What is pylectasis (pelvic dilation) of the kidneys in utero?

From the Guidelines

Pyelectasis of the kidneys in utero refers to a mild dilation of the renal pelvis, which is a relatively common condition occurring in about 1-2% of pregnancies, and is often a transient finding that resolves on its own without requiring treatment. This condition is typically detected during routine prenatal ultrasound examinations, usually in the second or third trimester of pregnancy. The condition is measured by the anterior-posterior diameter of the renal pelvis, with measurements between 4-10 mm considered mild to moderate pyelectasis 1.

Key Points to Consider

• Pyelectasis can sometimes be associated with urinary tract abnormalities or chromosomal disorders like Down syndrome, particularly when found alongside other ultrasound abnormalities 1.
• When pyelectasis is detected, additional ultrasound monitoring is typically recommended throughout the pregnancy to track whether the condition improves, remains stable, or worsens 1.
• After birth, the infant may need follow-up ultrasounds to ensure the condition resolves, with most cases resolving spontaneously either before birth or during the first year of life without requiring treatment 1.
• The underlying cause of pyelectasis is often a temporary delay in the development of the urinary tract system, which typically catches up as the fetus continues to grow.

Management and Follow-up

• For pregnant people with no previous aneuploidy screening and isolated pyelectasis, counseling to estimate the probability of trisomy 21 and a discussion of options for noninvasive aneuploidy screening with cfDNA or quad screen if cfDNA is unavailable or cost-prohibitive is recommended 1.
• For fetuses with isolated pyelectasis A1, an ultrasound examination at ≥32 weeks of gestation to determine if postnatal pediatric urology or nephrology follow-up is needed is recommended 1.
• For fetuses with pyelectasis A2-3, an individualized follow-up ultrasound assessment with planned postnatal follow-up is recommended 1.

From the Research

Definition and Prevalence of Pyelectasis

• Pyelectasis, also known as renal pelvic dilatation or hydronephrosis, is a condition where the renal pelvis is dilated in the fetus or newborn 2, 3, 4, 5, 6.
• The prevalence of pyelectasis in fetuses is around 1% to 3% 2, 5.
• Pyelectasis can be isolated or associated with other anomalies or chromosomal/genetic disorders 6.

Diagnostic Criteria and Classification

• Pyelectasis is diagnosed by measuring the anteroposterior renal pelvic diameter (APRPD) on ultrasound scan 2, 4, 6.
• The degree of pyelectasis is classified as mild (APRPD < 10mm), moderate (APRPD 10-15mm), or severe (APRPD > 15mm) 2, 4.
• The diagnostic value of renal pelvis diameter (RPD) is used to predict postnatal outcomes 5.

Postnatal Outcomes and Management

• Most cases of mild pyelectasis resolve spontaneously during pregnancy or after birth 2, 5, 6.
• Moderate and severe pyelectasis are associated with a higher risk of postnatal renal damage and require close multidisciplinary follow-up 4.
• Postnatal ultrasound is highly predictive of renal abnormalities and can guide the need for further investigations or surgical intervention 2, 4.
• Surgical intervention is required in cases of obstructive uropathies, such as pelvi-ureteric junction obstruction or vesicoureteral reflux 2, 3, 4.