Perimedial fibroplasia of the renal artery: a light and electron microscopic study.

Six cases of perimedial fibroplasia of the renal artery were studied by light and electron microscopy. The perimedial fibrous area was mainly composed of irregularly proliferated collagen fibers and scattered smooth muscle cells. We could not identify the usual fibroblast in any portion of the abnormal media despite examination with the electron microscope. There were many thin-walled, newly formed vessels sprouting from the adventitia in the fibrous area. We observed the complication of dissecting aneurysms in two cases. We also discussed the possible role of the smooth muscle cells in the fibrous area of perimedial fibroplasia.