What is the incidence of finding obstruction and vesicoureteral reflux (VUR) in a pediatric patient with a double collecting system noted on ultrasound, who has a history of febrile Urinary Tract Infections (UTIs)?

Incidence of Obstruction and VUR in Pediatric Patients with Double Collecting System and Febrile UTI

In pediatric patients with a double collecting system detected on ultrasound who present with febrile UTIs, you should proceed with voiding cystourethrography (VCUG) because the likelihood of finding vesicoureteral reflux is substantially elevated—ranging from 47-66% depending on whether the system is incomplete or complete—and these children require definitive diagnosis to prevent renal scarring and preserve kidney function. 1, 2

Specific Incidence Data for Double Collecting Systems

VUR Prevalence in Duplex Systems

• Complete duplex systems (CDS) have VUR in 66% of cases, which is significantly higher than the 26% baseline rate in single collecting systems (p <0.0001) 2
• Incomplete duplex systems (IDS) demonstrate VUR in 47% of cases, still substantially elevated compared to single systems (p = 0.007) 2
• Among 63 children with duplex systems identified after first UTI, complete and incomplete variants occurred with equal frequency 2

Obstruction and Associated Anomalies

• Ectopic ureterocele (a form of obstruction) occurs in 20% of complete duplex systems but is absent in incomplete duplex systems and single systems 2
• Poorly functioning pole moieties occur in 40% of complete duplex systems compared to only 4% in incomplete systems (p = 0.003) 2
• The overall prevalence of duplex systems among children evaluated after first febrile UTI is 8% (63 of 774 children) 2

Clinical Significance and Risk Stratification

Why VCUG is Indicated

• The 2024 EAU/ESPU guidelines specifically recommend VCUG for duplex kidneys with hydronephrosis in the setting of febrile UTIs, as the likelihood of VUR is much higher 1
• Children with febrile infections and abnormal renal ultrasound findings (which includes duplex systems) have elevated VUR risk and should all be evaluated with VCUG 1
• Ultrasound alone has a 100% false-negative rate for detecting duplex kidneys when VUR is present, meaning US cannot rule out reflux in these patients 1

Severity Considerations

• Complete duplex systems are associated with more severe VUR than incomplete systems or single collecting systems 2
• High-grade VUR (grades III-V) is present in 25.5% of all children with first febrile UTI, but this rate is substantially higher in duplex systems 3
• Renal scarring rates are similar between duplex systems (13%) and single systems (10%), but the functional consequences are more severe in duplex systems due to poorly functioning moieties 2

Recommended Diagnostic Algorithm

Immediate Steps

• Perform VCUG in all children with duplex collecting systems identified on ultrasound who have had febrile UTI 1, 2
• Consider DMSA scan to assess for acute pyelonephritis and baseline renal function, particularly to identify poorly functioning pole moieties 1
• The combination of abnormal ultrasound (duplex system) plus DMSA findings increases sensitivity for detecting high-grade VUR to 83.2% with a negative predictive value of 91.5% 4

Risk Factors Requiring Aggressive Workup

• Non-E. coli infections are associated with both higher VUR rates and infection recurrence 5
• Atypical infection presentation increases VUR likelihood 5
• Nephromegaly on initial ultrasound is a strong predictor of renal scarring (OR not specified but statistically significant) 3

Management Implications

Surgical Considerations

• 31.4% of children with abnormal ultrasound findings (including duplex systems) require subsequent management including surgical intervention, parental counseling, or renal function follow-up 3
• Complete duplex systems with ectopic ureterocele (20% of CDS) typically require surgical correction 2
• Poorly functioning pole moieties (40% of CDS) may require heminephrectomy or other definitive surgical management 2

Follow-up Strategy

• VUR resolution rates tend to be higher in incomplete duplex systems compared to complete duplex systems, influencing decisions about conservative versus surgical management 2
• Children with duplex systems and VUR require more intensive monitoring due to the higher risk of complications 2

Critical Pitfalls to Avoid

• Do not rely on ultrasound alone to exclude VUR in duplex systems—the false-negative rate is 100% for this specific finding 1
• Do not defer VCUG based on normal prenatal ultrasound, as 7 of 9 children with abnormal post-UTI findings (including duplex systems) had normal prenatal studies 1
• Do not assume incomplete duplex systems are benign—they still carry 47% VUR risk, nearly double the baseline rate 2
• Recognize that female patients are more commonly affected by duplex systems in the context of UTI 2