Duplex Collecting System

A duplex (duplicated) collecting system is a congenital anomaly with two separate pelvicalyceal systems draining a single kidney. It is the most common congenital urinary tract anomaly, with a prevalence of about 0.5 to 1 percent of the population. It is bilateral in 20 percent and more common in females (2:1).

It results from the division of the ureteric bud or the early development of two ureteric buds. The ureters either join (incomplete duplication, a bifid ureter, about 80 percent) or remain separate to the bladder (complete duplication, 20 percent).

In complete duplication, the Weigert-Meyer rule applies:

• The ureter draining the upper pole inserts inferior and medial to the lower pole ureter. It is prone to obstruction, ectopia or ureterocele.
• The ureter of the lower pole inserts superior and lateral, close to the ureteric tunnel. It is prone to vesicoureteral reflux.

Complications:

• Upper pole obstruction with a dysplastic moiety and ureterocele.
• Lower pole reflux and scarring.
• Ureteropelvic junction obstruction of either moiety.
• Stones, infection and ectopic insertion with incontinence.

In incomplete duplication, urine can pass between moieties in a "yo yo" fashion, causing pain and infection.

• Most (over 70 percent) are asymptomatic and incidentally found.
• Antenatal hydronephrosis, a cystic structure in the bladder (ureterocele), or a dilated upper pole.
• Urinary tract infection, pyelonephritis and febrile illness, especially in infants and young children.
• Continuous incontinence in girls with an ectopic upper pole ureter, despite normal voiding.
• Flank pain, haematuria, abdominal mass, hypertension in a few.
• Failure to thrive, and urosepsis in the severely obstructed.
• Examination is usually normal.

• Ultrasound: two separate central echogenic complexes in a kidney with an intervening parenchymal band, a dilated upper pole with a thinned cortex, a dilated tortuous ureter behind the bladder, and ureterocele.
• Voiding cystourethrogram: reflux, typically into the lower pole (the "drooping lily" sign: the lower moiety is displaced downward and laterally by a dilated upper moiety), and a ureterocele filling defect.
• MR urography or CT urography: the best way to define the anatomy, ureter insertions, level of ureteral fusion and function.
• Isotope renography: DMSA for scarring and split function of each moiety, MAG3 with furosemide for drainage.
• Cystoscopy and vaginoscopy for ectopic orifices.
• Urine culture, renal function, and blood pressure.

• Asymptomatic duplex systems without hydronephrosis or reflux: no treatment, with ultrasound follow up and counselling about symptoms of infection.
• Prophylactic antibiotics for antenatally detected hydronephrosis, reflux or ureterocele: trimethoprim 2 mg/kg once daily at night, or amoxicillin 10 to 15 mg/kg once daily in infants under 2 months. Stop when low risk with no reflux and no breakthrough infections.
• Management of the components depends on the pathology of each moiety:
  • Ureterocele: endoscopic puncture or incision, or open surgery (upper pole nephrectomy or total reconstruction).
  • Ectopic upper pole ureter with poorly functioning moiety: upper pole heminephrectomy with removal of the ureter. If the moiety has function, ureteroureterostomy or reimplantation (common sheath).
  • Lower pole reflux: antibiotic prophylaxis. In breakthrough infection, high grade reflux or scarring, use endoscopic injection of bulking agent (dextranomer hyaluronic acid, 0.5 to 1.5 mL) or ureteral reimplantation (Cohen or Politano-Leadbetter).
  • Use common sheath reimplantation when both ureters are in the same sheath.
  • Ureteropelvic junction obstruction of a moiety: dismembered pyeloplasty or ureterocalicostomy.
  • Incomplete duplication with yo yo reflux: ureteropyelostomy or ureteroureterostomy to the more functional system (also in symptomatic patients), with excision of the other moiety's ureter segment as needed.
• Surgical approaches: open, laparoscopic or robotic. The procedure chosen balances renal function (upper pole function below 10 percent: heminephrectomy; function preserved: reimplantation or drainage).
• Postoperative: ureteric stents, catheter drainage, antibiotic prophylaxis, renal ultrasound at 6 weeks and at 6 to 12 months, and VCUG at 3 to 6 months for reflux correction.
• Long term: monitor blood pressure and renal function, treat infections early, and regular review through childhood.