What are the considerations and recommended management for a prenatal ultrasound showing bilateral duplicated collecting systems with single ureters and mild ureteropelvic caliectasis (right 0.6 cm, left 0.9 cm)?

Management of Bilateral Duplex Collecting Systems with Mild Ureteropelvocaliectasis

For this prenatal finding of bilateral duplex collecting systems with single ureters and mild bilateral ureteropelvocaliectasis (right 0.6 cm, left 0.9 cm), perform a postnatal renal and bladder ultrasound after 48 hours of life, followed by voiding cystourethrography (VCUG) to evaluate for vesicoureteral reflux, which occurs in approximately 15% of children with prenatally diagnosed urinary tract dilation and has a 100% false-negative rate on ultrasound alone in duplex systems. 1, 2

Immediate Postnatal Imaging Strategy

Initial Ultrasound Timing

• Perform renal and bladder ultrasound after 48 hours of life (not during the first 48 hours, as physiologic third-spacing can underestimate dilation severity until day 7-10) 1
• The ultrasound should specifically assess:
  • Confirmation of bilateral duplex systems with separation of renal sinus echo complexes 3
  • Degree of hydronephrosis in each moiety (upper and lower poles separately) 1
  • Presence of ureterocele (cystic dilation at ureteral insertion) 3
  • Bladder wall thickness (thickening suggests outlet obstruction or reflux) 3
  • Renal parenchymal thickness and appearance 1
  • Ureteral dilation 1

Critical Pitfall to Avoid

• Do not rely on prenatal ultrasound findings alone—duplex systems were missed in 100% of cases in one series, and 78% of children with abnormal post-UTI findings had completely normal prenatal ultrasounds 4, 2
• Ultrasound alone cannot exclude vesicoureteral reflux in duplex systems, with a 100% false-negative rate for this specific finding 2

Mandatory VCUG Evaluation

Indication and Timing

• VCUG is mandatory for all duplex kidneys with hydronephrosis, as the likelihood of vesicoureteral reflux is significantly higher in this population 1, 2
• Perform VCUG at approximately 1 month of age for moderate hydronephrosis 1
• VUR occurs in 15% of children with prenatally diagnosed isolated urinary tract dilation, and the lower-pole moiety is most frequently affected in duplex systems 1

What VCUG Will Reveal

• Vesicoureteral reflux (present in 30% of urinary tract abnormalities in infants with antenatal hydronephrosis) 1
• Grade and laterality of reflux (higher grades of postnatal hydronephrosis correlate with more severe VUR) 1
• Whether reflux is primary or secondary to other urologic abnormalities 1
• Bladder wall thickening and posterior urethral anatomy (to exclude posterior urethral valves in males) 1

Risk Stratification Based on Postnatal Findings

Mild Dilation (APD <10 mm)

• If postnatal ultrasound shows anteroposterior renal pelvis diameter <10 mm with no other concerning features:
  • Spontaneous resolution occurs in 64-75% of cases 1, 4
  • Follow-up ultrasound at 1-6 months, then every 6-12 months if stable 4
  • Long-term surveillance with kidney ultrasound at least once every 2 years 4

Moderate-Severe Dilation (APD ≥10-15 mm)

• If postnatal ultrasound shows APD ≥10 mm or other concerning features (calyceal dilation, parenchymal thinning, ureteral dilation):
  • Higher risk of ureteropelvic junction obstruction and need for surgical intervention 4
  • More frequent monitoring with individualized follow-up based on VCUG and functional imaging results 1

Antibiotic Prophylaxis Decision Algorithm

Start Prophylaxis If:

• VUR is documented on VCUG (especially in children under 5 years) 1, 3
• High-grade hydronephrosis (APD ≥15 mm) is present 4
• Recurrent urinary tract infections occur 3

Prophylaxis Regimen

• First-line: Trimethoprim-sulfamethoxazole 4
• Alternatives: Nitrofurantoin, cefadroxil, or amoxicillin-clavulanate 4
• Continue prophylaxis until VUR resolves (many cases resolve spontaneously) or until surgical correction 1, 4

Functional Imaging: When to Order MAG3 Renal Scan

Indications for MAG3 Scintigraphy

• Persistent or worsening hydronephrosis on follow-up ultrasound 1, 3
• Renal parenchymal thinning develops 4
• Clinical obstruction symptoms arise 4
• Before contemplating surgical intervention to assess split renal function and drainage 1, 3

Timing

• Perform at ≥2 months of age (due to lower glomerular filtration rate in newborns) 1, 4

Interpretation

• T½ >20 minutes indicates obstructed drainage 3
• Differential renal function <40% for affected moiety suggests significant functional impairment 3
• Decline in differential function >5% on consecutive scans warrants surgical consultation 3

Urology Referral Criteria

Refer to Pediatric Urology When:

• Functional imaging demonstrates obstruction (T½ >20 minutes and differential function <40%) 3, 4
• Differential renal function declines >5% on serial scans 3
• Febrile UTIs recur despite prophylaxis 3, 4
• High-grade VUR (grades IV-V) persists 3
• Obstructive symptoms develop 4

Long-Term Surveillance Protocol

Annual Monitoring Should Include:

• Renal ultrasound to assess both kidneys for disease progression 3
• Urinalysis with culture if indicated 3
• Blood pressure monitoring (renal scarring risk is 73-95% with recurrent UTIs) 3

Consider Advanced Imaging If:

• Obstruction is suspected or to establish baseline differential function before intervention 3
• MR urography provides detailed anatomic and functional assessment without radiation, though sedation may be needed in young children 3, 5

Critical Management Pitfalls

Do NOT:

• Delay postnatal imaging based on reassuring prenatal findings—significant pathology can be present despite normal prenatal ultrasound 4, 2
• Skip VCUG in duplex systems with hydronephrosis—reflux cannot be excluded by ultrasound alone 2
• Perform ultrasound during acute UTI—this can produce transient hydronephrosis and false-positive findings 3
• Assume hydronephrosis equals obstruction—it may represent reflux, distended bladder, or postobstructive dilation requiring bladder decompression and repeat imaging 3

DO:

• Ensure adequate hydration before functional studies—dehydration may mask obstruction on imaging 3
• Notify pediatric provider at delivery of prenatal findings 1
• Evaluate for bladder and bowel dysfunction in toilet-trained children, as this doubles UTI recurrence risk 3

Aneuploidy Screening Consideration

• For patients with no previous aneuploidy screening and isolated urinary tract dilation, counsel regarding trisomy 21 risk (positive likelihood ratio 1.5, minimal risk) and discuss options for noninvasive screening with cell-free DNA or quad screen 1
• Do not recommend diagnostic testing solely for this indication 1
• For patients with negative serum or cfDNA screening, no further aneuploidy evaluation is needed 1