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Pediatric – Hydronephrosis

What is Antenatal Hydronephrosis?

Antenatal (before birth) hydronephrosis (fluid filled enlargement of the kidney) is 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 surveillance and possible surgery during infancy and childhood.


The most common cause of antenatal hydronephrosis is a narrowing of the ureter close to the kidney, usually developing before the fourth month of pregnancy.
Other causes include the following:

  • Blockage (in the kidney, at the uteropelvic junction [UPJ]; in the bladder, at the uterovesical junction; or in the urethra, due to the posterior urethral valves)

  • Reflux (condition in which the valve between the bladder and the ureter allows urine to flow back into the kidney when the bladder fills or empties)

  • Duplication anomaly (occurs in 1% of the population and involves two ureters leading from the kidney; one may have an obstruction called a uterocele)

  • Multicystic kidney (nonfunctional kidney)


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 hydronephrosis

  • Diuretic renal scan (to evaluate kidney function)


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.


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