Abdominal aortic aneurysm overview
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Abdominal Aortic Aneurysm Microchapters |
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Differentiating Abdominal Aortic Aneurysm from other Diseases |
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Abdominal aortic aneurysm overview On the Web |
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]
Overview
Abdominal aortic aneurysm, also written as AAA and often pronounced 'triple-A', is a localized dilatation of the abdominal aorta, that exceeds the normal diameter of the abdominal aorta by more than 50%.
Historical Perspective
The etymology of the word aneurysm comes from the Greek word for "dilatation". Abdominal aortic aneurysm as a medical condition has been recognized since ancient times, but was not been successfully treated until the early part of the 20th century.
Definition
The normal diameter of one's aorta depends on the patient's age, sex, height, weight, race, body surface area, and baseline blood pressure. On average, the normal diameter of the infrarenal aorta (where abdominal aortic aneurysms are located) is 2 cm. Therefore an abdominal aortic aneurysm is defined as a dilation of 3.0 cm or more.
An abdominal aortic aneurysm is to be distinguished from aortic ectasia which is defined as a mild generalized dilatation (<50% of the normal diameter of ≤ 2.9 cm) that is due to age-related degenerative changes in vessel wall.
Anatomy
The aorta below the renal arteries, also known as the infrarenal aorta, is the location of 90% of abdominal aortic aneurysms. Other possible locations are suprarenal and pararenal. The aneurysm can extend to include one or both of the iliac arteries.
Classification
Aneurysms are usually classified by their shape:
Fusiform Aneurysms
- Most common type seen in the infrarenal aorta
- Diffuse, circumferential
Saccular Aneurysms
- Involve only a portion of the circumference, with a characteristic outpouching of the vessel wall.
Pathophysiology
The underlying pathophysiology of abdominal aortic aneurysm involves genetic influences, smoking, hypertension, hemodynamic influences and underlying atherosclerosis. In rare instances infection, arteritis, and connective tissue disorders may play a role.
Associated Disorders
Abdominal aortic aneurysm is associated with a high prevalence of systemic atherosclerosis:
- 23%-86% have coronary artery disease
- 3%-20% have cerebrovascular disease
- 12%-42% have peripheral arterial disease
Differentiating Abdominal Aortic Aneurysm from other Disorders
An abdominal aortic aneurysm should be differentiated from other causes of abdominal pain such as acute cholecystitis.
Epidemiology and Demographics
Abdominal aortic aneurysm is the 13th leading cause of death in the US. Abdominal aortic aneurysms are more common in developed countries. Elderly, caucasian males who are smokers are at higher risk for developing an abdominal aortic aneurysm.
Risk Factors
Abdominal Aortic Aneurysm Development
The most significant modifiable risk factor for the development of an abdominal aortic aneurysm is smoking which increases the risk of aneurysm development 8 fold. Advanced age and family history are the strongest non-modifiable risk factors for the development of an abdominal aortic aneurysm. Hypercholesterolemia and hypertension are risk factors as well. Both diabetes mellitus and black race appear to be associated with a lower incidence of abdominal aortic aneurysm.
Abdominal Aortic Aneurysm Expansion
An increased rate of expansion of abdominal aortic aneurysm is related to systolic hypertension, wide pulse pressure, and ongoing smoking.
Abdominal Aortic Aneurysm Rupture
The risk of abdominal aortic aneurysm rupture is proportional to the size and rate of growth of the aneurysm. Abdominal aortic aneurysms greater than 5 cm diameter or those that grow faster than 1 cm per year have a significantly increased risk of rupture and are indications for elective operative repair. Advanced age, female gender, hypertension, active smoking, outpouchings, and mural thrombus are also risk factors for abdominal aortic aneurysm rupture.
Screening
Approximately 16% of large abdominal aortic aneurysms (diameter > 5.5 cm) rupture, causing 9,000 AAA-related deaths in the United States per year [1] 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%. In a landmark study randomizing 67,800 men, (The Multicenter Aneurysm Screening Study) aneurysm-related mortality was 53% lower in the screening group as compared with control patients.[2][3] The United States Preventive Services Task Force (USPSTF) recommends one-time screening for abdominal aortic aneurysm (AAA) by ultrasonography in any man aged 65 to 75 who has ever smoked. The USPSTF makes no recommendation for or against screening for AAA in men aged 65 to 75 who have never smoked. The USPSTF recommends against routine screening for AAA in women.
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References
- ↑ Gillum RF (1995). "Epidemiology of aortic aneurysm in the United States". Journal of Clinical Epidemiology. 48 (11): 1289–98. PMID 7490591. Retrieved 2012-10-27. Unknown parameter
|month=ignored (help) - ↑ Ashton HA, Buxton MJ, Day NE, Kim LG, Marteau TM, Scott RA, Thompson SG, Walker NM (2002). "The Multicentre Aneurysm Screening Study (MASS) into the effect of abdominal aortic aneurysm screening on mortality in men: a randomised controlled trial". Lancet. 360 (9345): 1531–9. PMID 12443589. Retrieved 2012-10-27. Unknown parameter
|month=ignored (help) - ↑ "Multicentre aneurysm screening study (MASS): cost effectiveness analysis of screening for abdominal aortic aneurysms based on four year results from randomised controlled trial". BMJ (Clinical Research Ed.). 325 (7373): 1135. 2002. PMC 133450. PMID 12433761. Retrieved 2012-10-27. Unknown parameter
|month=ignored (help)
Acknowledgements
The content on this page was first contributed by: C. Michael Gibson M.S., M.D. Template:WH Template:WS