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Hydronephrosis Outcome Prediction Score for Determining Resolution of Prenatal Hydronephrosis: An Analysis of the Multi-Center Society for Pediatric Urology Prenatal Hydronephrosis Task Force
Carol A. Davis-Dao, PhD1, Sarah H. Williamson, MD1, Melissa McGrath, BS2, C. D. Anthony Herndon, MD3, Antoine E. Khoury, MD1, Nora G. Kern, MD4, Gina M. Lockwood, MD5, Anne G. Dudley, MD6, Shannon Cannon, MD7, Rebecca S. Zee, MD PhD3, Valre W. Welch, NP3, Kai-wen Chuang, MD1, Heidi A. Stephany, MD1, Elias J. Wehbi, MD1, Luis H. Braga, MD PhD2.
1UC Irvine and CHOC Children's, Orange, CA, USA, 2McMaster University, Hamilton, ON, Canada, 3Children's Hospital of Richmond at Virginia Commonwealth University, Richmond, VA, USA, 4University of Virginia, Charlottesville, VA, USA, 5University of Iowa, Iowa City, IA, USA, 6Connecticut Children's Medical Center, Hartford, CT, USA, 7University of Wisconsin School of Medicine, Madison, WI, USA.

Background Prenatal hydronephrosis is one of the most common ultrasound findings and the majority of patients will resolve over time. Our objective was to evaluate the Hydronephrosis Outcome Prediction (HOP) Score, which utilizes three ultrasound measurements to predict the likelihood of resolution.Methods Patients with prenatally detected and postnatally confirmed isolated hydronephrosis were prospectively enrolled from 7 centers between 2007-2022. Baseline ultrasounds were included if performed between 3 days of life and 6 months with Society for Fetal Urology (SFU) grade, anterior posterior renal pelvis diameter (APD) and renal lengths available for analysis. Exclusion criteria were vesicoureteral reflux, primary megaureter, other urologic anomalies, and follow-up <3 months. The HOP score was adapted from Li et al.1 utilizing 3 initial ultrasound parameters: SFU grade, APD, and absolute percentage difference of renal lengths. HOP score was calculated on a 12-point scale with each parameter assigned a score from 0-4, 0 being least severe and 4 being most severe (TABLE). Hydronephrosis resolution was defined as SFU grade 0 or 1 and APD ≤10 mm without worsening on subsequent ultrasounds. Patients undergoing pyeloplasty were censored at time of surgery. Receiver operating characteristic curves were determined to establish HOP score thresholds for resolution and pyeloplasty. Results Of the 1983 patients enrolled, 601 met inclusion criteria. Included patients were 77% (461/601) male; median age at initial ultrasound was 1.4 months (IQR 0.73-2.6), and median follow-up was 23 months (IQR 14-38). In this cohort, 49% (294/601) resolved, 19% (114/601) underwent pyeloplasty, and 32% (193/601) continued follow-up. Median time to resolution was 11.5 months (IQR 4-20). Median HOP score for patients with resolution was 3.0 (IQR 3-5), compared to 5.0 (IQR 4-7) for continued follow-up, and 9.5 (IQR 8-12) for pyeloplasty. We established HOP score of ≤4 as a threshold for resolution with AUC of 0.75 (Figure). Of the 293 patients with HOP score ≤4, 218 (74%) resolved, only 6 (2.0%) underwent pyeloplasty, and of the 69 (24%) that remained under follow-up, none had SFU grade 4 at most recent ultrasound. Conversely, HOP score ≥8 was predictive of pyeloplasty with an AUC of 0.86. Conclusions A HOP score of 4 was a predictive threshold to estimate which patients will likely have spontaneous resolution of isolated hydronephrosis. Our findings suggest that patients with HOP score ≤4 on initial ultrasound are at low risk for progression as only 2% of these patients underwent surgery for obstruction. Conversely, a HOP score ≥8 predicted undergoing pyeloplasty. The HOP score can be easily measured from ultrasound data, is predictive of both resolution and pyeloplasty, and can be used to tailor diagnostic studies and follow-up visits.




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