Carotid artery dissection in a young adult: cystic medial necrosis associated with an increased elastase content.

A dissecting aneurysm of the right internal carotid artery was found in a 22-year-old man, who rapidly became unconscious and hemiparetic after an accident occurring during sport. The dissection was limited to the intima and internal elastic lamina. Patterns of cystic medial necrosis with mucoid degeneration were present in the right internal carotid artery proximal to the site of dissection, in the thoracic aorta, and in several visceral arteries. In the region of the right internal carotid artery affected with cystic medial necrosis, calcification and also splitting of the internal elastic lamina was found. Such calcification was also present at the site of the dissection, at the tip of the ruptured and recoiled elastic lamina. These changes, dissection as well as cystic medial necrosis, were associated with an elevated elastase content, a decrease of desmin and an increase of vimentin expression. Ultrastructurally, in areas affected by cystic medial necrosis a corresponding transformation of medial smooth muscle cell phenotype from the contractile to the metabolic state was found. The topographical relation of dissecting aneurysm, cystic medial necrosis, and an increased elastase content is suggestive of a causal relation, and the possibility of common etiological factors is discussed.