An acute aortic dissection involved the retroesophageal aortic diverticulum (RAD) and descending thoracic aorta in a patient with right aortic arch. The RAD, which was separated into false and true lumens by an intimal flap-the classic diagnostic sign of aortic dissection-was overlooked on transesophageal echocardiography and computed tomography but was clearly depicted on magnetic resonance imaging (MRI). It was found that MRI can delineate the anatomy of a congenital arch anomaly complicated by great vessels disease.