From the Guidelines
Computed tomography angiography (CTA) is the preferred imaging modality for diagnosing renal artery stenosis, providing excellent visualization of the renal arteries with high sensitivity and specificity. The procedure involves intravenous contrast administration followed by rapid image acquisition during the arterial phase. Typical protocols use 80-120 mL of iodinated contrast injected at 4-5 mL/second, with image acquisition timed using bolus tracking 1. CTA offers advantages including widespread availability, rapid acquisition time (typically under 5 minutes), and the ability to create three-dimensional reconstructions for better visualization of vascular anatomy.
Some key points to consider when using CTA for diagnosing renal artery stenosis include:
- Ensuring adequate hydration before and after the procedure to minimize the risk of contrast-induced nephropathy
- Considering holding metformin for 48 hours post-procedure in patients with reduced renal function to prevent lactic acidosis
- Being aware of the potential risks and benefits of CTA in patients with decreased renal function, and considering alternative modalities such as magnetic resonance angiography (MRA) or duplex ultrasound as needed 1
Alternative options for diagnosing renal artery stenosis include:
- Magnetic resonance angiography (MRA) for patients with contraindications to iodinated contrast
- Duplex ultrasound as a screening tool in experienced centers
- Catheter angiography, which remains the gold standard but is reserved for interventional cases due to its invasive nature 1
It's worth noting that the choice of imaging modality may depend on individual patient factors, such as renal function and the presence of contraindications to certain types of contrast agents. A multidisciplinary assessment of the patient's clinical presentation, comorbidities, and likelihood of response to intervention can help guide the decision-making process 1.
From the Research
Imaging Modalities for Renal Artery Stenosis
The following imaging modalities are used for the diagnosis of renal artery stenosis:
- Doppler ultrasound (US)
- Computed tomographic (CT) angiography
- Magnetic resonance (MR) angiography
- Digital subtraction angiography (DSA)
Comparison of Imaging Modalities
- CT angiography is more sensitive (96%) than Doppler US (63%) in the detection of stenosis, but the specificity of CT (88%) is similar to that of US (89%) 2
- Doppler US of the main renal artery is more sensitive than Doppler US of segmental arteries in the detection of stenosis 2
- The peak systolic velocity (PSV) provides high sensitivity and specificity as a direct measurement method in stenosis detection and grading, with most studies finding sensitivities and specificities of 85-90% for >50% stenosis at a PSV >180-200 cm/s in ROC curve analysis 3
- Colour duplex US with calculation of the resistive index (RI) and side-to-side differences of the resistive indices (delta RI) of intrarenal arteries is a valuable non-invasive test assessing the haemodynamic effects of a RAS, with a sensitivity of 92.5% and a specificity of 95.7% in the detection of haemodynamically effective RAS 4
- CT angiography has high sensitivity and specificity at the main renal artery level, with a lower radiation dose than previously assumed, and can be used as a diagnostic tool in patients with low to medium risk of renal artery stenosis, and as a screening and treatment planning tool in patients at high risk 5
Advantages and Disadvantages of Imaging Modalities
- Doppler US is a non-invasive, side effect-free, and cost-effective method, but has variable accuracy in studies 3
- CT angiography is more accurate than Doppler US, but has a higher radiation dose 2, 5
- MR angiography demonstrates an accuracy of >90%, but has possible side effects for patients, particularly in the case of pre-existing renal parenchymal damage 3
- DSA remains the gold standard, but has a higher radiation dose than CT angiography 5