Paraffin sections show a densely hypercellular dural based tumour. Tumour cells have moderately pleomorphic overlapping hyperchromatic nuclei and a small amount of cytoplasm. These are arranged in diffuse sheets within a vascular stroma. Vessels are predominantly capillary in type. Some "staghorn" vessels are noted. Scattered mitotic figures are identified (2/20 HPF). No areas of necrosis are seen. Tumour is seen to push against but not invade underlying brain parenchyma. Immunohistochemistry shows patchy CD34 staining in the tumour cells. They are also bcl-2 and CD99 positive. The topoisomerase index is 3-4%. EMA and inhibin are negative. The features are of meningeal haemangiopericytoma (WHO grade II).
FINAL DIANOSIS: solitary fibrous tumour of the dura (previously haemangiopericytoma) - WHO grade II.
Note: Due to molecular/genetic similarities haemangiopericytomas are no longer recognised as distinct entities. Instead, they represent cellular higher-grade solitary fibrous tumours. In the 2016 revised 4th Edition of the WHO classification of CNS tumours, they were grouped together under one diagnosis (solitary fibrous tumour/haemangiopericytoma), and in the 2021 5th edition the term haemangiopericytoma was dropped entirely.