Abdominal aortic aneurysms (AAA) are full-thickness dilations in the aorta that are >50% of the normal diameter; in most cases, ≥3.0 cm is considered aneurysm.1 AAA is accompanied by aortic compromise in the strength and composition of the vascular wall. Smooth muscle cells undergo apoptosis and the vessel’s extracellular matrix starts to break down due to changes in proteases, inflammatory mediators, and biomechanical forces leading to vessel expansion.
In addition to the biologic changes of the vessel, additional risk factors associated with AAA include older age (>65 years), male gender, history of cigarette smoking, White race, atherosclerosis, hypertension, family history of AAAs, and other large artery aneurysms. People with connective tissue diseases such as Marfan Syndrome and Ehlers-Danlos Syndrome are at higher risk due to a deficiency in vascular composition.1,2
Overall, the development and growth of aortic aneurysms is multifactorial, with genetic and environmental factors playing a role in the disease process. The prevalence of AAAs in men is estimated to be approximately 4% to 8% of the population.3 According to the Society for Vascular Surgery, ruptured AAA is the 15th leading cause of death in the country overall, and the 10th leading cause of death in men over the age of 55.3 Because AAA is likely to be encountered in the primary care setting, appropriate diagnosis and management are indispensable.
Presentation and Diagnosis
AAAs are often asymptomatic, which contributes to the peril associated with their growth and rupture.4 The mortality rate may approach 90% for patients who experience an AAA rupture while at home or upon arrival to the hospital. Even after emergent surgical repair, the mortality rate remains between 30% and 50%.5
Most AAAs are identified as incidental findings on ultrasound or computed tomography (CT) scan. However, screening tests may be ordered in patients with risk factors or when patients present symptomatically.6 According to Current Medical Diagnosis and Treatment, an abdominal ultrasound is the diagnostic screening tool of choice. It is highly sensitive and specific, noninvasive, and inexpensive. If an aneurysm is found or if the ultrasound is inconclusive, a CT scan may be conducted to provide more specific anatomic detail and measurements.4
Routine follow–up visits are indicated for the presence of aneurysms ≥3.0 cm. If the diameter measures 3.0 cm to 3.9 cm, imaging should be conducted every 3 years; 4.0 cm to 4.9 cm, every 12 months; and 5.0 cm to 5.4 cm, every 6 months.7
The primary goal of screening for AAAs is to reduce morbidity and mortality with early diagnosis.8 The US Preventive Services Task Force (USPSTF) recommendations are based on screening trials and cohort studies that evaluated and compared mortality outcomes both with and without screening.9 The guidelines advise that men aged 65 to 75 years who are current smokers or have any previous history of smoking undergo a one-time screening.6 USPSTF recommends practitioners offer screening for men aged 65 to 75 who have never smoked but have risk factors including medical history, family history, or if it is the patient’s preference.4 Based on systematic reviews and meta analyses, USPSTF concluded that educating patients about screening and inviting them to be screened may reduce AAA-related mortality by 35%.9
The Use of Pre-existing Imaging for Diagnosis
Unfortunately, even with the implementation of AAA screening guidelines, and the known decrease in AAA-associated mortality with early diagnosis, screening rates remain <50%.10 This may be attributable to compliance issues or to the lack of education concerning disease severity and outcomes.
Utilizing pre-existing imaging of the aorta may be an effective way to increase the number of patients that are being screened for an AAA. If imaging modalities such as ultrasounds, CT scans, or magnetic resonance imaging (MRI) were ordered for other causes, but included visualization of the aorta, approximately one-third of AAA screening ultrasounds would be unnecessary. Utilizing these alternate images as screening tools would increase AAA screening rates substantially.11
The majority of AAAs are asymptomatic and are most often detected as an incidental finding on ultrasound, CT, and MRI.12 Of those incidental diagnoses, as many as 31% of patients still undergo ultrasound screenings of the abdominal aorta.10 This begs the question, if the preexisting imaging exists, are they efficacious enough to be used for AAA screening?
Ruff et al conducted a retrospective study on the use of CT scans as a preliminary screening tool for AAAs in cases where the scan was ordered for another purpose. The researchers assessed the sensitivity of CT imaging from patients that had undergone an ultrasound for AAA screening as well as a CT scan for another indication within the past 3 years. Based on their findings, the overall sensitivity of CT scans previously evaluated compared with the ultrasound of the AAA was 97.6% and the specificity was 99.2%.11 This evidence is strong enough to suggest that using pre-existing CT scans is a practical screening tool.
Incidental AAA findings require follow-up to determine if the aneurysm should undergo conservative management or repair. A study conducted by Walraven et al assessed the completeness of follow-up for an incidental finding of AAA and its association to radiologic imaging and repair compared to mortality. They found that approximately 29% of diagnosed AAA patients had no follow-up imaging.13
Use of pre-existing scans requires effective interprofessional communication between the radiologist and the clinician, as well as appropriate patient education. Gordon et al conducted a retrospective study to access the frequency that incidental AAAs were diagnosed on CT, reported by the radiologist, and entered in the electronic medical record (EMR) by the clinician. They found that radiologists diagnosed new aneurysms and included them in the report or directly notified the clinician, but only 58% of these new findings were entered into the EMR.14 The sensitivity of imaging is only useful as a screening modality if the radiologist reports the findings and the clinician documents them.11
There is evidence that supports the usefulness of pre-existing imaging to diagnose AAAs. The current screening guidelines suggest ultrasound as first-line imaging, but the reality is that most people who are diagnosed with AAA do not undergo an ultrasound to detect the presence of an AAA. The majority of diagnoses are incidental findings on imaging done for another indication.12 Implementation of standard documentation practices would maximize imaging utilization and save lives by decreasing the cases of undiagnosed AAA before rupture, while decreasing the unnecessary repetition of underutilized patient screening.10,11
Since AAA rupture is the 10th leading cause of death in the United States, it is imperative to practice preventative medicine to improve overall patient outcomes.3
Allison Morgan, PA-S, is a student at Augusta University. Alicia Elam, PharmD, is an associate professor, Physician Assistant Department, Augusta University, Augusta, Georgia.
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