What Is Antenatal Hydronephrosis?

Antenatal (before birth) hydronephrosis (fluid-filled enlargement of the kidney) can be detected in the fetus by ultrasound studies performed as early as the first trimester of pregnancy. In most instances this diagnosis will not change obstetric care, but will require careful follow-up and possible surgery during infancy and childhood.

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What Causes Antenatal Hydronephrosis?

Possible causes of antenatal hydronephrosis include:

  • Blockage: this may occur at the kidney in the ureteropelvic junction (UPJ), at the bladder in the ureterovesical junction, or in the urethra (posterior urethral valve)
  • Reflux: vesicoureteral reflux occurs when the valve between the bladder and the ureter does not function properly, permitting urine to flow back up to the kidney when the bladder fills or empties. Most children (75%) outgrow this during childhood but need daily antibiotic prophylaxis to try to prevent kidney damage before they outgrow the reflux
  • Duplications: perhaps 1% of all humans have two collecting tubes from a kidney. These may show up on fetal ultrasound. Occasionally patients with duplication have a ureterocele, which is a balloon-like obstruction at the end of one of the duplex tubes
  • Multicystic kidney: this is a nonfunctional cystic kidney
  • No significant abnormality: many of these dilated kidneys prove to be normal after delivery

How Is Antenatal Hydronephrosis Managed?

Most cases of hydronephrosis diagnosed during pregnancy are just followed with ultrasound, monitoring the growth of the fetus and the condition of the kidneys. In these cases, a routine, normal delivery can be performed. Rarely, in a fetus with severe obstruction of both kidneys and insufficient amniotic fluid, drainage of the kidneys or bladder by tube or operation may need to be done. In these babies, however, the kidneys are often very abnormal and do not function properly regardless of treatment.

What Is Done to Evaluate the Hydronephrosis After the Baby Is Born?

Several studies may need to be performed to evaluate the kidneys:

  • Ultrasound (done during the newborn period)
  • Voiding cystourethrogram (to exclude vesicoureteral reflux, a cause of 25-30% of antenatal hydrophrenosis)
  • Diuretic renal scan (to evaluate kidney function)

What Can Be Done to Treat the Hydronephrosis?

The treatment of antenatal hydronephrosis depends on the underlying cause. Infants and children with who have vesicoureteral reflux are managed with antibiotics and surveillance with periodic ultrasounds and voiding cystograms. Infants and children with an obstruction or blockage of the urinary tract may require surgical correction. Babies with hydronephrosis without reflux or obstruction are followed with periodic ultrasounds to monitor the hydronephrosis and the growth of the kidneys. The management of multicystic dysplastic kidneys is controversial: the multicystic dysplastic kidney doesn't work, but the opposite kidney is usually normal. Some urologists recommend removal, whereas others do not remove the dysplastic kidney unless its large size causes problems or unless there is a question of tumor or blockage.

This information, although based on a thorough knowledge and careful review of current medical literature, is the opinion of doctors at The University of Texas Medical School and is presented to inform you about surgical conditions. It is not meant to contradict any information you may receive from your personal physician and should not be used to make decisions about surgical treatment. If you have any questions about the information above or your child's care, please contact our doctors.

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Houston, Texas 77030
Phone: (832) 325-7234

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