Ultrastructural studies on congenital generalized fibromatosis regressed spontaneously

Cellular components of a subcutaneous nodule from a male infant with congenital generalized fibromatosis consisted of myofibroblasts, fibroblasts, and their various intermediate types. The myofibroblasts were characterized by the presence of bundles of microfilaments and dense bodies similar to those in smooth muscle cells. Membrane-bound vesicles containing dense material were abundant in the extracellular space. They were probably lysosomes released by disintegration of cellular components. A possible role of the myofibroblasts and extracellular lysosomes in the regression of nodular lesions was discussed.