Aortic Dissection is one of those diagnoses that gets everyone’s heart rates up (despite beta blockers), and its something we (should) think about in all of our blunt trauma patients.
The proximal descending aorta is the great vessel most susceptible injury in blunt trauma, due to its relative mobility over the fixed abdominal aorta, which is held in place by the ligamentum arteriosum.
The chest x-ray is the best screening tool for thoracic aortic injury in blunt trauma patients.
When examining a supine AP chest radiograph in attempting to rule in or out aortic dissection, here are some pearls:
- Funny Mediastinum is the money: a widened or abnormal appearing mediastinum is found in nearly every traumatic thoracic aortic dissection. A clear aortic knob has 72% sensitivity, 47% specificity and 87% negative predictive value
- Mediastinal widening >8cm at the aortic knob: 53% sensitivity, 59% specificity and 83% negative predictive value
- 40% of widened mediastinums will ‘normalize’ with the patient in the erect position: if you can clear their spine and they have a wide mediastinum, and you weren’t otherwise going to scan their chest, then shoot an erect PA film.
- Other ‘classic signs:’ depression of the left main-stem bronchus, deviation of the naso-gastric tube to the right, apical pleural haemoatoma (cap), disruption of the calcium ring in the aortic knob (broken-halo): great to pimp interns on, pitiful sensitivity, not clinically useful if absent.
If your patient has a normal CXR (normal mediastinal width and aortic contour) the NPV for aortic injury is 98%.
What if it’s abnormal?
If your patient has a ‘funny’ or wide mediastinum, then the next step is CECT chest with arterial phase (At Grady the order is ‘CT Trauma Chest w Contrast’ or as part of ‘CT Trauma Chest Abdomen/Pelvis w Contrast’, lovingly referred to as the pan-scan). Modern scanners have great sensitivity: 97-100%, with a negative predictive value of 100% and specificity of 83-99%
What if the scan is equivocal? Then your patient needs an angiogram.
Other signs of thoracic aortic dissection: gush of bright red blood on chest tube insertion or significant on-going bloody output from the chest tube (>200ml/hr), then your patient should go to the OR for thoracotomy for whatever big structure is injured in the chest.