From the Guidelines
AAA imaging should typically involve ultrasound as the first-line screening method, followed by CT angiography for detailed evaluation, as recommended by the most recent guidelines 1.
Key Points for AAA Imaging
- Ultrasound is the preferred initial screening method due to its non-invasive nature, lack of radiation, and cost-effectiveness, with approximately 95% sensitivity and 100% specificity for detecting aneurysms.
- CT angiography with contrast is the preferred imaging modality for detailed evaluation when an aneurysm is detected or suspected, providing comprehensive information about aneurysm size, shape, location, relationship to branch vessels, and presence of thrombus.
- MR angiography serves as an alternative for patients with contrast allergies or renal insufficiency.
- For surveillance of known AAAs, ultrasound is typically performed at intervals based on aneurysm size, with more frequent imaging for larger aneurysms approaching the thresholds for intervention, as outlined in the 2022 ACC/AHA guideline for the diagnosis and management of aortic disease 1.
Surveillance Intervals
- For aneurysms 3.0 cm to 3.9 cm, longer surveillance imaging intervals have been shown to be safe, with annual surveillance ultrasound recommended for those 4.0 cm to 4.9 cm.
- Once the size of the AAA reaches ≥5.0 cm in men and ≥4.5 cm in women, the screening interval is shortened to every 6 months.
Choice of Imaging Modality
- CT provides superior visualization of the abdominal aorta and its branches and is an excellent alternative when ultrasound is inadequate.
- Non-IV contrast MRI techniques have also been shown to be useful in defining AAAs, serving as a reasonable alternative to CT in certain cases.
From the Research
AAA Imaging Modalities
- Ultrasound is the mainstay imaging modality for AAA screening and surveillance 2
- Contrast-enhanced CT angiography is currently considered the gold standard for preoperative imaging and image-based treatment planning in AAA repair 2
- Non-contrast MR angiography allows for accurate monitoring of aortic diameters in AAA patients 2
- Measurement of aortic diameters is more accurate with 3D-CT/MRI compared to ultrasound 2
Comparison of Imaging Modalities
- CT and MRI can correctly define the diameter of the aneurysm, while angiography may underestimate the diameter of lesions without peripheral calcifications 3
- CT and MRI can provide information on the involvement of renal arteries, while US may not be useful 3
- CT is more accurate than ultrasonography in evaluating abdominal aortic aneurysm, especially in obese patients or in the presence of gas in the bowel 4
Role of Imaging in AAA Management
- Cross-sectional imaging plays a crucial role in AAA surveillance, pre-procedural assessment, and post-EVAR management 5
- Imaging techniques such as 4D flow MRI have the potential to further improve individualized risk stratification in patients with AAA 2
- Molecular imaging techniques can visualize the molecular alterations associated with AAA, which can help in monitoring AAA growth and evaluating the risk of rupture 6