Proliferative fasciitis: ultrastructural study of two cases.

Two cases of proliferative fasciitis were studied by light and electron microscopy. The light microscopic features appear to be identical to those of proliferative myositis. Ultrastructural features include numerous cytoplasmic thin filaments, with occasional dense bodies, abundant rough endoplasmic reticulum, and cellular membrane-based vesicles. No Z bands or specialized cell junctions were identified. These findings suggest that the large balloon cells characteristic of the lesion probably are of myofibroblastic origin.