Distribution and variability of resistive index values in undilated kidneys in children

To assess better the utility of duplex Doppler sonography in the diagnosis of obstructive hydronephrosis in children, we specifically studied undilated urinary tracts with the intention of establishing a nomogram of resistive index (RI) values and determining if the RI value of 0.7 reliably precludes an undilated collecting system.

Renal duplex Doppler ultrasound was performed in a standard fashion on 47 children more than 12 months of age (93 renal units) where there was no suspicion of upper urinary tract dilation. RI and RI ratio (RIR) were calculated and statistical analysis performed.

There were 27 males and 20 females 12 to 180 months old (mean, 63.9 months). Kidney size ranged from 5.0 to 9.8 cm (mean, 7.28 cm), RI ranged from 0.34 to 0.94 (mean, 0.65), and RIR ranged from 1.00 to 1.76 (mean, 1.14). There was no statistically significant relationship between the RI and renal size or laterality, gender, or age (p > 0.05). However, between the ages of 24 and 108 months, the RI was significantly higher in females compared with males (p = 0.002). If one were to use 0.7 and 1.10 as discriminatory values for RI, 37% of renal units had values above 0.7, and 41% of RIR values were above 1.10.

We believe that RI values in undilated kidneys of children vary significantly and its routine use and reliability need to be evaluated further in the pediatric population.