Cutaneous adult myofibroma: a vascular neoplasm.

Infantile myofibromatosis is a distinctive type of fibromatosis that usually develops during the immediate perinatal period. There are variants with solitary and multiple tumors. Lesions confined to the skin, soft tissue, and bone carry a good prognosis, showing spontaneous regression. The prognosis, however, is much less favorable when visceral lesions are present and the outcome may be fatal. Only recently it became obvious that there is an adult counterpart of infantile myofibromatosis, characterized by solitary lesions that have a predilection for involve the dermis and show no tendency to regression, although they have an entirely benign biological behavior. These lesions have been named cutaneous myofibroma or solitary myofibroma of adults. We have studied the clinical, histopathological and immunohistochemical characteristics of 53 examples of cutaneous adult myofibroma. In addition, 2 cases were examined ultrastructurally. The patients were mostly adults with ages ranging from 6-83 years. The lesions presented as solitary, usually painless nodules of variable duration on the skin, usually located on the extremities. Histopathologically, four patterns were identified: nodular or cellular type, multinodular or biphasic type, leiomyoma-like or fascicular type, and vascular type. A correlation between the histopathologic pattern and the lesional age was observed: vascular type of cutaneous adult myofibroma in early lesions, nodular and multinodular lesions in fully developed lesions, and leiomyoma-like or fascicular type in late lesions. Immunohistochemically, the spindle cells were desmin negative, but expressed immunoreactivity for vimentin, pan-smooth muscle actin, and alpha-smooth muscle actin. Ultrastructurally, neoplastic cells showed characteristics of undifferentiated mesenchymal cells with features of fibroblasts, myofibroblasts and pericytes. Primitive vascular formations were seen in the form of irregular clefts between adjoining cells. We conclude that cutaneous adult myofibroma is a little-known benign vascular neoplasm probably derived from myopericytes.