Imaging for Suspected Iliac Artery Disease
Order a CTA abdomen and pelvis with bilateral lower extremity runoff with IV contrast to evaluate for iliac artery occlusive disease, and yes, perform an exercise/treadmill ABI at the same time since resting ABIs are frequently normal in isolated iliac disease. 1
Why CTA is the Optimal Study
The American College of Radiology gives CTA a moderate recommendation as the definitive imaging modality because cross-sectional imaging allows precise diagnosis of anatomic disease location and significance of stenosis/occlusion, which directly improves surgical planning for endovascular or open surgical revascularization. 1
Key advantages of CTA for iliac disease:
- Provides complete anatomic detail from the aorta through the lower extremities in a single study 1
- Accurately identifies the location and severity of stenosis/occlusion 1, 2
- Enables treatment planning by determining suitability for endovascular versus surgical intervention 1
- Demonstrates 93% sensitivity and 99% specificity for detecting high-grade (>75%) iliac stenoses when axial images are analyzed 3
- 100% sensitivity and 97-100% specificity for iliac artery occlusions 3
The Critical Role of Exercise ABI
ABIs may be completely normal at rest in patients with isolated iliac occlusive disease, making exercise/treadmill ABIs essential for objectively evaluating functional limitations. 1
Why exercise testing matters:
- Resting ABIs miss isolated aortoiliac disease 1
- Exercise ABIs unmask hemodynamically significant proximal disease that appears normal at rest 1
- Provides objective documentation of functional impairment 1
Alternative: Duplex Ultrasound
If CTA cannot be performed (contrast allergy, severe renal dysfunction), duplex ultrasound of the bilateral lower extremities including iliac segments is an acceptable alternative with 92% sensitivity and 96% specificity for detecting significant aortoiliac lesions. 1, 4
Important caveats about ultrasound:
- Duplex ultrasound has excellent negative predictive value (97-100%) for the iliac segment, meaning a negative study reliably excludes significant disease 1
- However, positive predictive value ranges from only 60-89%, so positive findings may require CTA confirmation 1
- Ultrasound is operator-dependent and may be limited by body habitus or bowel gas 4
Common Pitfalls to Avoid
Do not rely on resting ABI alone - this is the most critical error, as isolated iliac disease frequently presents with normal resting ABIs but becomes apparent only with exercise testing 1
Do not order lower extremity arterial duplex alone without specifically requesting iliac imaging - standard lower extremity studies may not adequately assess the iliac segments 4
When reviewing CTA, always examine axial images in addition to maximum intensity projections (MIP) - calcified plaques can obscure stenoses on MIP images alone, reducing sensitivity from 93% to only 53% 3