Hemangiopericytomas (HAPs) are rare, benign, or low-grade sarcomas (ie, connective tissue tumors) originating from pericytes (mesenchymal-derived cells surrounding capillaries and venules). The etiology of HAP is unknown, although chemical carcinogens and radiation may be contributory.

HAP occurs mainly in adults; children are rarely affected. Both sexes are affected equally. Because of the asymptomatic nature of HAP, the diagnosis may be delayed by months or even years, particularly for low-grade and slow-growing lesions. More aggressive forms of HAP exist as well. Morbidity and mortality are attributed to locally invasive disease and hematogenous metastases to the lungs (most common) or the intra-abdominal or retroperitoneal region.

Pediatric Patient Considerations:
HAP is rare in children, accounting for less than 10% all cases. A rare form of infantile HAP (in children less than 1 year old) is considered congenital.