What is the recommended management for a superficial (low) anal fistula?

Management of Superficial (Low) Anal Fistula

For a superficial or low anal fistula in adults with intact continence and no contraindications, fistulotomy is the definitive treatment of choice, achieving near-100% healing rates with a 10–20% risk of minor continence disturbances that are typically manageable. 1, 2

Treatment Algorithm

Step 1: Rule Out Absolute Contraindications to Fistulotomy

Before proceeding with fistulotomy, you must exclude the following contraindications:

• Anterior fistula in female patients – The asymmetrical anatomy and short anterior sphincter make fistulotomy unsafe, with high risk of catastrophic incontinence 3, 1, 2
• Active proctitis or proctocolitis – Macroscopic rectal inflammation contraindicates fistulotomy; use non-cutting seton instead 3, 1, 2
• Prior fistulotomy history – Previous sphincter division mandates sphincter-preserving approaches to prevent devastating incontinence 1, 2, 4
• Crohn's disease with active inflammation – CDAI >150 or evidence of perineal Crohn's involvement contraindicates fistulotomy 3, 2

Step 2: Perform Fistulotomy for Suitable Candidates

Fistulotomy (laying open the tract) is the procedure of choice for superficial/subcutaneous fistulas and low intersphincteric or transsphincteric fistulas involving ≤30% of the external sphincter. 3, 1

• Healing rates approach 100% when patient selection is appropriate 1, 2, 5
• The procedure provides single-operation cure, avoiding prolonged seton drainage 2
• Minor continence disturbances occur in 10–20% of cases but are generally manageable 1, 2, 6
• Marsupialisation after laying open the tract improves healing 3

Step 3: Alternative Sphincter-Preserving Approaches When Fistulotomy Is Contraindicated

Non-cutting (loose) seton placement is the preferred alternative:

• Maintains drainage and prevents abscess recurrence 3
• Can achieve fistula closure in 13.6–100% of cases and may serve as definitive treatment 1, 2, 4
• The seton should run through the sphincter complex ending in the internal opening 3, 2
• When combined with anti-TNF therapy in Crohn's disease, seton removal should occur after induction phase completion (approximately 1 month) 3

LIFT (ligation of intersphincteric fistula tract) is a second-line option:

• Reserved for cases where seton drainage has failed 1, 2
• Shows 41–59% failure rate in routine practice, limiting its first-line use 1
• Can achieve 82–100% healing in selected low transsphincteric fistulas without affecting continence 7

Critical Pitfalls to Avoid

• Never use cutting setons – They produce incontinence in approximately 57% of cases due to progressive sphincter transection 3, 1, 2, 4
• Avoid aggressive probing of the fistula tract, which causes iatrogenic injury 1, 2, 4
• Avoid aggressive dilation of the tract, which leads to permanent sphincter damage 1, 2, 4
• Do not perform repeat fistulotomy for recurrence (3–5% rate); instead use loose seton or LIFT 1, 4
• Do not assume all "low" fistulas are safe for fistulotomy – Any transsphincteric involvement requires careful patient selection even if anatomically low 1, 2

Special Considerations for Crohn's Disease

In patients with Crohn's disease and low anal fistulas:

• Fistulotomy may be considered only after excluding perianal abscess and in the absence of active proctocolitis 3
• Greater healing rates occur in patients without macroscopic rectal inflammation compared to those with active proctocolitis 3
• Many experts advocate non-cutting seton rather than fistulotomy when active rectosigmoid inflammation is present 3
• Combination of seton drainage with medical therapy (thiopurines, infliximab, or adalimumab) should be used for maintenance 3