An abdominal aortic aneurysm, by definition, is dilation of the abdominal aorta 1.5 its’ normal diameter. Most commonly, abdominal aortic aneurysm are uncovered incidentally through work up via CT or MRI scan for another condition.
Guidelines exist for screening asymptomatic patients for AAA, which will be the focus of this article. The incidental finding of AAA presents an interesting clinical and ethical dilemma for patients and clinicians, as decision making related to management is multifactorial.
Although most abdominal aortic aneurysms never rupture, ruptured AAAs are medically catastrophic and almost universally fatal. Many patients do not even make it to the emergency room after an AAA rupture because of rapid exsanguination.
Those who do will face high morbidity and mortality for emergency aneurysm repair. It is thought that up to 5% of sudden deaths in the elderly could be related to AAA rupture. It is also thought that 4 to 8 % of men ages 65 to 80 have an AAA and are unaware.
Risk Factors for AAA
Risk factors for the development of AAA include tobacco use, hypertension, advancing age, Caucasian race, and family history of AAA.
Certain genetic disorders such as Ehlers-Danlos syndrome and Marfan syndrome can cause aneurysm of the thoracic aorta.
Smoking is one of the single biggest and modifiable risk factors. It is thought that smoking 1 pack of cigarettes per day for 10 years carries a relative risk increase of 15 times likelihood of developing an AAA compared to a non-smoker.
Given the prevalence of AAAs in smokers, it is very important to discuss smoking cessation at every visit with patients. Patients should always be warned about the long term risks associated with smoking. Patients with documented AAAs should be reminded that continued smoking will facilitate expansion of AAAs.
Signs and Symptoms
The signs and symptoms of AAA are few. Usually patients with small abdominal aortic aneurysms will not have any symptoms. Patients with larger abdominal aortic aneurysms may complain of a palpable or pulsatile abdominal mass.
Patients with rupture of an AAA may not make it to the hospital due to rapid blood loss. Patients with slower blood loss may present to a health care provider with lightheadedness, dizziness, syncope, chest pain, difficulty breathing, or abdominal pain. The diagnosis should always be on the clinician’s radar with any of the above symptoms.
Abdominal Aortic Aneurysm Screening Guidelines
Given the importance of documentation of abdominal aortic aneurysms, it is important to discuss with patients the documented screening guidelines related to abdominal aortic aneurysms. As discussed previously, many AAA’s are found incidentally when looking for other conditions or pursuing workup for abdominal pain.
The United States Preventive Task Force Service makes recommendations related to screening for AAAs. In men ages 65-75 with a positive smoking history, the recommendation is a grade B for a one-time abdominal ultrasound to screen for AAA.
In males ages 65-75 with no history of smoking, the institution recommends an individualized approach between patient and provider, but ultimately give a Grade C recommendation.
In women who are smokers between ages 65 and 75, they document insufficient evidence to make a recommendation. In women who have never smoked, the recommendation is a grade D, indicating that no screening intervention should be performed. Patients with positive family history of a family member with documented AAA should be screened.
The main screening modality for abdominal aortic aneurysm screening is the abdominal ultrasound. The ultrasound is very sensitive and specific for documenting abdominal aortic aneurysm. Given the ultrasound’s low cost as well as high safety, it is the gold standard for screening.
If a patient with a positive history of smoking undergoes an ultrasound and has a negative result, there is a very low chance that the patient would develop a AAA in the next 5 years. Once the ultrasound has been performed, if there is a documented aneurysm, radiology can determine the frequency of ultrasound testing for the monitoring of progression or expansion of the aneurysm.
In patients with abdominal aneurysms 3 cm to 5 cm in size, surveillance is based on risk factors as well as the progression of aneurysm. It is generally recommended for surgical consult and evaluation if the aneurysm is greater than 5.5 cm, but can vary based on progression. The progression and risk factors also play a role, so the decision for further management should be based on the individual patient.
Despite the ultrasound being the gold standard for screening, a simple abdominal exam performed by the clinician can also be helpful to document AAA. Body habitus and size of the aneurysm certainly play a role in the ability to detect an aneurysm.
In patients with very small aneurysms, the ability to detect via exam is limited. Obviously obesity can make identification more challenging. The larger the aneurysm, the easier to detect via exam. Routine exam should not be used as the sole screening purposes.
Given the higher prevalence in the elderly as well as the consequences of catastrophic rupture, screening for abdominal aortic aneurysm is recommended in patients with risk factors.
Guidelines including the United States Preventive Task Force are available to help guide decision making.
As always, the entire clinical picture should be taken into account when deciding to screen and how frequent to rescreen.
The decision for treatment via medical or surgical therapy should be based on the patient’s risk factors, overall life expectancy, rate of expansion of the aneurysm, overall size, and medical comorbidities.
Chung, Jayer (2017). Epidemiology, Risk Factors, Pathogenesis and Natural History of AAA. UpToDate. Date of Access 16 January 2018.
Lefevre, M. L (2014). Screening for Abdominal Aortic Aneursym: USPSTF Recommendation Statement. Annals of Internal Medicine, 161 (4).
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