Hemangiopericytoma in a cat: a case report

In dogs and men, hemangiopericytoma is a well-recognised neoplasm, thought to originate from vascular pericytes. In cats, however, hemangiopericytoma is an extremely rare finding. The present report describes the pathological features of a 7-cm-diameter, dense, white, multilobulated tumour-like growth on the thigh of a ten-year-old Persian cat. Histologically, the mass consisted of polygonal neoplastic cells, concentrically arranged around thin-walled endothelium-lined blood vessels occasionally forming typical staghorn-configurations. In reticulin-stained sections, a dense meshwork of argyrophilic collagen fibres was evident, surrounding the central vessels and separating individual tumour cells. Within the tumour tissue, there were areas of extensive necrosis and degeneration. In the periphery, the tumour displayed a moderate infiltrative growth into the adjacent musculature. Immunohistochemical analysis revealed strong diffuse cytoplasmatic immunoreactivity for vimentin, a focal immunoreactivity for S-100, and a weak interstitial staining for laminin, whereas neoplastic cells stained negative for cytokeratin, desmin, actin, calponin, von Willebrand factor, glial fibrillary acidic protein, neuron specific enolase, CD79a, MAC387, lysozyme and MHCII. Ultrastructurally, the neoplastic cells contained few intracytoplasmatic filaments, and were surrounded by interlacing bundles of intercellular long-spacing collagen fibres. Occasionally, desmosome-like intermediate junctions were observed between neighbouring tumour cells. On the basis of histomorphology, ultrastructure and immunohistochemical reactivity, the neoplasm was diagnosed as a hemangiopericytoma, representing the second reported case of this rare tumour entity in a cat.