Abdominal aortic aneurysm natural history

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

An aortic aneurysm can progress to a ruptured abdominal aortic aneurysm, which is a medical emergency associated with an extremely high mortality. Serious complications can also occur as a result of an aortic dissection, such as myocardial infarction, shock, stroke, kidney failure, and arterial emboli. A ruptured AAA carries an overall mortality rate approaching 75%, which is much higher than the mortality rate of 2-6% in those patients who underwent elective surgical repair. Approximately 16% of large AAAs (diameter >5.5 cm) rupture, causing 9,000 AAA-related deaths in the United States per year. Several studies have shown that screening can drastically reduce the aneurysm rupture rate by 45-49% for men older than 60, and reduce AAA-related mortality by 21-68%.

Natural History

Abdominal aortic aneurysms expand slowly over time. It is for this reason that ultrasound surveillance is recommended. The risk for rupture of an aneurysm depends on several factors:

• Size of an aneurysm
  • Risk of rupture increases greatly once the size of aneurysm reaches 5.5 cm.
• Rate of expansion
  • If the rate of expansion exceeds 1 cm per year, this is an indication for surgery.
  • Growth tends to be more rapid in smokers than non-smokers.
• Gender
  • The risk of rupture is higher in women than in men.

Complications

When an abdominal aortic aneurysm ruptures, it is a true medical emergency. Aortic dissection occurs when the innermost lining of the artery tears and blood leaks into the wall of the artery. This most commonly occurs in the aorta within the chest. Complications include:

• Aortic rupture: 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 is 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-enhanced abdominal CT scan is needed for confirmation. Only 10-25% of patients survive a rupture due to large pre and post-operative mortality. Annual mortality from ruptured abdominal aneurysms in the United States alone is about 15,000.
• Acute aortic occlusion
• Aortocaval or aortoduodenal fistulae
• Arterial embolism
• Disseminated intravascular coagulation
• Heart attack
• Hypovolemic shock
• Kidney failure
• Stroke

Prognosis

Elective Surgery in the Absence of Abdominal Aortic Aneurysm Rupture

The outcome is usually good if an experienced surgeon repairs the aneurysm before it ruptures.

Emergency Surgery in the Setting of Abdominal Aortic Aneurysm Rupture

Rupture of an abdominal aortic aneurysm is associated with a 60% to 90% mortality before the patient reaches a hospital. It is associated with a 30% to 80% operative mortality among those patients who survive long enough to undergo surgery.