Infantile myofibromatosis. Report of two cases.

Two cases of infantile myofibromatosis were presented. Case 1 was a 6-month-old girl with multiple nodular lesions in the left parietal bone, dermis of abdominal wall, chest wall, right upper arm, and bilateral femur. Case 2 was a 12-month-old girl with solitary nodular lesions in the left parietal bone having a tendency to enlarge. Histologically, these tumorous lesions consisted of broad bundles of well oriented spindle-shaped cells superficially resembling smooth muscle tissue. In electron microscopy, the constituent cells combined ultrastructural characteristics of both fibroblasts and smooth muscle cells., Immunoperoxidase method showed that anti-smooth muscle antibodies binded to the cytoplasm of the bundle forming cells. From these results, it may be concluded that the lesion consisted of pure proliferation of myofibroblasts, and its peculiar growth behavior was discussed, though the histogenesis still remains obscure.