RENAL DUPLICATIONS

Renal duplications
Definitions
A duplex kidney has an upper pole and a lower pole, each with its own separate pelvicalyceal system and ureter. The two ureters may join to form a single ureter at the pelviureteric junction (bifid system) or more distally (bifid ureter) before entering the bladder through one ureteric orifice. Alternatively, the two ureters may pass down individually to the bladder (complete duplication). In this case, the Weigert-Meyer rule states that the upper pole ureter always opens onto the bladder medially and inferiorly to the ureter of the lower pole, thereby predisposing to ectopic placement of the ureteric orifice and obstruction (due to the longer intramural course of the ureter through the bladder wall). The lower pole ureter opens onto the bladder laterally and superiorly, reducing the intramural ureteric length, which predisposes to vesicoureteric reflux (in up to 85%).

Epidemiology
Ureteric duplication occurs in 1 in 125 individuals. Female to male ratio is 2:1. Unilateral cases are more common than bilateral, with right and left sides affected equally. Risk of other congenital malformations is increased.

Embryology
In duplication, two ureteric buds arise from the mesonephric duct (week 4 gestation). The ureteric bud situated more distally (lower pole ureter) enters the bladder first, and so migrates a longer distance, resulting in the superior and lateral position of the ureteric orifice. The proximal bud (upper pole ureter) has less time to migrate, and consequently the ureteric orifice is inferior and medial (ectopic). Interaction of each ureteric bud with the same metanephric tissue creates separate collecting systems within the same renal unit. With bifid ureters, a single ureteric bud splits after it has emerged from the mesonephric duct.

Complications
Ectopic ureters are associated with both upper renal pole hydronephrosis (secondary to obstruction) and hypoplasia or dysplasia (renal maldevelopment related to ectopic displacement of ureteric orifice). Lower pole ureters are prone to reflux, resulting in hydroureter and hydronephrosis. Bifid ureters can get urine continuously passing from one collecting system to the other, causing urinary stasis (predisposing to infection).

Presentation
Symptoms of UTI, flank pain, or incidental finding.

Investigation
- Renal ultrasound scan demonstrates ureteric duplication dilatation and hydronephrosis.
- IVU decreased contrast excretion from renal upper pole hydronephrosis (which may displace the lower pole downwards and outwards producing a drooping lily  appearance).
- Micturating cystourethrography (MCUG) will determine whether reflux is present.
- CT and MRI reveals detailed anatomical information.
- Isotope renogram (99mTc-DMSA) assesses renal function.

Treatment
In symptomatic patients, the aim is to reduce obstruction and reflux, and improve function. Common shealth ureteric reimplantation (where a cuff of bladder tissue is taken that encompasses both duplicated ureters) can treat both conditions. Where an ectopic ureter is associated with a poorly functioning renal upper pole, open or laparoscopic heminephrectomy with excision of the associated ureter may be considered.