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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
The aorta (1) runs through the abdomen in front of the spine.

Various branches come off the aorta including the renal arteries (2) which carry blood to the kidneys.

Around about the level of the tummy button the aorta divides into the two iliac arteries (3) to carry blood down into the pelvis and legs

Weakness in the wall of the aorta coupled with the high pressure inside the vessel can cause the aorta to bulge outwards, forming an aneurysm.

This can occur in any blood vessel but by far the most common site for an aneurysm is in the abdominal aorta. They usually start below the level of the renal arteries (2) and can extend into the iliac arteries (3).

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 experienced 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.

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:

To download our patient information sheet on AAA, please click here

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