Abdominal Aortic Aneurysm

Question 1

How common is it?

Answer 1

• The prevalence of abdominal aortic aneurysms (AAAs) is estimated at 1.3-12.7% in the UK.
• Symptomatic AAA in men has an incidence of 25 per 100,000 at age 50, which increases markedly to 78 per 100,000 in those over the age of 70.
• The incidence of AAA rose from the 1970s to 2000 but now appears to be declining

Question 2

What causes it?

Answer 2

• An aneurysm is a permanent and irreversible dilatation of a blood vessel by at least 50% of the normal expected diameter. Aortic aneurysms are classified as abdominal (the majority) or thoracic.
• The ‘normal’ diameter of the abdominal aorta is approximately 2 cm; it increases with age. An abdominal aneurysm is usually defined as an aortic diameter exceeding 3 cm.
• Most abdominal aortic aneurysms (AAAs) arise from below the level of the renal arteries, but can involve the renal ostia and arise supra-renally.
• Degeneration of elastic lamellae and smooth muscle loss.

Question 3

What risk factors are there?

Answer 3

• Severe atherosclerotic damage of the aortic wall; however, new evidence suggests this is not the only factor, and aneurysmal disease is probably a distinct arterial pathology.
• Family history - there are probably strong genetic factors. About 15% of first-degree relatives of a patient with an abdominal aortic aneurysm (AAA), mainly men, will develop an aneurysm.
• Tobacco smoking is an important factor.
• Male sex.
• Increasing age.
• Hypertension.
• Chronic obstructive pulmonary disease.
• Hyperlipidaemia.
• In population-based studies, people with diabetes have a lower incidence of aneurysms than non-diabetics have.
For a minority, there may be a specific cause - for example:
• Trauma.
• Infection - brucellosis, salmonellosis, tuberculosis, HIV.
• Inflammatory diseases, eg Behçet’s disease, Takayasu’s disease. Inflammatory aneurysms may have multifactorial pathology.
• Connective tissue disorders - Marfan’s syndrome, Ehlers-Danlos syndrome type IV.

Question 4

How does it present?

Answer 4

Unruptured AAA
Symptoms - often none, they may cause abdominal/back pain, often discovered incidentally on abdominal examination.
On examination - pulsatile and expansile abdominal swelling. AAA may be incidental finding on examination or on scans.

Ruputrued AAA
Symptoms & signs - intermittent or continous abdominal pain (radiates to back, iliac fossae or groins), collapse, an expansile abdomal mass and shock. If in doubt, assume a ruptured aneurysm. Ruptured AAA should be considered in any patient with hypotension and atypical abdominal symptoms.

Question 5

Differential diagnoses?

Answer 5

• The differential diagnosis for a ruptured TAA is that of chest pain, especially MI with cardiogenic shock but also massive pulmonary embolism.
• The differential diagnosis for ruptured AAA involves other causes of abdominal pain, including acute abdomen.

Question 6

How would you investigate the patient?

Answer 6

• Blood tests:
o FBC, clotting screen, renal function and liver function.
o Cross-match if surgery is planned.
o ESR and/or CRP if an inflammatory cause is suspected.
• ECG, CXR and possibly lung function tests.
• Scans:
o Ultrasound is simple and cheap; it can assess the aorta to an accuracy of 3 mm. It is used for initial assessment and follow-up
o CT provides more anatomical details, eg it can show the visceral arteries, mural thrombus, the ‘crescent sign’ (blood within the thrombus, which may predict imminent rupture), and para-aortic inflammation. CT with contrast can show rupture of the aneurysm.
o MRI angiography may be used. This is safer than conventional angiography, as it does not use nephrotoxic contrast medium.

Question 7

What treatment/s would you consider? What risks and benefits of treatment are there?

Answer 7

Ruptured aortic aneurysm is a surgical emergency.
Unruptured AAA can be managed by monitoring or by elective surgery or stenting. Rupture is more likely if hypertensive, smoker, female and strong family history.