What is the minimum volume of contrast injected to rule out bladder perforation?

Minimum Volume of Contrast for Cystography to Rule Out Bladder Perforation

A minimum of 300 mL of contrast should be instilled during retrograde cystography to rule out bladder perforation, or until the patient reaches tolerance to maximally distend the bladder. 1

Proper Technique for Retrograde Cystography

Retrograde cystography is the diagnostic technique of choice for evaluating suspected bladder injuries with high accuracy for detecting bladder rupture. The procedure can be performed using either plain film or CT imaging:

• For plain film cystography:

  • Retrograde, gravity filling of the bladder with contrast 1
  • Minimum volume of 300 mL or until patient reaches tolerance 1
  • At least two views required: one at maximal fill and one after bladder drainage 1
  • Additional oblique views may provide more information but aren't mandatory 1

• For CT cystography:

  • Similar technique using dilute water-soluble contrast to prevent artifacts 1
  • Minimum volume of 300 mL or until patient reaches tolerance 1
  • Provides excellent sensitivity (95-100%) and specificity (99-100%) for bladder rupture 2, 3

Important Technical Considerations

• Simply clamping a Foley catheter to allow excreted IV contrast to accumulate in the bladder is not appropriate as this technique will not provide adequate bladder distention and results in missed bladder injuries 1

• For male patients with suspected urethral injury, the recommended examination is retrograde urethrocystogram with contrast CT-scan 1:

  • Introduce urinary catheter in anterior urethra
  • Inflate cuff to only 1-2 mL
  • Allow opacification with contrast agent up to 350 mL 1

• Water-soluble contrast is preferred over barium to avoid complications if contrast spills into the peritoneal cavity 1

Clinical Indications for Cystography

Retrograde cystography should be performed in:

• Stable patients with gross hematuria and pelvic fracture (Standard; Evidence Strength: Grade B) 1
• Stable patients with gross hematuria and a mechanism concerning for bladder injury 1
• Patients with pelvic ring fractures and clinical indicators of bladder rupture 1
• Patients with clinical symptoms of lower urinary tract injury before attempting urinary catheterization in men 1

Clinical Indicators of Bladder Rupture

• Inability to void 1
• Gross hematuria 1
• Low urine output 1
• Increased BUN and creatinine (from peritoneal absorption of urine) 1
• Abdominal distention 1
• Suprapubic pain 1
• Low density free intraperitoneal fluid on abdominal imaging (urinary ascites) 1

Management Based on Findings

• Intraperitoneal bladder ruptures must be surgically repaired (Standard; Evidence Strength: Grade B) 1
• Uncomplicated extraperitoneal bladder injuries can be managed with catheter drainage alone 1
• Complicated extraperitoneal bladder ruptures (large injuries, bladder neck injuries, or those with concurrent rectal/vaginal injury) should be surgically repaired 1

Pitfalls to Avoid

• Inadequate bladder filling (less than 300 mL) may lead to false-negative results 1, 4
• Relying on passive accumulation of IV contrast in the bladder without active retrograde filling 1
• Failing to obtain post-drainage images, which are essential for complete evaluation 1
• Missing bladder perforations that may not show contrast extravasation but present with pneumoperitoneum or moderate/large ascites 5

Remember that asymptomatic perforations of the bladder wall occur frequently and may not be noticed by the surgeon during procedures such as transurethral resection of bladder tumors 4. Therefore, proper technique with adequate bladder distention is crucial for accurate diagnosis.