What is the best course of treatment for a patient with a complex fistula in ano?

Treatment of Complex Fistula-in-Ano

For complex fistula-in-ano, initial management requires loose seton placement after drainage of any associated abscess, followed by sphincter-sparing procedures (such as LIFT or advancement flap) once inflammation is controlled, with fistulotomy reserved only for simple, low-lying tracts that do not involve significant sphincter muscle. 1, 2

Initial Assessment and Imaging

Diagnostic workup must include:

• MRI of the pelvis as the initial imaging procedure to define fistula anatomy and identify occult abscesses 3
• Examination under anesthesia (EUA) by an experienced surgeon, which remains the gold standard for assessment 3
• Proctosigmoidoscopy to evaluate for concomitant rectal inflammation, particularly to exclude Crohn's disease 3
• Endoanal ultrasound as an alternative if rectal stenosis is excluded, though MRI combined with EUA provides the highest diagnostic accuracy 3

Critical pitfall: CT scan has poor spatial resolution in the pelvis (only 24% accuracy for fistula classification) and should be reserved for acute presentations when MRI is unavailable 3

Surgical Management Algorithm

Step 1: Abscess Drainage (If Present)

• More than two-thirds of complex fistulas have an associated abscess that must be drained before definitive intervention 3
• Perform emergent drainage if sepsis, immunosuppression, diabetes, or diffuse cellulitis is present 3, 1
• Never probe for fistulas during acute abscess drainage to prevent iatrogenic tract creation 2, 4

Step 2: Seton Placement

• Place a loose draining seton for all complex fistulas (high transsphincteric, suprasphincteric, or those involving significant sphincter muscle) 1, 2, 5
• Seton placement was the most common surgical technique in specialized units, used in 62% of cases, with successful primary tract eradication in 61% of patients 6
• The seton establishes drainage, prevents abscess recurrence, and allows time for medical optimization 2

Step 3: Medical Therapy Optimization

• Initiate antibiotics (metronidazole and/or ciprofloxacin) in combination with seton drainage 3
• For refractory disease, add thiopurines or anti-TNF therapy (infliximab or adalimumab) as second-line treatment 3
• Medical therapy to control inflammation is imperative before attempting definitive surgical closure 3

Step 4: Definitive Sphincter-Sparing Procedure

Once inflammation is controlled and drainage is adequate:

• Ligation of intersphincteric fistula tract (LIFT) 3, 2
• Mucosal advancement flap 3
• Video-assisted anal fistula treatment (VAAFT) 3

The timing of seton removal depends on subsequent therapy and degree of inflammation control 3

Special Considerations for Crohn's Disease

Complex and multifocal fistulas are more common in Crohn's disease, occurring in 13-27% of patients 3:

• Exclude underlying Crohn's disease in every patient, especially with recurrent abscesses 3
• Never surgically treat concomitant perianal skin tags in Crohn's patients, as this leads to chronic non-healing ulcers 3, 2
• Maintenance therapy with thiopurines, infliximab, or adalimumab combined with seton drainage is required after surgery 3, 2
• For refractory cases, consider diverting ostomy, with proctectomy as the last resort 3

What NOT to Do

Fistulotomy is contraindicated for complex fistulas involving significant sphincter muscle due to high incontinence risk 1, 2. Fistulotomy should only be considered for:

• Subcutaneous or superficial tracts 2
• Low intersphincteric fistulas in the lower third of the anal sphincter 2
• Strictly selected low-lying transsphincteric fistulas in Crohn's patients after careful evaluation 5

Antibiotic Therapy

• Antibiotics are not routinely indicated for adequately drained abscesses in immunocompetent patients 4
• Administer empiric broad-spectrum coverage (Gram-positive, Gram-negative, and anaerobes) if sepsis or immunocompromise is present 4
• For perianal fistulas, metronidazole and/or ciprofloxacin are the preferred antibiotics 3

Outcomes and Follow-up

• Clinical assessment (decreased drainage) is usually sufficient for routine monitoring 3
• MRI or endoanal ultrasound combined with clinical assessment is recommended to evaluate fistula tract inflammation improvement 3
• Minor incontinence rates range from 2.4% to 6% with appropriate surgical technique, with major incontinence occurring in only 1.3% of cases 6
• Recurrence risk after drainage alone can be as high as 44%, emphasizing the need for complete drainage and appropriate definitive management 1