Thoracic aortic dissection is rare but based on my forensic experience, a common cause of sudden unexpected death in adults usually involving the ascending aorta and rupturing into the pericardial cavity (hemopericardium) or involving the coronary arteries leading to myocardial ischemia.  This is an unusual case as the dissection arises at the apex of the arch beyond the pericardial reflection thus leak is into the mediastinum and left pleural space.  The other important issue, in this case, is the availability of a previous chest radiograph.  I was rung by the ED physician to comment on the CXR.  It was easy to make a rapid diagnosis of ruptured aortic dissection as I saw that the CXR was essentially normal the month previously.  We were then able to able to arrange rapid CT angiography for a definitive diagnosis.