The ultrastructure and etiology of chronic radiotherapy damage in human skin.

Ulcerated and nonulcerated skin from 5 patients with chronic radiation skin damage was examined using electron microscopy. Noticeable fibroblast disorganization was seen, with swollen and degenerating mitochondria, multiple vacuoles, and dilated irregular rough endoplasmic reticulum. Unusual crystalline inclusions were seen in some fibroblasts. In the ulcerated skin, contractile fibroblasts (myofibroblasts) were seen in 2 of 4 specimens. Stroma showed dense collagen and prominent elastosis. The microvasculature in the radiation-damaged tissue showed occasional lumen occlusion and vacuolization of endothelial cells, without consistent abnormality. These data suggest that permanent damage to fibroblasts or fibroblast stem cells may play an important role in chronic radiation skin ulceration.