Utility of color Doppler ultrasound in the evaluation of renal artery stenosis in comparison with contrast-enhanced magnetic resonance angiography.

Renal artery stenosis (RAS) is one of the main correctable causes of secondary systemic arterial hypertension. Color Doppler ultrasound (DUS), a non-invasive imaging modality, has been used to diagnose RAS in hypertensive patients. This study was conducted in the period between June 2008 and March 2010 to compare the sensitivity, specificity, accuracy and predictive values of DUS using contrast-enhanced magnetic resonance angiography (CEMRA) as the gold standard for the diagnosis of RAS. Fifty-seven consecutive patients with clinical findings suggestive of RAS (32 males and 25 females) with a mean age of 56 years (±7.92 years) were referred to the University Kebangsaan Medical Center to be screened for RAS using DUS and CEMRA. RAS was considered significant if the reduction in diameter was >60%. A total of 114 arteries were assessed, 65 in males (57%) and 49 in females (43%). On DUS, the parameters measured were the peak systolic velocity at the proximal main renal artery (PSV-P), distal main renal artery (PSV-D) and the suprarenal aorta (PSV-A) at the level of the renal hila and the acceleration time (AT) at the main renal artery. The renal-renal ratio (RRR), which is the value of PSV-P/PSV-D, and the renal-aortic ratio (RAR), which is the value of PSV-P/PSV-A, were then calculated. The accuracy, sensitivity, specificity and positive and negative predictive values of DUS in the detection of significant RAS were determined. All measured DUS parameters were positive for the detection of RAS, with an accuracy of 98.3%. On retrospective review, all the arteries that showed significant stenosis on CEMRA demonstrated an irregular outline on DUS. We conclude that DUS is accurate in the diagnosis of significant RAS but is not very sensitive as a screening tool.