What are the surgical management options for a patient with fistula in ano?

Surgical Management of Fistula-in-Ano

The surgical approach to fistula-in-ano must be stratified by sphincter involvement: perform immediate fistulotomy only for subcutaneous/superficial fistulas with no sphincter muscle involvement, while any fistula involving sphincter muscle requires loose seton placement to avoid incontinence. 1

Initial Assessment and Drainage

Before any definitive fistula surgery, drain all associated abscesses first—over two-thirds of fistulas have concurrent abscesses that must be addressed. 1

• Imaging with MRI or endoanal ultrasound is recommended before surgical drainage to define anatomy and identify complex tracts 1
• Examination under anesthesia (EUA) is mandatory for complex fistulas to accurately assess sphincter involvement 1
• Never probe or use hydrogen peroxide to search for occult fistulas during abscess drainage—this causes iatrogenic tract formation and complications 1

Algorithmic Approach Based on Fistula Anatomy

Low/Subcutaneous Fistulas (No Sphincter Involvement)

Perform immediate fistulotomy by laying open the entire tract from internal to external opening. 1, 2

• This can be done at the time of abscess drainage for truly subcutaneous fistulas 1, 2
• Debride the tract thoroughly with or without marsupialization 1, 2
• Healing rates exceed 95% with low recurrence in simple fistulas 3
• Critical caveat: This permanently converts the tubular tract into an open groove in the anal canal—patients must understand this creates a permanent anatomical defect 4

Intersphincteric or Low Trans-sphincteric Fistulas (Lower Third of Sphincter)

Fistulotomy may be considered in highly selected cases, but only if the patient has no Crohn's disease (CDAI <150), no active proctitis, and accepts the 10-20% baseline risk of continence disturbances. 1, 2

• In Crohn's disease patients with low-lying transsphincteric fistulas, fistulotomy can achieve good healing with acceptable incontinence rates when strictly selected 5
• Anterior fistulas in women are an absolute contraindication due to short anterior sphincter anatomy—these will cause incontinence 2
• Alternative sphincter-preserving approaches (LIFT, advancement flaps) should be discussed as they preserve normal anatomy 4, 3

Any Fistula Involving Significant Sphincter Muscle

Place a loose draining seton—this is non-negotiable to prevent incontinence. 1

• Use loose, fine silastic setons to establish drainage and prevent abscess recurrence 1
• The seton allows inflammation to subside before considering definitive treatment 1
• In Crohn's disease, loose setons combined with optimal medical therapy (infliximab, adalimumab, thiopurines) may be definitive treatment, with seton removal achieved in up to 98% at median 33 weeks 2

High Trans-sphincteric or Complex Fistulas

Use sphincter-preserving techniques exclusively—fistulotomy is contraindicated. 3, 6

• LIFT (ligation of intersphincteric fistula tract) achieves healing rates of 60-90% 3
• Endorectal advancement flaps have 64% weighted success in Crohn's patients 2
• Novel techniques (FiLaC, VAAFT) report 65-90% healing rates with good safety profiles 3
• For horseshoe fistulas, fistulectomy with primary closure of internal opening using advancement flaps achieves 88% healing 7

Critical Pitfalls to Avoid

Never use cutting setons—they carry a 57% incontinence rate. 2

• Inadequate drainage at initial procedure is the primary risk factor for recurrence (up to 44% recurrence after drainage alone) 2
• The anatomical changes from fistulotomy make repeat sphincterotomy "catastrophically dangerous" if fistula recurs 4
• Loculations, horseshoe-type abscesses, and delayed time from disease onset to incision all increase recurrence risk 2

Special Considerations for Crohn's Disease

Control luminal disease with thiopurines, infliximab, or adalimumab before and after surgery—this is imperative to increase healing likelihood. 1, 2

• Assess the rectum for proctitis at time of drainage—active proctitis dramatically reduces healing rates 1, 2
• Delay seton removal until anti-TNF induction is completed and proctitis has resolved 2
• For refractory cases, consider diverting ostomy, with proctectomy as last resort (though only one-fifth remain stoma-free long-term) 1, 2
• Do not surgically treat concomitant perianal skin tags—this leads to chronic non-healing ulcers 1

Postoperative Management

Avoid wound packing—it is costly, painful, and provides no benefit to healing. 1, 2

• Antibiotics are indicated only for sepsis, surrounding cellulitis, or immunosuppression 1, 2
• An empiric 5-10 day antibiotic course may reduce post-operative fistula formation from 24% to 16% 1
• Clinical assessment of decreased drainage is usually sufficient to evaluate response 1
• MRI or endoanal ultrasound combined with clinical assessment is recommended to evaluate fistula tract inflammation improvement 1