CTA Abdomen and Pelvis with Bilateral Lower Extremity Runoff with IV Contrast
For a patient with an abnormal ankle-brachial index (ABI), you should order a CTA of the abdomen and pelvis with bilateral lower extremity runoff with IV contrast 1.
Rationale and Clinical Algorithm
The 2024 ACR Appropriateness Criteria provides clear guidance on this imaging approach 1. When an abnormal ABI confirms peripheral arterial disease (PAD), cross-sectional imaging becomes essential for:
- Determining anatomic disease location - identifying whether disease is aortoiliac, femoropopliteal, or infrapopliteal
- Assessing stenosis severity and occlusion patterns - quantifying the degree of arterial narrowing
- Treatment planning - deciding between endovascular revascularization (EVR) versus open surgical (OS) revascularization
Why CTA Over Other Modalities
The ACC/AHA practice guidelines give CTA a moderate recommendation because it provides comprehensive anatomic detail that directly impacts treatment decisions 1. While CTA does increase initial contrast load, the detailed preprocedure planning it enables typically results in markedly decreased contrast doses during actual endovascular interventions 1.
Alternative Consideration: Duplex Ultrasound
Duplex ultrasound (DUS) can be performed as an adjunct to ABI for anatomic localization, with excellent accuracy for aortoiliac disease:
- 92% sensitivity and 96% specificity for significant aortoiliac lesions 1
- κ index of 0.81 showing good agreement with angiography/CTA 1
However, DUS has limitations with a positive predictive value of only 60% for iliac artery segments in some studies 1, making it better suited as a complementary rather than definitive imaging modality.
Important Caveats
Exercise/treadmill ABIs should be performed if initial resting ABI is normal in patients with suspected isolated aortoiliac disease, as ABIs may be falsely normal at rest in this specific anatomic pattern 1. This is a common pitfall—don't stop at a normal resting ABI if clinical suspicion remains high for aortoiliac occlusive disease.
In patients with heavily calcified/noncompressible vessels (common in diabetes), ABI results are severely limited 1. In these cases, toe-brachial index should be obtained alongside the CTA to evaluate distal ischemia.