Chapter 11: Descending Thoracic Aortic Injuries

BACKGROUND

The majority of descending thoracic aortic injuries occur due to blunt trauma, which in turn are caused by increased aortic pressures and shear stress resulting from a rapid deceleration mechanism. Blunt thoracic aortic injuries most commonly occur from motor vehicle collisions, motorcycle collisions, auto versus pedestrian, or a fall from height.¹ It has been estimated that 8000 blunt thoracic aortic injuries occur annually in the United States but the true incidence may be significantly higher since it has been reported that the vast majority of patients with these injuries die at the scene and may never be diagnosed or counted.² This is evidenced by two autopsy studies which found that a third of all deaths from blunt trauma had blunt thoracic aortic injuries and only 20% of these made it to the hospital alive.^3,4 Penetrating injuries to the thoracic aorta are much less common, usually occur from gunshot wounds, and typically present with massive hemothorax and in extremis. Survival to the hospital from penetrating injury to the thoracic aortic is even rarer.

The incidence of blunt thoracic aortic injury in patients reaching hospital care has increased with an overall incidence of 0.2% of blunt trauma admissions in those aged 15 to 65 years, 0.5% in those 56 to 65 years, and 1.5% in those older than 65 years. It is much less common in children younger than 16 years old (0.03%).^5,6 The most likely explanation for this trend is that the mechanism of injury is from torsion at points of aortic fixation and that aortic elasticity, which is likely protective, decreases with age. Studies have shown that at the time of injury there is a dramatic increase in intra-aortic pressure combined with rotational forces, which can cause a focused impulse at the aortic isthmus just distal to the origin of the left subclavian artery. Additionally, the increased composition of elastin in the ascending aorta and aortic arch causes it to have significantly greater elasticity than the descending thoracic and abdominal aortas. This explains why 75% of blunt aortic injuries occur at the isthmus, 22% occur more distally in the descending thoracic aorta, and only 4% occur in the ascending aorta.¹

Consistent with the force required to cause a blunt aortic injury, most patients also present with a severe injury to another body area with the most common being traumatic brain injury and severe abdominal injury. The average injury severity score (ISS) for these patients is 40, demonstrating the degree of overall injury seen in these patients.¹

ANATOMY

The descending thoracic aorta begins just distal to the origin of the left subclavian artery, runs along the posterior mediastinum anterior to the spine and just to the left of the esophagus, and terminates just superior to the origin of the celiac artery at the diaphragmatic hiatus (Fig. 11-1). While there are ...