Solitary infantile myofibromatosis: report of two cases.

Infantile myofibromatosis (IM) is an unusual tumor of infancy and early childhood. It typically presents as a solitary or multicentric nodular mass involving skin, soft tissue, bone, or viscera. We describe 2 cases of solitary infantile myofibromatosis (IM) of the soft tissue with typical light microscopic features. The first is a 7-month-old boy who had a rapidly growing tumor of the right thigh. The fragile tumor, measuring 7.0 x 6.0 x 3.5 cm was completely removed, but the patient was lost to follow-up after surgery. The second case, a 2-year-old boy, was referred from a local clinic due to a non-tender mass in the left abdominal wall. The tumor, measuring 2.0 x 2.0 x 1.6 cm, was completely excised. No recurrence or malignant transformation was found after 22 months of follow-up. The histopathologic, histochemical, and immunohistochemical features of the tumors were studied. Reticulin preparation showed that the tumor cells were outside the reticulin sheath of the vascular spaces and were individually enclosed by reticulin fibers. Tests for vimentin, anti-alpha-smooth muscle actin, and myoglobin were positive in the neoplastic spindle cells. IM has a variable appearance on radiologic images and often mimics an aggressive neoplasm. These factors can make a rapid and correct diagnosis difficult. IM must be considered in the differential diagnosis in any child who presents with either solitary or multiple tumors, particularly those occurring in the neonatal period.