Cellular composition of the so-called dermatofibroma (histiocytoma cutis).

9 typical cases of dermatofibroma or histiocytoma cutis resp. were studied by the aid of histochemical, enzyme histochemical and electron microscopical methods to examine the cellular composition of these lesions. The results suggest an anabolic and katabolic function of cells. Electron microscopically a broad spectrum of patterns of mesenchymal cells was found. Besides defined fibroblast-like and histiocyte-like elements a cell type was detected which was characterized by particular traits, as irregular nuclear outline, abundant rough endoplasmic reticulum, free ribosomes, bundles of filaments with single dense zones, micropinocytotic vesicles and a basement membrane-like material on the outer cell surface. This cell type constitutes the majority of cells in dermatofibroma or histiocytoma cutis resp. In some cells an arrangement of filament bundles resembling that in smooth muscle could be seen. By reason of these findings a certain resemblance to the so-called myofibroblasts can be stated. The variegation of the morphological picture suggests a multipotent precursor cell; the possibility of an origin from pericytes is discussed.