Management of Fistula-in-Ano: ASCRS-Based Guidelines
Immediate Surgical Decision Algorithm
For simple fistulas not involving sphincter muscle (subcutaneous/superficial), perform fistulotomy immediately at the time of abscess drainage; for any fistula involving sphincter muscle, place a loose draining seton and defer definitive treatment. 1, 2
Initial Assessment
Clinical Evaluation
- Obtain focused medical history and perform digital rectal examination to identify the fistula tract and assess complexity 2
- Check serum glucose, hemoglobin A1c, and urine ketones to screen for undetected diabetes mellitus, which is present in a substantial proportion of patients 3, 2
- In patients with systemic infection or sepsis, obtain complete blood count, serum creatinine, and inflammatory markers (C-reactive protein, procalcitonin, lactates) 3
Imaging Indications
- Request MRI, CT scan, or endosonography for atypical presentations, suspected occult supralevator abscesses, complex anal fistulas, or perianal Crohn's disease 3, 2
- Do not routinely image straightforward perianal abscesses with obvious simple fistulas 3
Surgical Management by Fistula Type
Simple Fistulas (Intersphincteric or Low Transsphincteric)
Perform fistulotomy by laying open the tract with debridement for subcutaneous, superficial, or intersphincteric fistulas in the lower third of the anal sphincter. 4, 2
- This approach achieves healing rates exceeding 95% with minimal recurrence 5
- Keep the incision as close as possible to the anal verge to minimize potential fistula length while ensuring adequate drainage 1
Complex Fistulas (High Transsphincteric, Suprasphincteric, Extrasphincteric)
Place a loose draining seton initially rather than performing immediate fistulotomy to prevent incontinence. 3, 1, 4, 2
- After inflammation is controlled with seton drainage, proceed with sphincter-sparing procedures such as ligation of intersphincteric fistula tract (LIFT) or advancement flaps 4, 2
- LIFT and rectal advancement flaps provide healing rates of 60-90% in complex fistulas 5
- Seton placement was the most common surgical technique in a large prospective series (62% of cases), particularly for complex fistulas, with successful primary tract eradication in 61% of patients 6
Horseshoe Fistulas
- Ensure sufficient drainage of the retroanal region 7
- Perform fistulectomy or curettage with primary closure of the internal opening using mucosa-submucosa advancement flap, rectal wall advancement flap, anocutaneous advancement flap, or direct closure 7
- This approach achieves 88% healing rates, though recurrence rates for flap procedures range from 23-35% 7
Critical Intraoperative Principles
What NOT to Do
Never probe to search for a fistula if one is not obvious during acute abscess drainage—this causes iatrogenic complications and creates false tracts. 3, 4, 2
- This is one of the most important pitfalls to avoid, as aggressive probing significantly increases complications 4, 2
Timing of Surgery
- Base timing on presence and severity of sepsis 3, 1, 2
- Patients with sepsis, immunosuppression, diabetes, or diffuse cellulitis require emergent drainage 1, 2
- Fit, immunocompetent patients with small perianal abscesses without systemic sepsis can be managed as outpatients 3, 1, 2
Antibiotic Therapy
Antibiotics are not routinely indicated for adequately drained anorectal abscesses in immunocompetent patients. 2
- Administer antibiotics only in the presence of sepsis, surrounding soft tissue infection, or immunocompromised status 3, 2
- When indicated, use empiric broad-spectrum coverage for Gram-positive, Gram-negative, and anaerobic bacteria 2
- Sample drained pus in high-risk patients or when multidrug-resistant organisms are suspected 3
Special Populations: Crohn's Disease
- Control disease-related inflammation with medical therapy before definitive surgical intervention 4
- Place loose setons for drainage and maintain with thiopurines, infliximab, or adalimumab after surgery 4
- Never surgically treat concomitant perianal skin tags in Crohn's patients—this leads to chronic non-healing ulcers 4
Postoperative Considerations
Wound Management
- No recommendation can be made regarding wound packing after drainage based on available literature 3
Risk Factors for Recurrence
- Recurrence after drainage alone occurs in up to 44% of cases 1, 2
- Inadequate drainage, loculations, horseshoe-type abscess, and delayed time from disease onset to incision increase recurrence risk 1, 2
- Complete drainage with adequate incision size is essential, as incomplete drainage is a major cause of recurrence 2
Incontinence Risk
- Major incontinence occurs in approximately 1.3% of cases, with minor incontinence in an additional 1.2% 6
- Manometric studies show significant decreases in resting pressure (25%) and squeeze pressure (21%) after surgery 7
- Immediate fistulotomy on fistulas involving sphincter muscle significantly increases incontinence risk 4, 2