Postnatal Calyceal-to-Parenchymal Ratio: A Promising Predictor for Surgical Correction of Ureteropelvic Junction Obstruction in Newborns

Objective: This study aims to explore a new parameter, the calyceal-to-parenchymal ratio (CPR) of postnatal renal ultrasonography (RUS) as a predictor of surgery in newborns with possible ureteropelvic junction obstruction (UPJO). Although UPJO remains the main surgical category of antenatally detected hydronephrosis, there is a lack of a gold-standard test that predicts the need for pyeloplasty. Subjects and methods: We retrospectively reviewed infants with a positive antenatal history of hydronephrosis who were confirmed to have grade 3 or 4 hydronephrosis on postnatal RUS between 2010 and 2020. We compared postnatal CPR between surgical and control groups and tested the correlation between postnatal CPR and diuretic renogram.Results: A total of 79 and 136 kidneys were included in the surgical and control groups, respectively. Kidneys that were managed with pyeloplasty between January 2010 and July 2020 were included in the surgical group, while kidneys from patients with comparable traits who were managed conservatively comprised the control group. At a mean age of 18.9 weeks at presentation and a mean follow-up period of 48.99 months, the median postnatal CPR was significantly greater in the surgical group (3.62 vs. 0.98, p<0.001). A postnatal CPR of 1.68 had a sensitivity and specificity of 96.2% and 84.8%, respectively, in predicting the need for future pyeloplasty (area under the curve (AUC)=0.966). There was a positive and significant correlation between postnatal CPR and the half-life of the renogram (p=0.018) but not significant with the differential function (p=0.090).Conclusion: Diuretic renography has little capability for predicting future pyeloplasty. Current RUS grading systems do not offer an objective measure of renal parenchyma. Numerous other RUS parameters are less frequently utilized in clinical practice, and many are challenging to assess and require sophisticated software or equipment.