Pelviureteric junction obstruction of the ipsilateral kidney caused by hydronephrosis secondary to crossed fused renal ectopia

Introduction Crossed fused renal ectopia is rare and usually asymptomatic. However, it is associated with urological anomalies. Case presentation A 15‐year‐old Japanese boy was transported to our hospital with right abdominal pain and hematuria after a soccer ball hit his right abdomen. Computed tomography revealed right hydronephrosis beyond the center of the body and no left kidney. Percutaneous nephrostomy was performed immediately, and a pyeloplasty was scheduled for 5 months later. Right hydronephrosis was noted to have been caused by left pelvic expansion due to a crossed fused ectopic kidney (secondary to a left pelviureteric junction obstruction). Subsequently, a left dismembered pyeloplasty was performed. Twenty‐four months later, pain and hematuria were absent, and the creatinine level was 1.1 mg/dL. Ultrasonography revealed a shrunken right kidney. Conclusion We encountered a unique urological anomaly with crossed fused renal ectopia. Comprehensive anatomical evaluation before surgery is important for maintaining long‐term renal function.