Dilatation in the duplex kidney: 3 unusual cases. Dilatation in the upper limb of a duplex ureter is usually secondary to obstruction and may be associated with a ureterocele. By contrast, vesicoureteric reflux is the usual cause of a dilated lower moiety ureter. We report 3 cases in which unusual or complex causes of dilatation of 1 limb of a duplex ureter were demonstrated. 