Solitary fibrous tumor (hemangiopericytoma)

Solitary fibrous tumours of the dura are are rare tumours of the meninges, often presenting as a large large and locally aggressive dural mass, frequently extending through the skull vault. They are difficult to distinguish from the far more commonmeningioma, but are treated similarly with surgical resection with or without radiotherapy to reduce the risk of of recurrence, which is high. 

MICROSCOPIC DESCRIPTION: 1&2. 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).

DIAGNOSISFINAL DIANOSIS: 1&2. Brainsolitary fibrous tumour: Meningeal of the dura (previously haemangiopericytoma (WHO) - 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.