The purpose of our study was to identify the radiographic signs that aid in the diagnosis of obstruction of the ureteropelvic junction of the lower pole (or moiety) of the kidney in children with complete duplication of the ureter and to describe the imaging appearance of this unusual cause of lower-pole hydronephrosis.

We reviewed the medical records and imaging studies of 16 children (11 boys and five girls) with complete ureteral duplication and ureteropelvic junction obstruction of the lower pole of the kidney over a 5-year period. standard criteria for determining urinary tract obstruction were used.

Sonograms showed a lower-pole abnormality (hydronephrosis or cystic mass) in all 15 children who underwent sonography. Voiding cystourethrography, performed for all children, showed vesicoureteral reflux into the lower pole in addition to ureteropelvic junction obstruction in eight children (seven boys and one girl). For the other eight, the diagnosis of lower-pole ureteropelvic junction obstruction was made by excretory urography, at times complemented with diuretic renography or retrograde ureterography.

Ureteropelvic junction obstruction of the lower pole of the kidney in children with complete duplication of the ureter should be a diagnostic consideration when there is dilatation of the lower moiety. Imaging changes parallel those of ureteropelvic junction obstruction in a nonduplicated system. This anomaly, unlike others seen in duplication, appears to be more common in boys than in girls.