Contralateral‐Normalized Renal Morphometric Ratios as Imaging Markers of Hydronephrosis Severity in Children Undergoing Pyeloplasty for Ureteropelvic Junction Obstruction

OBJECTIVES: Contralateral-normalized renal morphometric measurements may provide individualized assessment of renal morphology in children with ureteropelvic junction obstruction (UPJO). We aimed to evaluate longitudinal changes in these ratios following pyeloplasty and investigate their associations with hydronephrosis severity and postoperative outcome. METHODS: Sixty-one children undergoing pyeloplasty for unilateral UPJO were retrospectively evaluated. Affected-to-contralateral kidney length and parenchymal thickness ratios were calculated from preoperative and postoperative ultrasonographic measurements. Morphometric parameters were compared according to hydronephrosis severity and anatomical outcome. RESULTS: Following pyeloplasty, the median affected-to-contralateral kidney length ratio decreased from 1.16 to 1.05 and the parenchymal thickness ratio increased from 0.43 to 0.78 (both p < 0.001), corresponding to median changes of -16.0 mm (IQR, -22.6 to -10.0) in AP diameter and + 3.0 mm (IQR, 1.25-4.65) in parenchymal thickness. Compared with Grade 3 hydronephrosis, Grade 4 disease was associated with a significantly lower preoperative parenchymal thickness ratio (0.39 vs. 0.80, p < 0.001) and a higher kidney length ratio (1.22 vs. 1.05, p = 0.004). The preoperative parenchymal thickness ratio showed good discriminatory performance for identifying Grade 4 hydronephrosis (AUC 0.816, 95% CI [0.687-0.945], p < 0.001). No statistically significant association between the morphometric ratios and postoperative anatomical outcome was demonstrated. CONCLUSIONS: The contralateral-normalized parenchymal thickness ratio was associated with hydronephrosis severity and increased significantly following pyeloplasty, supporting its potential role as an adjunctive ultrasonographic measure of morphological change. No statistically significant association with postoperative anatomical outcome was demonstrated; however, outcome analyses were limited by the small number of adverse events. Further studies are required to validate the clinical utility of these measurements.