Doppler sonographic renal resistance index and resistance index ratio in children and adolescents with unilateral hydronephrosis

The aim of this study was to evaluate Doppler renal resistance index (RI) and RI ratio (RIR) in differentiating between obstructive and nonobstructive hydronephrosis in children and adolescents. The RI and RIR were measured in 32 healthy examinees (control group) and 29 patients with unilateral hydronephrosis. Ten patients had acute obstruction caused by a ureteric stone. Seven had obstructive hydronephrosis due to uretero-pelvic junction (UPJ) obstruction. Twelve patients had nonobstructive hydronephrosis. In controls the mean RI+/-S.D. was 0.615+/-0.04, and RIR 1.045+/-0.033. In children with acute obstruction RI was 0.692+/-0.035 and RIR 1.148+/-0.037. In UPJ obstruction RI was 0.631+/-0.054 and RIR 1.059+/-0.047. In nonobstructive dilatation RI was 0.61+/-0.038 and RIR 1.043+/-0.042. The RI and RIR differences were statistically significant between controls and patients with acute colic (p<0.01), and between patients with acute obstruction and with nonobstructive hydronephrosis (p<0.01). In detecting acute obstruction RIgreater than or equal to0.70 was found to have a 70% sensitivity and a 92% specificity. The RIRgreater than or equal to1.10 was found optimal to distinguish obstructive from nonobstructive dilatation (sensitivity 90%, specificity 83%). Both RI and RIR are significantly elevated in patients with acute obstruction. Renal Doppler seems to be useful in children and adolescents for the detection of acute renal obstruction, although it cannot differentiate chronic obstruction due to the UPJ obstruction and nonobstructive renal collecting system dilatation.