What is Abdominal Aortic Aneurysm?
An abdominal aortic aneurysm is a localized swelling and bulge in the lower part of the aorta due to weakening of the vessel wall. As the blood passes through the weakened portion of the vessel, it dilates or bulges and if this continues, it can rupture, which can be very fatal leading to internal bleeding, organ damage and even death. The aorta is a major blood vessel which is responsible for supplying blood to the body. As the aorta is the main supplier of blood, a ruptured abdominal aortic aneurysm is a potentially life threatening condition and can cause some serious bleeding. Many of the slow-growing and small abdominal aortic aneurysms do not rupture; however, the fast-growing and large abdominal aortic aneurysms may rupture. Treatment depends on the size and the rate of growth of the aneurysm. Treatment varies from watchful waiting to emergency surgery. Once an abdominal aortic aneurysm is detected, the doctors closely supervise it, so that immediate surgery can be done when and if required. Surgery done on an emergency basis for a ruptured abdominal aneurysm can be quite risky.
Pathophysiology of Abdominal Aortic Aneurysm
The occurrence and expansion of an aneurysm depends on the local hemodynamic factors and factors intrinsic to the arterial segment itself.
The aorta has a relatively low-resistance circuit for circulating blood and the lower extremities have higher arterial resistance. Repeated trauma of a reflected arterial wave on the distal aorta may injure an already weakened aortic wall and lead to aneurysmal degeneration. Systemic hypertension further increases the injury, accelerates the expansion of existing aneurysms, and also contributes to their formation. Aneurysm formation is due to multiple factors affecting the arterial segment and its local environment. Many aneurysms are atherosclerotic in nature. As the aneurysmal dilatation increases, the arterial wall tension also increases and this can result in rupture of the aneurysm. Increase in blood pressure (systemic hypertension) leads to increase in aneurysm size which in turn increases the arterial wall tension and therefore increases the risk of rupture. The vessel wall is supplied by the blood within its lumen although the aorta has vasa vasorum, therefore as the aneurysm develops, the most ischemic portion of the aneurysm is at the distal end, which results in weakening of the vessel wall there and aids in further expansion of the aneurysm. Thus eventually, all aneurysms if left to their natural course rupture without intervention.
Causes and Risk Factors of Abdominal Aortic Aneurysm
The exact cause of abdominal aortic aneurysm is not known. The risk factors include:
- Genetic factors.
- High blood pressure (hypertension).
- High cholesterol (hyperlipidemia).
- Men have a greater tendency towards developing it than women.
Although an abdominal aortic aneurysm can develop in anyone, it is more commonly seen in males over 60 years of age and who have one or more risk factors. The larger the aneurysm, the greater the risk of rupturing and bleeding.
Signs and Symptoms of Abdominal Aortic Aneurysm
The symptoms of rupture include:
- Abrupt, severe and constant pain in the abdomen or back.
- The pain may radiate to groin, buttocks or legs.
- Moist skin.
- Rapid heart rate.
Tests to Diagnoses Abdominal Aortic Aneurysm
- Evaluating the pulses in legs.
- A lump (mass) can be felt in the abdomen.
- A pulsating sensation is felt in the abdomen.
- The abdomen feels stiff or rigid.
Abdominal aortic aneurysm which presents without symptoms or problems can be diagnosed with the following tests:
- Chest x-ray.
- Computerized tomography (CT) scan of the abdomen.
- Abdominal ultrasound.
- Magnetic resonance imaging (MRI).
Treatment for Abdominal Aortic Aneurysm
- If the aneurysm is small and the patient is asymptomatic, then surgery is rarely required.
- The doctor will discuss with the patient about the risks of having surgery versus the risk of bleeding if surgery is not done.
- Ultrasound tests every 6 months to check the size of the aneurysm to see if it is getting bigger is recommended.
- If the patient has aneurysm which is bigger than 2 inches (5.5 cm) in width and is growing rapidly, then surgery is recommended. The aim is to perform surgery before any symptoms or complications develop.
Surgery is Done Via Two Methods:
- First is the traditional open repair where a large incision is made in the abdomen and the vessel with aneurysm is replaced with a graft (Dacron).
- The second approach is endovascular stent grafting. This procedure does not require making a large incision in the abdomen, so recovery and healing is much faster. This approach is beneficial for patients having other underlying medical conditions as this is a much safer approach for them; however, endovascular repair is rarely done for a bleeding or leaking aneurysm.
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