Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) or aneurism is the abnormal widening and outward ballooning of a part or parts of the aorta as it runs through the abdomen.

The normal aorta is about 2.5 cm wide (in diameter). An aneurysm is said to occur when a part becomes more than one and a half times wider than its normal diameter.

Men are five times more likely to have this disorder than women, and smoking increases the risk of having a AAA seven times.

There is an increased risk of an aneurysm rupturing if the diameter exceeds 4 cm. Surgery or endovascular graft repair is advised if the size of the aneurysm is 5.5cm of more.

Persisting or troublesome back pain even with an aneurysm of 3.5 - 5.5cm may also warrant a planned (elective) operation.

Untreated abdominal aortic aneurysm if ruptured has a 100% death (mortality) rate, while planned repaired abdominal aneurysm has about 1 - 4% mortality rate.

Latest research (New English Journal of Medicine, 11th May 2006), suggests that abdominal aortic aneurysm may be amenable to drug treatment in the future without the possible need for surgery or endovascular repair.

What is the Aorta?

The aorta is the main vessel that carries blood directly from the heart through the chest and abdomen where it later divides into the right and left iliac vessels, carrying blood to the legs.

The aorta is the largest blood vessel in the body. It starts off from the left part of the heart, curves or arches downwards and backwards and continues down the chest (thorax). In the chest, it is known as the Thoracic Aorta. A ballooning or aneurysm can occur here. If it does, it is called thoracic aortic aneurysm.

The aorta continues its downward course, passes through a natural opening in the diaphragm at the level of the tenth thoracic vertebra (spine bone) and becomes the abdominal aorta.

The abdominal aorta continues down and just below the umbilicus or belly button, it divides into the right and left iliac arteries, which will carry blood to the reproductive organs and the lower limbs.

The aorta gives off several major branches as it passes from the chest through the abdomen before it divides into iliac vessels. Two of such branches are the arteries to the right and left kidneys called the renal arteries.

Types of Abdominal Aortic Aneurysm

Abdominal aortic aneurysm can be described based on:

PART OR LEVEL OF THE AORTIC ANEURYSM

• Infra Renal Abdominal Aortic Aneurysm. Nine out of ten cases (90%) of abdominal aortic aneurysm occurs below the point or level in the aorta where the renal (kidney) arteries have come off it. This is called infra renal abdominal aortic aneurysm. It is the safer variety since the kidneys may not be badly affected both before and after surgery.
  

  
  

• Supra Renal Abdominal Aortic Aneurysm. If the ballooning of the aorta were to occur before the aorta gives off the renal branches, it is called supra renal abdominal aortic aneurysm.

  This can have serious consequence for the kidneys, as the ballooning above the level of the kidneys may mean less blood flow pressure to the kidney. The repair also has increased risk. This type only happens in one out of ten cases (10%) of abdominal aortic aneurysm.

Aneurysm of the abdominal aorta could extend to involve one or both terminal branches (iliac arteries).

LAYERS OF THE WALL OF THE AORTA INVOLVED

Depending on the number of the walls of the aorta involved, aortic aneurysms can be described as true or false aneurysm.

• True aneurysm has all three layers of the wall of the aorta involved. It is a true dilatation of the aorta.

  This is further divided into fusiform abdominal aortic aneurism (egg shaped) or saccular abdominal aortic aneurysm (bag shaped).

  The fusiform type of abdominal aortic aneurism is commoner, and may extend as long as over 20 cm to involve the iliac arteries.
  

  
  

• False abdominal aortic aneurism is one where not all three layers of the wall of the aorta is involved in the ballooning. This usually occurs due to penetrating injury or infection.

The exact cause of abdominal aortic aneurism (AAA) is not known. What is known is that it is mainly a disease of white males. It is rare in people of African descent, Asians and even Hispanics.

In the UK and US, abdominal aortic aneurism is believed to be present in 3 out of every 100 individuals after the age of 50. 2 -5 five men are affected for every woman found with this disorder, and four times commoner in whites compared to blacks. It is also commoner after the age of 50, with a peak incidence around 70 years of age.

Degeneration of the wall of the aorta due to chronic fat deposit (atherosclerosis) is thought to be the main cause of abdominal aortic aneurism (90% of cases). This leads to loss of the natural elasticity of the wall of the aorta, thus can not expand and recoil as it would otherwise do. The wall starts to stretch and crack. Over a long time the wall thins out. It could start to leak from a very weak spot or even rupture without warning!

Another cause of abdominal aortic aneurism is inherited defects in the structure of the proteins called collagen and elastin. These proteins are the building block of the wall of the aorta. Scanty or poor quality elastin causes the aorta to dilate (just as loosing the elastic on a pant will lead to it sagging and defective collagen encourages rupture. Thus a disease affecting both of these proteins means the strength of the blood vessels would be compromised.

Examples of such inherited cause of abdominal aortic aneurysm are Ehlers Danlos Syndrome and Marfan disease or Marfan syndrome.

Injuries to the aorta either from direct force like seat belt injury following a car crash, stab, or

from infections e.g.

syphilis,

fungi or mycotic infections

which causes very high rate of rupture) can cause abdominal aortic aneurysm.

Other causes of abdominal aortic aneurysm includes:

• Inflammatory diseases of the arteries called arteritis
  

  
  

• Subacute Bacterial endocarditis
  

  
  

• Cystic medial necrosis (death of the wall of the aorta)

Risk Factors For Developing Aortic Aneurysm

The risk of developing abdominal aneurysm can be reduced by:

• Stop Smoking. Cigarette smoking increases clogging of the walls of the blood vessels by fat. This therefore significantly increases the risk of developing abdominal aortic aneurysm. For those still smoking they have seven times likelihood of developing AAA. Those who have stopped smoking have their risk reduced to three fold, compared with a non-smoker.
  

  
  

• Alcohol A moderate amount of alcohol is good for the body. Excessive drinking is damaging. It predisposes to atherosclerosis and the development of abdominal aortic aneurysm. Consumption of up to 14 units of alcohol (7 pints of beer or 14 regular glasses of wine or 14 shorts of spirit) per week is the advised healthy limit of alcohol consumption for women, and up to 21 units (10 and a half pints of beer, or 21 regular glasses of wine or 21 shorts of spirit) per week for men.
  

  
  

• Hypertension. Hypertension increases the risk of developing abdominal aortic aneurysm several folds. If you are hypertensive, you need to take your medications regularly and see that the high blood pressure is well controlled.
  

  
  
  For some reasons, presence of diabetes tend to reduce the overall risk of an aneurysm rupture.
  
  

  
  

• Diet. Diet high in fat will increase the risk of abdominal aortic aneurysm. Eat less fat, more fruits and vegetables, regular light exercises.
  

  
  

• Family History. If you have someone in your family who had AAA, there is an increased chances that you may also develop AAA. You need not panic though. Let your family doctor know, and you would be enrolled into abdominal aortic aneurism screening programme at the age of 60 or 65.

Please read more on abdominal aortic aneurysm:

Symptoms of Abdominal Aortic Aneurysm

Diagnosis of Abdominal Aortic Aneurism

Complications of Abdominal Aortic Aneurism

Ruptured Abdominal Aortic Aneurism

Abdominal Aortic Aneurism Screening Programme

Abdominal Aortic Aneurism Repair

Complications of Abdominal Aortic Aneurism Repair

Useful Links and Resources

Latest Readings and Guide To Repair


Help With Fear of Anaesthesia before Surgery

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