Fetal Pyelectasis (Pelviectasis)

Enlargement of the part of the kidney that collects urine (the renal pelvis) from 4 to 10 millimeters in diameter is called fetal pyelectasis or “renal pelvic dilatation”. Dilation of the renal pelvis to greater than 10 mm is called severe pyelectasis or hydronephrosis. The illustration at right shows a normal kidney compared to a kidney with pyelectasis.  Pyelectasis is detected in 1 per 100 babies before birth, and is seen more commonly in male fetuses.  About 1 in 500 cases develops significant disease. Most mild cases resolve before  birth or within a few months after delivery. .

      Normal Pyelectasis

A fetus with severe pyelectasis or hydronephrosis is at increased risk of developing problems such as low amniotic fluid and kidney disease. In addition pyelectasis has a weak association with chromosome abnormalities, in particular Down syndrome. The severity of isolated pyelectasis does not appear to increase the risk for chromosome abnormality [5].

What Causes It?

The most common causes of severe pyelectasis or hydronephrosis are a blockage of the ureter (the tube that carries urine from the kidney to the bladder) where it joins the kidney  and backward flow of urine from the bladder (vesicoureteric reflux). Less common causes of hydronephrosis include posterior urethral valves, urethral atresia, ectopic ureteroceles, duplication of the collecting system, megacystis-microcolon-intestinal-hypoperistalsis syndrome, prune belly syndrome, and cloacal malformation.

Does Pyelectasis Need Treatment?

Pylectasis involving only one kidney does not need intervention, but requires followed up ultrasound evaluation after 28 weeks for possible worsening of the condition.  Severe hydronephrosis involving both kidneys is associated with increased risk of poor outcome, and is monitored for the development of low amniotic fluid.

An ultrasound is usually done 5 to 7 days after birth to reevaluate the infant’s kidneys. Most cases of mild pyelectasis where the renal pelvis measures less than 8 mm and involves only one kidney tend to resolve spontaneously either in utero or within a few months after delivery.  Pyelectasis greater than 8 mm is more likely to need surgical correction during childhood.

What are the Chances of Having Pyelectasis Again in a Future Pregnancy?

In a study of 64 women with the finding of pyelectasis in their fetuses, 43 (67%) had a recurrence of this finding in their next pregnancy.

What is the Risk of Down Syndrome in a Fetus with Pyelectasis?

Presently genetic testing of the fetus (amniocentesis) is offered if the risk of Down syndrome in the fetus is ~ 1 in 200 or greater. For a 34 year old woman the isolated finding of pyelectasis at midtrimester increases the risk of Down syndrome from 1 in 365 to 1 in 192.

For a woman 34 years of age or less with a normal triple marker screen for Down syndrome the risk benefit ratio does not favor amniocentesis when the only ultrasound finding is pyelectasis.

SEE http://www.obfocus.com/high-risk/birthdefects/pyelectasis.htm

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