[Ultrastructure of endocardial lesions in the carcinoid syndrome (author's transl)].

In a 67-year-old female patient with metastasising carcinoid of the small intestine there were right-sided endocardial plaques characteristic of the carcinoid syndrome. Ultrastructurally, the lesions showed proliferation of smooth muscle cells and myofibroblasts, which were surrounded by basement-membrane-like material and occasionally showed intercellular connections of the macula adhaerens type. The ground substance consisted of acid mucopolysaccharides, normal collagen fibrils, and microfibrils. The endocardial plaques in the carcinoid syndrome differ morphologically from other endocardial lesions by the lack of amorphous elastin. The formation of plaques and its relation to the endocrine activity of the carcinoid tumors is discussed, and pertinent literature is reviewed.