What is the recommended management for a seton fistula?

Management of Seton Fistulas

Seton placement in combination with antibiotics (metronidazole and/or ciprofloxacin) is the preferred strategy for managing symptomatic perianal fistulas, with loose seton placement recommended for complex fistulas after drainage of any associated abscess. 1

Initial Assessment and Classification

Before determining the appropriate management strategy, proper evaluation is essential:

1. Imaging: Contrast-enhanced pelvic MRI is the initial procedure of choice for assessment of perianal fistulas 1

   • Endoscopic anorectal ultrasound is a good alternative if rectal stenosis is excluded
   • Examination under anesthesia (EUA) remains the gold standard for definitive assessment

2. Proctosigmoidoscopy: Should be performed to assess for concomitant rectosigmoid inflammation, which has prognostic and therapeutic relevance 1

3. Classification: Fistulas are generally categorized as either:

   • Simple: Superficial, low intersphincteric or low transsphincteric fistulas
   • Complex: High transsphincteric, extrasphincteric, or multiple tracts

Management Algorithm

Step 1: Rule Out and Treat Abscess

• Any perianal abscess must be drained before considering other interventions 1
• More than two-thirds of patients have an abscess associated with their fistula

Step 2: Initial Management Based on Fistula Type

For Simple Fistulas:

• First-line: Seton placement + antibiotics (metronidazole and/or ciprofloxacin) 1
• For uncomplicated low anal fistulas only: Simple fistulotomy may be considered 1

For Complex Fistulas:

• First-line: Loose seton placement after drainage of any sepsis 1
• Setons allow inflammation around the tract to subside and prevent recurrence of abscesses

Step 3: Maintenance Therapy

• Medical therapy options: Thiopurines, infliximab, adalimumab, or combination of drainage and medical therapy 1
• Seton management:
  • For simple fistulas: Setons may be removed once drainage has improved
  • For complex fistulas: Timing of removal depends on subsequent therapy 1
  • Some patients benefit from long-term seton placement, with studies showing 73.7% complete symptom resolution and 18.4% significant improvement with this approach alone 2

Step 4: Treatment of Refractory Cases

• Patients not responding to antibiotics may require second-line therapy with thiopurines or anti-TNFs 1
• For those refractory to medical treatment, consider:
  • Alternative surgical approaches (mucosal advancement flap, LIFT procedure)
  • Diverting ostomy in severe cases
  • Proctectomy as last resort 1

Specific Considerations

1. Seton types and techniques:

   • Non-cutting/loose setons: Used primarily for drainage and to prevent abscess formation
   • Cutting setons: May be used in select cases but carry higher risk of incontinence

2. Duration of seton placement:

   • Average time to seton removal ranges from 9-36 weeks across studies 3, 2
   • Long-term placement may be appropriate for some patients, with one study showing 97.6% healing rate with staged cutting seton approach 4

3. Antibiotic therapy:

   • Ciprofloxacin appears to be better tolerated than metronidazole 5
   • Typically used for 10-12 weeks in conjunction with seton placement

4. Monitoring response:

   • Clinical assessment (decreased drainage) is usually sufficient 1
   • MRI or anal endosonography can be used to evaluate improvement of fistula track inflammation

Pitfalls and Caveats

1. Avoid premature seton removal as this may lead to recurrence of abscess formation

2. Do not treat perianal skin tags surgically as this can lead to chronic, non-healing ulcers 1

3. Recognize that concomitant luminal disease affects outcomes - active luminal Crohn's disease should be treated concurrently for optimal results 1

4. Monitor for incontinence - while generally well-tolerated, some degree of incontinence to flatus (up to 15.6%) may occur with seton treatment 4

5. Be aware that additional procedures may be needed - approximately 27.6% of patients may require additional operative procedures to unroof collections or replace setons 2