Birth Defects Genital Urinary Tract Hydronephrosis

Hydronephrosis is a condition affecting the kidneys. It can develop at any time in life, but is often caused by a congenital structural abnormality present from birth. In hydronephrosis, the kidneys become overfilled with urine when a blockage prevents liquid waste from traveling through the urinary system.

Kidney Function

Normally, the kidneys filter excess fluid and waste products, and then the urine, a mix of fluid and wastes, flows down tubes called the ureters. The urine collects in the bladder until it is expelled from the body through the urethra. In renal hydronephrosis, full or partial blockage of the ureter stops or slows the passage of urine to the bladder, causing a backup of urine in the kidneys.

How Hydronephrosis Affects Kidney Function

When urine cannot pass through the ureter, the kidney becomes swollen from fluid retention. The degree of swelling depends on the severity of the hydronephrosis. Cases can range from mild to severe depending on the degree of blockage.

Blockages can occur in several locations:

  • Between the kidney and ureter
  • Between the ureter and the bladder
  • Anywhere along the ureter.

Hydronephrosis can be unilateral, affecting one side of the urinary system, or bilateral, affecting both sides. Bilateral hydronephrosis is more serious.

Hydronephrosis Symptoms

Some affected infants may have no symptoms of the hydronephrosis, but infants in severe cases may experience pain or infection. Any case of urinary tract infection in an infant should be treated by a doctor, and the child should be examined for possible abnormalities in the kidney or urinary system.

If fetal ultrasound indicates possible hydronephrosis, the doctor monitors the fetus to determine the course of the condition and to classify the hydronephrosis according to severity level.


Mild to moderate cases may resolve on their own, or the kidneys may compensate for the reduced function. More severe cases, such as a greater degree of blockage or bilateral hydronephrosis, may require surgical intervention.

Children who have been diagnosed prenatally with moderate to severe hydronephrosis may be given antibiotics and monitored to determine the best course of treatment. When necessary, surgery can relieve the blockage in the urinary system that is causing the hydronephrosis. Kidney damage can eventually result from untreated hydronephrosis, so constant monitoring and evaluation are critical.


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