Striated membranous structures in human hearts. An ultrastructural study.

Straited membranous structures (SMS), which consisted of sheets or ribbons of 130 to 220 A in thickness, showed variable patterns of periodic substructure, and resembled SMS described in renal and ocular tissues in various diseases, were found in extracellular locations in a) mitral valve (2 patients) and tricuspid valve (1 patient) of 2 patients with mitral valvular prolapse, b) mitral valve and femoral artery of 1 patient with Marfan's syndrome and prolapsed mitral valve, and c) myocardium (2 patients) and thickened endocardium (3 patients) of 3 patients with congenital heart disease associated with muscular obstruction to right ventricular outflow. Striated membranous structures measured up to several microns in diameter, often were highly folded and convoluted, and sometimes appeared circular in outline. Some SMS measured from 130 to 150 A in thickness and had indistinct edges and poorly defined periodicity. The majority of SMS, however, had greater thicknesses, in the range of 200 A, and a periodicity characterized by alternating light and dark bands with a spacing that varied from 100 to 160 A. The structures were associated with thickened basement membranes, elastic fibers, and membrane-bound bodies of the type thought to be involved in elastogenesis. Evidence available suggests that SMS results from an unusual pattern of arrangement of a component, possibly Type IV collagen, of basement membrane material.