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Congenital Hydronephrosis

Kidneys are constantly making urine. Urine normally drains out of kidneys completely. It flows down the ureter, the tube that connects the kidney to the bladder, then into the bladder. The bladder then empties whenever the body feels the need to do so. Congenital hydronephrosis is a medical term to describe children who were born with a build-up of urine in their kidneys.


Children with congenital hydronephrosis can be divided into three groups based on the causes:

  • Blockage in the urinary tract. The urinary tract is made up of the kidneys, ureters, bladder and urethra. The blockage could happen at any point along the urinary tract. Depending on the location of blockage, common conditions we see here are ureteropelvic junction obstruction, ureterovesical junction obstruction with or without ureterocele, posterior ureteral valve. Sometimes there is no structural blockage but the bladder has functional problem in emptying due to underlying disease affecting the nervous system, a condition called neurogenic bladder.
  • Urine flows upward from the bladder back to the ureters and kidneys, a condition called vesicoureteral reflux (VUR, link). Normally urine only flows in a one-way direction, from the kidney to bladder.
  • Sometimes hydronephrosis is not associated with reflux or blockage. This occurs when there is some delay in the development of the ureters.


Fetal ultrasound is a routine test for prenatal care. This is how most of the children with congenital hydronephrosis are diagnosed. Others are found in different settings, for example, following a urinary tract infection, or as an incidental finding when doctors order imaging tests for other problems like abdominal pain.

Depending on the appearance and severity of hydronephrosis on the film, nephrologists might consider additional imaging studies to help us determine whether there is obstruction or reflux that has caused hydronephrosis. Two studies we often ask for are voiding cystourethrogram (VCUG) and nuclear medicine scan with support from child life service:

  • VCUG is an imaging study of a series of X-rays. It needs a contrast agent that is administered through a catheter into the bladder via the very end point of the urinary tract where urine exits the body. This allows us to look at the appearance of the bladder, and whether the urine goes upward, as well as the shape of the urethra. VCUG is considered the gold standard in diagnosis of reflux and posterior urethra valve (PUV).
  • Nuclear medicine scan allows us to evaluate blockage between the kidney and bladder, and the severity of the obstruction if there is any. This procedure uses a low dose nuclear medicine injected through the vein and the child will get poked for IV access. It also requires a catheter inserted into the bladder, the same catheter used for VUCG study as mentioned above. The study takes about 1-2 hours to complete.


If there is no underlying obstruction or reflux, a hydronephrosis usually will go away as the child grows up. Congenital hydronephrosis caused by mild obstruction could resolve on its own as well. Children may need repeat ultrasounds and follow up with us for a period of time varying from months to years, before we feel it is safe for discharge. Normally they do not develop advanced renal disease or need specific treatment.

One sided hydronephrosis with an otherwise healthy bladder, even when it is severe, usually has a very good outcome once the obstruction is removed or the reflux gets repaired by a urologist (surgeon who specializes in the urinary tract).

Severe congenital hydronephrosis can progress to more advanced chronic kidney disease (CKD), including end stage renal disease (ESRD), especially when both kidneys get involved and the bladder has issues of emptying. As a matter of fact, this is the most common cause of ESRD in children. These children often need multiple surgeries. They require long term follow up with both nephrologists and urologists. Children may need frequent treatment for recurrent urinary tract infection and medications to manage issues related to CKD. Children with ESRD may require dialysis treatment before they get ready for kidney transplant evaluation.