Myopericytoma - a unifying term or a unique entity?

Myopericytoma are uncommon, slow-growing benign perivascular neoplasms that show hemangiopericytoma-like vascular pattern. We report a 52-year-male patient with a painless palpable nodule in the left thumb for the past 9 months. The mass, on the thenar aspect, was 15x12mm in size. X-ray revealed a soft tissue swelling with no bony association. The excised nodule was a non-capsulated, well-circumscribed vascular neoplasm composed of proliferating spindle to ovoid bland cells with eosinophilic cytoplasm. A concentric perivascular arrangement of the cells was seen interspersed by thin-walled, branching, staghorn blood vessels. Nuclear atypia, mitotic figures and necrosis were not observed. Immunohistochemistry revealed diffuse positivity of the tumour cells for smooth muscle actin while staining negative for CD34 and desmin - features suggestive of origin from the perivascular myoid cell. Morphological features of myopericytoma are shared with hemangiopericytoma, glomus tumors, myofibroma and solitary fibrous tumour which form the important differential diagnoses. It is a relatively newly described disease entity recognized by the World Health Organisation classification of tumours.