Solitary infantile myofibromatosis in the femur.

We report on a case of the solitary type of infantile myofibromatosis of the right femur in an 11-month female. Radiographically, a well-defined osteolytic lesion was seen in the diaphysis of the right femur. Pathological study revealed that the spindle-shaped cells with eosinophilic cytoplasm were arranged in a fascicular and intertwining fashion. The cleft-shaped vascular spaces were observed between tumor nodules. Immunohistochemical staining caused many tumor cells to react for vimentin, alpha-smooth muscle actin and desmin. Ultrastructural study revealed numerous thin and intermediate types of filaments in the cytoplasm of the cells. To our best knowledge, this is the third reported case of solitary infantile myofibromatosis of long bones.