Thoracic aortic injury

# Mechanism

## Blunt trauma (more common)
- Rapid deceleration (e.g. motor vehicle accident, fall from great height)
- Crush injury

## Penetrating trauma
- Stab wound
- Gun shot wound

# Pathology

## Trauma to the aorta may result in:
- Aortic laceration: a tear in the intima which may extend through the vessel wall. The tear is typically transverse.
- Aortic transection: laceration of all three layers of the vessel wall, also known as aortic rupture.
- Pseudoaneurysm: aortic rupture contained by adventitia or periaortic tissues.
- Mural haematoma: haematoma within the wall of the aorta.
Aortic dissection is a longitudinal tear in the aortic wall and is rarely a sequelae of trauma.

## Localization
- Aortic isthmus 90%
- Ascending aorta 5%
- Diaphragmatic hiatus 5%
The isthmus is portion of the proximal descending thoracic aorta between the left subclavian artery origin and the ligamentum arteriosum. Tethering of the aorta by the ligamentum arteriosum is believed to account for the high frequency of aortic injury in this region.
The above figures represent the site of injury in those patients who present to hospital. The ascending aorta is injured in 20 to 25% of cases at autopsy but most of these patients die at the scene from serious complications such as a ruptured aortic valve, coronary artery laceration or haemopericardium with pericardial tamponade.

# Diagnosis

## Clinical presentation
70% of patients with thoracic aortic injury die at the scene of the trauma. In those who make it to hospital, clinical diagnosis is difficult. The signs and symptoms are non-specific and distracting injuries are often present. Clinical presentation may include chest or mid-scapular back pain, signs of external chest trauma or haemodynamic instability. Clinical suspicion is usually based on mechanism and severity of the injury, the hemodynamic status of the patient and/or the presence of related injuries. The diagnosis ultimately relies on appropriate imaging.

## Chest X-Ray
Initial screening investigation in the trauma patient. The mediastinum on a portable supine film may difficult to assess, especially if taken in expiration or if the patient is rotated. Direct signs of aortic injury are not visible on chest x-ray but indirect signs may be detected: mediastinal hematoma, other chest injuries.
Signs of mediastinal haematoma:
- Widened mediastinum
- Indistinct or abnormal aortic contour
- Deviation of trachea or NGT to the right
- Depression of left main bronchus
- Widened paraspinal stripe
- Left apical pleural cap
The detection of mediastinal hematoma on chest x-ray has a high sensitivity for aortic injury but a low specificity because most mediastinal hematoma is due to other causes such as tearing of mediastinal vessels, sternal injury or thoracic spine injury. Only 12.5% of mediastinal hematoma is due to aortic injury. However, the negative predictive value of a normal chest x-ray of good quality is 96% to 98%.
 CT chest

## Non-contrast CT
May show indirect signs of aortic injury:
- Mediastinal hematoma
- Other chest injuries

## CT Angiography
The investigation of choice. Excellent at showing direct signs of aortic injury as well as indirect signs. Sensitivity 100%, specificity 100%.
Signs of mediastinal hematoma on CT angiography:
- Abnormal soft tissue density around the mediastinal structures
- Location is important  periaortic hematoma much more suggestive of aortic injury than isolated mediastinal haematoma remote from the aorta.
Signs of aortic injury:
- Intraluminal filling defect (intimal flap or clot)
- Abnormal aortic contour (mural haematoma)
- Pseudoaneurysm
- Extravasation of contrast

## Conventional Angiography
Rarely performed due to the advent of high quality CT angiography.
Signs of aortic injury on conventional angiography:
- Resistance in advancing guidewire
- Intraluminal filling defect (intimal flap or clot)
- Abnormal aortic contour (mural haematoma)
- Pseudoaneurysm
- Extravasation of contrast

# Complications
- General risks of angiography
- Dissection or rupture due to guidewire or catheter

# Other imaging methods
Generally not used in the acute setting.
- MRI
- Transoesphageal echocardiography
- Intravascular ultrasound

# Differential Diagnosis
Other causes of widened mediastinum on chest x-ray:
- Technical factors
- Vascular ectasia
- Mediastinal lipomatosis
- Mediastinal masses
Mimics of mediastinal hematoma on CT:
- Artefact
- Thymic tissue
- Unopacified vessels
- Pericardial recesses
- Paramediastinal lung atelectasis
Mimics of aortic injury on CTA or conventional angiography:
- Artefact
- Streaming of contrast
- Aortic atheroma
- Ductus diverticulum
- Infundibulum of branch vessel

# Management
Aortic injury is a surgical emergency. Treatment is with an aortic stent graft or open repair.

# Complications
- Death from aortic rupture and haemorrhage
- Chronic traumatic pseudoaneurysm
- Embolization from pseudoaneurysm