What kinds of mechanisms can actually cause a thoracic aortic injury? Most physicians are aware that it involves sudden deceleration. This includes falls from a height and head-on car crashes. However, other mechanisms are associated with this injury as well.

Sudden acceleration can also tear the aorta. This can occur from a rear-end type car crash where one car is stopped and the other is traveling at a high rate of speed. It can also occur when pedestrians are struck by a car.

T-bone crashes also have a significant association with aortic injury. Twenty years ago, this was not really recognized, but now we know better.

One very interesting mechanism that I’ve seen about 5 times is the torso crush. This can occur when heavy objects tip over onto someone’s chest. I’ve seen this injury when multiple sheets of plywood have fallen on someone, and when a ditch caved in and the patient was crushed by dirt.

So when should you be concerned about the aorta enough to image it? In all cases, there must be a significant mechanism (see above). Falling over or being bumped at low speed just can’t do it. It’s also very rare in children under 10. I use the following guidelines:

• Significant mechanism plus any one chest x-ray finding (see last 2 days of discussion)
• Extreme mechanism alone. I define this as a closing velocity > 60mph, although you probably won’t know exactly how fast they were really going. You’ll need to estimate based on the usual speed on that particular road in the case of a car crash. Err on the side of predicting a higher speed. Extreme mechanism also includes pedestrian struck at moderate speed or better and torso crush.
• Physical signs or symptoms consistent with aortic injury. These include tearing chest pain, especially between the shoulder blades, and pulse discrepancy (right radial pressure higher than left radial)

The gold standard screening test is now the helical chest CT. If the results are indeterminate, then a good old-fashioned aortogram may be needed.