What is a duplex kidney?

A duplex kidney is when a child is born with a double kidney on one side (“duplex” is Latin for “double”). The part of the kidney that is duplicated is usually the collecting system (or renal pelvis), which is where urine collects before it is passed into the ureter (tube) that leads to the bladder. This rarely causes problems and may only be noticed by chance during a scan of the patient.

In more extensive duplex kidneys, the ureter may be duplicated as well. This may be a partial duplication, with the two ureters joining together in a Y-shape, coming together before connecting to the bladder. However, there can also be a complete second ureter, which can be problematic. It may connect to the bladder in an unusual place, which can cause vesicoureteral reflux, or it may even connect directly to the urethra (the tube leading from the bladder out of the body), bypassing the bladder completely, and causing a constant dribble of urine.

Symptoms of a duplex kidney

Duplex kidneys and duplicated ureters that drain directly into the bladder rarely cause any symptoms.

However, if there is a complete second ureter, this often functions poorly and can be connected to a number of problems:

• Urinary tract infections (UTIs) – problems in urine drainage make it easier for bacteria to enter the urine and travel to the bladder. Under certain conditions, infections can even spread up to the kidneys.
• Ureterocele – the end of the ureter doesn’t develop properly, causing urine to be obstructed and become backed up. The ureter begins to swell and balloon where it enters the bladder and the length of the tube may become swollen as more urine backs up along it.
• Vesicoureteral reflux – urine is able to flow back through the ureter, sometimes even as far as the kidney. This may be because of an abnormal connection between the ureter and the bladder or as a result of a ureterocele.
• Hydronephrosis – the ureter and kidney swell due to urine being backed up. This may be due an abnormal connection between the ureter and the bladder or as a result of a ureterocele, and can lead to kidney damage.
• Ectopic ureter – the ureter does not connect to the bladder, instead being blocked or leaking into another part of the body. This can lead to vesicoureteral reflux, hydronephrosis, swelling, and incontinence.

Medical tests to diagnose a duplex kidney

Duplex kidneys are usually diagnosed with imaging tests, such as ultrasound, CT or MRI scans. However, if they are asymptomatic, they may not be noticed until adulthood.

Treatments for duplex kidneys

Duplex kidneys that are not causing problems do not require treatment. However, if they are causing symptoms and affecting the patient’s health or quality of life, doctors may recommend one of the following:

• Nephrectomy – kidney removal. It is rare to remove the entire kidney, and this will only be done if the affected kidney is functioning poorly, but the other is fine. This should decrease the risk of urine infections and eliminate incontinence.
• Heminephrectomy – part of the affected kidney and duplicated ureter are removed.
• Ureteroureterostomy – in the case of an ectopic ureter, it is split near the bladder and joined to the normal ureter, allowing urine from the upper kidney to drain as normal.
• Ureteral reimplantation – the location where the abnormal ureter meets the bladder is moved. The ureter is cut away and moved to a part of the bladder where it can drain more easily. This procedure carries the risk that in the future the ureter may narrow and cause blockages.

Which type of specialist treats duplex kidneys?

Urologists and paediatric urologists treat duplex kidneys in adults and children respectively. The condition is more commonly treated in children, as if it causes symptoms it will usually do so from birth.