ABSTRACT
The site of injury to the thoracic aorta is variable depending on whether the injury is identified at autopsy or during clinical evaluation. Injuries involving the isthmus represent 70-90% of those described in surgical series while the percentage of those occurring in the ascending aorta increases in autopsy series,
highlighting the greater lethality of more proximal injuries.(1, 3, 6, 10-12) The fact that the proximal descending aorta is the location of injury for most patients who arrive alive at a hospital is explained in part by the additional connective tissue layer offered by the mediastinal pleura in the descending segment which may contain the aortic rupture and allow formation of a false aneurysm. (8) On the other hand, injuries to the ascending aorta may result in tamponade and are more commonly associated with blunt cardiac trauma, both of which significantly increase mortality.(1, 7, 9, 13)
Other locations of blunt aortic injury include the distal descending thoracic aorta and the transverse arch; the former is frequently observed in association with fractures of the thoracic vertebrae. Multiple sites of aortic injury and synchronous arch vessel injuries are identified in a smaller number of patients and are frequently lethal.(3, 4, 6, 9, 14, 15)
Initial descriptions of the injury mechanism responsible for blunt thoracic aortic injury focused on rapid horizontal or vertical deceleration as occurs during a high-speed motor vehicle crash or fall from a significant height.(6, 16, 17) It appears however that this alone may be insufficient to injure the thoracic aorta, at least under the forces commonly observed in motor vehicle crashes. Cadaveric impact models, using a fixed thorax to minimize chest deformation, fail to reproduce thoracic aortic injury even when subjected to forces exceeding 200 times gravity.(18) This highlights the potential importance of other biomechanical factors that occur at the moment of injury including chest wall deformation (as may occur with steering wheel impact) and aortic pressure changes (see below).
