Meninges, Solitary fibrous tumour

Solitary fibrous tumour (SFT) is a fibroblastic mesenchymal neoplasm, predominantly of adults, that can occur in essentially any location, including the meninges. The term hemangiopericytoma, describing a diffusely cellular neoplasm having many overlapping features with SFT, is considered obsolete as the two are now recognized as being the same entity, sharing a recurrent intrachromosomal rearrangement (12q) resulting in NAB2-STAT6 fusion. Microscopically, SFT shows patternless ovoid to spindle cells in a fibrous stroma with abundant collagen. A staghorn vascular pattern is prominent and characteristic. In this case, areas of increased cellularity resemble classic hemangiopericytoma. A fat-forming variant has been described. Grading is based on mitoses, hypercellularity, and necrosis. Immunohistochemistry shows positivity for CD34, CD99, and bcl2. Aberrant localization of STAT6 to the nucleus (due to NAB2-STAT6 fusion) can be detected with STAT6 immunohistochemistry and is sensitive and specific. Prognosis varies from benign to aggressive, correlated with tumour grade.