Prenatal urinary tract dilation

Prenatal urinary tract dilation (UTD) is the most common urinary tract abnormality detected on prenatal ultrasound, occurring in up to 5% of all pregnancies. It is most often physiologic and resolves spontaneously within the first 3 years of life. Neonates with persistent or significant postnatal UTD should be evaluated for vesicoureteral reflux (VUR) and congenital anomalies of the kidney and urinary tract (CAKUT). In addition to treating the underlying cause, postnatal management includes antibiotic prophylaxis and periodic ultrasounds to evaluate for resolution. Surgery may be indicated for patients with severe UTD or a high risk of kidney failure.

• Occurs in < 5% of pregnancies ^[1][2]
• ♂> ♀ (2:1) ^[3]
• Most common urinary tract abnormality detected on prenatal ultrasound ^[1][3]

Epidemiological data refers to the US, unless otherwise specified.

• Physiologic (most common; usually resolves spontaneously) ^[1][4][5]
• Vesicoureteral reflux ^[1][4]
• Congenital anomalies of the kidney and urinary tract, e.g.: ^[4][6]
  • Ureteropelvic junction obstruction
  • Ureterocele
  • Ectopic ureter
  • Ureterovesical junction obstruction and megaureter
  • Urethral atresia
  • Posterior urethral valves

• Typically detected on routine prenatal ultrasound in the second or third trimester. ^[1][4]
• Prenatal ultrasound findings include: ^[4][5][7]
  • ↑ anteroposterior renal pelvis diameter ^[5]
  • Calyceal dilation
  • Ureteral dilation
  • Renal parenchymal abnormalities (e.g., cortical thinning, hyperechogenicity)
  • Bladder abnormalities (e.g., wall thickening, ureterocele)
  • Oligohydramnios

Significant and/or bilateral UTD on ultrasound suggests an underlying pathology (e.g., posterior urethral valves, urethral atresia) rather than a transient physiologic dilation. ^[4]

Approach ^[4][5]

• Perform prenatal risk stratification for UTD if detected on prenatal ultrasound to:
  • Guide timing and nature of prenatal and postnatal monitoring
  • Determine the need for consultation with a specialist
• If CAKUT are identified on prenatal imaging, consult a multidisciplinary team (e.g., maternal fetal medicine, genetics) before delivery. ^[8]
• Ensure postnatal management with a pediatric specialist (e.g., nephrology, urology) for infants with:
  • Increased risk for urinary tract anomaly on any prenatal ultrasound
  • Persistent UTD

In approx. 80% of patients, prenatal UTD resolves spontaneously within the first 3 years of life. The higher the grade of dilation, the lower the likelihood of spontaneous resolution. ^[4][5][9]

Infants with prenatal ultrasound findings that suggest increased risk for urinary tract anomaly require postnatal imaging before discharge from the hospital after birth. ^[4]

Prenatal management ^[4][5]

Postnatal management of prenatal UTD ^[3][4]

• For neonates with severe bilateral UTD (e.g., due to bladder outlet obstruction), consult a specialist for urgent management.
• Use prenatal risk stratification for UTD to determine the need for RBUS
  • For UTD that has resolved on prenatal ultrasound
    • No further evaluation is indicated if resolved < 32 weeks' gestation, and all prenatal imaging is low risk.
    • If resolved > 32 weeks' gestation, obtain RBUS between 3–9 months after birth.
  • Obtain an RBUS for all other infants:
    • Before hospital discharge: if increased risk for urinary tract anomaly OR suspected urinary tract obstruction
    • Within 6 weeks of birth: if low risk of urinary tract anomaly, or inconclusive findings on prenatal ultrasound
• Consult a specialist (e.g., urology, nephrology) for postnatal risk stratification and management of UTD, e.g.:
  • Timing of repeat RBUS
  • Management of the underlying cause (e.g., advanced diagnostics for VUR, surgery for significant UTD). ^[3]
  • Antibiotic prophylaxis for UTD
    • First line: amoxicillin ^[1][4]
    • Alternatives: cephalexin, trimethoprim/sulfamethoxazole (if > 2 months of age) ^[2]
• Management of acute UTI in children with known UTD requires additional considerations, e.g.:
  • Diagnostics for VUR, if not already performed
  • Catheterized urine sample if initial urinalysis suggests UTI
  • See also "Prevention of pediatric UTI."

Maintain a high index of suspicion for UTI in children with UTD and fever. ^[4]

Postnatal risk stratification and management ^[1][4][5]

Postnatal risk stratification is based on findings on the first postnatal ultrasound.