Proliferative fasciitis: ultrastructure and histogenesis

Abstract
The ultrastructure was studied of 2 cases of proliferative fasciitis (PF) which affected the fascia and subcutaneous fat. Two basic cell types were observed in the lesions: fibroblast-like, and giant cells. The fibroblast-like cells had myofibroblastic ultrastructural characteristics. The giant cells showed a well-developed, rough endoplasmic reticulum, irregularly distributed filaments and clear lipid droplets in their cytoplasms. Ultrastructurally, the giant cells seemed to belong to a cellular line capable of synthesizing ground substances and extracellular fibers, but with a modified phenotype. A consistent feature was the presence of nodular aggregates of numerous proliferating perivascular cells. Transitional forms between perivascular, fibroblast-like, and giant cells were observed. Our hypothesis is that perivascular cells (activated pericytes) are the source of the fibroblast-like and giant cells in proliferative fasciitis.