The prevalence of abdominal aortic aneurysms (AAAs) is decreasing, thought to be caused by a decrease in smoking. But the risk of death if one ruptures is as high as 81%. So, screening is still an important part of preventive medicine.
When the abdominal aorta enlarges to greater than 3.0 cm, it is considered an aneurysm. Risk factors that can lead to an enlarged aorta include older age, male sex, smoking, history of AAA in a first-degree relative, hypertension, history of other aneurysms, coronary artery disease, cerebrovascular disease, atherosclerosis, and hypercholesterolemia.
History of AAA in a first-degree relative puts patients at double the risk of developing an abdominal aortic aneurysm. Interestingly, diabetes has been associated with a reduced risk of AAA. People of African American, Asian, and Hispanic descent have a reduced risk of AAA.
Screening is performed using abdominal duplex ultrasound. It has high sensitivity (94%-100%) and specificity (98%-100%), is low cost, and has low risk to the patient. The U.S. Preventive Services Task Force breaks its screening recommendations into four categories:
1. Men aged 65-75 years who have ever smoked (at least 100 cigarettes in their lifetime): One-time screening (grade B, moderate net benefit).
2. Men aged 65-75 years who have never smoked: Selectively offer screening (grade C, small net benefit). “To determine whether this service is appropriate, patients and clinicians should consider the patient’s medical history, family history, other risk factors, and personal values.”
3. Women without a smoking history or family history of AAA: Do not perform screening (grade D, recommendation against the service).
4. Women aged 65-75 years who have a smoking history or family history of AAA: There is insufficient evidence on whether or not to screen for AAA (grade I, insufficient evidence).
To assess screening and treatment of AAAs, the USPSTF looked at four randomized, controlled trials largely focused on men older than 65 years. With the combined data, they found 246 men would need to be screened to prevent 1 AAA rupture, and 305 men would need to be screened to prevent 1 death from AAA.
The USPSTF does note that, while the risk of death is lower for elective AAA repair than ruptured AAA, there is still increased risk with elective surgery. In addition, increased screening and detection increases the rate of elective surgery. Overdiagnosis and overtreatment could represent a harm.
Surgical repair of AAA in men depends on the size of the aneurysm and rate of growth.
For men, surgical repair is standard when the AAA reaches 5.5 cm or if the AAA is growing faster than 1.0 cm per year and is larger than 4.0 cm. For women, surgical repair is often recommended between 5.0 cm and 5.4 cm in size.
Surgical repair is not recommended for AAAs that are less than 5.0 cm because the annual risk of rupture is 0%-1% below 5.0 cm. The risk increases to 11% for aneurysms that are 5.0-5.9 cm in size.
There are two methods of surgical repair: endovascular aneurysm repair and open repair. Recommendations for the surveillance of AAA between 3.0 cm and 5.5 cm is regular ultrasound surveillance, with the interval becoming shorter as the aneurysm size becomes larger. Exact intervals differ from one guideline group to another.