Understanding Pediatric Hydronephrosis
Hydronephrosis (pronounced: high-dro-nef-RO-sis) is a common condition where the kidney becomes swollen because urine (pee) can’t drain out properly. It’s like a balloon filling up with too much water—the kidney stretches.
It is not a disease itself, but rather a sign that there is a drainage problem in the urinary system.
How is it Diagnosed?
Hydronephrosis is often found in one of two ways:
- Before Birth (Prenatal): This is the most common way it’s found. A routine prenatal ultrasound (sonogram) during pregnancy detects the swelling in the baby’s kidney(s). This is sometimes called fetal hydronephrosis.
- After Birth (Postnatal): It may be detected on an ultrasound done after a baby or child has a Urinary Tract Infection (UTI), unexplained pain, or other urinary issues.
Good News: In about half of all cases found before birth, the swelling is mild and goes away on its own before or soon after the baby is born. This is called transient hydronephrosis.
What Causes the Swelling?
The urinary system is designed to allow urine to flow one way: from the kidney, down the ureter (the tube), into the bladder, and out the urethra. Hydronephrosis happens when this flow is blocked or when urine flows backward.
The two main causes are:
| Cause | What Happens |
| Obstruction (Blockage) | Something physically stops the urine from draining. Common blockages include a narrowing where the kidney meets the ureter (UPJ Obstruction). A flap of tissue in the urethra (in boys only) that blocks bladder drainage (Posterior Urethral Valves or PUV). |
| Reflux (Backward Flow) | Urine flows backward from the bladder up toward the kidney (Vesicoureteral Reflux or VUR). This happens when the valve where the ureter enters the bladder doesn’t close properly. |
Important Note: Hydronephrosis is a birth difference; it is not caused by anything the parents did or did not do during pregnancy.
What Are the Symptoms?
Most babies and young children with mild or moderate hydronephrosis have NO symptoms and feel no pain.
If symptoms do occur, they are often a sign of a more severe blockage or an infection:
- Urinary Tract Infection (UTI): This is the most common symptom in children. Parents should look for:
- Fever
- Painful or frequent urination
- Cloudy or foul-smelling urine
- Irritability or failure to thrive (in infants)
- Pain: Sudden or intense pain in the back, side (flank pain), or belly.
- Blood in the urine (hematuria).
Treatment Options: Watching vs. Fixing
Treatment depends entirely on the severity of the swelling and the underlying cause. A Pediatric Urologist or Pediatric Nephrologist will monitor your child.
| Treatment Approach | Who Needs It? | What is Done? |
| Observation & Monitoring | Most cases, especially those with mild to moderate swelling, or if the cause is unknown. | The condition is closely monitored with regular ultrasounds (every 3 to 6 months) to see if the swelling improves or stays stable. No surgery or medication is typically needed. |
| Preventive Antibiotics | Children with moderate to severe hydronephrosis or those with Vesicoureteral Reflux (VUR). | A low, daily dose of antibiotics is given to prevent a UTI. When urine is trapped, the risk of bacteria growing and causing a kidney infection is higher. |
| Surgery | Cases that are severe, cause pain, or show evidence of kidney damage or declining kidney function. | The goal of surgery is to remove the blockage or correct the reflux to allow urine to flow freely. The most common procedure for a blockage is a pyeloplasty, where the narrow or blocked section of the ureter is removed and the tube is reconnected. |
Outlook
For the vast majority of children, hydronephrosis is a very manageable condition. With proper monitoring and, if needed, treatment, children who had hydronephrosis can expect to have normal kidney function and lead healthy lives.