Acute Kidney Injury After Endoscopic Ureterocele Incision in a Duplex System with Contralateral Multicystic Dysplastic Kidney: From Obstructive Complication to Surgical Resolution—A Case Report

Background and Clinical Significance: Endoscopic ureterocele incision is the preferred initial treatment for ureteroceles associated with duplex collecting systems due to its capability for rapid decompression via a minimally invasive technique with generally favorable outcomes among pediatric patients. However, the postoperative trajectory in children with solitary functioning renal units remains inadequately characterized. We present a severe, yet reversible, case of postrenal acute kidney injury (AKI) following endoscopic ureterocele incision in an infant with a contralateral multicystic dysplastic kidney (MCDK). This case emphasizes the pathophysiological implications of failed ureterocele decompression and the vital importance of rigorous postoperative monitoring. Case Presentation: A female infant with a right MCDK and a left duplex collecting system featuring an upper pole ureterocele underwent transurethral endoscopic incision due to progressive hydronephrosis. Within 24 h following surgery, the patient exhibited oliguria, oedema, worsening hydronephrosis, hyponatremia (125 mmol/L), metabolic acidosis, and increasing serum creatinine levels, indicative of postrenal AKI. Arterial blood gas analyses indicated severe renal-driven metabolic acidosis with bicarbonate levels of 13.9 mmol/L, accompanied by respiratory compensation and normal lactate levels. Imaging studies revealed deteriorating hydronephrosis of the upper and lower poles of the left kidney. Emergency open nephrostomy placement in the lower pole, after failed jj insertion in the lower pole ureteral orifice, resulted in the immediate restoration of urinary drainage and progressive biochemical recovery. The patient required a brief period of intensive care monitoring, followed by hospitalization in pediatric and urological departments. Longitudinal imaging demonstrated persistent but stable upper pole dilatation with preserved parenchyma. Definitive management was later achieved through right nephrectomy of the non-functioning MCDK. Conclusions: In patients with solitary functioning renal units, the endoscopic ureterocele incision may result in postoperative local oedema, potentially leading to clinically significant obstructive AKI. This case underscores the necessity for intensified surveillance and individualized postoperative management strategies in anatomically complex pediatric patients.