MICROSCOPIC DESCRIPTION: 1-4. Paraffin sections show a moderately hypercellular tumour. This consists of spindle and epithelioid cells with a loose fascicular and storiform architectural arrangement. A vague whorling architecture is also noted in some areas. Tumour cells show mild nuclear and cellular pleomorphism. Occasional mitotic figures are identified (2/10 HPF). No areas of necrosis are seen. There is no evidence of brain invasion. Immunohistochemistry shows strong staining in tumour cells for CD34 and bcl-2. No staining for epithelial membrane antigen (EMA), progesterone receptor (PgR) or ALK-1 is seen. The features are of solitary fibrous tumour (WHO Grade II). The topoisomerase labelling index is approximately 3%.
DIAGNOSIS: 1-4. Olfactory groove tumour: Solitary fibrous tumour (WHO Grade II).