Fourteen patients with aortic dissection without intimal rupture were examined by means of magnetic resonance (MR) imaging, computed tomography (CT), or both. MR imaging showed a marginal high-intensity area along the aortic wall, while CT showed a nonopacified crescentic area along the aortic wall. These areas decreased in size within a short period and normalized after 1 year. Two autopsies demonstrated intramural hemorrhage without intimal tears. The dissected lumen seen in these cases is believed to represent intramural hemorrhage due to rupture of the vasa vasorum without intimal tear; this entity is believed to represent aortic dissection.