Ultrastructure of medial smooth muscle and myofibroblasts in human arterial dysplasia.

Ultrastructural characteristics of 20 dysplastic human renal arteries were documented. Loss of smooth muscle with collection of fibrous connective tissue predominated in medical fibrodysplasia, whereas excessive accumulations of elastic fibrils typified perimedial dysplasia. Myofibroblasts were a unique feature of both forms of arterial dysplasia. These modified smooth muscle cells seemed to be the source of abnormal connective tissue synthesis. Transformation of medial smooth muscle cells to myofibroblasts represented a morphologic continuum. Intramedial vasa vasorum were often isolated from surrounding cellular elements by unusual amounts of mural ground substances. The results of this study lend further support to the hypothesis that ischemia and direct physical forces effect hormonally altered cells in the pathogenesis of arterial dysplasia.