Electron microscopic findings of human auricular appendages

Summary Auricular appendages were obtained from 20 patients ranging in age from 4 to 64 years with chronic heart diseases at the time of operation and observed with an electron microscope. Myo-endocardial fibrosis was seen in the majority of cases. Proliferation of smooth muscle cells was noticed in the areas of thickened myo-endocardial spaces. These smooth muscle cells played an important role in the production of ground substance, collagen, and elastic fibers in the fibrotic lesions.Microfibrils and elastic tissue were also observed in close association with the basement membrane of cardiac muscle cells and capillaries.Cytoplasmic filaments were observed both dispersed and aggregated in bundles in the endothelial cells on the thickened endocardium.On leave of absence from Second Department of Pathology, School of Medicine, Gunma University, Maebashi, Japan.