Hydronephrosis is when one or both kidneys swell with backed up urine. This swelling can lead to kidney infection or kidney damage.Hydronephrosis is not a condition but a symptom of another condition.
Urinary Tract System
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Hydronephrosis is caused by urinary tract problems that makes it difficult for urine to leave the kidneys. Urine may be slowed or blocked by:
  • An obstruction, bulge, or narrowing in the tube that carries urine from the kidney to the bladder
  • In boys, flaps of tissue obstructing the tube that carries urine out of the body or narrowing of the tip of the penis
Other conditions that may cause problems with urine flow include:
  • The backwards flow of urine from the bladder into the kidneys
  • Problems with the tube that carries urine to the bladder or in the way that it connects
  • Occasionally, an abnormal kidney
In most cases, the child is born with one of these conditions that affect the urinary tract. For some, the condition develops later on. Sometimes the cause of hydronephrosis is not known.

Risk Factors

Hydronephrosis is more common in boys than girls.


Hydronephrosis may cause:
  • Pain in the back, sides, abdomen, or groin
  • Blood in the urine
  • Trouble feeding
  • Poor growth
  • Symptoms of urinary tract infection


Most often hydronephrosis is diagnosed during pregnancy during a maternal ultrasound.After birth you will be asked about your child’s symptoms and medical history. A physical exam will be done. Your doctor may be able to feel the swollen kidney during the physical exam. Your child's bodily fluids may be tested. This can be done with:
  • Urine tests
  • Blood tests
Imaging tests evaluate bodily structures. These may include:
  • Ultrasound—may be done before and/or after birth
  • Voiding cystourethrogram—x-rays of the bladder and urethra taken during urination
    • Note: This test is only done if there is hydronephrosis still present after birth.
  • MRI scan
  • CT scan
  • Cystoscopy

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