Objective: To analyze the factors indicating renal injury in patients with bilateral ureteropelvic-junction obstruction (UPJO). Methods: We investigated 26 patients, 35 kidney units (KUs), who were diagnosed with bilateral UPJO and underwent unilateral or bilateral pyeloplasty between January 2000 and December 2011. During pyeloplasty, ipsilateral kidney biopsy was performed. Kidney biopsy results were divided into 3 categories. Hydronephrosis was analyzed using both the Society of Fetal Urology (SFU) and Onen's grading system. We investigated factors related with the renal histopathologic results of 29 KUs. We additionally analyzed whether there were factors predicting contralateral pyeloplasty after initial unilateral pyeloplasty. Results: Ten KUs (34.5%) showed grade 1 histopathologic change, whereas 10 KUs (34.5%) and 9 KUs (31.0%) showed grade 2 and 3 change, respectively. Preoperative differential renal function (DRF) and serum creatinine levels were not different among groups (P =.697 and.516, respectively). Hydronephrosis grade was not different when graded by SFU system (P =.100) while significantly different by Onen's system (P <.001). Among 23 patients with initial unilateral pyeloplasty, additional contralateral pyeloplasty was required in 6 patients (26.1%). There were no significant preoperative factors predicting the need for additional operations. Conclusion: In bilateral UPJO, DRF, and SFU grade of hydronephrosis did not correctly reflect renal injury. Onen's hydronephrosis grade showed a significant relationship with renal histopathologic grade and could be an indicator for renal injury in bilateral UPJO.
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