Histopathological and Immunohistochemical Characteristics of a Local Aggressive Canine Hemangiopericytoma (CHP) After Surgery

Perivascular wall tumors (PWTs) are mesenchymal neoplasms in the group of soft tissue sarcomas (STSs) and are defined as neoplasms deriving from mural cells of blood vessels, excluding the endothelial lining. In the present paper, we describe the gross morphology, histopathology and immunoreactivity of a hemangiopericytoma (HP) as a PWT in a dog with recurrence after surgical excision. The mass was 3-4 cm, solitary, soft, unencapsulated, well circumscribed and grey to brown color. Cut surfaces of the mass contained discrete, round and relatively homogeneous tumors without any lobulation and liquefied foci in the centers. Histologically, the tumor was richly vascularized which arranged in staghorn vessels pattern. The neoplastic cells were uniform in appearance with mild to moderate pleomorphism and had spindle-shaped to oval/round nuclei with vesicular to hyperchromatic chromatin and eosinophilic to the amphophilic cytoplasm with variable amounts of the collagenous stroma. In the immunohistochemical evaluation, proliferating stromal and vascular cells in this tumor demonstrated strong immunoreactivity for vimentin and α-smooth muscle actin. Although, these cells were negative for S100, lysozyme, CD31, and CD34. The present findings show that hemangiopericytoma in dogs can be a locally aggressive behavior with a repeated recurrence that led to the surgical amputation of limbs or even euthanasia of dogs.