Fine Structure of Granulation Tissues from Deep Injury

Granulation tissues from a group of severely burned children aged 1 mo to 16yr were obtained for study by transmission electron microscopy. Fine structural Characteristics were evaluated in the context of their possible significance to subsequent hypertrophic scarring. Microvessels often show the products of a thrombus. Some small vessels are occluded and are usually seen in the older granulations. Endothelial and perivascular satellite cells contain prominent amounts of rough endoplasmic reticulum, few mitochondria but even less of other organelles. Around all vessels are multiple layers of basal lamina. Fibrin is found in all of the granulations from 13 days to 6½ mo postinjury. It is seen intraluminally and interstitially. Although in the younger granulations a few fibrin fragments appear “sticking” to occasional macrophages, neutrophils or fibroblasts there is no evidence of a massive clearance mechanism. Fibroblast type cells demonstrate morphology which may be predominantly vesicular, granular, or organeller. Myofibroblasts are abundant and virtually all exhibit microtendons. The significance of the persistent and pervasive fibrin in a deep injury to probable development of subsequent hypertrophic scarring may lie in promoting endothelial cell proliferation which would occlude the microvessels. Occlusion would then produce hypoxia which, in turn, would stimulate excessive, fibroblast proliferation and overproduction of collagen and certain mucopolysaccharides.