The role of the renal resistive index ratio in diagnosing obstruction and in the follow-up of children with unilateral hydronephrosis

Objective To assess the role of the renal resistive index ratio (RIR) in di scriminating equivocal upper urinary tract dilatation in children, and thus in establishing the need for surgery, in comparison with traditional diagn ostic tools. Patients and methods The study comprised 40 children with unilateral hydron ephrosis unrelated to vesicoureteric reflux, posterior urethral valves, meg aureter or a duplex system. In all patients one or more of the following 'i ndices of obstruction' were positive; an anteroposterior renal pelvic diame ter of >20 mm, a half-time diuretic 'washout' (T/2) of >20 min, a separate renal function of <40%, and symptoms of obstruction (pain, sepsis), All the se variables were measured on admission and after a mean (range) follow-up of 9 (2-24) months. After this period, all patients who were symptomatic or with two or more of the variables above the normal range were considered a s obstructed and underwent a dismembered pyeloplasty. The variables were th en re-assessed 6 months after surgery. The RIR was evaluated using duplex D oppler ultrasonography with a 3.5-5 MHz transducer, by the same operator, D ifferences between obstructive and unobstructive unilateral hydronephrosis were estimated from the mean values of the variables assessed and Student's t-test used to determine significant differences. The correlation between the T/2 and RIR before and after surgery was also evaluated. Results During follow-up the RIR was abnormal in 27 of 30 patients with hyd ronephrosis who were considered to be 'obstructed'. Twenty-three of these p atients, selected for surgery, had a positive diuretic renogram; 11 had los s of differential renal function and 16 had recurrent clinical symptoms, Th ere were significant differences in the mean RIR and T/2 between obstructed and unobstructed patients. Six months after dismembered pyeloplasty, the R IR returned to normal in all patients except three in whom it was previousl y >1.1. The diuretic renogram, if initially showing pathology, always becam e normal, The RIR did not change in patients with an unchanged and severe l oss of differential renal function before and after surgery. Conclusions In this study the RIR was a good index of obstruction in childr en with unilateral hydronephrosis and it correlated well with the results o f diuretic renography. The specificity of the RIR was reduced whenever ther e was severe renal damage.