The comparison of the resistivity index values in the ultrasonographic evaluation of a unilateral atrophic/hypoplastic kidney.

In the study, we aimed to determine the sensitivity of the renal resistivity index (RI) in differentiating hypoplastic and atrophic kidneys in patients with small-sized kidneys, and to evaluate its capacity to predict the renal involvement confirmed by the DMSA scintigraphy. We retrospectively reviewed the ultrasonography (US) and DMSA findings, and medical records of pediatric patients with unilateral diminutive kidneys followed between January 2017 and June 2018. The RI measurements were performed twice, and the mean RI was calculated for each kidney of all patients. Sixty-three (male/female, m/f = 28/35) pediatric patients aged 107.2 ± 49.4 months (range 14-206 months) were included in this study. The DMSA scintigraphy revealed abnormal changes to atrophic kidneys in 38 patients and hypoplastic kidneys in 25. There were no differences between the groups with atrophy and hypoplasia by age, gender, urine density, and creatinine. The patient group with atrophic kidneys had a mean RI of 0.55 ± 0.21, and patients with hypoplastic kidneys had a mean RI of 0.67 ± 0.03. The mean RI and systolic/diastolic rates of the patients with atrophy were significantly lower than of the patients with hypoplastic kidneys ( = 0.042 and  = 0.048, respectively). There was a positive correlation between RI and DFR in the group with atrophy ( = 0.461,  = 0.016), but this was not the case for the group with hypoplastic kidneys (= -0.066,  = 0.889). The resistivity index might be very useful for differentiating atrophy and hypoplasia in patients with unilateral small kidneys and can be used instead of scintigraphic evaluation.