Structure of the collagen nodule from hypertrophic scars and keloids.

The collagen nodule is the structural unit of all hypertrophic scars in keloids. It is never found in the fully mature scars. A study of the fine structure of the nodule might reflect its origin, and, hence, origin of the hypertrophic scar and keloid. Nodules are composed of a marked increase of unidirectional collagen fibrils aligned in a highly stressed orientation. There is also a marked increase in the number of fibroblasts. Few microvessels appear within the nodule; rather, they remain peripheral and encompass the main body of the nodule as a net. There is a heavier concentration of microvessels (3-13 micrometer in diameter) at the terminal ends, many of which are occluded. The occlusion appears due principally to an apparent increase in the number of endothelial cells. The character of the nodule and its relationship with a peripheral semioccluded microvascular network suggests an origin of the hypertrophic scar and keloid to be related to revascularization of a deep wound.