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Prenatal Hydronephrosis

For questions or to make an appointment, contact the Department of Pediatric Urology at UPMC Children's Hospital of Pittsburgh at 412-692-4100.

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What is Prenatal Hydronephrosis?

Prenatal hydronephrosis is the swelling of a kidney in a fetus or infant. This is typically caused by a buildup of urine in the kidney when the urine backs up inside the renal pelvis (an area of the kidney). Treatment may involve observation, antibiotics, or surgery to correct the cause that is blocking the urine.

The kidneys are two large bean-shaped organs located in the mid-back, just below the rib cage. They filter waste products from the blood and excrete them from the body in the form of urine.

Urine is stored in a part of the kidney called the renal pelvis and then flows down the ureters, two thin tubes that connect the kidney to the bladder. From the bladder, urine leaves the body through a tube called the urethra.

Prenatal Hydronephrosis Causes

Potential causes of prenatal hydronephrosis are:

  • Ureteropelvic junction (UPJ) obstruction (most common): A blockage at the point where the renal pelvis joins the ureter.
  • Vesicoureteral reflux: A backflow of urine from the bladder.
  • Megaureter: An abnormality of one or both of the ureters.
  • Ureterocele: A birth defect that affects the kidney, ureters, and bladder, blocking the flow of urine.
  • Ectopic ureter: A condition where a child is born with a ureter that does not connect at the bladder, but instead drains outside of the bladder.
  • Bladder disorders: Disorders such as posterior urethral valves, neurogenic bladder, or congenital bladder outlet obstruction due to urethral stricture.

Diagnosing Prenatal Hydronephrosis

Hydronephrosis is typically diagnosed before birth in a prenatal ultrasound. It also may be suspected in a child who experiences a urinary tract infection or abdominal pain.

The most important diagnostic test is the ultrasound. This can show how dilated the kidney is, whether both kidneys are involved, and whether the ureter is also dilated or the bladder is distended.

Additionally, the ultrasound can give valuable information about the appearance of the functioning part of the kidney.

The diagnosis of reflux is made using an x-ray called a voiding cystourethrogram (VCUG). A urinary catheter (tube) is placed into the child's bladder and fills the bladder with x-ray dye. During urination, the path of the dye is followed. If it goes up toward the kidneys, reflux is diagnosed.

UPJ obstruction is often confirmed with a test called diuretic renal scan (DRS). A tiny amount of weak radioactive material is injected into a vein. A scanner follows the tracer's progress through the urinary system. If all or most of the tracer remains in the kidney and does not wash out in the urine, blockage is diagnosed.

Prenatal Hydronephrosis Treatment

Sometimes, hydronephrosis goes away without treatment. Often, mild cases do not adversely affect kidney function and require only monitoring.

Treatment is required only when kidney function is impaired or the kidney becomes greatly enlarged. The underlying cause of hydronephrosis determines the course of treatment.

Long-term follow-up is recommended for hydronephrosis, regardless of treatment type. Periodic ultrasounds to monitor the kidneys are recommended once kidney function and growth are stable.


Most cases of vesicoureteral reflux are treated with daily antibiotic therapy. Prenatal hydronephrosis is often treated with antibiotics to prevent kidney infections.


In cases where surgery is recommended, the operation is highly successful and carries relatively little risk.

For severe UPJ obstruction, surgery is usually required. The operation to correct UPJ obstruction is called a pyeloplasty. Usually this surgery is performed through an incision in the side.

With recent advances in minimally invasive surgical techniques, pediatric urologists can correct UPJ obstruction without the need for open surgery. The new technique provides significant benefits in reduced postoperative pain, faster recovery, and minimal sca rs.

In one such procedure, called laparascopic pyeloplasty, a laparascope (a slim tube with a tiny video camera mounted on the end) is inserted into a small incision in the navel. While watching the procedure on a TV monitor, the surgeon inserts instruments throu gh other small incisions to repair the obstruction.

The blocked part of the ureter is removed and the healthy ureter reconnected to the kidney. A temporary tube called a stent may be placed inside the ureter to drain the kidney until surgery heals.

Currently, this operation is being used in older children and adults, although eventually it will be applicable to toddlers or even infants. The hospital stay for either open or laparoscopic pyeloplasty is usually only one to three days.

The success rate is generally 95 percent for all open operations, and appears to be similar for the laparoscopic operation.