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Duplex Kidney

Duplex kidney at a glance

  • Duplex kidney is a developmental condition in which one or both kidneys have two ureter tubes to drain urine, rather than a single tube.
  • Duplex kidney, also called duplicated collecting system, occurs in about 1 percent of children and usually requires no medical treatment.
  • However, duplex kidney may be associated with conditions that require treatment by a urologist, including flow of urine back into the kidney instead of to the bladder and obstruction of urine flow through the ureter tube.

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What is duplex kidney?

Duplex kidney is the duplication of the ureter tube, which drains urine from the kidney to the bladder. The condition results in two tubes rather than the normal single ureter tube for each kidney.

Duplex kidney (also known as duplicated collection system) occurs in about 1 percent of children and usually requires no medical treatment. Medical concerns relate to obstruction of urine flow or urine flowing back into the kidney.

The function of the kidneys is to filter waste from the blood and convert it to urine to be dispelled from the body. The urine travels from the kidney to the bladder via the ureter tube. The bladder expels urine through the urethra tube, which emerges at the tip of the penis in boys and at the upper region of the vagina in girls.

In the duplex kidney condition, the kidney forms in two, duplicate parts with separate ureter tubes, as well as a separate blood supply. In about half of duplex kidney cases, both kidneys are affected with the duplicate ureter and blood supply.

These double ureter tubes may join together in a “y” shape before they reach the bladder and combine their delivery of urine. Or in other instances, each duplicate ureter will drain into the bladder via its own attachment.

In either case, the result is the same — and generally the same as in a normal kidney with only one ureter.

Diagnosis and symptoms of duplex kidney

Ultrasound images before birth often detect duplex kidney. Symptoms include:

  • Urinary tract infections (UTIs).
  • An obstruction of the urinary tract resulting in poor urine flow.
  • Urinary incontinence is marked by frequent leaking of urine.
  • In girls, one symptom is tissue protruding from the urethra opening in the vagina.

Aside from the ultrasound detection (using an x-ray-like machine that emits high-frequency sound waves), the symptoms above are caused by the following complications associated with duplex kidney.

Complications from duplex kidney

There is reason for concern when a duplex kidney is associated with urologic conditions requiring treatment. Duplex kidney may result in urine flowing back into the kidney rather into the bladder and also may cause obstruction of urine.

Vesicoureteral reflux

Vesicoureteral reflux (VUR) occurs when urine flows back to the kidneys from the bladder, rather than from the bladder and out of the body through the ureter tubes.

The valve that normally prevents urine reflux is called the vesicoureteral valve. The danger for children with VUR is that a resulting urinary tract infection (UTI) weakens the urinary tract’s ability to prevent bacteria from entering the kidney.

In turn, this can result in kidney damage and infection. Serious conditions can even result in death due to acute infection and scarring of the kidney (reflux nephropathy).

Treatment for vesicoureteral reflux

VUR may go away with no treatment in some children, which is more likely in younger children and in less severe cases. Antibiotics are generally the first treatment to stop the UTI.

Surgery can reconstruct the area where the ureter connects to the bladder. This lengthens the ureter tunnel and allows it to act as a valve that closes as the bladder fills, preventing urine reflux.

Obstruction of urine

Two conditions related to duplex kidney that can result in obstruction of urine flow are ureterocele and an ectopic ureter.


A ureterocele occurs when the ureter balloons just inside where it connects to the bladder. A ureterocele may also extend outside the bladder neck and the urethra.

The ballooning of the ureter causes an obstruction of urine flow due to narrowing. Ureteroceles can vary in size from very small to almost filling up the bladder.

Treatment for ureteroceles

Ureteroceles may require simple management of symptoms or surgery, depending on the size of the ballooning, the functioning of the kidney and bladder, and the degree of urine obstruction.

  • Endoscopic surgery involves a cytoscope, a lighted tube with a camera that generates images a urologist can view. The cytoscope is put into the urethral opening and if a ureterocele is found, it can be punctured with a small incision during the procedure.
  • Ureteral reimplantation is a procedure in which a doctor connects the ectopic ureter correctly to the bladder.
  • Partial nephrectomy is the removal of the upper portion of the duplex kidney that has the ectopic ureter.

Ectopic ureter

An ectopic ureter is when the ureter does not attach correctly to the bladder and urine empties outside of the bladder rather than inside it. In cases of duplex kidney, one ureter drains properly into the bladder while the duplicate ureter does not. The duplicate ureter is the ectopic ureter.

In boys, the ectopic ureter drains into the urethra near the prostate; in girls it drains into the urethra or reproductive organs.

Treatment for ectopic ureter

Surgical treatments include:

  • Ureteral reimplantation (see above)
  • Cutaneous distal ureterostomy involves bringing the ectopic ureter of a newborn to the skin’s surface so it drains externally (into the diaper). After about 18 months, the ureter is correctly implanted into the bladder.
  • Partial nephrectomy (see above)
  • Ureteropyelostomy is an option when the ectopic ureter in the upper section of a duplex kidney can be connected to the lower section of the duplex kidney that is functioning normally.

Risks of treatments for duplex kidneys

The surgeries described above to treat the complications related to duplex kidney carry the same complications of any surgery. These include:

  • Blood clots
  • Blood loss
  • Pain
  • Infection
  • Reactions to anesthesia
  • Injury to tissue or organs.

A urologist can discuss these issues with each patient and devise the proper treatment plan.