Thoracic aortic dissection is a type of traumatic aortic injury commonly seen in high-speed motor vehicle collisions 1. Approximately 75-80% of thoracic aortic dissection occurs in motor vehicle accidents, at speeds of above 50km/h.
While the pathophysiology behind aortic dissection is not clear, there are three main, interplaying mechanisms for traumatic aortic injury:
- Rapid deceleration - this may cause torsion and shearing of the aorta against its fixed segments - particular the aortic root, ligamentum arteriosum and diaphragm
- Increased intrasvascular pressure - pressures of up to 2000 mmHg may be generated as a result of compression to the aorta which may in turn damage the vessels of the aortic wall
- Osseous pinch - compression of the aorta between the anterior chest wall and the vertebral column may give rise to aortic injury, as well as subclavian and carotid injury
Chest radiographs are commonly used for screening in motor vehicle accidents. Radiographic signs of aortic injury include:
- Mediastinal widening (greater than 8cm or 25% of the thoracic width)
- Transverse aortic arch abnormality
- Loss of aorto-pulmonary window
CT is considered the diagnostic test of choice for traumatic aortic injury. It has a sensitivity which is greather than 98%. Signs of aortic injury on CT include the presence of 1:
- intimal flap
- traumatic pseudoaneurysm
- contained rupture
- intraluminal mural thrombus
- abnormal aortic contour
- sudden change in aortic caliber
Since the 1990s, there has been a shift away from open surgical repair of aortic injury. Instead, thoracic endovascular aortic repair (TEVAR) has gradually replaced open repair as the mainstay of operative aortic injury management 2. It is associated with significantly lower operative times, procedural blood loss and intraoperative blood transfusion compared to open repair.
Renal artery injury is an uncommon occurrence, occurring in 2.5-4% of traumatic renal injuries.
Management for renal artery injury is controversial - this is due to its relatively rare nature. There are three main options in RAI 3:
- Nephrectomy - only in well patients with two kidneys
- Vascular repair
- Conservative monitoring - can be complicated by renovascular hypertension4
In this case, the affected left kidney is markedly hypodense compared to the contralateral kidney, which is well perfused with hyperdense contrast. This is due to the absence of arterial vascular supply on the left side.
Case contributed by A/Prof. Pramit Phal.