From the Guidelines
Computed Tomography Angiography (CTA) can be performed on patients with bilateral Renal Artery Stenosis (RAS), but it requires careful consideration of risks and benefits due to the use of iodinated contrast media. For these patients, the nephrologist and radiologist should collaborate to determine if CTA is appropriate based on the patient's current renal function 1. Prior to the procedure, adequate hydration is essential - typically intravenous normal saline (0.9% NaCl) at 1-1.5 mL/kg/hour for 6-12 hours before and after contrast administration. Nephroprotective medications like N-acetylcysteine (600-1200 mg orally twice daily, the day before and day of the procedure) may be considered, though evidence for their efficacy is mixed. The lowest possible dose of iso-osmolar or low-osmolar contrast should be used.
Some key points to consider when deciding to perform a CTA on a patient with bilateral RAS include:
- The risk of contrast-induced nephropathy, which could potentially worsen already compromised renal function in these patients who have reduced renal blood flow 1.
- The use of alternative imaging modalities like Magnetic Resonance Angiography (MRA) without gadolinium, CO2 angiography, or Doppler ultrasound, which might be preferable for patients with severely compromised renal function (eGFR <30 mL/min/1.73m²) 1.
- The importance of individualized assessment of each patient, taking into account their specific risk-benefit profile and the potential consequences of the procedure 1.
According to the 2016 AHA/ACC guideline on the management of patients with lower extremity peripheral artery disease, CTA is a useful diagnostic tool for anatomic assessment, but its use should be determined on a case-by-case basis, considering the patient's renal function and other factors 1. The guideline recommends that the choice of examination should be determined in an individualized approach to the anatomic assessment for each patient, including risk-benefit assessment of each study type.
In terms of the technical aspects of the procedure, CTA produces excellent 3D images of the aorta and renal arteries, with a sensitivity and specificity for detecting significant RAS of 59% to 96% and 82% to 99%, respectively, compared with catheter-based contrast angiography 1. However, the use of iodinated contrast media requires careful consideration, particularly in patients with compromised renal function.
Overall, while CTA can be a valuable diagnostic tool for patients with bilateral RAS, its use should be carefully considered and individualized to each patient's specific needs and risk profile.
From the Research
Computed Tomography Angiography (CTA) in Bilateral Renal Artery Stenosis
- CTA is a sensitive and specific technique for visualizing renal arteries and diagnosing renal artery stenosis (RAS) 2, 3, 4.
- The risk of contrast nephropathy (CN) in patients with impaired renal function undergoing CTA is a concern, but studies have shown that with proper prophylactic measures, such as oral hydration, the risk can be minimized 2, 5.
- A study comparing CTA to digital subtraction angiography (DSA) found that CTA is not associated with an increased risk of contrast media nephropathy despite using a greater dose of contrast media 3.
- Another study found that CTA performed with a nonionic, low-osmolar contrast medium and prophylactic oral hydration is a minimally invasive technique with low risk of contrast nephropathy in patients with chronic renal insufficiency 2.
- The safety of CTA in patients with bilateral renal artery stenosis can be inferred from studies that have shown its safety in patients with chronic renal insufficiency and suspected ischemic nephropathy 5.
- Optimized scan protocols, including the use of contrast agents and bolus triggering, can improve the accuracy of CTA in diagnosing renal artery stenosis 6.
Key Considerations
- Patients with bilateral renal artery stenosis should be carefully evaluated for the risk of contrast nephropathy before undergoing CTA 2, 3, 5.
- Proper prophylactic measures, such as oral hydration, should be taken to minimize the risk of contrast nephropathy 2, 5.
- The use of nonionic, low-osmolar contrast media and optimized scan protocols can help reduce the risk of contrast nephropathy and improve the accuracy of CTA 2, 6.