pattern discernible. However, in several areas, small calibre open vascular spaces are noted. These are lined by unremarkable endothelium. A moderately fibrous stroma is noted in several areas of the tumour. A very occasional mitotic figure is identified. There are no areas of necrosis. No evidence of invasion into brain parenchyma is seen.
Immunohistochemistry shows strong staining of tumour cells for CD34 and bcl-2. There is also moderate nuclear staining for progesterone receptor (PgR). No staining for epithelial membrane antigen (EMA), cytokeratin AE1/AE3, GFAP, ALK-1 or tyrosinase is seen in tumour cells. The features are of haemangiopericytoma (WHO Grade II). The topoisomerase labelling index is <1%.
FINAL DIAGNOSIS: Haemangiopericytoma (WHO Grade II)