What are the treatment options for an anal fistula?

Treatment of Anal Fistula

For simple, low anal fistulas (subcutaneous, superficial, or low intersphincteric), fistulotomy is the definitive treatment with healing rates approaching 100%, while complex fistulas involving significant sphincter muscle require sphincter-preserving techniques such as loose seton drainage combined with medical therapy. 1

Initial Assessment Requirements

Before any definitive treatment, you must:

• Perform examination under anesthesia (EUA) to accurately define fistula anatomy and rule out abscess 1, 2
• Obtain contrast-enhanced pelvic MRI as the initial imaging procedure (or endoscopic anorectal ultrasound if rectal stenosis is excluded) 1, 2
• Perform proctosigmoidoscopy to evaluate for concomitant rectal inflammation, which critically affects treatment decisions and prognosis 1, 2
• Drain any associated abscess first - more than two-thirds of patients with fistulas have an abscess that must be drained before definitive intervention 2

Treatment Algorithm Based on Fistula Anatomy

Simple Low Fistulas (Subcutaneous, Superficial, Low Intersphincteric)

Perform fistulotomy (laying open the tract) as the procedure of choice, with healing rates approaching 100% 1, 3. This involves:

• Laying open the primary tract and any side tracts 4
• Debridement with or without marsupialisation 4
• Marsupialization after fistulotomy reduces bleeding and allows faster healing 5

Complex Fistulas (Involving Sphincter Muscle)

Place a loose, non-cutting seton as the primary treatment 4, 1. The seton:

• Establishes drainage and prevents abscess formation 4
• Allows inflammation to subside 4
• May serve as definitive treatment when combined with medical therapy, with seton removal in up to 98% at median 33 weeks 4

After inflammation control, consider sphincter-preserving techniques:

• Ligation of intersphincteric fistula tract (LIFT): Success rates of 53% in Crohn's disease, 77% in cryptoglandular fistulas 1
• Advancement flap: Success rates of 61-66% in Crohn's disease patients, 64-80% overall 4, 1
• Fistula plug or fibrin glue: Variable success rates (24-88% for plug, 14-74% for glue) 6

Absolute Contraindications to Fistulotomy

Never perform fistulotomy in these situations:

• Active proctitis or rectosigmoid inflammation 1, 2
• Crohn's Disease Activity Index >150 4, 1
• Evidence of perineal Crohn's disease involvement 4, 1
• Anterior fistulas in female patients - high risk of incontinence due to short anterior sphincter 4, 1
• Complex fistulas involving significant sphincter muscle 4

Critical Pitfalls to Avoid

• Never use cutting setons - they result in incontinence rates up to 57% and keyhole deformity 4, 1
• Never probe aggressively for fistula tracts during initial examination - this creates iatrogenic complexity 4, 1
• Never perform fistulotomy at time of acute abscess drainage if sphincter muscle is involved - place a loose seton instead 4
• Never excise concomitant perianal skin tags - this leads to chronic non-healing ulcers 4, 2

Special Considerations for Crohn's Disease

For Crohn's-related fistulas, treatment requires a combined approach:

• Control sepsis first with loose seton placement 2
• Initiate medical therapy: Antibiotics (metronidazole and/or ciprofloxacin) combined with seton drainage 2
• Maintenance therapy: Thiopurines, infliximab, or adalimumab 4, 2
• Seton removal timing: Keep seton in place until at least the induction phase of anti-TNF therapy is completed (approximately one month) 4
• Definitive surgery only after inflammation is medically controlled 2

Timing of Definitive Treatment

• For simple fistulas without proctitis: Immediate fistulotomy is appropriate 1
• For complex fistulas or those with proctitis: Maintain seton drainage until inflammation resolves, then consider sphincter-preserving techniques 1, 2
• Monitor clinically for decreased drainage; MRI or endosonography combined with clinical assessment evaluates tract inflammation improvement 1