Hydronephrosis (Pediatric)

What is hydronephrosis?

Hydronephrosis is a swelling or dilation within the kidney or ureter, the tube connecting the kidney to the bladder, and often results from a blockage at the top of the ureter near the kidney, an area known as the ureteropelvic junction (UPJ). The blockage traps urine in the kidney, causing it to build up and stretch the kidney or ureter. Less commonly, urine backs up from the bladder and leads to hydronephrosis.

One or both kidneys can be affected. The condition's severity depends on the extent of blockage and the degree to which the kidney is stretched, ranging from mild to severe. In the most severe cases, UPJ obstruction leads to abnormalities in the level of amniotic fluid that can impair fetal lung development.

How common is hydronephrosis and what causes it?

Some studies show that as many as 2 percent of all prenatal ultrasound examinations reveal some degree of hydronephrosis, making it one of the most commonly detected abnormalities in pregnancy. Why the ureter becomes blocked during development is unclear. Hydronephrosis is more often seen in males than females.Some studies show that as many as 2 percent of all prenatal ultrasound examinations reveal some degree of hydronephrosis, making it one of the most commonly detected abnormalities in pregnancy. Why the ureter becomes blocked during development is unclear. Hydronephrosis is more often seen in males than females.

How is hydronephrosis detected during pregnancy?

Ultrasound can detect the fetal kidneys and bladder by 14 or 15 weeks gestation, though 20 weeks of pregnancy is the ideal time to detect hydronephrosis as the fetus is larger and the kidneys are producing urine. When a UPJ obstruction is identified, the kidneys are closely examined for other findings more common with UPJ, such as cysts (known as multicystic dysplastic kidney) or an abnormal shape (commonly called horseshoe kidney).

How will my pregnancy be managed if hydronephrosis is detected?

You will have an in-depth ultrasound study to confirm the diagnosis and evaluate the kidneys and bladder closely to ensure no other abnormalities are present. The ultrasound will be performed by a Maternal-Fetal Medicine (MFM) specialist, an obstetrician with expertise in prenatal ultrasound and high-risk pregnancy. Many times a pediatric urologist will also review the findings with you and discuss possible treatment after birth. If you choose, amniocentesis will be performed to rule out a chromosomal abnormality, such as Trisomy 21, in the baby. You will have periodic sonograms to monitor the baby’s kidneys and fluid. Ultrasounds may be repeated every 2 to 3 weeks to check the obstruction and level of amniotic fluid in cases of bilateral UPJ obstruction or when a kidney is missing or cystic in appearance.

In addition to a pediatric urologist, you will meet our team of specialists involved in caring for your baby after birth. If surgery is needed then, you may tour our Neonatal Intensive Care Unit (NICU) in advance and learn how your baby will be cared for in the first few days after birth. You may also meet with a genetic counselor and a geneticist to talk about your family history, review the causes of hydronephrosis, and understand what to do if and when you become pregnant again. If the hydronephrosis is minimal and the UPJ obstruction is only present in one kidney, you can expect a normal delivery and do not need to change your prenatal care. Rarely if the hydronephrosis is severe and the UPJ obstruction is found in both kidneys, or one of the kidneys is missing or has a cystic appearance, our medical team may advise an earlier delivery. In this case, we will discuss the options in detail, so you can make the best decision for you and your baby.

How is hydronephrosis treated after birth?

Every newborn with a prenatal diagnosis of hydronephrosis undergoes a detailed physical exam for signs of consequences from UPJ obstruction. Babies with severe cases of prenatal hydronephrosis have an ultrasound of the kidneys and bladder a few days after birth; those with less serious cases may not need the exam for a few more days. If the ultrasound is normal, a repeat will be performed a few weeks later to confirm that result. An X-Ray called a VCUG is also performed for many children with hydronephrosis.  Half of the babies with prenatal diagnosis of UPJ obstruction and hydronephrosis have a normal result on their newborn scan.  Many babies with prenatal diagnosis of hydronephrosis receive antibiotics to lower the chances for a urinary tract infection, a common problem linked to hydronephrosis.

If we find a UPJ obstruction on a newborn's ultrasound, we will determine treatment based on the obstruction's severity. For a mild or moderate obstruction and a kidney with normal function, our medical team may decide to monitor the kidneys and repeat the ultrasound in a few months. That repeat scan will determine any changes in the kidney’s ability to function normally. In severe cases, when the kidney shows decreased function, pyeloplasty surgery may be needed to remove the obstruction and reconstruct the urinary tract. Surgery is generally performed after the baby is fully evaluated and stable; emergency surgery is not necessary. The success rate for surgery is 90 to 95 percent.

If prenatal ultrasounds show cysts in the kidney, we will perform an ultrasound of the kidney and an X-ray called voiding cystourethrogram (VCUG) to determine how the cystic kidney is affected and make sure the other kidney is normal.

What is the long-term outlook for babies with hydronephrosis?

Many cases of hydronephrosis resolve on their own before the baby’s birth. Long-term follow-up studies also suggest most cases of hydronephrosis at birth will resolve over time with the kidneys working normally. When newborn testing shows a persistent condition, the long-term outlook depends on whether the obstruction is present in one or both kidneys and is cystic in appearance. The most severe cases are hydronephrosis due to UPJ obstruction in both kidneys, or when the condition is present in just one kidney but the opposite kidney is missing or cystic in appearance. If the prognosis is more serious, kidney transplantation may be needed to achieve normal function.

What are the chances I could have another baby with hydronephrosis? 

Minimal hydronephrosis is not genetic and is not hereditary. However, hydronephrosis may coincidentally occur in future pregnancies. If UPJ obstruction is determined to be the cause of the hydronephrosis, the chances for future children with the same obstruction may be as high as 50 percent.

In addition, certain genetic conditions can cause the kidneys to have cysts and generally carry a 25 percent chance for future children to have the same condition. Regardless of the cause, you should have a prenatal ultrasound examination in the second trimester with all future pregnancies to check the developing kidneys and bladder.