What is the recommended approach for examining and managing a fistula?

Recommended Approach for Examining and Managing a Fistula

MRI is the most accurate imaging modality for diagnosis and classification of fistulae and should be the first-line diagnostic test for comprehensive assessment of fistula anatomy. 1, 2

Initial Assessment

Physical Examination

• Perform complete physical assessment of the fistula and document findings 1
• Evaluate for:
  • Swelling of surrounding area
  • Presence of collateral veins
  • Characteristics of discharge
  • External opening location
  • Induration along suspected tract
  • Signs of local inflammation or abscess formation

Diagnostic Imaging

1. MRI with IV contrast (preferred first-line):

   • Sensitivity 81-100%, specificity 67-100% 2
   • Best for visualizing complete fistula anatomy, extensions, and abscesses 1
   • Use multichannel phased array body coil rather than endoanal coil for better visualization of extent 1
   • Essential sequences: T2-weighted with fat suppression, T1-weighted with IV contrast, diffusion-weighted imaging 2

2. Transrectal/Endoanal Ultrasound (alternative):

   • Reasonable alternative when MRI unavailable or contraindicated 2
   • Sensitivity 87-92%, specificity 43-64% 2
   • Superior to clinical examination but inferior to MRI for complex or deep-seated fistulae 1

3. Examination Under Anesthesia (EUA):

   • Complements imaging findings
   • Provides opportunity for both staging and initial treatment 1
   • Combining MRI with EUA improves diagnostic accuracy 1

Classification of Fistulae

Based on imaging and examination findings, classify fistula as:

• Simple vs. complex
• Low vs. high
• Anatomical type:
  • Intersphincteric
  • Transsphincteric
  • Suprasphincteric
  • Extrasphincteric

Management Approach

Step 1: Control Sepsis

• Drain any abscesses immediately 3
• Place non-cutting seton for complex fistulae to establish drainage 1, 3

Step 2: Determine Underlying Cause

• Evaluate for inflammatory bowel disease (especially Crohn's disease)
• Consider malignancy, radiation injury, or other causes
• For Crohn's disease-related fistulae:
  • Induce remission of intestinal disease before definitive repair 3
  • Assess rectal inflammation with endoscopy 1

Step 3: Definitive Management

Based on fistula classification:

1. Simple Fistulae:

   • Fistulotomy - laying open the tract 4
   • Appropriate for low intersphincteric and low transsphincteric fistulae

2. Complex Fistulae:

   • Consider temporary stoma diversion for large, recurrent, or irradiated fistulae 3
   • Surgical options:
     • Fistulectomy with primary closure
     • Advancement flap repair
     • LIFT procedure (ligation of intersphincteric fistula tract)
     • Fibrin glue injection or bioprosthetic plug insertion 4
     • For post-radiation or recurrent fistulae: interposition of well-vascularized tissue (e.g., gracilis muscle flap) 3

Step 4: Follow-up and Monitoring

• Regular clinical assessment
• Repeat imaging (MRI preferred) to confirm healing before stoma reversal if applicable 3
• Monitor for recurrence

Special Considerations

Perianal Crohn's Disease Fistulae

• MRI is strongly preferred for comprehensive assessment 2
• Assess rectal inflammation with endoscopy 1
• Medical therapy (anti-TNF agents) often needed in conjunction with surgical drainage 1
• Reassess with clinical evaluation plus MRI and endoscopic examination of rectum 1

Common Pitfalls to Avoid

• Relying solely on clinical examination (may miss 25-40% of extensions) 2
• Failing to use IV contrast with MRI (limits visualization of active inflammation) 2
• Missing supralevator extensions (better visualized with MRI than ultrasound) 2
• Attempting definitive repair before controlling sepsis or underlying disease 3
• Performing fistulotomy on high or complex fistulae (risk of incontinence) 4

By following this systematic approach to fistula examination and management, clinicians can optimize outcomes while minimizing complications such as recurrence and incontinence.