Aortic dissection

Aortic dissection is the most common form of the acute aortic syndromes and a type of arterial dissection. It occurs when blood enters the medial layer of the aortic wall through a tear or penetrating ulcer in the intima and tracks along the media, forming a second blood-filled channel within the wall.

The majority of aortic dissections are seen in elderly hypertensive patients. In a very small minority, an underlying connective tissue disorder may be present. Other conditions / predisposing factors may also be encountered, in which case they will be reflected in the demographics. Examples include 5:

Aortic dissection is arbitrarily divided into:

  1. acute: within 14 days of first symptom onset
  2. chronic: after 14 days

Patients are often hypertensive (although they may be normotensive or hypotensive) and present with anterior or posterior chest pain and a tearing sensation in the chest. 

Depending on the extent of dissection and occlusion of aortic branches, end organ ischaemia may also be present (seen in up to 27% of cases) 5, including:

  • abdominal organ ischaemia
  • limb ischaemia
  • ischaemic or embolic stroke
  • paraplegia: involvement of the artery of Adamkiewicz

In some cases of aortic rupture, the involvement of coronary arteries may result in collapse and death. Symptoms of cardiac tamponade (Beck's triad) may also be encountered.

The normal lumen lined by intima is called the true lumen and the blood-filled channel in the media is called the false lumen.

In most cases the vessel wall is abnormal.

Imaging is essential in delineating the morphology and extent of the dissection as well as allowing for classification (which dictates management). Two classification systems are in common usage, both of which divide dissections according to the involvement of the ascending aorta:

  1. Stanford classification
  2. DeBakey classification

In recent years, the Stanford classification has gained favour with cardiothoracic surgeons. Approximately 60% of dissections involve the ascending aorta (Stanford A / DeBakey I and II) 5.

Chest radiography may be normal or demonstrate a number of suggestive findings, including:

  • widened mediastinum (more than 8 cm at the level of the aortic knob on portable anteroposterior chest radiographs) 9,10
  • double aortic contour
  • irregular aortic contour
  • inward displacement of atherosclerotic calcification (more than 1 cm from the aortic margin) 9,11

CT, especially with arterial contrast enhancement (CTA) is the investigation of choice, able not only to diagnose and classify the dissection but also to evaluate for distal complications. It has reported sensitivity and specificity of nearly 100% 3,5.

Non-contrast CT may demonstrate only subtle findings; however, a high-density mural haematoma is often visible. Displacement of atherosclerotic calcification into the lumen is also a frequently identified finding.

Dissections involving the aortic root should ideally be assessed with ECG-gated CTA which nearly totally eliminates pulsation artefact. Pulsation artefact can mimic dissection, is very common and seen in up to 92% of non-gated CTA studies 8.

Contrast-enhanced CT (preferably CTA) gives excellent detail. Findings include 1-3,5:

An essential part of the assessment of aortic dissection is identifying the true lumen, as the placement of an endoluminal stent graft in the false lumen can have dire consequences. Distinguishing between the two is often straighforward, but in some instances, no clear continuation of one lumen with normal artery can be identified. In such instances, a number of features are helpful 3:

  • true lumen
    • often compressed by the false lumen and the smaller of the two
    • outer wall calcifications (helpful in acute dissections)
    • origin of coeliac trunk, SMA and right renal artery usually from true lumen
  • false lumen
    • often larger lumen size due to higher false luminal pressures 
    • beak sign
    • cobweb sign (as slender linear areas of low attenuation specific to the false lumen due to residual ribbons of media that have incompletely sheared away during the dissection process) 3
    • often of lower contrast density due to delayed opacification
    • may be thrombosed and seen as mural low density only (more common in chronic dissections)
    • origin of left renal artery usually from false lumen
    • surrounds true lumen in Stanford type A 

Chronic dissection flaps are often thicker and straighter than those seen in acute dissections 3.

Transoesophageal echocardiography (TOE) has very high sensitivity and specificity for assessment of acute aortic dissection, but due to limited access and its invasive nature, it has largely been replaced by CTA (or MRA in some instances) 5.

Although in general MRA has been reserved for follow-up examinations, rapid non-contrast imaging techniques (e.g. true FISP) may see MRI having a larger role to play in the acute diagnosis, particularly in patients with impaired renal function 4. It has similar sensitivity and specificity to CTA and TOE 5 but suffers from limited availability and the difficulties inherent in performing MRI on acutely unwell patients.

Conventional digital subtraction angiography has historically been the gold standard investigation. CTA has now replaced it as the first line investigation, not only due to it being non-invasive but also on account of better delineation of the poorly opacifying false lumen, intramural haematoma and end-organ ischaemia. 

Angiography still is required for endoluminal repair.

Risks of angiography include general risks of angiography plus the risk of catheterising the false lumen and causing aortic rupture.

  • aggressive blood pressure control with beta blockers as they reduce both blood pressure and also heart rate hence reduce extra pressure on the aortic wall
  • immediate surgical repair (for type A dissection or complicated type B dissection)

Complications of all types of aortic dissection include:

  • dissection and occlusion of branch vessels
    • abdominal organ ischaemia
    • limb ischaemia
    • ischaemic stroke
    • paraplegia: involvement of artery of Adamkiewicz
  • distal thromboembolism
  • aneurysmal dilatation: this is an indication for endovascular or surgical intervention 6
  • aortic rupture

A type A dissection may also result in:

Although the combination of blood pressure control and surgical intervention has significantly lowered in hospital mortality, it remains significant, at 10-35%. Over the 10 years following diagnosis another 15-30% of patients require surgery for life-threatening complications 5.

The differential on chest x-ray is that of a dilated thoracic aorta.

On CT, a number of entities that can mimic a dissection should be considered 5:

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Article information

rID: 918
Systems: Vascular, Chest
Synonyms or Alternate Spellings:
  • Dissection of the thoracic aorta
  • Dissection of the aorta
  • Dissection of aorta

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Cases and figures

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    Figure 1: diagram of pathogenesis
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    DeBakey I

DeBake...
    Figure 2: De Bakey Type I / Stanford A
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    DeBakey II

DeBak...
    Figure 3: De Bakey Type II / Stanford A
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    DeBakey III

DeBa...
    Figure 4: De Bakey Type III / Stanford B
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    Type A aortic dis...
    Case 1: Stanford type A
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    Case 2: Stanford type B
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    Case 3: Stanford type B
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    Case 4: Stanford type B
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    Case 5: Stanford type B
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     Three-channel ao...
    Case 6: showing a three-channel aorta
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    Case 7: Stanford type A with rupture into pericardium
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    Infrarenal dissec...
    Case 8: dissection confined to the infrarenal aorta
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    Case 9: Stanford type A / Debakey Type I
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    Fig. 1

AP MIP
    Case 10: Stanford type B dissecting aneurysm
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    Case 11: Stanford type A
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    Case 12: Stanford type A
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    Case 13: Stanford type A
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    Case 14: Stanford type A
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    Case 15: Stanford type A
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    Case 16: Stanford type A
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    Case 17
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    Case 18: Stanford type A
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    Case 19: Stanford type B
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    Case 20: treated with a aortic stent
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    Case 21: with dissecting aneurysm
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    Case 22: Stanford type A : background Marfan syndrome
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    Case 23: with spinal cord ischaemia
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