Collagenous colitis: an ultrastructural study of a case.

A case of so-called collagenous colitis is described. This entity, featured clinically by watery diarrhea, is characterized histologically by a 50-60 micrometer fibrous layer immediately beneath the surface epithelium. Ultrastructural changes in the endothelial cells and the basement membranes of the superficial capillaries of the colonic lamina propria, as well as concentric collagenous encasement of these capillaries, are described.