An ultrastructural pathologist's views on fibroblasts, modified smooth muscle cells, wound healing, stenosing arteriopathies, Kawasaki disease, Dupuytren's contracture, and the stroma of carcinomas.

It wasn't until 1960 that the dense bodies of the peripheral actin arrays of fibroblasts were finally visualized, i.e., stress fibers (SFs). Mistakenly assumed that its SFs turned the fibroblast into a unique cell situated somewhere in a continuum between it and a smooth muscle cell (SMC), it was descriptively named a "myofibroblast" (MF). Automatically, spindle cells with SFs and/or smooth muscle actin by SMA IHC-staining, became MFs, although endothelial cells, pericytes, modified SMCs (mSMC), and myoepithelial cells all contain SFs. An invisible "intermediate" cell was hypothesized to exist somewhere between SMA-negative and positive fibroblasts, and named a "proto-myofibroblast". The sub-epithelial spindle cells of normal and malignant tumors of the GI, GU, and respiratory tracts are all fibroblasts with SFs. The second erroneous myofibroblast came from a 1971 rat wound healing study and its 1974 human counterpart. Updated analysis of the papers' TEMs proved that the cells are mSMCs and not fibroblasts (AKA: MFs). The pathognomonic cells of Dupuytren's contracture are mSMCs and fibroblasts and that of the stenosing arteriopathy of Kawasaki Disease and other similar arteriopathies are mSMCs. TEM remains a powerful tool.