Treatment of Simple Low Trans-sphincteric or Inter-sphincteric Anal Fistula
Recommended Treatment Approach
For simple low trans-sphincteric or inter-sphincteric anal fistulas in otherwise healthy adults without Crohn's disease or active proctitis, fistulotomy is the treatment of choice, offering healing rates approaching 100% with minimal risk of incontinence. 1, 2
Pre-operative Assessment
Before proceeding with any surgical intervention, the following steps are mandatory:
- Perform examination under anesthesia (EUA) to accurately define fistula anatomy and rule out occult abscess, which is present in more than two-thirds of fistula cases 1, 2
- Obtain proctosigmoidoscopy to evaluate for concomitant rectosigmoid inflammation, as active proctitis is an absolute contraindication to fistulotomy 3, 1, 2
- Consider contrast-enhanced pelvic MRI or endoscopic anorectal ultrasound if anatomy is unclear or complex features are suspected 3, 1, 2
- Drain any associated abscess first before definitive fistula treatment, as sepsis control is the critical first step 1
Absolute Contraindications to Fistulotomy
Never perform fistulotomy in the following scenarios, as these carry unacceptably high complication risks:
- 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
Surgical Technique for Fistulotomy
When contraindications are absent, proceed with fistulotomy:
- Lay open the primary fistula tract and any side tracts completely 1
- Ensure the wound heals from the inside out, as premature surface closure leads to recurrence 1
- Expected healing rates approach 100% for simple low fistulas 1, 4, 5
- Risk of continence disturbances is 10-20%, though typically minor 1
Alternative Approach: LIFT Procedure
For patients with concerns about continence or cosmetic deformity, consider sphincter-preserving alternatives:
- Ligation of intersphincteric fistula tract (LIFT) offers success rates of 77% in cryptoglandular fistulas and 82-100% in low trans-sphincteric fistulas 1, 6, 7, 4
- LIFT preserves tissue architecture and has no significant impact on continence scores 6, 7
- Particularly valuable for female patients with anterior fistulas or patients with pre-existing sphincter compromise 6
Postoperative Management
After fistulotomy, implement the following care protocol:
- Monitor for fever or systemic symptoms indicating spreading infection, which requires urgent evaluation 1
- Ensure wound healing progresses from depth to surface, preventing premature skin closure that causes recurrence 1
- Expect operating time of approximately 22 minutes and hospital stay of 1-2 days 5
- Wound healing typically completes within 4-6 weeks with proper care 5
Critical Pitfalls to Avoid
- Never probe aggressively for fistula tracts during initial examination, as this creates iatrogenic complexity 1, 2
- Never use cutting setons, which result in incontinence rates up to 57% and keyhole deformity 1, 2
- Never proceed with fistulotomy if proctitis is present, even if the fistula appears simple anatomically 1, 2
Special Consideration: Crohn's Disease
If Crohn's disease is present or suspected, the treatment algorithm changes completely:
- Place a loose, non-cutting seton as primary treatment combined with antibiotics (metronidazole and/or ciprofloxacin) 3, 1, 2
- Initiate anti-TNF therapy (infliximab or adalimumab) once sepsis is controlled 3, 1
- Consider fistulotomy only for uncomplicated low fistulas in carefully selected Crohn's patients without proctitis 3
- Fistulotomy in Crohn's disease requires absence of proctitis, low number of daily bowel motions, and Parks classification of superficial, intersphincteric, or low trans-sphincteric 3