What is a Voiding Cystourethrogram (VCUG)?

Voiding Cystourethrogram (VCUG)

A voiding cystourethrogram (VCUG) is a fluoroscopic imaging technique that evaluates the bladder and urethra during filling and emptying, allowing assessment of both anatomical and functional aspects of the urinary tract, particularly for detecting vesicoureteral reflux (VUR). 1

Procedure and Purpose

• VCUG involves filling the bladder with contrast material through a catheter and taking X-ray images during both filling and voiding phases
• Primary uses include:
  • Evaluation of urinary dysfunction
  • Assessment of urethral and bladder anatomy
  • Detection of vesicoureteral reflux (VUR)
  • Post-urinary tract surgery follow-up 1
  • Evaluation of children with urinary tract infections (UTIs) 2

Clinical Findings and Diagnostic Value

VCUG can detect several important conditions:

• Vesicoureteral reflux (VUR) and its grading (I-V)
• Cystocele (bladder extending below the pubic symphysis)
• Urethral angle changes and hypermobility
• Urethral diverticula
• Bladder trabeculation (thickening)
• Post-void residual volume
• Urethral narrowing with/without upstream dilation 1

Standardized Protocol Recommendations

The American Academy of Pediatrics Sections on Urology and Radiology recommend:

• Multiple filling-voiding cycles (at least 2) to identify intermittent VUR 3
• This is crucial as studies show 21.2% of VUR cases are only diagnosed after an initial negative cycle 3
• Documentation of important parameters:
  • Scout image
  • Post-void residual volume
  • Infused volume
  • VUR grade
  • Volume at which reflux occurs
  • Whether reflux occurs during filling or voiding 4

Clinical Applications

VCUG is particularly important in pediatric patients:

• The American Urological Association recommends VCUG for follow-up of children with UTIs, typically between 12-24 months after infection 2
• Follow-up intervals may be longer for patients with higher grades of VUR (grades III-V), bladder/bowel dysfunction, and older children 2
• VCUG is most commonly performed in younger children, with 74.1% of children under 1 year of age receiving cyclic studies compared to only 6.9% of children older than 5 years 3

Advantages and Limitations

Advantages:

• Provides focused imaging of bladder and urethra during active voiding
• Allows objective measurement of changes after surgical repair
• Gold standard for evaluating and diagnosing VUR 5

Limitations:

• Limited to anterior compartment structures (bladder and urethra)
• May show lower prevalence of urethral hypermobility compared to MR defecography 1
• Involves radiation exposure (though cyclic studies have shown lower median radiation doses compared to single-cycle studies) 3

Alternative Imaging Options

• Voiding urosonography (VUS) is a useful alternative with comparable sensitivity (80-100%) and specificity (77.5-98%) 2
• Nuclear medicine cystography is recommended by the American Urological Association as an alternative 2
• For comprehensive pelvic floor assessment, MR defecography provides evaluation of all pelvic floor compartments 1

Important Considerations

• Despite published standardized protocols, significant variations exist in how VCUGs are performed across institutions 5
• Key parameters like volume at which reflux occurs remain underreported despite their importance in predicting spontaneous resolution and risk of breakthrough UTIs 4
• Younger children are significantly more likely to have cyclic studies performed, which improves detection of intermittent reflux 3