Enlargement of the renal pelvis (the part of the kidney that collects urine) from 4 to 10 mm in diameter is commonly referred to as 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. Dilatation of the urinary tract is detected in utero in
	Normal	Pyelectasis

The fetus found to have a dilated renal pelvis is at increased risk of developing urological problems . In addition pyelectasis has a weak association with chromosome abnormalities, in particular Down syndrome [3,4]. The severity of isolated pyelectasis does not appear to increase the risk of chromosome abnormality [5].

What Causes It?

The most common causes of renal pelvis dilatation, which persists after birth are obstruction of the ureter at its junction with the renal pelvis (ureteropelvic junction) and vesicoureteric reflux (the ureter allows urine to flow backwards from the bladder) [6]. 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 progression to pathological hydronephrosis.
Severe hydronephrosis involving both kidneys is associated with increased risk of poor outcome, and is monitored for the development of low amniotic fluid [11].

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 [7-10].

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 190 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 [12,13].

REFERENCES

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3 . Smith-Bindman R, et al. Second-trimester ultrasound to detect fetuses with Down's syndrome. JAMA 2001;285:1044-55
4. Chudleigh PM, The association of aneuploidy and mild fetal pyelectasis in an unselected population: the results of a multicenter study. Ultrasound Obstet Gynecol. 2001 ;17:197-202.
5.Roshanfekr D, Vonpechman W, Petrikovsky B Severity of isolated fetal pyelectasis and risk of aneuploidy. Obstet Gynecol 2000;95(4 Suppl 1):S72
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7. Ahmad G, Outcome of fetal pyelectasis diagnosed antenatally.
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8. Cohen-Overbeek TE, Mild renal pyelectasis in the second trimester: determination of cut-off levels for postnatal referral. Ultrasound Obstet Gynecol. 2005 ;25:378-83.
9. Adra AM, Fetal pyelectasis: is it always "physiologic"? Am J Obstet Gynecol. 1995 ;173:1263-6.
10. Sairam S, Natural history of fetal hydronephrosis diagnosed on mid-trimester ultrasound. Ultrasound Obstet Gynecol. 2001;17:191-6.
11. Flake AW, Ureteropelvic junction obstruction in the fetus. J Pediatr Surg. 1986;21:1058-63.PUBMED
12. Havutcu AE,et al. The association between fetal pyelectasis on second trimester ultrasound scan and aneuploidy among 25,586 low risk unselected women. Prenat Diagn. 2002 ;22:1201-6.
13.Corteville et al.. Fetal Pyelectasis & Down Syndrome: Is Genetic Amniocentesis Warranted? Obstet Gynecol 1992; 79:770-2

Created: 12/15/2005