The stromal cell reaction of pigmented villonodular synovitis: An electron microscopic study

Synovium obtained from a patient with pigmented villonodular synovitis was studied with the electron microscope. Attention was directed to the stromal cell hyperplasia, a histological feature of this disease. It was shown that the participating cells were of two main types. The more abundant cell resembled the fibroblast of connective tissue in general, and appeared capable of collagen and mucopolysaccharide synthesis. The second cell type was similar to a macrophage and contained numerous hemosiderin inclusions.