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Renal artery stenosis: grading with image-directed Doppler US evaluation of renal resistive index
W B Schwerk1, I K Restrepo, M Stellwaag
1Department of Internal Medicine, Philipps-University, Marburg, Germany.
Purpose:
To determine the role of intrarenal Doppler ultrasound (US) in detection of moderate to severe (> 50%) renal artery stenosis (RAS).
Materials And Methods:
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.
Results:
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%.
Conclusion:
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.