Treatment of Anal Fistula
For simple low intersphincteric or low transsphincteric fistulas without proctitis, perform fistulotomy immediately with healing rates approaching 100%; for complex fistulas involving significant sphincter muscle, place a loose non-cutting seton as primary treatment. 1
Mandatory Pre-Treatment Assessment
Before any definitive intervention, complete the following evaluation:
- Perform examination under anesthesia (EUA) to accurately define fistula anatomy and rule out abscess—this is the gold standard assessment 1, 2
- Obtain contrast-enhanced pelvic MRI as initial imaging, 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 requiring drainage before definitive intervention 1
Treatment Algorithm Based on Fistula Complexity
Simple Low Fistulas (Intersphincteric or Low Transsphincteric)
Perform fistulotomy by laying open the primary tract and any side tracts, with healing rates approaching 100% 1, 2, 3
- This is the procedure of choice for uncomplicated intersphincteric fistula with external opening into perianal skin, provided there is no active proctitis and preserved sphincter function 2
- Fistulotomy is considered the most effective treatment and is relatively safe for simple and most distal fistulae 3, 4
Complex Fistulas (High Transsphincteric, Suprasphincteric, Extrasphincteric)
Place a loose, non-cutting seton as primary treatment to establish drainage and prevent abscess formation, with success rates up to 98% 1, 2
- After inflammation resolves with seton drainage, consider sphincter-preserving techniques 1
- Ligation of intersphincteric fistula tract (LIFT) has success rates of 77% in cryptoglandular fistulas and 53% in Crohn's disease 1, 3
- Advancement flap has success rates of 64-80% overall and 61-66% in Crohn's disease patients, requiring single internal opening, no proctitis, and no anal stenosis 1, 2, 3
Absolute Contraindications to Fistulotomy
Never perform fistulotomy in the following scenarios:
- Active proctitis or rectosigmoid inflammation present 1, 2
- Crohn's Disease Activity Index >150 1, 2
- Evidence of perineal Crohn's disease involvement 1, 2
- Anterior fistulas in female patients (high incontinence risk) 1, 2
Special Management for Crohn's Disease-Related Fistulas
Control sepsis first with loose seton placement, then initiate medical therapy:
- Place seton for drainage and maintain until at least the induction phase of anti-TNF therapy is completed (approximately one month) 1
- Initiate infliximab or adalimumab once sepsis is controlled—this is the most effective medical therapy for complex perianal fistulizing Crohn's disease 1, 5
- Combine anti-TNF therapy with thiopurines for enhanced efficacy in complex disease 1, 2, 5
- Start antibiotics (metronidazole and/or ciprofloxacin) with seton drainage 2, 5
For severe refractory Crohn's disease with complex perianal fistula and malnutrition, consider temporary diverting ileostomy to allow control of luminal disease and promote fistula healing 5
Critical Pitfalls to Avoid
- Never use cutting setons—they result in incontinence rates up to 57% and keyhole deformity 1, 2
- Never probe aggressively for fistula tracts during initial examination, as this creates iatrogenic complexity 1, 2, 5
- Never perform fistulotomy in Crohn's disease—this leads to poor healing and potential incontinence 5
- Never attempt definitive fistula closure procedures in the presence of active proctitis 5
Timing Considerations
- 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
- For Crohn's disease: keep seton in place long-term while on maintenance anti-TNF therapy 5