What are the types of perianal fistulas and their management options?

Types of Perianal Fistulas and Their Management

Perianal fistulas are classified according to their anatomical course in relation to the anal sphincter complex, with treatment strategies varying based on the type of fistula, presence of complications, and underlying conditions such as Crohn's disease. 1

Anatomical Classification of Perianal Fistulas

The Parks classification system uses the external sphincter as the central point of reference:

1. Superficial fistulas (low):

   • Located beneath the anal mucosa without crossing any sphincter muscle
   • Least complex type

2. Intersphincteric fistulas (low or high):

   • Tract penetrates the internal sphincter and runs through the intersphincteric space to the perianal skin
   • Can be further classified as low or high depending on location

3. Transsphincteric fistulas (low or high):

   • Tract penetrates both internal and external sphincters or the puborectal muscle
   • Low: runs through lower one-third of external anal sphincter
   • High: runs through upper two-thirds of external anal sphincter

4. Suprasphincteric fistulas (high):

   • Tract runs upward in the intersphincteric space, then downward crossing the levator ani muscle to reach perianal skin

5. Extrasphincteric fistulas (high):

   • Tract originates from rectal wall and runs down through levator ani muscle without penetrating the sphincter complex 1, 2

Clinical Classification

For practical management purposes, fistulas are also classified as:

Simple Fistulas

• Low origin (superficial, low intersphincteric, or low transsphincteric)
• Single external opening
• No pain or fluctuation suggesting abscess
• No rectovaginal component
• No anorectal stricture
• May still be complicated by active rectal disease

Complex Fistulas

• High origin (high intersphincteric, high transsphincteric, extrasphincteric, or suprasphincteric)
• May have multiple external openings
• Often associated with perianal abscess
• May include rectovaginal fistula
• May have anorectal stricture
• Often associated with active rectal disease 1, 2

Diagnostic Approach

Accurate diagnosis requires:

1. Physical examination: Initial assessment but may miss deep or complex fistulas
2. Endoscopic evaluation: To assess for rectal inflammation, especially in suspected Crohn's disease
3. Advanced imaging:
   • Examination under anesthesia (EUA) - approximately 90% accuracy
   • MRI with phased-array or endoanal coils
   • Endoanal ultrasound
   • CT with IV contrast for suspected abscesses 1, 2

Management Strategies

General Principles

• Drainage of sepsis is always first-line therapy before initiating immunosuppressive treatment
• Treatment approach must balance fistula healing with preservation of continence
• Presence of proctitis significantly affects management decisions and prognosis 1

Management Based on Fistula Type

Simple Fistulas

• Fistulotomy: Primary treatment for non-Crohn's simple fistulas
• Antibiotics: Often used as adjunctive therapy

Complex Fistulas

• Seton placement: To facilitate drainage and prevent abscess formation
• Medical therapy: Particularly important for Crohn's disease-related fistulas
  • Anti-TNF agents (infliximab has best documentation)
  • Antibiotics and thiopurines as adjunctive treatments
  • Oral tacrolimus for patients failing anti-TNF therapy
• Advanced surgical techniques for selected cases:
  • Fistula plug insertion
  • Video-assisted ablation
  • Stem cell therapy 1, 2, 3

Special Considerations for Crohn's Disease

• Mucosal healing is the primary goal in the presence of proctitis
• Definitive surgical repair should only be considered in the absence of luminal inflammation
• Multidisciplinary approach combining surgical and medical management is essential
• Long-term remission rates remain suboptimal (approximately 50%) 1, 3

Complications and Monitoring

• Recurrent complex fistulas without obvious cause should raise suspicion for underlying Crohn's disease
• Malignancy can develop in chronic fistulas, particularly in Crohn's disease, requiring vigilant monitoring
• Despite optimal management, complex perianal fistulas often persist with low rates of complete closure 2

Important Pitfalls to Avoid

1. Failing to drain abscesses before initiating immunosuppressive therapy
2. Aggressive surgical approaches in active Crohn's disease that may worsen sphincter function
3. Overlooking rectal inflammation when planning treatment
4. Neglecting to monitor chronic fistulas for malignant transformation
5. Underestimating the impact of complex fistulas on quality of life and need for long-term follow-up

The management of perianal fistulas requires careful assessment of fistula anatomy, underlying causes, and presence of complications to develop an appropriate treatment strategy that addresses both symptom control and preservation of anal function.