How to treat a patient with a diagnosed fistula in ano?

Treatment of Fistula-in-Ano

For patients with fistula-in-ano, immediate surgical drainage with loose seton placement is the primary treatment after excluding or draining any associated abscess, followed by definitive sphincter-sparing procedures once inflammation is controlled. 1, 2

Initial Assessment and Sepsis Control

The first priority is identifying and draining any associated abscess, as more than two-thirds of fistulas have concurrent abscesses that must be addressed before definitive intervention. 2

• Timing of drainage depends on sepsis severity: emergent drainage is required for patients with systemic sepsis, immunosuppression, diabetes, or diffuse cellulitis; otherwise proceed within 24 hours 1
• MRI of the pelvis is the preferred imaging modality to define fistula anatomy and identify occult abscesses, with higher diagnostic accuracy than CT 2
• Examination under anesthesia (EUA) by an experienced surgeon combined with MRI provides the highest diagnostic accuracy 2
• Proctosigmoidoscopy should be performed to evaluate for concomitant rectal inflammation and exclude Crohn's disease, which occurs in 13-27% of complex fistula cases 2
• Never probe for fistulas during acute abscess drainage, as this causes iatrogenic complications 1

Classification-Based Treatment Algorithm

Simple Fistulas (Intersphincteric, Low Transsphincteric)

Fistulotomy by laying open the tract with debridement is the treatment of choice for subcutaneous, superficial, or intersphincteric fistulas in the lower third of the anal sphincter. 1

• Fistulotomy achieves healing rates higher than 95% with low recurrence and minimal postoperative complications 3
• For simple low transsphincteric fistulas, patient selection is crucial to determine if safe fistulotomy or sphincter-saving technique should be used 3
• The incision should be kept as close as possible to the anal verge to minimize potential fistula length while providing adequate drainage 4

Complex Fistulas (High Transsphincteric, Suprasphincteric, Horseshoe)

All complex fistulas require initial loose seton placement after abscess drainage, followed by sphincter-sparing procedures once inflammation is controlled. 2

• The loose draining seton establishes drainage, prevents abscess recurrence, and allows time for medical optimization 2
• After inflammation control, proceed with sphincter-sparing procedures such as ligation of intersphincteric fistula tract (LIFT) or rectal advancement flaps, which achieve healing rates of 60-90% 3
• Novel techniques including fistula laser closure (FiLac) and video-assisted anal fistula treatment (VAAFT) are safe with reported healing rates of 65-90% 3
• Horseshoe fistulas can be treated with fistulectomy combined with closure of the internal opening using mucosa-submucosa advancement flap, rectal wall advancement flap, or anocutaneous advancement flap, achieving 88% healing rates 5

Special Considerations for Crohn's Disease

For Crohn's disease patients with perianal fistulas, medical therapy to control disease-related inflammation is imperative before definitive surgical intervention. 4, 1

• First-line medical therapy includes metronidazole and/or ciprofloxacin for simple fistulas 6
• Complex fistulas require anti-TNF therapy (infliximab 5 mg/kg at weeks 0,2, and 6, then every 8 weeks) combined with immunomodulators (azathioprine 1.5-2.5 mg/kg/day or mercaptopurine 0.75-1.5 mg/kg/day) after adequate infection control 6
• Never initiate anti-TNF therapy without first excluding and draining abscesses, as this leads to worsening sepsis and treatment failure 6
• Maintenance therapy with thiopurines, infliximab, or adalimumab combined with seton drainage is required after surgery 4, 1
• Concomitant perianal skin tags should never be surgically treated in Crohn's patients, as this leads to chronic non-healing ulcers 4, 1
• Patients refractory to medical treatment should be considered for diverting ostomy, with proctectomy as last resort 4

Surgical Technique Specifics

Intersphincteric Fistulas

• If intersphincteric abscess is present, immediate drainage into the rectal lumen through the internal opening is required, with consideration of limited internal sphincterotomy 1
• For definitive management, fistulotomy is appropriate for lower third involvement; sphincter-sparing procedures like LIFT for higher involvement 1

Drainage Principles

• Complete and accurate drainage is essential, as inadequate drainage, loculations, horseshoe-type anatomy, and delayed intervention increase recurrence risk up to 44% 4
• Sufficient drainage of the retroanal region is of utmost importance in horseshoe fistulas to prevent recurrence 5

Monitoring and Follow-up

• Clinical assessment (decreased drainage) is usually sufficient for routine monitoring 2
• MRI or endoanal ultrasound combined with clinical assessment is recommended to evaluate fistula tract inflammation improvement 2
• Minor incontinence rates range from 2.4% to 6% with appropriate surgical technique 2, 7