ABDOMINAL AORTIC ANEURYSM - a patient's guide
Dr Murray MacCormick - General Surgeon

What is an Abdominal Aortic Aneurysm?

An aneurysm is a blowout (distortion) of the aorta, which is the main high pressure artery leading from the heart and which distributes blood to all parts of the body. In most of these aneurysms the wall remains intact - a true aneurysm. If the aorta actually ruptures, a life-threatening situation arises (internal bleeding).

Aneurysms come in different shapes and sizes. Sometimes they are sausage shaped and sometimes they are balloon shaped.

In other much rarer situations the blood gets out through a hole in the wall of the aorta and this is called a false or pseudoaneurysm. These aneurysms are not the same as the congenital aneurysms that usually occur in the arteries of the brain and which are one of the causes of stroke. We are not going to discuss this type of problem here because the causes, effects and management are totally different.

Another potential point of confusion is the so-called dissecting aneurysm. This is another totally different situation and is not a true aneurysm and should more properly be called simply aortic dissection. Again we will not discuss this condition here as it is also managed differently.

Why do Aortic Aneurysms develop?

We don't know the answer to this question in most cases. Usually there is some element of atheroma (arteriosclerosis, or hardening) of the arteries throughout the body. The obvious difference here though is that the aorta is dilated to form the aneurysm whereas in atherosclerosis the arteries are narrowed and partially blocked by the deposits of plaque.

A great deal of research is being done to try to find answers to the questions about development of aortic aneurysms looking at the microscopic structure of the wall of the aorta but at this time there is still no complete answer.

Who gets AAA?

AAA occurs typically in the middle aged or older person and is two or three times more common in men than in women. AAA can nevertheless occur in younger persons.

There is a definite familial tendency in some families with the condition so there must be some hereditary factor. In some families nearly all the males get AAA at a younger age than usual - the so-called "Black Widow Syndrome" (very rare).

What is the significance of AAA?

Obviously if a blowout is allowed to go on stretching and enlarging indefinitely it will eventually reach a point where the wall is so weakened that the pressure of blood inside will cause it to burst. This is frequently fatal.

Where a person with a leaking or ruptured aneurysm does reach a hospital alive there is still a 60% or higher mortality (risk of death) rate even in the best of hospitals worldwide. On the other hand if the diagnosis is made before the aneurysm starts to leak then the survival rate for surgical repair is over 95%. It is of enormous importance therefore to identify and treat AAA at a stage before the risk of rupture is high.

What are the symptoms of AAA?

Most aneurysms of the aorta cause no symptoms at all until reaching the point of impending rupture. Some may cause very nonspecific symptoms such as backache or vague abdominal pain but this is not common.

Occasionally a person may notice prominent pulsation in the abdomen such as when resting a book on the tummy to read.

When an AAA begins to stretch rapidly or starts to leak then the symptoms can mimic a number of other conditions. During the stretching phase the patient may complain of backache but quite frequently there will be left-sided flank pain spreading down the left side towards the groin.

This may be mistaken for renal or ureteric colic. If there is significant blood loss from the rupture then the patient may be shocked and faint or feel dizzy of cold. As a general rule if any unusual pain or illness occurs in someone who is known to have an AAA then the possibility of leakage should be considered.

How is AAA diagnosed?

Some AAA can be felt easily through the abdominal wall but many of them cannot. This means we have to rely on other ways to make this important diagnosis.

While some are found by specifically looking, a large proportion are only found by chance. For example, when the person has an ultrasound examination for some other problem.

Ultrasound is the first choice for detecting an AAA Once the presence of an AAA is established, other techniques may or may not be used to get more precise information.

What sort of information do we need about an AAA?

The single most important fact is the size. The width of an AAA is a direct guide to the likelihood of rupture in the future. In addition to the width it is also necessary to know what part of the aorta is involved in the blowout and in particular whether any of the major branches supplying the organs are coming off the aneurysm. This is sometimes only apparent with additional tests such as CT scanning or angiography (where dye is injected into the bloodstream and x-rays taken to show the exact anatomy).

