Aortic intramural hematoma (IMH) has been considered a variant or precursor of aortic dissection with no entry tear or false lumen flow; however, the pathophysiological mechanism, risk factors, and evolution are rather different from those of classic dissection. Hematoma forms within the aortic wall as a result of either hemorrhage of the vasa vasorum or, less commonly, an intimal fracture of an atherosclerotic plaque. The marked relationship between IMH and atherosclerotic disease explains the older age of these patients compared with those with aortic dissection, the higher incidence of arterial hypertension, and the tendency for descending aorta involvement (50% to 60%).
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