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RELATIVE RENAL LENGTH DISCREPANCY AS AN INDICATOR OF RENAL OBSTRUCTION IN CHILDREN WITH UPJO-LIKE
William Luke, MD-C, Smruthi Ramesh, BHSc, Melissa McGrath, BASc, Roseanne Ferreira, MD, Luis H. Braga, MD, PhD.
McMaster University, Hamilton, ON, Canada.

BACKGROUND: Pyeloplasty is the gold standard for management of UPJO, however controversy exists regarding the best test or parameters to diagnose obstruction. Changes in renal length have previously been shown to correlate with degree of hydronephrosis and loss of renal function, however this has yet to be validated in a large prenatal hydronephrosis(PHN)population. Herein, we investigate how relative renal length(RRL)changes over time in patients with prenatal hydronephrosis treated with and without pyeloplasty. We hypothesize that patients treated with pyeloplasty will have a larger decrease in RRL discrepancy.METHODS: From our prospectively collected PHN database(n=928) between 2008-19, we identified patients with UPJO-like. Those with <3months of follow-up, bilateral HN, or other urinary system anomalies were excluded. Ipsilateral and contralateral renal measurements were obtained. RRL was calculated as[100%*(Contralateral Renal Length - Ipsilateral Renal Length)/Contralateral Renal Length], and the decrease in RRL discrepancy was quantified as absolute relative renal length difference(ARRLD). ARRLD was calculated as the difference between the absolute value of RRL measurements from initial ultrasound to the absolute value at the time of the final ultrasound. The primary outcome of the study was ARRLD, which was calculated as [|RLL at first Ultrasound|-|RLL at final Ultrasound|]. We also calculated relative renal length growth(RRLG) of the contralateral kidney over the course of the study as[(RLL at final Ultrasound)-(RLL at first Ultrasound)]. Results were analyzed with ANOVA, and paired T-test.RESULTS: 332 patients were identified with a mean follow-up time of 30 months. Mean patient age at first ultrasound was 3 months. There was a statistically significant decrease in absolute RRL difference (p<0.001) in patients who had pyeloplasty (Mean ARRLD: 8.9%, 95% CI: 12.6%, 5.3%), compared to those who did not (Mean ARRLD: 1.2%, 95% CI 2.2%, 0.1%). The contralateral kidney grew significantly more in both pyeloplasty(Mean RRL Growth(RRLG): 11.4%, 95% CI: 6.7%, 16.1%), and no pyeloplasty groups(Mean RRLG: 2.1%, 95% CI 0.7%, 3.5%), with pyeloplasty patients experiencing more proportional contralateral growth(p<0.001). Average ipsilateral renal length was significantly larger than contralateral length in pyeloplasty(6.3 cm vs 5.5 cm, p<0.001) and non-pyeloplasty groups(5.8 cm vs 5.6 cm, p<0.001). The difference in renal length between ipsilateral and contralateral kidneys at first ultrasound was significantly greater in the pyeloplasty vs non-pyeloplasty group(0.87 cm vs 0.25 cm, p<0.001). RRL at the time of first ultrasound was significantly less in the surgical group vs the non-operative one(Mean:-21.6% vs -6.6%, p<0.001).CONCLUSION: Pyeloplasty was associated with an increase in ARRLD. Specifically, patients who underwent surgery had a larger decrease in magnitude of renal length difference, at the end of the study compared to patients who did not.This difference appears to stem from a relative increase in contralateral renal length, though it is unclear if that is due to a decrease in ipsilateral hydronephrosis distorting renal length. Given the initial disparity in RRL, and the significant trend towards equally sized kidneys postoperatively, the results of this study are indicative of a role for initial RRL in identifying patients at an increased likelihood of having an obstruction.


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