What is the initial approach to managing perianal fistulas?

Initial Management of Perianal Fistulas

The initial approach to managing perianal fistulas should include contrast-enhanced pelvic MRI for assessment, followed by examination under anesthesia (EUA) for definitive diagnosis, with concurrent drainage of any abscesses and placement of setons for complex fistulas, combined with appropriate antibiotic therapy. 1, 2

Diagnostic Approach

• Contrast-enhanced pelvic MRI is considered the initial imaging procedure of choice for assessment of perianal fistulas, with endoscopic anorectal ultrasound (EUS) being a good alternative if rectal stenosis is excluded 1
• Proctosigmoidoscopy should be routinely performed during initial evaluation to assess for concomitant rectosigmoid inflammation, which has significant prognostic and therapeutic implications 1, 2
• Examination under anesthesia (EUA) is considered the gold standard for definitive diagnosis and classification of perianal fistulas when performed by an experienced surgeon 1
• Fistulas are typically classified as either "simple" or "complex" in clinical practice, which guides treatment decisions 1, 2

Initial Management Strategy

For Simple Perianal Fistulas:

• Rule out perianal abscess and drain if present before any definitive treatment 1, 3
• For uncomplicated low anal fistulas, simple fistulotomy may be considered as initial surgical management 1, 4
• First-line medical treatment includes antibiotics (metronidazole 400 mg three times daily and/or ciprofloxacin 500 mg twice daily) 1, 2
• Seton placement in combination with antibiotics is the preferred initial strategy for symptomatic simple perianal fistulas 1, 2

For Complex Perianal Fistulas:

• Imaging before surgical drainage is strongly recommended 1
• EUA for surgical drainage of sepsis is mandatory, with abscess drainage and loose seton placement as the initial step 1, 5
• Seton placement after surgical treatment of sepsis is recommended, with timing of removal dependent on subsequent therapy 1, 2
• Active luminal Crohn's disease, if present, should be treated concurrently with appropriate management of fistulas 1, 2

Second-Line Treatment Options

• For simple fistulas not responding to antibiotics, thiopurines (azathioprine 1.5-2.5 mg/kg/day or mercaptopurine 0.75-1.5 mg/kg/day) or anti-TNF agents can be used as second-line therapy 1
• For complex fistulas, anti-TNF therapy (particularly infliximab) combined with immunomodulators is considered first-line medical treatment after surgical drainage and seton placement 1, 2
• The most commonly used surgical techniques for persistent fistulas include simple fistulotomy, chronic seton, mucosal advancement flap, ligation of intersphincteric fistula tract (LIFT), fibrin glue, fistula plug, and video-assisted anal fistula treatment (VAAFT) 1, 6

Monitoring Response to Treatment

• In routine practice, clinical assessment (decreased drainage) is usually sufficient to evaluate response to treatment 1
• MRI or anal endosonography in combination with clinical assessment is recommended to evaluate improvement of fistula track inflammation 1, 2
• It's important to note that clinical closure does not always equal MRI closure, with high risk of recurrence without complete fibrotic tract on MRI 2

Treatment Challenges and Considerations

• Despite combined medical-surgical approaches, long-term remission rates for perianal fistulas may be as low as 50% 6, 7
• Complex perianal fistulas often require a multidisciplinary approach with both surgical and medical management for optimal outcomes 2, 7
• Monitoring for development of malignancy in chronic perianal fistula tracts is recommended as a long-term consideration 2