What Is Hydronephrosis?

Hydronephrosis means that the kidneys are abnormally dilated or overfilled with urine. There are several causes, many of which do not cause any harm to the kidneys, but in some cases hydronephrosis can be associated with poorly functioning kidneys. Hydronephrosis can affect one (unilateral) or both (bilateral) kidneys, and it resolves on its own in about half of all cases.

What Causes Hydronephrosis?

Hydronephrosis can be caused by blockage at some part of the urinary tract or by reflux of urine (abnormal backflow of urine from the bladder). It can also be due to the abnormal development or formation of the kidney in the absence of obstruction or reflux. There are few genetic causes of hydronephrosis and it can occur with other conditions in the baby.

There are three major categories of hydronephrosis:

  • Vesicoureteral reflux is when urine does not properly flow from the kidneys to the bladder, but instead abnormally backs up in the ureter (the tube connecting the kidneys to the bladder).
  • Blockage/obstruction occurring in four possible places:
    • Where the kidney meets the ureter (ureteropelvic junction – UPJ)
    • Where the ureter meets the bladder (ureterovesical junction – UVJ)
    • Within the urethra (the tube that carries urine from the bladder out of the body, occurring only in males) (posterior urethral valves – PUV)
    • Incorrect attachment of the ureter to the bladder (ectopic ureter or ureterocele)
  • Idiopathic hydronephrosis that has no obvious cause and usually resolves on its own before or after birth

Symptoms of Hydronephrosis

Newborns and infants with hydronephrosis usually show few or no symptoms at all. Older children who have moderate to severe cases may experience:

  • Pain in the side or abdomen
  • Blood in the urine

Older children may be more likely to get urinary tract infections, in which symptoms include:

  • Persistent feeling of needing to urinate
  • Pain in the lower abdomen during urination
  • Cloudy or bloody urine
  • Back or side pain
  • Fever
  • Vomiting

How Is Hydronephrosis Diagnosed?

Your physician can usually detect hydronephrosis through a routine prenatal ultrasound during the second trimester. If so, your physician may refer you to our Fetal Medicine Institute for a high-resolution (level II) ultrasound and MRI scans to evaluate your baby’s condition.

The Fetal Medicine Institute at Children’s National may recommend further testing after your baby is born. This testing may include:

  • X-ray of the bladder to check for vesicoureteral reflux
  • Diagnostic imaging of the kidneys to assess function and proper urine drainage

Read more about the high-risk prenatal care services at the Fetal Medicine Institute of Children’s National.

Treatments for Hydronephrosis

There are four main options for treatment, depending on the severity of hydronephrosis in your baby:

  • Close observation for mild or moderate cases, including ultrasounds before and after birth
  • Antibiotics after your baby is born to prevent infection, in select cases where infection may be more likely to occur
  • Surgery to repair any urinary tract blockage, in more severe cases
  • Fetal surgery to place a drainage tube in your baby’s bladder, in the most severe cases

The urologists and surgeons at our Fetal Medicine Institute have extensive experience in the management of hydronephrosis. We develop plans that ensure continuity of care from the early stages of pregnancy, after birth, and across childhood. 

Children's Team

Children's Team




Fetal Medicine Institute

Our fetal medicine team provides specialized, expert care for babies during pregnancy, delivery, and the postnatal period.


Learn how our highly skilled team works across divisions to treat kidney disease in children.

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John Myseros' Story

John Myseros

Dr. Myseros began at Children’s National more than five years ago and has a personal and professional interest in the care of children with tumors of the brain and spinal cord.

Read More of John Myseros' Story