What are the types and treatment options for perianal fistulas?

Types and Treatment of Perianal Fistulas

The optimal management of perianal fistulas requires classification into simple or complex types, with first-line treatment being a combination of surgical seton placement and medical therapy with anti-TNF agents (preferably infliximab) for most cases. 1

Classification of Perianal Fistulas

• Perianal fistulas are classified as simple or complex according to the American Gastroenterological Association 1:

  • Simple fistulas: Low intersphincteric or trans-sphincteric fistulas with a single external opening
  • Complex fistulas: High intersphincteric, high trans-sphincteric, extrasphincteric, or suprasphincteric fistulas, often with multiple external openings

• Accurate diagnosis requires imaging with MRI or endoanal ultrasound to define fistula anatomy, and endoscopy to assess for active rectal disease 1

Treatment Approach

Initial Management

• Examination under anesthesia should include assessment of the rectal mucosa, as the presence of proctitis is associated with lower rates of fistula healing 2

• The standard of care involves initial seton placement followed by medical therapy, particularly anti-TNF agents 1

Medical Treatment Options

• For simple perianal fistulas: 1

  • First-line: Metronidazole and/or ciprofloxacin
  • Second-line: Azathioprine or mercaptopurine
  • Third-line: Infliximab

• For complex perianal fistulas: 1

  • First-line: Anti-TNF therapy (preferably infliximab) combined with immunomodulators
  • Adjunctive therapy: Antibiotics such as metronidazole and ciprofloxacin

• Infliximab has demonstrated superior efficacy for fistulizing Crohn's disease: 3

  • 68% of patients receiving 5 mg/kg infliximab showed fistula response (≥50% reduction in draining fistulas)
  • Complete closure of all fistulas was achieved in 52% of infliximab-treated patients compared to 13% with placebo

Surgical Treatment Options

• For simple fistulas: Fistulotomy has the highest success rate 1

• For complex fistulas: Non-cutting setons, advancement flaps, and ligation of intersphincteric fistula tract (LIFT) are considered based on fistula characteristics 1

• Commonly performed procedures for perianal Crohn's disease include: 2

  • Removal of draining seton (70.7%)
  • Fistulotomy (57.1%)
  • Advancement flap (38.9%)
  • Fistula plug (36.4%)
  • LIFT procedure (31.8%)

• Video-assisted anal fistula treatment (VAAFT) combined with advancement flap has shown 82% success rate at 9 months in complex fistulizing Crohn's disease 2

Combined Approach

• A combined medical and surgical approach yields better outcomes than either approach alone 4:

  • Complete remission rates: 52% with combination therapy vs. 43% with single therapy
  • Non-response rates: 23% with combination therapy vs. 34% with single therapy

• Careful preparation of the fistula track with curettage to destroy epithelial tissue and ligation of the internal opening should be considered as standard treatment 2

Management of Refractory Cases

• For refractory cases, options include: 1

  • Hyperbaric oxygen therapy
  • Fecal diversion
  • Proctectomy (last resort for severe disease with irreversible perineal destruction)

• Expanded allogeneic adipose-derived stem cells have shown promise for treatment-refractory complex perianal fistulizing Crohn's disease 2

Important Considerations

• Clinical closure does not equal MRI closure, with high risk of recurrence without complete fibrotic tract on MRI 1

• Active luminal disease should be treated concurrently, as perianal fistulas are often associated with active disease elsewhere 1

• Long-term monitoring is essential as perianal fistulas in Crohn's disease have high rates of primary non-healing, surgical morbidity, and recurrence 5

• Maintenance therapy with immunomodulators should be considered after initial response to prevent recurrence 1

• Regular monitoring for development of malignancy in chronic perianal fistula tracts is recommended 1