Abdominal aortic aneurysm

An aortic aneurysm is a general term for any swelling (dilatation or aneurysm) of the aorta, usually representing an underlying weakness in the wall of the aorta at that location. While the stretched vessel may occasionally cause discomfort, it is the risk of rupture causing severe pain, massive internal hemorrhage and, without prompt treatment, resulting in a quick death. In addition the aneurysm may split (Aortic dissection) which may block vessels that branch off from the aorta or release blood clots (emboli) causing blockage to blood-flow elsewhere. more...

Pathology

The physical change in the aortic diameter can occur secondary to an intrinsic defect in the protein construction of the aortic wall, trauma, infection, or due to progressive destruction of aortic proteins by enzymes. The last is the most common cause of aneurysmal disease although the origin of this enzymatic destruction is not known.

Signs, symptoms and diagnosis

• Most intact aortic aneurysms do not produce any symptoms. Untreated, aneurysms tend to become progressively larger, although the rate of enlargement is unpredictable for any individual. Rarely, clotted blood which lines most aortic aneurysms can break off and result in an embolus. They may be found on physical examination. Medical imaging is necessary to confirm the diagnosis.

Abdominal Aortic Aneurysm

Aortic aneurysms are more common in the abdominal aorta, one reason for this is that elastin, the principle load bearing protein present in the wall of the aorta, is reduced in the abdominal aorta as compared to the thoracic aorta (nearer the heart). Most are true aneurysms that involve all three layers (tunica intima, tunica media and tunica adventitia), and are are generally asymptomatic before rupture.

The prevalence of AAAs increases with age, with an average age of 65-70 at the time of diagnosis. AAAs have been attributed to atherosclerosis, though other factors are involved in their formation.

An AAA may remain asymptomatic indefinitely. There is a large risk of rupture once the size has reached 5 cm, though some AAAs may swell to over 15 cm in diameter before rupturing. Before rupture, an AAA may present as a large, pulsatile mass above the umbilicus. A bruit may be heard from the turbulent flow in a severe atherosclerotic aneurysm or if thombosis occurs. Unfortunately, however, rupture is usually the first hint of AAA. Once an aneurysm has ruptured, it presents with a classic pain-hypotension-mass triad. The pain is classically reported in the abdomen, back or flank. It is usually acute, severe and constant, and may radiate through the abdomen to the back.

The diagnosis of an abdominal aortic aneurysm can be confirmed at the bedside by the use of ultrasound. Rupture could be indicated by the presence of free fluid in potential abdominal spaces, such as Morrison's pouch, the splenorenal space, subdiaphragmatic spaces and peri-vesical spaces. A contrast-enchanced abdominal CT scan is needed for confirmation.

Only 10-25% of patients survive rupture due to large pre- and post-operative mortality. Annual mortality from ruptured abdominal aneurysms in the United States alone is about 15 000. Another important complication of AAA is formation of a thrombus in the aneurysm.

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