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 main renal arteries is subject to numerous limitations. Using semiquantitative analysis of the Doppler curve, which can be recorded from intrarenal arteries, it is possible to detect RAS unaffected by the problems of direct Doppler scanning of the renal arteries. Methods. Both angiography of the renal arteries and colour duplex ultrasonography (US) of the intrarenal vessels (interlobar arteries) were performed in 214 patients (53.2 +/- 14.1 years) with severe arterial hypertension. Angiography was used as 'gold standard' in the diagnosis of RAS and the Doppler results were compared with the subsequent findings on angiography. At angiography, the reduction of diameter > 70% was assessed as haemodynamically; effective RAS. For the duplex Doppler diagnosis of RAS the following parameters were calculated: (a) resistive index (RI) of each kidney, and (b) side-to-side differences of the resistive indices (Delta RI) between the right and left kidney. Results. Angiography demonstrated 59 RAS (> 70%) in 53 patients. including six with bilateral RAS. By means of duplex US we found a significant difference of RI between kidneys with RAS (0.38 +/- 0.11) and without RAS (0.63 +/- 0.08; P<0.001). In addition, a significant difference of the Delta RI was noted in patients with RAS (24.4% +/- 12.5%) and the controls without RAS (3.69% +/- 2.7%). Using a combination of both RI and Delta RI, threshold values of RI =0.45 resp. Delta RI = 8% yields a sensitivity of 92.5% and a specificity of 95.7% in the detection of haemodynamically effective RAS. Conclusions. Colour duplex US with calculation of the RI and Delta RI of intrarenal arteries is a valuable noninvasive test assessing the haemodynamic effects of a RAS. Low costs and safety support the use of the Doppler technique in screening for renovascular disease.