Perivascular myofibroblasts and microvascular occlusion in hypertrophic scars and keloids.

Microvessels in normal skin, granulation tissue, hypertrophic scar, keloid, and mature scar from human subjects were studied by transmission electron microscopy. Comparative observations suggested that most microvessels in hypertrophic scar and keloid are occluded or partially occluded, apparently owing to an excess of endothelial cells. Endothelial cell contraction was also supported by the observations, and perivascular satellite cells (pericytes), some of which were identified as myofibroblasts, were observed in hypertrophic scars and keloids. Among findings from statistical analyses were that 1) the patency of microvessels in hypertrophic scar and granulation tissue is similar, as is that of microvessels in keloid and mature scar, but the patency of all these microvessels is significantly less than that of microvessels in normal skin, and 2) endothelial cell density is greater in nonpatent vessels than in patent vessels. The observed extent of microvascular occlusion supports a previously published theory that hypoxia is involved in the generation of hypertrophic scar.