Findings
-The CXR demonstrates a widened mediastinum, indistinct aortic knob, and mediastinal shift to the right.
-The CT demonstrates an intimal flap in the descending aorta, a widened mediastinum secondary to periaortic hematoma, and a left-sided pleural effusion.
Discussion
-Aortic transection or rupture usually occurs as a result of high-impact blunt trauma e.g. MVA. 75%-90% result in immediate death. 18% of MVA-related deaths are secondary to aortic transection. Aortic transection is second only to head injury as the leading cause of injury-related death. Aortic transection must be distinguished from aortic dissection, which is a separation of the layers of the aortic wall, usually caused by a tear in the weakened intima. This patient demonstrates both with mediastinal hemorrhage and a Stanford Type B dissection.


http://eradiology.bidmc.harvard.edu/Classics/item.aspx?section=Emergency+Radiology&labelpk=33f0adab-853f-4010-a0e2-0756b3f1eac5&pk=6e919e0b-2a48-409b-a53c-32e51be6165a