Traumatic aortic injury

Traumatic aortic injury is a major cause of mortality in patients with blunt thoracic trauma. The commonest cause is motor vehicle accidents, but also includes falls and blast injuries, the common mechanism being deceleration. About 80-90% of patients who sustain this injury die prior to hospital admission. Most patients who reach hospital alive have a tear at the aortic isthmus just distal to the subclavian artery. The injury is caused by shearing stress between the aortic arch, which is relatively fixed and the more mobile descending aorta.

Rapid diagnosis and surgical treatment is essential as 40% of patients will die within 24 hours without treatment.

Clinical signs include upper limb hypertension (due to acute coarctation effect) and wide pulse pressure. In patients, who survive aortic injury, s

Fig. 3.3 Angiogram of acute aortic injury. There is a focal bulge immediately distal to left subclavian artery. This is a typical site for acute aortic injury seen in deceleration accidents. 127

Fig. 3.3 Angiogram of acute aortic injury. There is a focal bulge immediately distal to left subclavian artery. This is a typical site for acute aortic injury seen in deceleration accidents. 127

the integrity of the aorta is often maintained only by the adventitia. Widening of the mediastinum on chest X-ray is caused by mediastinal blood. This is not usually due to aortic bleeding as this leads to sudden death. Mediastinal blood can come from injury to other vessels, e.g. azygous, paraspinal vessels. The great utility of the chest X-ray is not in diagnosing acute aortic injury but in excluding it. A normal chest X-ray has a negative predictive value of 98%. Numerous signs on the chest X-ray have been described in association with traumatic aortic injury. These signs are identified secondary to the associated mediastinal haematoma rather than the aortic injury itself. The signs include rightward tracheal shift, rightward deviation of any nasogastric tube, right paratracheal widening and widening of the paraspinal lines. Two of the most valuable signs are loss of contour of the aortic arch and contour abnormalities of the superior mediastinum, mediastinal widening, upper rib fractures, a left apical pleural cap are further recognised signs.

Fig. 3.4 Angiogram of acute aortic injury. This projection has been chosen to best illustrate the dissection/intimal flap which is seen projecting into the aortic lumen. This corresponds to the intimal flap seen on the contrast enhanced CT (Fig. 3.2).

Further investigation should be undertaken if aortic injury is suspected. There is debate regarding the place of contrast enhanced CT and angiography. CT is an excellent way of identifying mediastinal haematoma; it will visualise contour abnormalities of the aorta. The example above (Figs 3.1 and 3.2) demonstrates acute aortic injury with mediastinal blood and an intimal flap within the lumen of the aorta. In addition, there are rib fractures and pleural effusions.

Angiography has traditionally been regarded as the standard reference technique for evaluating patients with traumatic aortic injury. The typical appearance of acute aortic injury is demonstrated in Figs 3.3 and 3.4. There is abnormal outpouching of the aorta just distal to the origin of the left subclavian artery. The angiographic appearance is of a contained pseudoaneurysm. In addition, there is a linear component due to an intimal flap seen distal to the pseudoaneurysm.

Treatment is with prompt surgical repair. Control of blood pressure is advised until surgical repair can be accomplished.

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