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The University of Chicago Medicine - Comer Children's Hospital

Hydronephrosis FAQ

The kidneys, located in the back of the abdomen just below the ribs, are important for a variety of bodily functions. One of the kidneys' major functions is to filter blood and remove waste products that are excreted through the urine.

The kidneys are connected to thin tubes called ureters, which carry the urine to the bladder. During early growth and maturation of the kidneys, sometimes conditions develop that may change the way the kidney looks or functions. One such condition is hydronephrosis.

Hydronephrosis results from dilation or stretching of the inside of the kidney. This part of the kidney is called the "collecting system" because the urine made in the solid outer part of the kidney collects in the funnel shaped kidney pelvis and then drains down the ureters to the bladder.

Normally, the urine drains so well from the kidney to the bladder that no urine is visible in the kidney on ultrasound studies. Hydronephrosis is the term used to describe the extra urine seen in the kidney. Sometimes, the urine dilates both the kidney and the ureter resulting in hydroureternephrosis.

Hydronephrosis has not been linked to anything parents may have done during pregnancy, but it can be hereditary. Usually, these abnormalities are seen during the mother's prenatal ultrasound evaluation. In some cases, however, hydronephrosis may not be recognized until after birth or later in childhood. 

We know that there are several causes of hydronephrosis. Often, it results from a narrowing at the point where the ureter leaves the kidney. This condition is called ureteropelvic junction obstruction (UPJ obstruction). The hydronephrosis depends on the extent of the blockage and the amount of stretching of the kidney. Hydronephrosis ranges from mild to moderate to severe. The cause of this narrowing is not currently known, but probably develops before the fourth month of pregnancy.

A second cause of hydronephrosis is reflux or the backward flow of urine from the bladder back up into the ureters and kidneys. This condition may be hereditary, and is a common cause of serious urinary tract infections in children.

Blockage at the lower end of the ureter is another cause of hydronephrosis and hydroureter. The ureter may enter the bladder in an abnormal area or may be covered with a thin membrane that prevents the drainage of urine into the bladder. The exact cause of the obstruction may not be known until special tests are performed. 

Your child's pediatrician will need to be told that your baby was diagnosed with hydronephrosis before birth. In the first days of life, your baby’s urinary tract will be studied with an ultrasound to look more carefully at the kidneys and bladder.

After this is done, your child's pediatrician will ask the pediatric urologist to evaluate your baby. This consultation may happen before your baby goes home from the hospital or one to two weeks later in the pediatric urology clinic at the University of Chicago Medicine Comer Children's Hospital. Your baby will need to take a low dose of antibiotic once a day to prevent infection until the exact cause of the hydronephrosis is known.

In the first two weeks of life, your baby will undergo a special bladder X-ray called a voiding cystourethrogram (if needed). During this study, a small tube is placed into the bladder through the urethra. Our pediatric radiologist will fill the bladder with a special dye and watch as your baby urinates. If your baby has reflux, the radiologist will see the urine go backwards from the bladder to the kidneys as the bladder fills or as the baby urinates. At the end of the study, the bladder tube will be removed and your baby will urinate out the remaining dye.

Some babies will need an additional test called a kidney or renal scan to determine how well the kidney drains and how well it functions. This will be done when the baby is 6 to 8 weeks old. If the drainage from the kidney is slow because of UPJ obstruction, your baby will require careful follow up with additional ultrasounds every two months in the first year of his or her life. 

At Comer Children’s, the pediatric urologist will examine all options before performing surgery for hydronephrosis. In children with mild hydronephrosis or reflux, it is safe to carefully monitor these children. This is called observational therapy. Observational therapy involves closely watching your child's health and kidney growth while your child takes low dose antibiotics to prevent infection. Typically, the problems correct themselves as the child grows.

Some conditions causing hydronephrosis will need to be corrected with surgery. In some cases, the pediatric urologist will operate through a small telescope placed into your baby’s bladder while the baby is still very young. Early relief of an obstruction in the bladder or ureter will allow your baby’s urinary tract to heal and develop normally.

If your child has severe hydronephrosis from UPJ obstruction, a surgery to correct the blockage can be safely done using minimally invasive or robotic surgical techniques. These advanced surgeries are performed through very small incisions, and offer several benefits compared to open surgery, including a shorter hospital stay, a quicker recovery, reduced pain and less scarring. Outcomes for minimally invasive and robotic surgeries are on par--or superior--with open surgery. Surgery to repair reflux becomes necessary in children who develop infections while under observational therapy. Our pediatric urologists are able to correct reflux with an outpatient procedure performed through a small telescope placed into the bladder through the urethra.