What imaging modalities are used to diagnose renal artery stenosis (RAS)?

From the Guidelines

Imaging for renal artery stenosis should begin with Doppler ultrasound as the initial screening test, followed by CT angiography (CTA) or MR angiography (MRA) for definitive diagnosis, as recommended by the 2024 ESC guidelines 1. The choice of imaging modality depends on patient factors, including renal function, contrast allergy history, and whether intervention might be needed.

• Doppler ultrasound is a non-invasive, low-cost, and radiation-free initial screening test.
• CTA offers excellent spatial resolution and can detect stenosis greater than 50%, with the protocol involving administration of intravenous contrast followed by thin-slice imaging of the renal arteries.
• MRA is an excellent alternative for patients with impaired renal function or contrast allergies, particularly using non-contrast techniques like time-of-flight MRA. The 2024 ESC guidelines recommend assessing clinical high-risk features and kidney viability when evaluating renal artery revascularization in patients with atherosclerotic RAS 1. Clinical suspicion for renal artery stenosis should be highest in patients with resistant hypertension, unexplained renal dysfunction, recurrent flash pulmonary edema, or abdominal bruits, as stated in the ACR Appropriateness Criteria 1. The American College of Radiology Appropriateness Criteria and the ACC/AHA 2005 practice guidelines also support the use of Doppler ultrasound as a screening test, followed by CTA or MRA for definitive diagnosis 1. However, the most recent and highest-quality study, the 2024 ESC guidelines, should be prioritized when making a definitive recommendation 1.

From the Research

Imaging Modalities for Renal Artery Stenosis

• Catheter angiography with pressure gradient measurements is considered the definitive gold standard for diagnosing renal artery stenosis, but it is also the most invasive 2.
• Ultrasonography is a non-invasive, safe, and cost-effective method, but it has variable accuracy and is operator-dependent 2, 3.
• Contrast-enhanced computed tomographic angiography and magnetic resonance angiography are intermediate in terms of accuracy and expense, with accuracies of over 90% 2, 3.
• Magnetic resonance angiography without contrast has become more accurate and rivals contrast-enhanced techniques in some patients 2.

Diagnostic Criteria and Techniques

• Ultrasonography uses four different criteria, including peak systolic velocity (PSV) and renal aortic ratio (RAR), to diagnose renal artery stenosis, with PSV providing high sensitivity and specificity 3.
• A PSV of >180-200 cm/s is considered diagnostically relevant for stenosis grading, with sensitivities and specificities of 85-90% for >50% stenosis 3.
• Contrast-enhanced ultrasound can improve accuracy, and other methods such as the ratio of PSV in the aorta to PSV in the renal artery (RAR) or indirect criteria can be used to improve accuracy 3.

Comparison of Imaging Modalities

• Magnetic resonance angiography (MRA) and Doppler ultrasonography are non-invasive and safe diagnostic techniques with high sensitivity and specificity, but their accuracy depends on technicians and software 4.
• A study comparing MRA and Doppler ultrasonography found that MRA had a sensitivity and specificity of 100% and 25%, respectively, while Doppler ultrasonography had a specificity and positive predictive value of 67% 4.
• Computed tomographic angiography (CTA) and MRA demonstrate an accuracy of over 90%, but may have possible side effects for patients, particularly in the case of pre-existing renal parenchymal damage 3.