Radiological signs
Traumatic aortic injury can be suspected already on a plain chest X-ray (in the supine position). The changes are indirect and require confirmation:
- Widening of the superior mediastinum: the ratio of mediastinal width to thoracic width (M/C ratio) reaches approximately 0.3.
- Widening of the right paratracheal stripe.
- Tracheal deviation to the right from the midline.
- Alteration of the aortic arch: the contour (aortic knuckle) is enlarged and often partially obscured against the background of a mediastinal hematoma.
CT injury classification
To systematize CT findings, the Presley Trauma Center CT Grading System is used. It is based on the defect size, presence of hematoma, and involvement of adjacent structures.
| Grade | Injury characteristics | Presence of mediastinal hematoma |
|---|---|---|
| I (Normal) | Ia: normal aorta. Ib: normal aorta. | Ia: none. Ib: present |
| II (Minimal) | Small pseudoaneurysm (<1 cm), thrombus, or intimal flap (<1 cm). | IIa: none. IIb: present |
| III (Limited) | Well-defined pseudoaneurysm (>1 cm), flap/thrombus. IIIa: without involvement of the arch/ascending aorta. IIIb: with involvement of the great vessels. | Always present |
| IV (Complete rupture) | Ill-defined irregular pseudoaneurysm, intimal flap, or thrombus. | Always present |
In acute complete rupture (total aortic disruption), CT visualizes a large pseudoaneurysm with partial anterior contrast extravasation. An extensive mediastinal hematoma may displace adjacent structures (e.g., the left pulmonary artery).
Imaging modalities: CT angiography and MRI
Computed tomography (CT angiography) This is the most widely used modality. Its main advantages are immediate availability (proximity to intensive care units) and high speed. CT is ideal for assessing polytrauma (head, chest, abdomen) and planning endovascular treatment.
Typical CT signs of trauma include contrast extravasation, local caliber changes, a dissection flap, and aortic contour abnormality (indicating intimal and medial tear). In questionable cases, the diagnosis is confirmed using intravascular ultrasound (IVUS), whereas conventional aortography adds little significant information.
Magnetic resonance imaging (MRI) Rapid MRI sequences (BBFSE) allow the examination to be performed in minutes without contrast. The method is excellent at differentiating partial wall injury from complete injury (greater than 270 degrees of the circumference) and determining the age of an intramural hematoma. The main drawback is limited access to MRI scanners in emergency situations.
Differential diagnosis and false-positive results
Diagnostics of trauma can be complicated by false-positive CT findings. These are caused by motion artifacts, streak artifacts (from unraised arms or contrast in the left brachiocephalic vein), severe atheromatosis, and certain anatomical structures (superior intercostal vein, bronchial artery funnel).
The key task for the diagnostician is to differentiate a traumatic pseudoaneurysm from a normal variant such as the ductus diverticulum (ductus diverticulum).
- Traumatic pseudoaneurysm: has an asymmetric shape, a sharp proximal edge at the transition to the normal wall, and is accompanied by a mediastinal hematoma.
- Diverticulum: has a smooth symmetric contour, blunt (smoothed) junctions with the normal aorta, and occurs without a mediastinal hematoma.
It is important to remember that a pseudoaneurysm is unstable: its wall is represented exclusively by the adventitial layer, unlike true aneurysms (e.g., in Marfan syndrome or atherosclerosis), where all vessel layers are locally dilated.
Briefly: answers to topical questions
In which anatomical segment of the thoracic aorta does traumatic rupture most frequently occur?
Traumatic rupture most frequently occurs in the aortic isthmus (isthmus). This anatomical segment, located 1.5–2 cm distal to the origin of the left subclavian artery, accounts for 90% of all traumatic ruptures. The injury occurs at the site where the mobile thoracic aorta is rigidly fixed by the ligamentum arteriosum (ligamentum arteriosum).
What is the primary biomechanism of traumatic rupture of the thoracic aorta in motor vehicle collisions?
The primary biomechanism of traumatic rupture of the thoracic aorta in motor vehicle collisions is sudden deceleration. The following trauma mechanisms are distinguished:
- Sudden deceleration (deceleration) — occurs during an impact at speeds over 50 km/h; the rupture occurs at the site of rigid vessel fixation.
- Torsion (twisting) — occurs due to displacement of the heart to the left during anteroposterior compression.
- Osseous pinch (osseous pinch) — compression of the heart and aorta between the sternum and the spinal column.
What late complications are characteristic of unrecognized thoracic aortic trauma?
Late complications of unrecognized blunt thoracic aortic trauma in surviving patients include the formation of a stable false aneurysm and the development of arteriovenous fistulas. Such a delayed outcome is possible in 6–20% of cases when surrounding tissues (e.g., the pleura) temporarily contain profuse hemorrhage from the injured vessel and prevent instant death of the victim at the scene.
To remember the radiological signs of aortic trauma in the supine position, look for "widening and rightward displacement": the mediastinum and paratracheal stripe widen, the trachea is displaced to the right, and the aortic arch is obscured within the hematoma.
Class and exam questions
What is the fundamental difference between a true aneurysm and a post-traumatic pseudoaneurysm?
In a true aneurysm, all layers of the aortic wall are diffusely or locally dilated. A false aneurysm (pseudoaneurysm) occurs after traumatic rupture; it is unstable, and its wall is formed exclusively by the adventitial layer.
Why is MRI rarely used in acute aortic trauma despite its high accuracy?
The single, yet critical limitation of MRI is its low availability in intensive care units and the difficulty of use in emergency situations in unstable patients.
How to distinguish an arterial duct diverticulum from a pseudoaneurysm on CT?
The diverticulum has smooth symmetric contours, smoothed edges, and is not accompanied by a hematoma. A pseudoaneurysm is always asymmetric, has a sharp edge, and is often surrounded by a mediastinal hematoma.
What else to study on this topic
- Intravascular ultrasound (IVUS) in inconclusive CT angiography results
- Imaging features of intramural hematoma (IMH) on MRI
- Atherosclerotic and genetic aneurysms of the thoracic aorta: differential diagnosis
- The role of matrix metalloproteinases (MMP-2, MMP-9) in aortic wall remodeling
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