What is the best initial imaging modality for severe stenosis of the left common iliac artery?

Best Imaging Modality for Severe Stenosis of Left Common Iliac Artery

CT Angiography (CTA) of the abdomen and pelvis with bilateral lower extremity runoff is the best initial imaging modality for evaluating severe stenosis of the left common iliac artery. 1

Rationale for CTA as First-Line Imaging

• CTA provides excellent visualization of vessel anatomy while being less invasive than conventional angiography, with sensitivity and specificity of 90-100% for detecting significant stenoses 2
• CTA enables comprehensive assessment of the entire vascular tree from the aorta through the lower extremities in a single examination, allowing for complete evaluation of inflow and outflow vessels 1, 3
• CTA offers volumetric (3D) imaging with extensive post-processing capabilities, including multiplanar reformatted and maximum-intensity projection images that create a detailed arterial road map 2
• CTA simultaneously analyzes both vascular structures and surrounding anatomy, allowing for assessment of potential extravascular causes of arterial compromise 2

Technical Considerations for CTA

• A multislice CT scanner should be used with collimation of 0.6 mm and reconstruction slice thickness between 0.5-1.0 mm 1
• Body-weight adapted injection of non-ionic iodinated contrast agent (≥350 mg/mL) using a power injector (≥4 mL/s) is recommended 1
• Arterial compression should be assessed using arterial cross-sections produced by sagittal reformation of data, as axial slices alone can lead to misrepresentation of stenosis degree 2

Alternative Imaging Modalities

MR Angiography (MRA)

• MRA with contrast provides excellent soft tissue contrast and vascular assessment with sensitivity and specificity of 95% for diagnosing segmental stenosis and occlusion 1
• MRA has limitations including longer acquisition times, potential contraindications in patients with certain implanted devices, and tendency to overestimate the degree of stenosis 1
• MRA cannot visualize arterial calcifications, which may be important for planning interventions, especially in heavily calcified lesions 1

Duplex Ultrasound

• Duplex ultrasound is useful as an initial screening tool with sensitivity and specificity of approximately 90-95% for detecting stenoses >50% from the iliac to popliteal arteries 1
• Limitations include operator dependence, difficulty visualizing iliac vessels due to bowel gas or patient body habitus, and decreased accuracy with multiple sequential lesions 1
• Duplex ultrasound may underestimate the extent of disease when multiple "tandem" stenotic segments are present 1

Digital Subtraction Angiography (DSA)

• While historically considered the gold standard, DSA is now primarily reserved for cases where endovascular intervention is planned rather than for diagnostic purposes alone 1
• DSA is invasive with risks of catheterization complications and has been largely replaced by non-invasive imaging modalities 1
• DSA provides the advantage of measuring pressure gradients across stenoses, which can be valuable for determining hemodynamic significance 1

Clinical Pathway for Iliac Artery Stenosis Evaluation

1. Initial assessment with ankle-brachial index (ABI) and duplex ultrasound to confirm presence of peripheral arterial disease 1
2. CTA of abdomen and pelvis with bilateral lower extremity runoff as the primary imaging modality for comprehensive anatomic evaluation 1
3. Consider MRA as an alternative if CTA is contraindicated (e.g., severe renal impairment, contrast allergy) 1
4. Reserve DSA for cases where intervention is planned or when non-invasive imaging is inconclusive 1

Common Pitfalls to Avoid

• Relying solely on axial slices in CTA can lead to underestimation of stenosis in up to 43% of cases 2
• Heavily calcified atheromatous disease can limit interpretation of CT images 2
• Duplex ultrasound may be limited by bowel gas, obesity, or vessel tortuosity when evaluating iliac arteries 1
• Single-plane angiography may underestimate stenosis compared to intravascular ultrasound measurements 4

By following this approach, clinicians can obtain the most comprehensive and accurate assessment of left common iliac artery stenosis to guide appropriate treatment decisions.