Medial smooth-muscle cell lesions and dissection of the aorta and muscular arteries.

We report a case of aortic, coronary, and renal artery dissections associated with pregnancy. The histologic changes related to the hemorrhages included smooth-muscle cell (SMC) proliferation with fibrosis, elastin fragmentation and collagen degeneration, and SMC vacuolar degeneration and coagulation necrosis. These lesions seemed to be prototypes for dissection, since they were associated with aortic and muscular artery dissections in three additional cases unrelated to pregnancy. In each case, dissections seemed to result from SMC activity that also involved the systemic vasculature, veins, and visceral smooth muscle in histologic patterns that could be explained as a product of SMC metabolism. We propose that the histologic changes associated with dissections are best explained as a product of the metabolism of SMCs that function as multifunctional mesenchyma in a manner controlled by variable penetrance of a gene that controls their metabolism.