Valoración de la estenosis de las arterias renales utilizando la angioresonancia magnética sin contrastecorrelación con la angiotomografía computarizada

Resumen

Aims and objectives: Renal artery stenosis is a treatable cause of hypertension. Aprox. 90% is caused by atherosclerosis and it affects mostly the ostium and proximal part of the artery. The aim of this study is to verify the correlation between computed tomography angiography (CTA) and Time-of-Flight magnetic resonance angiography (TOF-MRA) in the evaluation of renal arteries stenosis, in order to prove the reliability of unenhanced MRA and the possibility of replacing the CTA. Patients can therefore benefit from the absence of radiation and contrast media, reducing its possible side effects. Even thought new unenhanced MR angiographic sequences have emerged, TOF is available in most MR scans. Methods and materials: Patient demographics, CTA and MR imaging findings, were retrospectively obtained from the electronic medical records. TOF-MRA where carried out in a 1.5T scan, using a 6-channel body coil. The CTA where performed in a 16-detector CT scan, with a nonionic, low-osmolarity iodinated contrast agent, and standard protocols where used. A total of 58 patients who underwent a CTA and a TOF-MRA of the renal arteries were reviewed and images from 120 renal arteries were independently assessed by two radiologists. A consensus reading was used for those arteries with discrepant readings. The degree of stenosis was classified in four groups: <30%, between 30-60%, >60% and occlusion. Clinically significant stenosis was considered when greater than 60%. Imaging findings were statistically compared between both techniques and both observers and the kappa coefficient was used to test the degree of concordance. Sensitivity, specificity, positive predictive value and negative predictive value were measured. Results: 7 main arteries were not assessable on the TOF-MRA because 3 were not included in the FOV, 2 had movement artifacts and 1 patient was claustrophobic and the test was not finished. In our study, there is a good agreement between both techniques for the degree of stenosis in the ostium/proximal part of the renal arteries (kappa: 0.79). Sensitivity, specificity, positive predictive value and negative predictive value are 89%, 99%, 89% and 99%, respectively. When the stenosis is < 60%, there is a small difference between both techniques with regard to quantification of stenosis degree, which isn&apos;t clinically relevant. When the stenosis is > 60% there is a signal loss in the stenosis and the signal reappears distal to the stenosis, whereas in an occlusion there is no distal signal. 9 renal arteries have positive findings for significant stenosis identified by CTA and only one of them is not identified with the TOF-MRA. There is one false positive case, due to an anatomical variation: the origin of the renal artery is on the anterior side of the aorta with a caudal-to-craneal direction, so the artery is not perpendicular to the plane of acquisition and the signal is suppressed. The evaluation of the distal part of the artery is limited with the TOF-MRA (sensitivity, specificity, positive predictive value and negative predictive value are 66,7%, 98,2%, 50% and 99%, respectively). Conclusion: 1. TOF-MRA is a reliable technique (but not 100% precise) for assessing stenosis of the proximal part of the main renal arteries. 2. A negative test may exclude clinically relevant stenosis and patients can benefit from the absence of radiation and contrast media. 3. A positive test should be confirmed with other imaging technics because there are some limitations that may cause a false positive image. 4. TOF-MRA could be considered an alternative in patients with contraindications for ionizing radiation or contrast media.