What is the best treatment option for a patient with a low transsphincteric (anal) fistula?

Treatment of Low Transsphincteric Anal Fistula

For low transsphincteric fistulas, fistulotomy is the recommended treatment in carefully selected patients without active proctitis, while loose seton placement is preferred when proctitis is present or in patients with compromised sphincter function. 1

Patient Selection for Fistulotomy

The decision between fistulotomy and seton placement hinges on specific clinical criteria that must be systematically evaluated:

Ideal Candidates for Fistulotomy

• Simple, low transsphincteric fistulas involving only the lower third of the anal sphincter 1
• Absence of active rectal inflammation (proctitis) - this is critical as proctitis dramatically reduces healing rates and increases complications 1
• In Crohn's disease patients: CDAI <150 and no evidence of perineal Crohn's involvement 1, 2
• No concomitant abscess present - any abscess must be drained first 3, 2

Absolute Contraindications to Fistulotomy

• Anterior fistulas in female patients - the asymmetrical anatomy and short anterior sphincter make fistulotomy highly likely to cause incontinence 2
• Active proctitis or proctocolitis - healing rates plummet and complications increase substantially 1
• Presence of active abscess - requires drainage with loose seton first 3, 2
• Evidence of perineal Crohn's disease involvement 2

Treatment Algorithm

Step 1: Control Sepsis

• Drain any associated abscess surgically - more than two-thirds of fistula patients have an associated abscess 3
• Place a loose seton to establish drainage if abscess is present, allowing inflammation to subside and preventing recurrence 1, 3

Step 2: Assess for Proctitis

• Perform proctosigmoidoscopy to evaluate for concomitant rectal inflammation 3
• If proctitis is present: loose seton is the only appropriate option; proceed to medical therapy and maintain seton drainage 1
• If no proctitis: proceed with evaluation for definitive fistulotomy 1

Step 3: Definitive Treatment Based on Anatomy

For Low Transsphincteric Fistulas WITHOUT Proctitis:

Fistulotomy is the treatment of choice 1, 4

• Lay open the entire fistula tract from internal to external opening 1
• Debride thoroughly with or without marsupialization 1
• Healing rates exceed 95% in simple low fistulas 4
• Recurrence rates are significantly lower (21.1%) compared to drainage alone (44%) 5

For Low Transsphincteric Fistulas WITH Proctitis or High-Risk Features:

Loose seton placement is mandatory 1

• Maintain seton drainage until inflammation is controlled with medical therapy 1, 3
• Setons may serve as definitive treatment when combined with optimal medical therapy, with removal possible in up to 98% of patients at median 33 weeks 1

Alternative Sphincter-Sparing Option:

LIFT (Ligation of Intersphincteric Fistula Tract) can replace fistulotomy even for low transsphincteric fistulas, particularly in patients with compromised sphincter function 1, 6

• Primary healing rate of 82% in low transsphincteric fistulas 6
• No significant change in continence scores 6
• Converts transsphincteric to intersphincteric fistula if primary healing fails, allowing subsequent fistulotomy with external sphincter preservation 6

Special Considerations for Crohn's Disease

Medical therapy must be optimized before and maintained after any definitive surgical intervention 1, 3

• Use thiopurines, infliximab, or adalimumab for maintenance 1, 3
• Fistulotomy can achieve good results in strictly selected Crohn's patients with low-lying transsphincteric fistulae without proctitis 7
• Greater healing rates occur in patients without macroscopic rectal inflammation compared to those with active proctocolitis 1

Critical Pitfalls to Avoid

• Never perform fistulotomy in the presence of active proctitis - this leads to poor healing, chronic wounds, and potential need for proctectomy 1
• Avoid cutting setons - they carry a 57% incontinence rate 2
• Do not excise concomitant perianal skin tags in Crohn's patients - this leads to chronic non-healing ulcers 3, 8
• Never probe for fistulas if not obvious - this causes iatrogenic complications 2

Expected Outcomes

Fistulotomy in properly selected patients:

• Healing rates >95% 4
• Recurrence rates 3-21% 9, 7, 5
• Minor incontinence (transient soiling) in 11.5% of patients, typically resolving within 4-6 months 9
• No major incontinence when selection criteria are strictly followed 9, 7

The key to success is rigid adherence to patient selection criteria, particularly the absence of proctitis and appropriate fistula anatomy.