Renal artery stenosis: evaluation with colour duplex ultrasonography

Background: Detection of renal artery stenoses (RAS)by means of duplex Doppler ultrasound with direct scanning of the mainrenal arteries is subject to numerous limitations. Using semiquantitativeanalysis of the Doppler curve, which can be recorded from intrarenalarteries, it is possible to detect RAs unaffected by the problems of directDoppler scanning of the renal arteries. Method: Bothangiography of the renal arteries and colour duplex ultrasonography (US) ofthe intrarenal vessels (interlobar arteries) were performed in 214 patients(53.2±15.1 years) with severe arterial hypertension. Angiographywas used as 'gold standard' in the diagnosis of RAS and the Doppler resultswere compared with the subsequent findings on angiography. At angiography,the reduction of diameter >70% was assessed as haemodynamicallyeffective RAS. For the duplex Doppler diagnosis of RAS the followingparameters were calculated: (a) resistive index (RI) of each kidney, and(b) side-to-side differences of the resistive indices (&Dgr;RI) betweenthe right and left kidney. Results: Angiographydemonstrated 59 RAS (>70%) in 53 patients, including six withbilateral RAS. By means of duplex US we found a significant difference ofRI between kidneys with RAS (0.48±0.11) and without RAS(0.63±0.08; P<0.001). In addition, a significantdifference of the &Dgr;RI was noted in patients with RAS(24.4%±12.5%) and the controls without RAS(3.6%±2.7%). Using a combination of both RI and &Dgr;RI,threshold values of RI=0.45 resp. &Dgr;RI=8% yields a sensitivity of92.5% and a specificity of 95.7% in the detection of haemodynamicallyeffective RAS. Conclusion: Colour duplex US withcalculation of the RI and &Dgr;RI of intrarenal arteries is a valuablenon-invasive test assessing the haemodynamic effects of RAS. Low costs andsafety support the use of the Doppler technique in screening forrenovascular disease.