What are the best imaging and physical exam tests for suspected enterovesicular fistula (abnormal connection between the intestine and bladder) or complex fistula?

Best Imaging and Physical Exam Tests for Suspected Enterovesical Fistula

For suspected enterovesical fistula, CT with intravenous contrast is the preferred initial imaging modality due to its high sensitivity (76.5%) for fistula detection and excellent ability (94.1%) to define the underlying etiology. 1

Physical Examination Findings

When performing a physical examination for suspected enterovesical or complex fistula:

• Vaginal examination: Check for presence of fecal material in the vagina, which is a direct sign of a fistula
• Rectal examination: Look for tender, indurated areas above the anorectal ring
• Perineal inspection: Check for surgical scars, anorectal deformities, or external openings of fistulas 1
• Urinalysis: Order for evidence of fecal material in urine

Key Clinical Symptoms to Document

• Pneumaturia (air in urine) - present in 75% of cases 2
• Fecaluria (fecal material in urine) - present in 63% of cases 2
• Recurrent urinary tract infections - present in 57-73% of cases 3, 2
• Passage of urine through rectum (in some cases) 3

Diagnostic Algorithm

First-line Investigations:

1. CT with intravenous contrast:

   • Highest diagnostic yield for enterovesical fistulas 1
   • Can identify both the fistula and underlying etiology
   • Findings include: intravesical air (90%), focal bladder wall thickening (90%), thickening of adjacent bowel wall (85%), and extraluminal mass often containing air (75%) 4
   • Add rectal or oral contrast with delayed scanning to better detect enterovesical fistulas 1

2. Cystoscopy:

   • High detection rate (89%) for enterovesical fistulas 2
   • Direct visualization of the fistula opening in the bladder

Second-line Investigations:

1. MRI with intravenous contrast:

   • Excellent soft-tissue contrast for evaluating vesicovaginal and enterovesicular fistulae 1
   • Particularly useful for complex fistulas or when CT is inconclusive
   • May alter surgical management in up to 15% of patients 1

2. Cystography:

   • High detection rate (90%) for enterovesical fistulas 1
   • CT cystography has largely replaced fluoroscopic cystography 1

3. Contrast Enema:

   • Lower sensitivity (34-75%) compared to other modalities 1, 3
   • Use water-soluble contrast rather than barium if performed 1
   • CT is preferred over contrast enema for suspected enterovesical fistulas 1

4. Urine Cytology:

   • Check for fecal material in urine (86% positivity rate) 2

Location-Based Findings

• Fistulas secondary to diverticulitis, rectosigmoid neoplasms, or uterine tumors typically involve the left and/or posterior aspects of the bladder 4
• Fistulas from Crohn's disease of the terminal ileum or cecal lesions typically involve the right lateral or anterior aspects of the bladder 4

Common Pitfalls to Avoid

• Relying solely on conventional fistulography, which has accuracy as low as 16% 1
• Failing to consider the underlying etiology (diverticulitis is most common, followed by malignancy) 5
• Not performing cystoscopy, which has a high detection rate for enterovesical fistulas 2
• Using barium instead of water-soluble contrast if performing contrast studies, as barium can cause streak artifacts on subsequent CT scans 1

By following this diagnostic approach, you can efficiently diagnose enterovesical fistulas and guide appropriate management decisions to improve patient outcomes.