Abdominal aortic aneurysm screening

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Caitlin J. Harrigan [2]; Vishnu Vardhan Serla M.B.B.S. [3]

Overview

Approximately 16% of large abdominal aortic aneurysms (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%. 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. 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.

Why Screen for AAAs?

• Patients with abdominal aortic aneurysms (AAAs) are often asymptomatic, with the first clinical event often being fatal or life-threatening.
• Due to this apparent "detection gap," between the asymptomatic disease and clinically apparent disease screening may be of benefit.
• AAAs are usually asymptomatic during this "detection gap", with the possibility of as many as one in three rupturing if left untreated.
• A ruptured AAA carries an overall mortality rate approaching 75%, with a 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%.

Landmark Trial in AAA Screening: The Multicenter Aneurysm Screening Study (MASS)

• In the largest population-based screening study to date, the Multicenter Aneurysm Screening Study (MASS) randomized 67,800 men (age 65-74) equally to either a group that received an ultrasound screening for AAA or a control group.
• In the screening group, men with an abdominal aorta larger than 3 cm in diameter were followed with serial ultrasounds for a mean duration of 4.1 years.
• When the aneurysm reached 5.5 cm, grew more than 1 cm/year or became symptomatic, it was repaired surgically.
• The aneurysm-related mortality was 53% lower in the screening group.
• However, despite the relative risk reduction in the MASS trial, there were 65 AAA-related deaths in the intervention group (absolute risk of 0.19%), and 113 AAA-related deaths in the control group (absolute risk 0.33%).

Cost-Effectiveness of Screening

It is estimated that abdominal aortic aneurysm screening is as cost-effective as mammography for breast cancer detection as well as therapeutic interventions such as coronary artery bypass graft surgery with a cost of $11,285 per quality adjusted life year saved.

Abdominal Aortic Aneurysm Screening Safety

• Physical examinations may detect large AAAs, but is not specific or sensitive enough to detect smaller ones.
• The cornerstone of AAA screening is ultrasonography. It is available in almost every medical center and many physician offices.
• Abdominal aortic ultrasonography is fast, inexpensive, safe and well-tolerated by most patients
• It is highly accurate with 95% sensitivity and 100% specificity for AAAs
• The most important limitations of ultrasonography are:

• Operator dependence
• Reduced accuracy in those patients with bowel gas, periaortic disease and those patients who are obese
• These limitations present less of an issue for highly experienced sonographers, and in accredited, validated, high-volume institutions

• Computed tomography (CT) and magnetic resonance angiography are accurate for diagnosing AAA, but are less often used as a first-degree screening modality because of the lack of availability, and the risks and side-effects of iodinated contrasts for CT.

Abdominal Aortic Aneurysm Screening Ethics

• Screening using ultrasonography causes no serious side effects, and is therefore ethically acceptable.
• Several studies have shown that screening for AAAs and diagnosing asymptomatic small aneurysms in clinical practice were not associated with long-term emotional or psychological stress to patients
• A simple screening ultrasound test costs approximately $500, for which Medicare usually reimburses $160
• Lack of insurance coverage raises the ethical dilemma of AAA screening being available only to the elite who can afford it

Abdominal Aortic Aneurysm Identification As a Trigger to Screen for Polyvascular Disease

• Small, asymptomatic AAAs (3-5.5 cm) may serve as a marker for vascular disease elsewhere, thus finding one provides good reason to aggressively start to modify risk factors.

Abdominal Aortic Aneurysm Screening Follow-Up Intervals

• Periodic ultrasonographic surveillance is recommended for aneurysms smaller than the repair cutoff
• If an abdominal aortic aneurysm is 4 to 5.4 cm then surveillance ultrasounds can be obtained every 6 to 12 months
• If an abdominal aortic aneurysm is 3 to 4 cm then surveillance ultrasounds can be obtained every 2 to 3 years
• However, definite and unified parameters for appropriate surveillance intervals have not yet been determined because clinical trials have enrolled heterogeneous populations and used different standards for diagnosis and management
• In general, older men may need more frequent follow-up scans, as men older than 70 years have three times the rate of progression than younger men
• Aneurysm diameters determined by ultrasound may vary up to 0.5 cm, which should be considered when recommending optial times for rescanning and repair

Screening Recommendations by The Unites States Preventive Service Task Force

• The USPSTF recommends one-time screening for abdominal aortic aneurysm (AAA) by ultrasonography in men aged 65 to 75 who have 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.

2005 ACC/AHA Practice Guidelines for the Management of Patients With Peripheral Arterial Disease (Lower Extremity, Renal, Mesenteric, and Abdominal Aortic) (DO NOT EDIT)

Screening High-Risk Populations (DO NOT EDIT)

Class I

"1. Men 60 years of age or older who are either the siblings or offspring of patients with AAAs should undergo physical examination and ultrasound screening for detection of aortic aneurysms. (Level of Evidence: B)"

Class IIa

"1. Men who are 65 to 75 years of age who have ever smoked should undergo a physical examination and 1-time ultrasound screening for detection of AAAs. (Level of Evidence: B)"

Sources

http://www.uspreventiveservicestaskforce.org/uspstf/uspsaneu.htm