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| 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 |
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Normal |
Pyelectasis |
1 per 100 pregnancies. However, only 1 in
500 cases results in significant pathology [1,2]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
1. Bianci D, Crombleholme T, D'Alton M. Fetology: Diagnosis and Management of
the Fetal Patient. New York, NY: McGraw-Hill; 2000.
2. Mouriquand PD, Whitten M, Pracros JP. Pathophysiology, diagnosis and
management of prenatal upper tract dilatation. Prenat Diagn. 2001;21:942-951
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
6. Marra G, Barbieri G, Moioli C, Assael BM, Grumieri G, Caccamo ML. Mild fetal
hydro-nephrosis indicating vesicoureteric reflux. Arch Dis Child Fetal Neonatal
Ed 1994; 70: F147-F150.
7. Ahmad G, Outcome of fetal pyelectasis diagnosed antenatally.
J Obstet Gynaecol. 2005 ;25:119-22.
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
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