What is the recommended approach for managing perianal fistulas?

Management of Perianal Fistulas

The recommended approach for managing perianal fistulas involves a combined medical-surgical strategy with classification of fistulas as simple or complex, followed by appropriate targeted interventions based on this classification. 1

Initial Assessment and Classification

• Imaging and Examination:

  • Contrast-enhanced pelvic MRI is the first-line imaging modality for assessment 1
  • Endoscopic anorectal ultrasound (EUS) is a good alternative if rectal stenosis is excluded 1
  • Examination under anesthesia (EUA) by an experienced surgeon is the gold standard for definitive assessment 1
  • Proctosigmoidoscopy should be performed to evaluate concomitant rectal inflammation 1

• Classification:

  • Perianal fistulas are classified as either "simple" or "complex" 1
  • Simple fistulas: Low fistulas involving minimal sphincter muscle
  • Complex fistulas: High fistulas involving significant portions of sphincter, multiple tracts, or associated with rectal inflammation

Management Algorithm

1. For Simple Perianal Fistulas:

• First-line treatment: Seton placement combined with antibiotics (metronidazole and/or ciprofloxacin) 1

• For uncomplicated low anal fistulas: Simple fistulotomy may be considered 1

• For refractory simple fistulas not responding to antibiotics:

  • Second-line therapy: Thiopurines (azathioprine 1.5-2.5 mg/kg/day or mercaptopurine 0.75-1.5 mg/kg/day) 1
  • Alternative: Anti-TNF agents (infliximab or adalimumab) 1

2. For Complex Perianal Fistulas:

• Initial management:

  • Rule out and drain any perianal abscess 1
  • Seton placement after surgical treatment of sepsis 1

• Medical therapy:

  • Treat active luminal Crohn's disease if present 1
  • Anti-TNF therapy (infliximab 5 mg/kg at weeks 0,2, and 6, followed by maintenance every 8 weeks) 1, 2
  • Combine with immunomodulators (azathioprine or mercaptopurine) to reduce immunogenicity and improve efficacy 2

• Surgical options:

  • Chronic seton placement (timing of removal depends on subsequent therapy) 1
  • For selected cases without rectal inflammation: mucosal advancement flap, ligation of intersphincteric fistula tract (LIFT), fibrin glue, fistula plug, or video-assisted anal fistula treatment (VAAFT) 1

Special Considerations

For Rectovaginal Fistulas:

• Fistulotomy should rarely be used due to sphincter injury risk 1
• Treatment options include primary closure, transanal advancement flap, sleeve advancement flap, or transvaginal advancement flap 1
• Success rates for these procedures range from 50% to 100% 1

Monitoring Treatment Response:

• Clinical assessment (decreased drainage) is usually sufficient for routine practice 1
• MRI or anal endosonography combined with clinical assessment can evaluate improvement of fistula track inflammation 1

Common Pitfalls and Caveats

1. Never excise perianal skin tags in Crohn's disease as this can lead to chronic, non-healing ulcers 1

2. Avoid simple hemorrhoidectomy in patients with Crohn's disease due to high risk of complications including poor wound healing and anorectal stenosis 1

3. Ensure drainage of any abscess before anti-TNF therapy to prevent overwhelming septicemia 2

4. Recognize that maintenance therapy is essential for sustained fistula closure, with most patients requiring long-term treatment 2

5. Consider that more than two-thirds of patients have an abscess associated with their fistula that must be drained before any definitive intervention 1

6. Be aware that temporary diverting ileostomy or colostomy is now rarely performed as most patients never have intestinal continuity restored 1

By following this structured approach to perianal fistula management, clinicians can optimize outcomes while minimizing morbidity and preserving quality of life for patients with this challenging condition.