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Aortic aneurysm


An aneurysm is an abnormal widening or bulging of an artery. It occurs when a weakened area in the wall of an artery stretches and bulges as blood is pumped through it. An abdominal aortic aneurysm (AAA) is an aneurysm that occurs in the section of the aorta (the largest artery in the body) that runs through the abdomen. It is one of the most common types of aneurysm.
 
Abdominal aortic aneurysms, particularly those bigger than 5 to 6 centimetres in diameter, are at risk of rupture. Rupture of an abdominal aortic aneurysm is a medical emergency and carries a high risk of death. Surgery is required immediately.

General information

The aorta carries oxygen-rich blood from the heart to the rest of the body. The section of the aorta that runs through the chest is called the thoracic aorta. The section of the aorta that runs through the abdomen is called the abdominal aorta.  Aortic aneurysms are not uncommon and can occur anywhere along the length of the aorta. They may be only a few millimetres wide or they can expand to six centimetres or more in diameter.

Abdominal aortic aneurysms are the most common form of aortic aneurysm, making up three quarters of aortic aneurysm cases. They most commonly occur after the age of 60 years and men are affected about three times more frequently than women are. Each year in New Zealand approximately 400 deaths are attributed to abdominal aortic aneurysms.

The reason why abdominal aortic aneurysms develop is not fully understood. It is known that they have a tendency to run in families, so it is thought that genetic factors may play a role. Other risk factors for developing abdominal aortic aneurysms include: 
  • Being a male aged over 60 years (around 5% of men overe 60 years of age will develop AAA)
  • Atherosclerosis (a build up of fatty deposits in the arteries)
  • High blood pressure
  • Smoking
  • Congenital abnormalities (eg: Marfan’s syndrome)
  • Diseases that can weaken the aorta wall (eg: Tuberculosis, Syphilis)

Signs and symptoms

Symptoms will depend on the location, nature and size of the aneurysm. Sometimes no symptoms are present until the aneurysm is large and at risk of rupturing.

Symptoms of abdominal aortic aneurysms may be vague and non-specific such as backache or abdominal pain. Patients may also note a pulsating bulge in the abdomen – particularly when lying down. An abdominal aortic aneurysm is usually lined by a blood clot. Occasionally, parts of this blood clot can be dislodged and travel downwards to block arteries to the leg (embolism). This may produce symptoms such as pain in the lower legs.

More acute symptoms, which may occur when an abdominal aortic aneurysm is expanding quickly or leaking, can include:  

  • A deep, pulsating, boring pain in the abdomen 
  • Pain in the left flank spreading down the left side towards the groin. 

If an abdominal aortic aneurysm ruptures, sudden pain, dizziness or weakness may be felt. Loss of consciousness may also occur.

Diagnosis

Abdominal aortic aneurysms that do not produce any symptoms are often found incidentally during diagnostic tests or treatments for other medical conditions.  If an abdominal aortic aneurysm is suspected, a complete medical history will be taken and a physical examination will be performed. A referral to a vascular surgeon may also be made at this stage.

An ultrasound scan is usually the first diagnostic test undertaken to confirm the presence of an abdominal aortic aneurysm. Other tests undertaken to confirm the diagnosis and pinpoint the location and size of the aneurysm may include computerised tomography scan (CT scan) and X-rays. Tests to assess the functioning of the heart, lungs and kidneys may also be undertaken.

Treatment

Many factors are taken into account when deciding how to treat an abdominal aortic aneurysm: 

  • The size of the aneurysm – the greater the size, the greater the risk of rupture
  • The location of the aneurysm
  • The proximity to or involvement with any of the arteries that branch from the aorta
  • The person’s general state of health and the presence of other medical conditions.

The two main treatment approaches include watchful waiting and surgical repair:

Watchful waiting

If the abdominal aortic aneurysm is small and is not causing any symptoms, the surgeon may recommend a “wait and watch” approach. This involves careful monitoring of symptoms and regular scans (usually every six months) to check for changes in the aneurysm. This usually involves ultrasound and  CT scanning.  High blood pressure will be treated with medications during this time to reduce the pressure on the aneurysm. Other conditions such as high cholesterol will also be treated.  Lifestyle changes such as stopping smoking and achieving and maintaining a healthy body weight will also be recommended.
 
In some cases a watchful waiting approach may be taken when the risks of surgery are deemed to outweigh the risks of monitoring the aneurysm, even though the aneurysm may be large and causing symptoms. This is often the case when co-existing medical conditions are present - particularly those affecting the heart, lungs or kidneys.  Age is also a factor, as the risks of surgery increase with age. 

Surgical Treatment

If the aneurysm is large or is causing symptoms, surgical repair of the aneurysm is usually recommended. The type of surgical repair used will depend on the location, size and shape of the aneurysm, the general state of health of the patient and the urgency of the surgery. In general, once an abdominal aortic aneurysm reaches 5cm in diameter, elective surgical repair is considered. Aneurysms that are smaller than 5cm but are producing acute symptoms may need to be surgically repaired on an urgent basis. In cases of aneurysm rupture, emergency surgery to repair the artery is required immediately.

The two main surgical techniques used to treat an abdominal aortic aneurysm are:

Open Surgical Repair:
During open surgical repair an incision is made in the abdomen and the aneurysm is located and exposed. The aorta is clamped to prevent bleeding and the aneurysm is then opened and repaired, often using a synthetic patch made of Dacron or Teflon.  A one to two day stay in an intensive care unit is expected after surgery, followed by a five to 10 day stay in hospital. Complete recovery is usually achieved within two to three months.

Endovascular Stent Graft:
This technique involves inserting a specialised synthetic stent graft into the aneurysm via a tube inserted in an artery in the groin. Under x-ray guidance the graft is fed up into the aorta until it lies within the aneurysm. It is then expanded so that it snugly lines the inside of the aneurysm. This enables blood to flow through the aorta without putting pressure on the aneurysm.  This technique only requires a small incision in the groin and has the advantage of a shorter hospital stay and a much quicker recovery time. 

Prevention

The development of aortic aneurysms cannot be prevented and little can be done to reduce the risk of the aneurysm expanding or rupturing.  It is important however to maintain a general state of good health.  This includes not smoking, maintaining a healthy body weight and exercising regularly.  Controlling existing conditions such as angina or high blood pressure is also important, as is regular monitoring of the aneurysm.  Where there's a strong family history of aortic aneurysm, regular screening may be recommended.

References

Anderson, K.N., Anderson, L.E. & Glanze, W.D. (eds.) (2006) Mosby’s medical, nursing, & allied health dictionary (6th ed.) St. Louis: Mosby-Year Book
Boon, N.A. and Fox, K.A.A. (1995) Diseases of the cardiovascular system.  In C.R.W. Edwards, Bouchier, I.A.D. (1995) Davidson’s principles and practice of medicine (17th ed.) Edinburgh: Churchill Livingstone
De Bellis, D. (2006) Aortic Aneurysm. The Gale Enclyclopedia of Medicine. Third Edition. Jacqueline L. Longe, Editor. Farmington Mills, MI. Thompson Gale.
Nair, N., Sarfati, D., Shaw, C. (2012) Population screening for abdominal aortic aneurysm: evaluating the evidence against screening criteria. In the New Zealand Medical Journal. 24-February-2012, Vol 125 No 1350
 
Last Reviewed – 8 July 2013
 
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