Infantile myofibromatosis of the triceps detected by prenatal sonography.

A routine prenatal sonographic examination at 36 weeks' menstrual age revealed a solid and slightly inhomogeneous soft-tissue tumor on a fetus's left upper arm. The mass in the left triceps brachii muscle measured 8 x 7 x 5 cm at birth. Because of progressive flexion contracture of the left elbow joint, at 2 months of age the infant underwent radical resection of the tumor, sparing some muscle fibers. Light microscopic and immunohistochemical studies revealed myofibromatosis. Neither tumor nor functional disorder of the arm was evident 3 years after surgery.