Renal Pyelectasis on Prenatal Ultrasound – Next Steps?
Renal pyelectasis literally means “pelvis dilation” of the kidney, and is defined as an anteroposterior diameter of the renal pelvis of ≥ 4mm up to 20 weeks of gestation.
CLINICAL ACTIONS :
When seen in isolation, with no other fetal abnormalities
If aneuploidy screening has not yet been done, then screening or diagnostic testing should be offered
If patient opts for aneuploidy testing and result is negative, no further evaluation is required
Counsel patients that screening tests are not diagnostic and therefore there is still residual risk for chromosomal anomalies
If aneuploidy screen result is positive, refer for genetic counseling and consideration of diagnostic testing options
Ultrasound at 32 weeks of gestation is suggested to rule out persistent pyelectasis and possible obstruction of the urinary tract
If the renal pelvis is > 7 mm at 32 weeks, then post-natal follow up is suggested
If other anomalies are detected
ACOG guidance recommends offering invasive testing using microarray in the setting of fetal structural anomalies seen on prenatal ultrasound
Renal pyelectasis is reported in 0.6-4.5% of fetuses in the second trimester. It is most commonly a transient physiologic state in which the renal pelvis, the structure that is essentially the funnel for urine exiting the kidney into the ureter, is dilated and measures larger than what is considered normal for a particular gestational age. The presence of renal pyelectasis as an isolated finding, in the setting of a negative aneuploidy screen, is not itself an indication for invasive testing; however, ACOG does give all women the option (both high and low risk) for invasive testing. Note, if the renal pelvis is still dilated in the third trimester, the urinary tract may require attention following delivery to ensure normal kidney function and prevent infection in the newborn.
Normal renal pelvis measurement is up to 1cm throughout gestation
Values above 1cm are almost always pathological
Resolution of dilation based on second trimester measurement
Between 4 and 7 to 8 mm: 80% resolution
>9 mm: <15%
More commonly observed in male fetuses
A targeted ultrasound is essential to look for other fetal anatomic anomalies
Note: ACOG guidance recommends offering invasive, diagnostic testing for all pregnant women regardless of age and even in the presence of a normal anatomy scan
Offering invasive testing using microarray in the setting of fetal structural anomalies on prenatal ultrasound is recommended
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