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Background
Few studies have investigated use of prior imaging in abdominal aortic aneurysm (AAA) screening. One study showed 97% sensitivity of preexisting CT within 3 years of a screening ultrasound and implemented a metric for radiologists to include AAA in the final impression. Another study based in Nova Scotia showed a cost savings of $17,000 CAD (~ $1,3000 USD) over 4 months if imaging was reviewed within 5 years prior to ordering a screening ultrasound. To our knowledge in the US there has been no investigation into reviewing prior imaging across modalities to avoid ordering a screening ultrasound.

Educational Goals / Teaching Points
To evaluate prevalence and reliability of prior imaging studies in patients greater than 65 years of age who qualify for AAA screening ultrasound. Many patients who receive screening ultrasounds for AAA are noted to have a prior study that identifies a normal or aneurysmal aorta. Further screening guidelines for AAA should address use of prior imaging in lieu of an additional screening ultrasound to streamline costs to patients as well as the healthcare system.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Using our institutional electronic medical record and PACS, patients aged 65 or older who underwent screening ultrasound for AAA during 2017 - 2022 were identified. Subsequent queries were done to identify patients within this subset who received prior imaging studies that visualize the aorta (i.e., CT of the abdomen, abdomen/pelvis, conventional aortogram, MRI of the abdomen, MRI lumbar spine, PET/CT, complete abdominal ultrasound, limited abdominal ultrasound, renal ultrasound). A retrospective chart review was completed to identify which patients received one of these studies after the age of 65 prior to screening ultrasound. Note was made of which screening studies partially or completely visualized the abdominal aorta. A total of 1012 patients were included in the study. Of these patients, 106 (10.5%) had a prior imaging study (92 patients were above the age of 65 at the time of study). And only 5 of them had AAA identified on screening. The aorta was adequately imaged in 94 patients (89%), 28 using MRI lumbar spine, 50 using CT of the abdomen/pelvis, 6 using complete abdominal ultrasound, 6 using renal ultrasound, and 3 using PET/CT. Thirty-nine imaging studies completely assessed the abdominal aorta.

Conclusion
The majority of patients prior imaging had adequate assessment of the aorta, making their subsequent screening ultrasound redundant. Reevaluation of screening guidelines for AAA to include use of prior imaging could reduce unnecessary imaging studies and resulting costs. This could allow radiologists to include the diagnosis of AAA in the final impression of relevant studies to satisfy the screening requirement.