What is the management of an anal fistula with a seton in situ?

Management of Anal Fistula with Seton in Situ

An anal fistula with a seton in situ is an abnormal tunnel between the anal canal and perianal skin with a surgical thread or silastic drain placed to maintain drainage and prevent abscess formation while awaiting definitive treatment or as a long-term management strategy. 1

What is an Anal Fistula?

An anal fistula is an abnormal connection between the anal canal and the perianal skin. It typically develops following an anorectal abscess and creates a tract that allows persistent drainage of infectious material.

Types of Anal Fistulas:

• Simple fistulas: Subcutaneous or low intersphincteric/trans-sphincteric
• Complex fistulas: High trans-sphincteric, suprasphincteric, extrasphincteric, or multiple tracts

Role of Setons in Fistula Management

A seton is a thread-like material (usually silastic, rubber band, or surgical suture) that is placed through the fistula tract to:

1. Maintain drainage: Prevents abscess formation by keeping the tract open
2. Allow inflammation to subside: Reduces surrounding tissue inflammation
3. Facilitate later definitive treatment: Prepares the tract for subsequent surgical closure
4. Serve as definitive treatment: In some cases, particularly in Crohn's disease

Types of Setons:

• Loose/draining setons: Non-cutting setons that maintain drainage without cutting through tissue
• Cutting setons: Gradually cut through the sphincter (NOT recommended due to high risk of incontinence) 1

Management Approach

Initial Management:

1. Drainage of sepsis: Before any treatment, any abscess must be drained using loose setons 1
2. Seton placement: Loose, fine, silastic setons are most commonly used to establish drainage and prevent recurrent abscesses 1

Definitive Management Options:

1. Fistulotomy: For superficial, subcutaneous, or low fistulas (lower third of anal sphincter) 1

   • Contraindicated for anterior fistulas in women due to high risk of incontinence 1

2. Long-term seton drainage:

   • May be definitive treatment when combined with medical therapy 1
   • Setons can be removed in up to 98% of cases at a median of 33 weeks 1
   • Studies show 73.7-78% complete symptom resolution with seton alone 2

3. Endorectal advancement flap:

   • For high fistulas (upper two-thirds of sphincter complex)
   • Success rates of approximately 64% in Crohn's disease 1

4. Combined approaches:

   • Seton drainage with medical therapy (anti-TNF agents) shows improved healing rates compared to either therapy alone 1

Special Considerations for Crohn's Disease:

1. Medical therapy: Thiopurines, infliximab, or adalimumab should be used as maintenance therapy 1
2. Timing of seton removal: Best done after completion of anti-TNF induction phase and resolution of proctitis 1
3. Refractory cases: Consider diverting ostomy, with proctectomy as last resort 1

Outcomes and Prognosis

• Success rates:

  • Long-term seton drainage alone: 73.7-78% complete symptom resolution 2
  • Combined with medical therapy: Higher success rates

• Recurrence rates:

  • 7.1-8% with seton treatment alone 2
  • Higher in Crohn's disease (39%) 3

• Incontinence risk:

  • Loose setons: Minimal risk of incontinence (26-36%) 3
  • Cutting setons: High risk (54-57%) - therefore NOT recommended 1, 3

Common Pitfalls and Caveats

1. Avoid cutting setons: These can result in keyhole deformity and fecal incontinence 1

2. Avoid fistulotomy in anterior fistulas in women: High risk of incontinence 1

3. Optimal timing for seton removal: If removed too early, risk of recurrent abscess; if left too long, tract may epithelialize and not close 1

4. Concomitant proctitis: Must be treated medically before any definitive surgical treatment 1

5. Asymptomatic fistulas: May not require surgical intervention, especially low anal-introital fistulas 1

In conclusion, management of anal fistulas with setons requires a strategic approach that balances drainage of infection, preservation of continence, and definitive closure of the fistula tract. Loose setons are effective both as a bridge to definitive treatment and as a long-term management strategy, particularly in complex cases and Crohn's disease.