Hydronephrosis | Diagnosis

How is hydronephrosis diagnosed?

The first step in treating your child is forming an accurate and complete diagnosis. Hydronephrosis isn’t a disease. Instead, it indicates an impairment in your child’s urinary flow causing a kidney to swell. In diagnosing hydronephrosis, your doctor will search for what is causing the impairment to determine the best treatment for your child.

You may hear your child’s hydronephrosis described as:

  • “prenatal” or “antenatal,” — meaning before the birth
  • “postnatal” or  “neonatal” — meaning after the birth

These terms simply name when the diagnosis happened. (They are not saying anything about the condition itself.) 

Prenatal testing

Signs of hydronephrosis may first show up on a routine prenatal ultrasound (sonography). The test transmits high-frequency sound waves into the uterus. The echoes that bounce back are recorded and made into an image of your baby. It will show the size and shape of your child’s kidneys, as well as the amount of amniotic fluid. It also can help reveal obstructions in the urinary system.

However, doctors usually can’t make a precise diagnosis of hydronephrosis based on ultrasound findings.

If an ultrasound indicates your child may have hydronephrosis, your obstetrician will monitor your pregnancy more closely and may perform more frequent ultrasound testing to check for any changes over time. While your child is being monitored, your caregivers will take precise measurements of your child’s kidneys and the level of amniotic fluid.

Postnatal testing

For newborns and older children, doctors may use some or all of the following tests to help determine the cause and nature of the hydronephrosis:

  • Renal ultrasound (RUS): By focusing on the kidneys, this ultrasound gives a good picture of the hydronephrosis. This is the first postnatal test your doctor will perform and will help determine whether further studies are needed.
  • Voiding cystourethrogram (VCUG): This special kind of x-ray is used to check for reflux, a common cause of hydronephrosis. It also may show an obstruction in the urethra. Using a small tube called a catheter, doctors will fill your child’s bladder with a liquid dye containing iodine. As the bladder fills and your child urinates, the flow of the liquid will be visible on x-ray images.
  • Renal scan (MAG 3): This test allows doctors to see your child’s kidneys and learn more about how they are functioning. This kidney scanning test helps measure the difference in function between the two kidneys and also estimates the degree of blockage in the urinary system. After a tiny amount of radioactive material (radioisotope) is injected into your child’s bloodstream, a special camera (called a gamma camera) is used to take pictures of the kidneys as the radioactive material moves through them, showing how well they are filtering and draining.

After we complete all necessary tests, our experts meet to review and discuss what they have learned about your child's condition. Then we will meet with you and your family to discuss the results and outline the best treatment options.