Abdominal Aortic Aneurysm

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Abdominal aortic aneurysm

First let us define some terms:

Aneurysm: an abnormal swelling in a blood vessel
Aorta: is the main artery that carries blood away from the heart to the rest of the body
Aortic aneurysm: an abnormal swelling of the aorta
Abdominal aortic aneurysm (AAA): an abnormal swelling (aneurysm) of that part of the aorta that lies in the abdomen; this is the commonest site of aneurysmal disease

AAA are present in about one in twenty men (5%) and one in fifty to a hundred (1-2%) women aged over 60 years. The main risk factors are smoking and high blood pressure and, possibly, high cholesterol levels.

If an AAA is large then it may be felt either by the patient or their doctor on examination. However, as the swelling in the tummy is usually non-tender and grows very slowly, many patients are unaware that they have an AAA. If a patient has a waist circumference of greater than 42 inches then even if the AAA is large there is a greater than 50% chance that even an experience doctor will not be able to feel it on abdominal examination.

For these reasons all patients suspected of having an AAA should undergo an ultrasound scan of their abdomen to confirm (or refute) the diagnosis and to obtain an accurate measurement of the size of any aneurysm detected.

Most patients with AAA do not know they have one and most do not cause any symptoms until, suddenly one day, they burst (called a ruptured AAA) usually without any warning. Only about 10% of patients who suffer a ruptured AAA survive.

As AAA are difficult to detect and rarely cause problems until it is ‘too late’, there is a very strong argument for population screening. The UK government is currently considering introducing AAA screening whereby every man on reaching his 65^th birthday will be offered an ultrasound scan. If the scan is normal (95% of cases) then the person can be reassured and discharged from follow-up. However, if an AAA is present (5% of cases) then the patient can either be enrolled in a surveillance programme or offered repair depending on the size of the AAA (please see below).

So, if you are a man, smoke (or have smoked), have high blood pressure, or if anyone in your family has had an AAA (the condition tends to run in families), then you should probably see a vascular surgeon to have an examination and an ultrasound scan when you reach 60 years of age

The treatment of AAA depends largely on their size as the bigger an AAA the more likely it is to burst (rupture) and cause premature death:

Description	Diameter of aorta (cm)	Estimated annual risk of rupture (%)	Estimated 5 year risk of rupture (%)*
Normal aorta	2-3	0	0 (unless AAA develops)
Small AAA	4-5	1	5-10
Moderate AAA	5-6	2-5	30-40
Large AAA	6-7	3-10	> 50
Very large AAA	> 7	> 10	Approaching 100

*The estimated 5 year risk is more than 5 times the estimated annual risk because over that 5 years the AAA, if left untreated, will continue to grow in size

All patients found to have an AAA should be started on Best Medical Therapy (BMT) comprising:

Smoking cessation: complete and permanent
Control of blood pressure
Anti-platelet agent such as Aspirin 75mg daily
Lipid lowering therapy with a statin such as Simvastatin 40mg daily at night

BMT will reduce the risks of the AAA growing and so the risks of rupture.

Once formed, most AAA continue to grow in size; especially if patients continue to smoke and do not control their blood pressure. The rate of growth is unpredictable so all patients with an AAA should be enrolled in an AAA surveillance programme where patients are seen and examined, and undergo an ultrasound scan of their abdomen, every 3-6 months.

Large trials have indicated that, in general, the risks of repairing small AAA outweigh the benefits. So, unless an AAA is causing pain or other symptoms (which is unusual) most vascular surgeons will not recommend repairing an AAA unless it exceeds 5.5cm in maximum diameter.

There are two ways of repairing an AAA:

Date this page was last updated : 26 August 2009