Postnatal urinary tract dilation classification system for predicting the need for surgical intervention among neonates and young infants
Jisun Hwang2 , Pyeong Hwa Kim1 , Hee Mang Yoon1 , Sang Hoon Song1 , Ah Young Jung1 , Jin Seong Lee1 , Young Ah Cho1
1Asan Medical Center, Seoul, Korea
2Hallym University Dongtan Sacred Hospital, Hwaseong-si, Korea
Corresponding Author: Hee Mang Yoon ,Tel: 82-2-3010-0906, Fax: 82-2-476-4719 , Email:
Received: March 2, 2022;  Accepted: July 23, 2022.  Published online: August 2, 2022.
Purpose To validate the postnatal urinary tract dilation (UTD) classification system by correlating it with the need for surgical intervention. Methods Young infants who underwent ultrasound (US) examinations for prenatal hydronephrosis were retrospectively identified. The kidney units (KUs; either right, left, or bilateral) were graded from UTD P0 (very low risk) to P3 (high risk) based on seven US criteria from the UTD system. Surgery-free survival curves were constructed using the Kaplan–Meier method. Univariable and multivariable Cox proportional hazards regression analysis clustered by patients was performed. Interobserver agreement was analyzed using the weighted kappa. Results A total of 504 KUs from 336 patients (mean age, 18.3 ± 15.9 days; range, 1–94 days; males, n = 276) were included, with a median follow-up of 24.2 months. A total of 58 KUs underwent surgical intervention. Significant differences were observed among the Kaplan–Meier curves stratified into UTD groups (P < .001). The presence of anterior–posterior renal pelvic diameter ≥15 mm (hazard ratio [HR], 8.602; 95% confidence interval [CI], 1.558–43.065), peripheral calyceal dilation (HR, 8.190; 95% CI, 1.558–43.065), ureteral dilation (HR, 2.619; 95% CI, 1.274–5.380), parenchymal thickness abnormality (HR, 3.371; 95% CI, 1.574–7.223), bladder abnormality (HR, 12.209; 95% CI, 3.616–41.225) were significantly associated with the occurrence of surgery. The interobserver agreement was moderate to almost perfect agreement for US features (κ = 0.564–0.898) and substantial for final UTD grades (κ = 0.716). Conclusion The UTD classification system is reliable and appropriately stratifies the risk of surgical intervention.
Keywords: Hydronephrosis; ultrasonography; infant; prognosis; reproducibility of results
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