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Hydronephrosis is a condition characterized by the dilation or stretching of the inside of the kidney where urine collects.

Antenatal (before birth) hydronephrosis (fluid enlargement of the kidney) is detected in the fetus by ultrasound studies performed as early as the first trimester of pregnancy.  In most cases, the diagnosis of antenatal hydronephrosis does not significantly change prenatal care, but will require follow-up ultrasounds and possible surgery during infancy and childhood.

Common causes of hydronephrosis include:

Vesicoureteral Reflux

Reflux is the most common abnormality causing hydronephrosis and occurs because the valve between the bladder and the ureter does not function appropriately.  This abnormality enables urine to flow backwards from the bladder into the ureter, and kidney.  Most children outgrow reflux, but require close monitoring and may benefit from low-dose antibiotics to prevent kidney infection.  Approximately 25% of children will eventually require surgery to correct the reflux, either because they fail to outgrow the reflux, or because of breakthrough urinary tract infections.


Blockage of the kidney may occur in several locations.  The most common site for obstruction to occur is the ureteropelvic junction (UPJ).  This is the site where the kidney drains into the beginning of the ureter.  A blockage may also occur where the ureter drains into the bladder, called the ureterovesical junction (UVJ).

Posterior urethral valves (PUV)

In boys, a blockage may occur in the urethra, where the urine drains from the bladder out of the body. This is called a posterior urethral valve (PUV). True obstructions usually require surgical correction. 

Multicystic Dysplastic Kidney

A multicystic dysplastic kidney (MCDK) is a kidney that has no function because it is made up of multiple fluid-filled cysts.  Most of the time, the cysts shrink and eventually disappear.  Occasionally, the cysts are very large, requiring surgery to remove the kidney.

Management During Pregnancy

In nearly all cases of antenatal hydronephrosis, additional ultrasound exams are the only special treatment necessary during the pregnancy.  Rarely, a fetus is found to have severe obstruction of both kidneys and an abnormally low amount of amniotic fluid.  Early intervention is sometimes recommended for these babies.  For most cases of antenatal hydronephrosis, the pregnancy is not affected, and delivery is performed normally. 

Management After Birth

After the baby is born, an initial ultrasound is usually performed at the hospital.  Sometimes, depending on the severity of the hydronephrosis, we suggest the baby be started on a low-dose antibiotic until we are able to complete the required testing.  If the hydronephrosis is still present on the postnatal ultrasound, we first check to see if the baby has reflux.  This is done with a voiding cystourethrogram (VCUG), which requires a catheter inserted into the bladder and x-ray pictures.  Infants with reflux are managed with routine ultrasounds and possibly low-dose antibiotics.

In babies without reflux who continue to show significant hydronephrosis after birth, it may be necessary to assess for a possible obstruction.  This is done with a diuresis renal scan, which requires an IV, and sometimes a urinary catheter.  Most blockages require surgical correction.  If the blockage is mild or partial, the baby may be followed closely with ultrasounds, and sometimes additional renal scans.  Over time, the hydronephrosis will either improve and be followed with continued observation, or worsen, which may require surgery.

Some babies will have hydronephrosis without reflux or obstruction.  These children are usually followed with periodic ultrasounds to monitor the hydronephrosis and make sure the kidneys are growing appropriately, and that obstruction does not develop as they grow.

At Beaumont, every child receives care tailored to his or her condition and symptoms. No matter what treatment(s) your child needs, we will keep you informed at all times. You are an important part of your child’s treatment team, and we value your input.