The aorta is the main blood vessel in the abdomen, running down from your heart. It is normally about the diameter of a garden hose. In older people, particularly those who smoke, part of it can enlarge and balloon up. This is called an abdominal aortic aneurysm (often abbreviated to AAA, pronounced 'triple-A').
This doesn't cause any symptoms and the person is usually unaware they have it, until it leaks or bursts. The medical term for this is rupture. If the aneurysm ruptures, it can be fatal.
In the UK there is a screening programme for men over the age of 65, to see if they have a triple-A. An operation to repair the aneurysm may be advised if it is larger than 5.5 cm, as above this size the risk of rupture increases significantly.
What is an abdominal aortic aneurysm?
Aneurysms can occur in any artery but they most commonly occur in the aorta. Most aortic aneurysms occur in the section of the aorta that passes through the lower abdomen. These are known as abdominal aortic aneurysms (AAAs - pronounced by doctors as 'triple-As').
The normal diameter of the aorta in the abdomen is about 2 cm, a bit like a garden hose. A triple-A (AAA) is said to be present if a section of the aorta within the abdomen is 3 cm or more in diameter.
AAAs vary in size. As a rule, once you develop one, it tends gradually to become larger over the years. The speed at which it becomes larger varies from person to person. However, on average, a triple-A tends to become larger by about 10% per year.
These pictures show the typical location of a triple-A: low down in the tummy below the level of the kidneys.
By BruceBlaus [CC VY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)], via Wikimedia Commons
In most cases
Generally an aneuyrysm of the aorta occurs in older people and in those who smoke. A triple-A (AAA) is rare in people under the age of 60. So, ageing has a major role to play.
Your inherited (genetic) make-up plays a part, as you have a much higher chance of developing a triple-A if one of your parents has, or had, one.
Atheroma may also play a part. Most AAAs are lined with some atheroma. Anyone can develop atheroma but it develops more commonly with increasing age. Certain risk factors also increase the chance of atheroma forming. They include smoking, high blood pressure, diabetes, raised cholesterol level, taking little exercise, and obesity. These are the same risk factors that increase the chance of atheroma forming in the heart (coronary) arteries, which can cause angina and heart attacks.
The wall of the aorta normally has layers of smooth muscle and layers made from tissues called elastin and collagen. Elastin and collagen are strong supporting tissues. What seems to happen is that a part of the aorta loses its normal strength and elasticity in some people as they become older. There seem to be complicated biochemical processes that cause these changes. Some people are more prone than others to these changes.
In a minority of cases
Rare causes of AAAs include injury or infection of the aorta. Also, certain uncommon hereditary conditions can affect the blood vessel structure. In these uncommon situations an aneurysm may develop at a relatively young age.
How common are abdominal aortic aneurysms?
About 4 in 100 men and about 1 in 100 women over the age of 65 have a triple-A (AAA). It becomes more common with increasing age. However, most people with a triple-A are not aware that they have one (see below in the section on symptoms). A triple-A is rare in people under the age of 60.
Usually there are no symptoms and the person is entirely unaware they have a triple-A (AAA). At the time of diagnosis, 7 in 10 people with a triple-A will not have had any symptoms due to the aneurysm. The ballooning of the aneurysm does not cause any symptoms unless it becomes large enough to put pressure on nearby structures. If symptoms do occur, they are likely to be mild tummy (abdominal) or back pains. There are many causes of mild abdominal and back pain. Therefore, the diagnosis may be delayed unless the aneurysm is large enough to be felt by a doctor when he or she examines your abdomen.
Sometimes small blood clots form on the inside lining of a triple-A. These may break off and be carried down the aorta and block a smaller blood vessel further on. These blood clots are called emboli and can be dangerous. For instance, complete blockage of an artery that supplies a foot may lead to loss of blood to part of the foot. This can cause pain in the foot and tissue death (gangrene) if left untreated.
If the aneurysm does burst then you are likely to have sudden severe abdominal and/or back pain. This is commonly soon followed by collapse as the internal bleeding causes a big drop in blood pressure.
How is an abdominal aortic aneurysm diagnosed?
- Sometimes a doctor feels the bulge of an aneurysm during a routine examination of the abdomen. However, many AAAs are too small to feel.
- An X-ray of the abdomen (often done for other reasons) may show calcium deposits lining the wall of a triple-A (AAA) in some, but not all, cases. In this way the triple-A is picked up by chance.
- An ultrasound scan is the easiest way to detect a triple-A. This is a painless test. It is the same type of scan that pregnant women have, to look at the baby in the womb. The size of the aneurysm can also be measured by ultrasound. As discussed later, it is important to know the size.
- A more detailed scan, such as a computerised tomography (CT) scan, is sometimes done. This may be done if your doctor needs to know whether the aneurysm is affecting any of the blood vessels (arteries) that come off the aorta. For instance, if the aneurysm involves the section of the aorta where the arteries to the kidneys branch off, surgeons need to know this information if they plan to operate.
