Aortic dissection
Updates to Article Attributes
Aortic dissection is one 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.
Epidemiology
The majority of aortic dissections are seen in elderly hypertensive patients. In a very small minority, and 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. Example include 5:
- structural aortic abnormalities
- bicuspid aortic valve
- aortic coarctation
- abnormal connective tissues
- Turner syndrome
- pregnancy
- intra-aortic balloon pumps 7
Clinical presentation
Aortic dissection is arbitrarily divided into :
- acute: with 14 days of first symptom onset
- 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 chest.
Depending on the extent of dissection and occlusion of 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 artery of Adamkiewicz
In some cases aortic rupture, involvement of coronary arteries may result in collapse and death. Symptoms of cardiac tamponade (Beck(Beck's triad) may also be seen.
Pathology
The normal lumen lined by intima is call the true lumen and the blood-filled channel in the media is called the false lumen.
In most cases the vessel wall is abnormal.
- hypertension (pathogenesis: medial degeneration)
- inherited connective tissue disorders (pathogenesis: medial degeneration)
- atherosclerosis (pathogenesis: penetrating ulcer)
- vasculitis (pathogenesis: inflammation)
- pregnancy (pathogenesis: unknown)
- iatrogenic: aortic catheterisation, intra-aortic balloon pump
Radiographic features
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 involvement of the ascending aorta:
Approximately 60% of dissections involve the ascending aorta (Stanford A / DeBakey I and II) 5.
Plain film
Chest radiography may be normal, or demonstrate a number of suggestive findings, including:
- widened mediastinum
- double aortic contour
- irregular aortic contour
- inward displacement of atherosclerotic calcification
CT
CT, especially with arterial contrast enhancement (CTA) is the investigation of choice, able not only to diagnose and classify the dissection, but also evaluate for distal complications. It has reported sensitivity and specificity of nearly 100% 3,5.
Non-contrast CT may demonstrate only subtle findings, however high density mural haematoma is often visible. Displacement of atherosclerotic calcification into the lumen is also a frequently identified.
Post contrast CT (CTA preferably) gives excellent detail. Findings include 1-3,5:
- intimal flap
- double lumen
- dilatation of aorta
- complications (see below)
- an atypical variant that may be seen is aortic intramural haematoma
An essential part of assessment of aortic dissection is identifying the true lumen, as placement of endoluminal stent graft in the false lumen can have dire consequences. Often distinguishing between the two is obvious, 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 false lumen
- outer wall calcifications (helpful in acute dissections)
-
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)8
- often of lower contrast density due to delayed opacification
- may be thrombosed and seen as mural low density only (more common in chronic dissections)
Chronic dissection flaps are often thicker and straighter than those seen in acute dissections 3.
Transoesophageal echocardiography
Transoesophageal echocardiography (TOE) has very high sensitivity and specificity for assessment of acute aortic dissection, but due to limited access and invasive nature, it has largely been replaced by CTA (or MRA in some instances) 5.
MRI
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.
DSA - angiography
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 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 risk of catheterising the false lumen and causing aortic rupture.
Treatment and prognosis
- aggressive blood pressure control
- immediate surgical repair (for type A dissection or complicated type B dissection)
Complications
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:
- coronary artery occlusion
- aortic incompetence
- rupture into pericardial sac with resulting cardiac tamponade
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.
Differential diagnosis
The differential on chest x-ray is that of a dilated thoracic aorta.
On CT a number of entities which can mimic a dissection should be considered 5:
- pseudodissection due to motion artifact and contrast streaks
- mural thrombus
- intramural haematoma: really an atypical type of aortic dissection
- penetrating atherosclerotic ulcer
-</ul><p>In some cases aortic rupture, involvement of <a href="/articles/coronary-arteries">coronary arteries</a> may result in collapse and death. Symptoms of cardiac tamponade (Beck's triad) may also be seen.</p><h4>Pathology</h4><p>The normal lumen lined by intima is call the<em> true lumen</em> and the blood-filled channel in the media is called the <em>false lumen</em>.</p><p>In most cases the vessel wall is abnormal.</p><ul>- +</ul><p>In some cases aortic rupture, involvement of <a href="/articles/coronary-arteries">coronary arteries</a> may result in collapse and death. Symptoms of cardiac tamponade (<a title="Beck's triad" href="/articles/becks-triad-1">Beck's triad</a>) may also be seen.</p><h4>Pathology</h4><p>The normal lumen lined by intima is call the<em> true lumen</em> and the blood-filled channel in the media is called the <em>false lumen</em>.</p><p>In most cases the vessel wall is abnormal.</p><ul>
-<li>aneurysmal dilatation: this is an indication for endovascular or surgical intervention <sup>6 </sup>- +<li>aneurysmal dilatation: this is an indication for endovascular or surgical intervention <sup>6 </sup>
Unable to process the form. Check for errors and try again.