Hemangio means blood vessels and pericyte is a type of connective tissue cell. Hemangiopericytoma is a metastatic vascular tumor arising from the pericyte cells that affects the cells surrounding the small blood vessels called capillaries. A pericyte is a non-specialized embryonic cell which differentiates into whatever type of cell the body requires to function and regenerating new tissue as needed. In this case, the pericyte is damaged and instead of forming useful tissue it forms a tumor. Hemangiopericytomas grow continuously at the site of origin and over time takes up all the space, affect the nearby organs and impair their function. This can be fatal when it occurs in the chest close to the heart and lungs. If treated before it has grown to unmanageable proportions, the prognosis is usually good. This tumor is more common in large-breeds than in small-breeds.
Hemangiopericytomas usually present themselves as a soft, fluctuant or firm mass, usually slow growing on a limb or in some cases on the trunk of the animal. Sometimes Rapid growth can also be seen in case of high grade variant tumor.