Should everyone with an abdominal aortic aneurysm have surgery?
No. For many people with a triple-A (AAA), the risk of surgery outweighs the risk of the aneurysm bursting. Surgical repair of a triple-A is a major operation and carries risks. A small number of people will die during, or shortly after, the operation. If you have a small triple-A, the risk of death caused by surgery is higher than the risk of bursting. Therefore, surgery is usually not advised if you have a triple-A less than 5.5 cm wide. However, regular ultrasound scans will normally be advised to see if it becomes larger over time.
Surgery is commonly advised if you develop an AAA larger than 5.5 cm. For these larger aneurysms the risk of rupture is usually higher than the risk of surgery. However, if your general state of health is poor, or if you have certain other medical conditions, this may increase the risk if you have surgery. So, in some cases the decision to operate may be a difficult one.
Emergency surgery is needed if a triple-A ruptures. On average, about 8 in 10 people who have a ruptured aortic aneurysm will die due to the sudden severe bleeding. However, emergency surgery is life-saving in some cases.
What operations are performed?
There are two types of surgical operation to repair a triple-A (AAA).
The traditional operation is to cut out the bad piece of aorta and replace it with an artificial piece of artery (a graft). This is a major operation and, as mentioned, carries some risk. Some people die during this operation. However, it is successful in most cases and the aneurysm is totally fixed. The long-term outlook is good. The graft usually works well for the rest of your life.
A newer technique allows the aorta to be repaired by a method called endovascular repair. This has become a popular option in recent years. In this method a tube is passed up from inside one of the leg blood vessels (arteries) into the area of the aneurysm. This tube is then passed across the widened aneurysm and fixed to the good aorta wall, using metal clips. The advantage to this type of repair is that there is no tummy (abdominal) surgery. This technique is therefore safer than the traditional operation and you need to spend less time in hospital. A disadvantage is that some people have to undergo a further operation at a later stage to refine the initial procedure.
Surgical techniques continue to develop and improve. Your surgeon will advise about the pros and cons of surgery, the different types of operation and the best option for you.
Other treatments may be important
If you have a triple-A (AAA), you are likely to have a significant amount of the fatty substance (atheroma) that lines the blood vessel. Therefore, you are at risk of having significant atheroma formation in other arteries, such as the heart (coronary) arteries and brain arteries. Therefore, you are likely to be at increased risk of developing heart disease and having a stroke.
In fact, most people who develop a triple-A do not die of the aneurysm but die from other vascular conditions, such as a heart attack or stroke.
Therefore, you should consider doing what you can to reduce the risk of these conditions by other means. For example:
- Eat a healthy diet which includes keeping a low salt intake.
- Exercise as much as you are able.
- Lose weight if you are overweight.
- Do not smoke.
- If you drink alcohol, do so in moderation.
- If you have high blood pressure, diabetes or a high cholesterol level, they should be well controlled on treatment.
- You may be prescribed a statin drug to lower your cholesterol level and low-dose aspirin to help to prevent blood clots from forming.
Screening for abdominal aortic aneurysm
Research studies suggest that a routine ultrasound scan is worthwhile for all men aged 65. This is because most people with a triple-A (AAA) do not have symptoms. Following a routine scan, surgery can be offered to men found to have an aneurysm over 5.5 cm wide. Follow-up scans can be offered to monitor those with smaller aneurysms between 3 cm and 5.4 cm wide.
In early 2008, the Government in the UK announced that a national screening programme should be rolled out for men aged 65, while men aged over 65 should be able to self-refer. Implementation of the NHS AAA Screening Programme in England began in Spring 2009 and screening covered the whole of England by March 2013. Screening was also introduced in Scotland, Wales and Northern Ireland in 2013. Screening for AAA is offered only to men, as the condition is much more common in men than in women.
What is the chance of an abdominal aortic aneurysm rupturing?
The chance of bursting (rupture) is low if a triple-A (AAA) is small. As a rule, the risk of rupture increases with increasing size. This is much like a balloon - the larger you blow it up, the greater the pressure and the greater the chance it will burst. The diameter of a triple-A can be measured by an ultrasound scan. As a rule, for any given size, the risk of rupture is increased in smokers, women, those with high blood pressure and those with a family history of AAA.
Further reading and references
; The Task Force for the Diagnosis and Treatment of Aortic Diseases of the European Society of Cardiology (Aug 2014)
; NICE Interventional Procedure Guidance, March 2006
; Surgery for small asymptomatic abdominal aortic aneurysms. Cochrane Database Syst Rev. 2015 Feb 82:CD001835. doi: 10.1002/14651858.CD001835.pub4.
; Screening for abdominal aortic aneurysm. Cochrane Database Syst Rev. 2007 Apr 18(2):CD002945.
; Current status of endovascular devices to treat abdominal aortic aneurysms. Biomed Eng Comput Biol. 2013 Apr 105:25-32. doi: 10.4137/BECB.S10970. eCollection 2013.