With more mothers having ultrasound scans during pregnancy, doctors are discovering more cases of hydronephrosis, a condition in which the kidney is swollen with urine due to a blocked or narrowed ureter. (Ureters are the tubes that drain urine from the kidneys into the bladder.) Before the introduction of widespread prenatal ultrasound testing, children weren't diagnosed with this condition unless they had symptoms, often after the age of 3 or 4.

Some researchers have found that up to two percent of all babies, mostly boys, have prenatal hydronephrosis. Fortunately, most of these children will never have any symptoms because the condition will either clear up or the kidneys will compensate so they work normally. But for severe or moderate cases that produce symptoms, the treatment is usually surgery.

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The three main conditions that cause hydronephrosis are:

  • Non-Obstructive Hydronephrosis — Swelling in the kidney that has no effect on kidney function.
  • Ureteropelvic Junction (UPJ) Obstruction — The ureter is "kinked" or narrow where it joins the kidney.
  • Vesicoureteral Reflux — There is an abnormal backflow of urine from the bladder into the ureter and up to the kidney. This may be caused by an abnormality in how the ureter connects with the bladder, by nerve problems or by dysfunctional voiding.

Other conditions that can cause hydronephrosis in children include:

  • Ectopic Ureter — The ureter either bypasses the bladder completely or connects to the bladder in the wrong place.
  • Megaureter — Both of the ureters are too wide.
  • Multicystic Dysplastic Kidney — A kidney doesn't function because of cystic tissue.
  • Neurogenic Bladder — The normal nerve pathways associated with urination don't work properly.
  • Nonneurogenic Neurogenic Bladder — An emotionally influenced form of urinary retention.
  • Posterior Urethral Valves — The normal valve in the urethra (the tube that drains urine from the bladder to outside the body) is too narrow to allow free urine flow. This condition occurs only in boys.
  • Ureterocele — The urine swells the portion of the ureter closest to the bladder because the ureter opening is too small for the free flow of urine into the bladder.
  • Ureterovesical Junction (UVJ) Obstruction — The valve where the ureter connects with the bladder is absent or nonfunctional. The pressure generated by the bladder emptying will force urine backward into the ureter and kidney, causing dilation without a mechanical obstruction.
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Children with mild and sometimes even moderate hydronephrosis usually don't have symptoms. Research suggests that the kidney compensates for hydronephrosis to maintain normal function.

However, severe hydronephrosis can damage the kidney, resulting in infections, pain and bleeding. Symptoms of urinary infection can include painful urination, cloudy urine, back pain and fever. Nephrosis, or kidney disease, can cause difficulty passing urine, either by being irregular or uncontrolled.

Hydronephrosis is usually diagnosed in one of two ways: A prenatal ultrasound reveals that the fetus has dilated kidneys, or an ultrasound that's performed to evaluate another medical problem, such as a urinary tract infection or incontinence, shows hydronephrosis. Prenatal ultrasounds detect hydronephrosis in about one out of every 100 pregnancies.

Once hydronephrosis is noted, the baby will often need additional tests to find out the severity of the condition. These tests are important because diagnosing and treating a potential abnormality early can prevent urinary tract infections and permanent kidney damage or scarring.

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If your child's not already on antibiotics, we will give you a prescription for a low-dose, daily antibiotic. The types of antibiotics we use are very specific to the urinary tract and have very few side effects, if any. The kind of antibiotic your child receives will depend on his or her age, weight and allergies.

The antibiotics are used to prevent the hydronephrosis from causing kidney infections. Once the special X-ray tests have been completed, we can estimate how long your child will need to take the antibiotics.

The need for surgery depends on the severity of the hydronephrosis and is different for each child. Typically, non-obstructive hydronephrosis and grade I to III hydronephrosis don't need surgery and resolve over time. Children diagnosed with dilation from ureterovesical junction abnormalities called megaureters rarely, if ever, need surgical repair. Children with grade IV hydronephrosis, the most severe, are the most likely to need surgery to prevent kidney damage and recurrent infection. The surgery to correct hydronephrosis is called pyeloplasty.

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UCSF Research & Clinical Trials


Reviewed by health care specialists at UCSF Benioff Children's Hospital.

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