A duplex urinary tract, irrespective of the degree of duplication, is present in 0.8% at autopsy, of which about 20–35% is bilateral. The majority of duplex systems are incomplete, indicating that the ipsilateral ureters fuse before entering the bladder. A complete duplex system shows anomalies of the upper moiety, with associated ureterocele or ectopic ureter, and of the lower moiety, frequently associated with vesicoureteral reflux. Renal ectopia is a rare (1/1000) congenital defect where the kidney is not located in the renal fossa, and is associated with a high rate of hydronephrosis, vesicoureteral reflux, and abnormal contralateral kidney. In a horseshoe kidney (present in 1/400 to 1/1800), fusion of the two kidneys takes place, but the two renal moieties are still located on both sides of the midline. As the lower poles are fused in the midline, a horseshoe kidney is usually located lower than normal and orientation of the renal axis is shifted, which may guide diagnosis during abdominal ultrasound.
Editorial Comment: How I do it open distal ureteroureterostomy for ectopic ureters in infants with duplex systems and no vesicoureteral reflux under 6 months of age
