From the Guidelines
The best test for diagnosing an abdominal aortic aneurysm (AAA) is an abdominal ultrasound, as it provides reliable visualization of the aorta with sensitivity and specificity exceeding 95% for detecting AAAs 1. When performing an ultrasound for AAA screening, the technician will measure the aorta in both anteroposterior and transverse planes, with an aortic diameter of 3.0 cm or greater considered aneurysmal.
Key Points to Consider
- Ultrasound is preferred for initial screening and routine surveillance due to its lack of radiation exposure, lower cost, and excellent accuracy 1.
- For patients with a suspected or known AAA requiring more detailed evaluation, CT angiography (CTA) with contrast is recommended as it provides comprehensive information about aneurysm size, shape, extent, relationship to branch vessels, and presence of rupture or leak 1.
- CTA offers superior anatomical detail needed for surgical planning or when complications are suspected, and is considered the reference standard for AAA diagnosis and management decision making 1.
- MRI can be used as an alternative for patients who cannot undergo CT scanning due to contrast allergies or kidney dysfunction 1.
Important Considerations
- The choice of imaging modality may depend on the clinical presentation and risk factors of the patient, with CTA being recommended for evaluation of symptomatic patients with acute onset abdominal or back pain 1.
- Dual-energy CTA can be used to characterize AAAs with reduced IV iodinated contrast dose without compromising imaging quality 1.
From the Research
Imaging Modalities for Abdominal Aortic Aneurysm (AAA)
The best test for AAA can be determined by considering the various imaging modalities available, including their advantages and limitations.
- 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
Comparing the different imaging modalities, we can see that:
- MRI provides detailed information on the site and extension of the aneurysm, as well as the extent of branches involvement and the presence of thrombosis 3, 4, 5.
- CT is extremely valuable in emergency cases and in the detection of calcifications, but provides insufficient information on the involvement of the vessels originating from the aorta 3, 4.
- Angiography has limitations due to its morbidity and inability to demonstrate eventual thrombi and adjacent structures 3, 4.
- US is useful in the screening of abdominal aortic aneurysms, but lacks the accuracy and reliability necessary for a complete preoperative evaluation 3, 4, 5.
Recent Developments
Recent studies have explored the use of new imaging techniques, such as 4D flow MRI, which has the potential to further improve individualized risk stratification in patients with AAA 2.