Management of Low Anal Fistula
For a low anal fistula, fistulotomy (laying open the tract) is the definitive treatment of choice, offering healing rates exceeding 95% with minimal recurrence. 1, 2
Initial Assessment
Before proceeding with treatment, you must determine:
- Fistula complexity: Low fistulas involve minimal sphincter muscle (subcutaneous, superficial, or lower third intersphincteric tracts), while complex fistulas involve significant sphincter or have associated features like rectal inflammation, multiple tracts, or Crohn's disease 1, 3
- Presence of abscess: Rule out concurrent perianal abscess, which requires immediate drainage before definitive fistula treatment 3, 4
- Underlying disease: Off-midline fistulas mandate evaluation for Crohn's disease, HIV/AIDS, tuberculosis, or malignancy 3
- Rectal inflammation status: In Crohn's patients, proctosigmoidoscopy is essential since active proctocolitis changes the surgical approach 3
Definitive Treatment for Low Fistulas
Non-Crohn's Patients
Perform fistulotomy by laying open the tract with debridement for subcutaneous, superficial, or intersphincteric fistulas in the lower third of the anal sphincter. 1 This approach achieves healing rates above 95% with low recurrence and minimal complications 2
Crohn's Disease Patients
The approach differs significantly:
- If no active proctocolitis: Fistulotomy may be considered for truly low fistulas, though there is a trend toward lower healing rates compared to non-inflammatory fistulas 3
- If active proctocolitis present: Use a noncutting seton instead of fistulotomy to avoid incontinence risk 3
- Initial management: Place seton combined with antibiotics (metronidazole and/or ciprofloxacin) 3
- Refractory cases: Add thiopurines or anti-TNF agents as second-line therapy after antibiotic failure 3
Critical Pitfalls to Avoid
- Never perform fistulotomy in the anterior perineum of female patients due to the short anterior sphincter and high incontinence risk 3
- Never probe for fistulas during acute abscess drainage to prevent iatrogenic tract creation 1, 5
- Avoid treating concomitant perianal skin tags in Crohn's patients, as this leads to chronic non-healing ulcers 1
- Do not use cutting setons, which result in 57% incontinence rates and keyhole deformity 3
Special Considerations
Conservative Management Trial
About 50% of acute fissures (not fistulas) heal with conservative care, but this does not apply to established fistula tracts 3. Once a fistula is confirmed, surgical intervention is required for definitive treatment 1, 2
Timing of Intervention
- Emergent drainage: Required for sepsis, immunosuppression, diabetes, or diffuse cellulitis 5, 4
- Within 24 hours: For all other cases to minimize recurrence risk 5
- Delayed intervention: Increases recurrence rates up to 44% 5, 4
Incision Placement
Make incisions as close to the anal verge as possible to minimize potential fistula tract length while ensuring adequate drainage 5, 4