Urologic Anomalies: Hydronephrosis (Pediatric)

What is hydronephrosis?

Hydronephrosis is a swelling or dilation within the kidney or ureter, the tube connecting the kidney to the bladder. This condition generally arises from a blockage at the top of the ureter near the kidney, known as the ureteropelvic junction or UPJ. This traps urine in the kidney, causing it to build up, stretching both the kidney and the ureter. Less commonly, urine backs up from the bladder. This obstruction can reduce the amount of amniotic fluid, impairing fetal lung development.

How common is hydronephrosis and what causes it?

Some studies suggest that as many as 2 percent of all prenatal ultrasounds reveal some degree of hydronephrosis, making it one of the most commonly detected abnormalities during pregnancy. However, it isn’t always congenital—it can also develop as a result of another illness or injury, such as kidney stones.

How is hydronephrosis detected during pregnancy?

Ultrasound can detect the fetal kidneys and bladder by 14 or 15 weeks of gestation. At 20 weeks, it can detect hydronephrosis and visualize the kidneys in detail. When a UPJ obstruction is identified, the kidneys are closely examined for other findings such as cysts (multicystic, dysplastic kidney) or abnormal shape (horseshoe kidney).

Periodic sonograms may be required to monitor the baby’s kidneys and fluid balance.

How will hydronephrosis affect the pregnancy?

If the hydronephrosis is minimal and the UPJ obstruction is only present in one kidney, you do not need to alter your prenatal care.

When the hydronephrosis is severe and UPJ obstruction is found in both kidneys, or when one of the kidneys is missing or has a cystic appearance, your medical team may feel it best for you to deliver earlier than expected. 

If the prenatal ultrasounds show cysts in the kidney, an ultrasound of the kidney soon after birth and a special X-ray called a voiding cystourethrogram may be done to assess how much the cystic kidney is affected and make sure the other kidney is normal.

Amniocentesis may also be performed to rule out a chromosomal abnormality

What is the treatment for hydronephrosis?

Many cases of hydronephrosis resolve on their own before the baby’s birth. Long-term follow-up studies also suggest this problem will right itself over time, with both kidneys working normally.

If surgery is needed, you may tour the Neonatal Intensive Care Unit (or NICU) and discuss how your baby will be cared for in the first few days after delivery.

What are the chances of having another baby with hydronephrosis?

Minimal hydronephrosis is not genetic and is not believed to run in families. However, hydronephrosis may occur in future pregnancies, as a coincidence.

If UPJ obstruction is the cause of hydronephrosis, the chance of having future children with the same obstruction may be as high as 50 percent.

Certain genetic conditions can also cause the kidneys to form cysts, and these cases are associated with a 25 percent risk of having future children with the same condition.