Abdominal Aortic Aneurysm
What is an abdominal aortic aneurysm (AAA)?
An aortic aneurysm is defined as an abnormal dilatation of the aorta.
How common are abdominal aortic aneurysms?
Approximately 4% of people over the age of 65 in the UK have an abdominal aortic aneurysm. They are six times more likely in men than women. AAA account for 12,000 hospital admissions in England per year and cause the death for 6000 people in England and Wales annually.
What causes abdominal aortic aneurysms?
There may be both a genetic susceptibility and environmental factors influencing the development of abdominal aortic aneurysms. Individuals found to have AAA often also have other cardiovascular diseases, such as previous strokes or heart attacks, or peripheral arterial disease. Several of the risk factors for these conditions are common also to AAA; cigarette smoking, high blood pressure and high cholesterol etc. Interestingly diabetes would appear to be protective against AAA formation. Rarely AAA develop as a result of infection or following previous injury to the aorta. AAA may also run in families and 20% of patients have a relative who has also had an AAA.
How do abdominal aortic aneurysms present?
75% of abdominal aortic aneurysms are asymptomatic at the time of identification, being discovered during routine health checks or investigations for other medical conditions. Alternatively, an AAA may cause symptoms as a result of compression on adjacent structures, with back pain being a potential complaint. There may also be a pulsatile lump in the abdomen that can occasionally be tender. AAA may rupture, which is life-threatening and requires emergency surgery. Circulation Clinic does not offer emergency treatment for ruptured AAA and we advise all patients to seek help through the standard emergency channels.
When should an abdominal aortic aneurysm be repaired?
An AAA should be considered for repair when the risk of rupture outweighs the risk of surgery. The best predictor of rupture is the AAA diameter (see table 1). Currently, the proposal in the UK is that all patients with an AAA that measures 5.5cm or greater should be considered for repair. There are, however, occasions when repair may be considered at a lower size threshold e.g. if the AAA is rapidly expanding or is causing significant symptoms.
How are abdominal aortic aneurysms repaired?
There are two methods for repairing AAA: open surgery or "keyhole" endovascular aneurysm repair (EVAR, fig.2). Open surgical repair is performed through an abdominal incision under general anaesthesia. The aneurysmal aorta is reconstructed with a synthetic graft that is physically sewn into the aorta above and below the aneurysmal segment. In order to achieve the best outcomes meticulous pre-operative planning, intra-operative technique and post-operative care is essential. EVAR is a less invasive option involving the insertion of stents to re-line the aorta from within: access to the aorta is gained through the arteries in the groins. Not everybody's aneurysm is suitable for this operation, depending on its size and shape.
Which is better - EVAR or open surgery?
There have been a number of trials comparing EVAR to open surgical repair. They report early (within 30 days of the operation) survival benefits associated with EVAR due to its less invasive nature. However, these initial early benefits may be offset by the increased likelihood of requiring further interventions if the initial repair was an EVAR: one third of EVARs may require a secondary procedure within 3 years of the initial operation. Furthermore, EVAR, unlike open surgical repair, requires ongoing surveillance to identify stent failure early with regular ultrasound or CT scans.
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Figure 1: CT scan of Abdominal Aortic Aneurysm
Table 1: Rupture risk of AAA according to maximum diameter.
Figure 2: Complex EVAR with stents into kidney arteries (FEVAR)