Abdominal Aortic Aneurysm
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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.
Cause of Abdominal Aortic Aneurysm
The exact cause of aortic aneurysm (AAA) is not known. However, the following factors are thought to contribute to the formation of an abdominal aneurysm:- Degeneration of the wall of the aorta due to chronic fat deposit (atherosclerosis). This 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 aortic aneurysm 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 nicker 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.
- Inflammatory diseases of the arteries called arteritis
- Subacute Bacterial endocarditis
- Cystic medial necrosis (death of the wall of the aorta)
In the UK and US, abdominal aneurysm 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.
Risk Factors
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.
Symptoms of Abdominal Aneurysm
Abdominal aneurysm often do not cause any symptoms at the initial stage, unless they become large enough (up to 3 to 5cm). Aortic aneurysms are often accidentally picked up during routine examination or scans or X-ray for other medical reasons.The common symptoms of abdominal aneurysm include:
- Dull ache and fullness in the lower central abdomen and or lower back
- Feeling of a pulsating lump in the lower central abdomen
- Left side lower abdominal pain
- left side lower back pain
- Sudden onset lower abdominal pain that spread to the back with or without an associated fainting episode or collapse
These symptoms or combination of them could vary greatly from one person to the other. If you suspect that you might be having abdominal aortic aneurysm, please contact your doctor immediately. It is a serious surgical emergency, if it ruptures.
Treatment Options: To Operate Or Not To
The exact size or point at which an operation is absolutely necessary for an aneurysm of the aorta is not known with certainty. However, it is generally agreed that a surgical repair of an aneurysm should take place if the abdominal aortic aneurism is more than 4.0cm.Results from screen programs suggest that at 5.5cm, everyone with this condition should have it repaired. If at 3.5cm though, there is lower abdominal pain, or any symptoms with the aneurysm, then repair is warranted.
A planned repair of an aneurysm is best. The survival rate is about 98%. This is in sharp contrast to an emergency repair, following a burst, where successful operation rate drops from less then 50 percent to zero!
There are two main treatment options for repair of an abdominal aneurysm:
- Open Surgery
- Stent (key hole surgery) also called endovascular repair
It is generally agreed that the endovascular repair is safer, and more appropriate for a planned surgery especially if the aneurysm is below the kidney level, and it is not already ruptured.
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