This 65 y/o male presented with chest and upper back pain. A portable chest x-ray and selected early and late phase images from a gadolinium enhanced MR angiogram shown above demonstrate findings of a Type B dissecting thoracic aortic aneurysm. The aortic knob is enlarged and there is a subtle "double aortic knob" sign. The Gd enhanced MR angiogram shows the origin of the descending aortic dissection at the left subclavian extending down to the level of the renal arteries. Differential flow in the true and false lumens is easily seen on the early and late phase images. Incidentally noted is a high grade stenosis of the left renal artery.