This is important information about the AAA itself but it is also necessary to know a lot about the general state of the patient's health before any recommendation can be made about further management. So a variety of other tests of the heart, lungs and kidneys will be done as part of the overall assessment and planning.

When should an AAA be treated surgically?

Although guidelines vary around the world, the most widely accepted qualification is an AAA that is 50 millimetres or more in maximum width. This is based on the risk of rupture once the AAA has got to that size. This is referred to as elective choice for surgery but if an AAA presents as an emergency with rupture or threatened rupture then the size of the AAA is not an absolute criteria.

In general if there is any suspicion that an AAA is causing acute symptoms then urgent repair will be considered unless there is a good reason not to offer surgery. It has already been mentioned that other factors need to be considered before proceeding with repair of an AAA - there is no credit in doing an operation to repair an aneurysm if the patient is not physically able to survive the surgery or the anaesthetic. So severe heart, lung or kidney disease, or incurable cancer may mean that surgery is too risky. Age alone is not an absolute criteria for the surgeon but is often an important factor for the patient and his family.

What is the treatment of an AAA?

The only curative treatment for an AAA is surgical repair. This requires replacing the expanded aneurysm segment with a graft made of a synthetic material usually Dacron or Teflon. For many years this has been done as an "open" abdominal procedure with most patients spending some time in an intensive care unit and then from five to ten days in hospital. This is still the "gold standard" in repair of AAA.

Over the last few years there has been considerable interest in other methods. Laparoscopic (minimally invasive, "keyhole") techniques are still in the early development stage but may yet prove to have a role in the future.

The main drive towards less invasive surgery however is in the use of "endoluminal" methods. This is now common practice in selected cases where the aneurysm has certain favourable characteristics. The operation is done under x-ray control and a specially packaged sleeve graft is passed through a small incision in the groin and slid up the inside of the artery until it lies within the AAA. Once the graft is in the precise position it can be released and unfolded like an umbrella to line the AAA from within. This has the advantage of being much easier on the patient who will often be able to leave the hospital after only one night. It must be stressed that this method is new and therefore has not stood the test of time. It is very expensive, and is not applicable to all AAA's. It is available in some centres in New Zealand.

What are the results and outcomes of treatment?

Like all major surgery there is some risk of complications with repair of AAA. Most of these are standard to all major surgery, such as cardiac or chest problems, and they are guarded against as much as possible. The risk of not surviving an operation for AAA repair is 1-2% in most centres. Non-fatal complications occur more often but are not often permanent. Apart from general things there are specific possible problems. It is possible for a man to be impotent after operations on the lower aorta and very rarely complications may include bleeding into the bowel if the graft rubs against the intestine, and spinal cord weakness.

What happens if an AAA is not treated?

Most aneurysms slowly enlarge with the passage of time and if the person lives long enough the AAA will rupture. It is very uncommon for this rupture to occur in an AAA of less than 45-50 millimetres in diameter. On the other hand some small AAA's never enlarge during years of careful monitoring, so it is not always possible to predict what will happen in any particular case.

Who should do the job?

In common with most operations the best outcomes are obtained by surgeons who do a large number of operations for AAA, so the best person for the job is an experienced practising vascular surgeon.

Where should the operation be done?

Not all hospitals are able to offer this surgery. Elective repair of AAA should be done in a hospital that handles major vascular surgery on a regular basis.

What should I do if I think I may have an AAA?

See your doctor who will examine you and organise an abdominal ultrasound test.

What can I do to protect my AAA from rupturing or enlarging?

This question is often asked. The answer is there is nothing that we know of that will alter the natural course of development of an AAA. Of course anything that will improve general health is important, especially stopping smoking, taking regular exercise, and controlling weight and blood pressure.

Most people should be advised to live a normal lifestyle but at the same time have regular checks to monitor the AAA for any signs of expansion so that repair can be planned for the appropriate time before rupture becomes a potential risk.