Ultrastructural evidence of myofibroblasts in circumscribed fibromatosis.

The myofibroblast, which exhibits ultrastructural features of both smooth muscle cells and fibroblasts, is the predominant cell type in the granulation tissue of healing wounds. Similar cells were identified in an ultrastructural study of a case of circumscribed fibromatosis. Myofibroblasts have been described in several apparently unrelated conditions, suggesting that the acquisition of smooth muscle-like features is one of a limited number of ways in which fibroblasts may react to abnormal stimuli.