A rare type of soft tissue tumor that begins in cells that wrap around blood vessels. Infantile hemangiopericytomas may be benign (not cancer) or malignant (cancer). They usually occur in infants and young children but may also be found before birth by ultrasound. They can occur anywhere in the body, but usually occur in the arms, legs, pelvis, or head and neck. In children older than 1 year, infantile hemangiopericytomas are more likely to spread to other parts of the body, including the lymph nodes and lungs. Children younger than 1 year may have a better prognosis.