What is pyolectasis (pyelectasis) in utero?

From the Guidelines

Pyelectasis in utero refers to a mild dilation of the renal pelvis, occurring in 1% to 2% of pregnancies, and is most commonly a transient finding that is a normal variant. This condition is typically detected during routine prenatal ultrasound screening, usually in the second trimester, and several terms have been used to describe it, including pyelectasis, pelviectasis, and hydronephrosis 1.

Key Points

• Pyelectasis is considered present when the renal pelvis measures less than 4 mm being normal between 16 and 27 weeks of gestation and less than 7 mm being normal between 28 weeks of gestation and delivery 1.
• The association between trisomy 21 and pyelectasis has been well described in several series, and the finding of pyelectasis confers a positive likelihood ratio of 1.5, suggesting a minimal risk 1.
• 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 cell-free DNA or quad screen if cell-free DNA is unavailable or cost-prohibitive is recommended 1.

Management

• 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.

Pathologic Causes

• Common pathologic causes of pyelectasis include vesicoureteral reflux, ureteropelvic junction obstruction, ureterovesical junction obstruction, multicystic dysplastic kidneys, and posterior urethral valves 1.

From the Research

Definition and Detection of Pyelectasis

• Pyelectasis, also known as renal pelvic dilatation or hydronephrosis, is a condition where the renal pelvis is dilated, and it can be detected prenatally using ultrasonography 2, 3, 4, 5, 6.
• The criteria for detecting fetal pyelectasis are still controversial, but it is generally defined as a mean renal pelvis dimension greater than 5 or 10 mm before or after 28 weeks of gestation, respectively 2.

Incidence and Postnatal Outcomes

• The incidence of pyelectasis in fetuses is around 4.4% 2, and it is more frequent in males than females 3.
• Postnatal outcomes of fetuses with prenatal diagnosis of pyelectasis show that most cases resolve spontaneously or remain stable during pregnancy 3, 4, 5.
• However, some cases may progress to hydronephrosis or require surgical intervention due to obstructive urinary tract abnormalities or severe vesicoureteral reflux 2, 3, 4, 5, 6.

Classification and Management

• Pyelectasis can be classified as mild, moderate, or severe based on the anteroposterior renal pelvis diameter 4.
• Mild pyelectasis is generally defined as a diameter between 5-7 mm, moderate as 7-10 mm, and severe as greater than 10 mm 4.
• The management of pyelectasis depends on the severity and progression of the condition, as well as the presence of other anomalies or chromosomal disorders 2, 3, 4, 5, 6.

Predictive Value and Follow-up

• The positive predictive value of pyelectasis for urinary tract malformations is around 13.7% 2.
• Prenatal diagnosis of pyelectasis improves the outcome of affected children due to early surgical intervention and follow-up 5.
• Postnatal follow-up is recommended for cases that normalized before birth, as well as for those with persistent or progressive pyelectasis 5, 6.