Prevalence:

• 1 in 2,000 births
• More common in males.

Ultrasound diagnosis:

• Pelvicalyceal dilatation without ureteral dilatation. The degree of pelvicalyceal dilatation is variable and, occasionally, perinephric urinomas (encapsulated collection of urine due to a tear in the renal pelvis or calyces or the ureter) and urinary ascites may be present.
• Unilateral in 80% of cases.

Associated abnormalities:

• The incidence of chromosomal abnormalities and genetic syndromes is not increased.

• Abnormalities of the contralateral kidney: multicystic kidney, ectopia, renal agenesis.

Investigations:

• Detailed ultrasound examination.

Follow up:

• Ultrasound scans every 4 weeks to monitor the evolution of hydronephrosis and assess amniotic fluid volume.

Delivery:

• Standard obstetric care and delivery.

Prognosis:

• The majority of infants have moderate or good function and can be managed expectantly. Pyeloplasty is performed if there is deterioration of renal function.

Recurrence:

• No increased risk of recurrence.