From the Guidelines
Pyelectasis on an ultrasound refers to a dilation of the renal pelvis, which is a normal variant in most cases, occurring in 1% to 2% of pregnancies 1.
Key Points
- Pyelectasis is also known as urinary tract dilation (UTD) or pelviectasis, and may indicate renal or urinary tract pathology, but is often a transient finding 1.
- The anterior-posterior renal pelvis diameter is used to define norms for antenatal UTD, with <4 mm being normal between 16 and 27 weeks of gestation and <7 mm being normal between 28 weeks of gestation and delivery 1.
- Additional ultrasound features to be evaluated include the presence of calyceal dilation, parenchymal thickness and appearance, ureteral dilation, bladder abnormalities, and amniotic fluid volume 1.
- Pyelectasis is considered a soft marker for aneuploidy, particularly trisomy 21, but its association with aneuploidy is minimal, with a positive likelihood ratio of 1.5 1, 1.
- In most cases, pyelectasis resolves on its own, with approximately 80% of cases resolving by the time of delivery 1.
- Some cases of pyelectasis may have a pathologic cause, such as vesicoureteral reflux, ureteropelvic junction obstruction, or multicystic dysplastic kidneys 1.
From the Research
Definition of Pyelectasis
Pyelectasis, also known as renal pelvic dilatation or hydronephrosis, is a condition where the renal pelvis is dilated, and it is frequently found on fetal ultrasound 2.
Diagnosis and Classification
The diagnosis of pyelectasis is typically made using ultrasound, and it can be classified as mild, moderate, or severe based on the degree of dilatation 3. Mild pyelectasis is defined as a pelvocalyceal fluid-filled space with a measurement of ≥ 4 mm and < 10 mm 4.
Postnatal Outcomes
Studies have shown that most cases of pyelectasis remain stable or resolve spontaneously during pregnancy 2, 3. However, some cases may progress to hydronephrosis or be associated with postnatal renal reflux or renal obstruction 2, 4.
Management and Follow-up
Postnatal evaluation and management of fetal pyelectasis typically involve ultrasound and further testing such as voiding cystourethrography (VCUG) or magnetic resonance imaging (MRI) if necessary 5. Regular follow-up ultrasound is important to monitor renal development, urinary tract dilatation, and the appearance of the renal parenchyma 5.
Key Findings
- Pyelectasis is more common in males than females 2, 6
- The magnitude of fetal renal pyelectasis does not correlate with postnatal outcome 3
- Fetal pyelectasis of ≥ 5 mm is associated with an increased risk of postnatal hydronephrosis 6
- Regular follow-up and postnatal evaluation are recommended for fetuses with pyelectasis 2, 5, 6
Important Considerations
- Pyelectasis can be a benign condition, but it can also be associated with underlying renal or urinary tract abnormalities 4, 6
- Accurate diagnosis and classification of pyelectasis are crucial for determining the appropriate management and follow-up 3
- A comprehensive follow-up plan is essential to prevent complications and progressive loss of renal function 5