Renal artery stenosis: grading with image-directed Doppler US evaluation of renal resistive index.

Abstract

To determine the role of intrarenal Doppler ultrasound (US) in detection of moderate to severe (> 50%) renal artery stenosis (RAS). In 72 patients, 142 kidneys were examined with conventional angiography and color duplex US. Renal size, mean intrarenal-arterial resistive index (RI), and difference of mean RIs between both kidneys (delta RI) were determined and compared with severity of RAS as determined with quantitative angiography. In 32 patients, angiography showed mild RAS < or = 50% in 13, moderate RAS in 10, and severe RAS in nine. Both renal size and mean RI values were decreased significantly (P < .001) only for severe RAS compared with values in 40 control subjects. For delta RI, no significant difference was noted between controls and patients with mild RAS; highly significant differences, however, were noted for both moderate and severe RAS (P < .001). Sensitivity and specificity of a cutoff delta RI of > 5% were 82% and 92% for RAS > 50% and 100% and 94% for moderate RAS and RAS > 60%. Color Doppler US and analysis of intrarenal Doppler spectra are recommended as a useful method for noninvasive diagnosis and grading of RAS. In bilateral RAS > 50%, however, calculation of delta RI is potentially biased by undergrading of stenosis.