Aortic dissection: atypical patterns seen at MR imaging.

Aortic dissection is typically manifested by an intimal flap separating true and false lumens. Atypical patterns lacking an intimal flap can occur, however, and are less well recognized. In this study, the authors review their experience with atypical patterns at magnetic resonance (MR) imaging. They evaluated the T1-weighted and gradient-echo MR images of the entire aorta in 64 patients with aortic dissection. In nine patients (14%) aortic wall thickening was the only sign of dissection in the thorax. In three of these cases, an intimal flap was found in the abdominal aorta; the other six patients had no flap in any region of the aorta, and this led to false-negative angiographic results in three cases. Aortic wall thickening as an atypical sign of dissection was seen more frequently in acute (29%) than in chronic (7%) dissection and was seen in only patients without Marfan syndrome. Two patients with atypical acute dissection at initial examination developed a clearly identifiable intimal flap at follow-up. Aortic wall thickening may represent the only sign of aortic dissection. In some cases, imaging the entire aorta can enable recognition of dissection in atypical cases.