What is the best course of treatment for a patient with a complex fistula in ano?

Treatment of Complex Fistula-in-Ano

Initial management of complex fistula-in-ano requires loose seton placement after drainage of any associated abscess, followed by sphincter-sparing procedures once inflammation is controlled, with medical therapy playing a critical role in Crohn's-related cases. 1

Initial Assessment and Diagnosis

Imaging and Examination:

• MRI of the pelvis is the preferred initial imaging modality to define fistula anatomy and identify occult abscesses, with superior diagnostic accuracy compared to CT scans 1
• Examination under anesthesia (EUA) by an experienced surgeon combined with MRI provides the highest diagnostic accuracy 1
• Proctosigmoidoscopy must be performed to evaluate for concomitant rectal inflammation and exclude Crohn's disease, which occurs in 13-27% of patients with complex and multifocal fistulas 1
• Endoanal ultrasound can serve as an alternative if rectal stenosis is excluded, though it has lower diagnostic accuracy than MRI 1

Immediate Management of Associated Abscess

Drainage Timing:

• More than two-thirds of complex fistulas have an associated abscess that must be drained before definitive intervention 1
• Emergent drainage is required for patients with sepsis, immunosuppression, diabetes, or diffuse cellulitis 2, 1
• For stable patients without these risk factors, drainage should occur within 24 hours 2

Surgical Approach to Drainage:

• Perform incision and drainage of the abscess 2
• Never probe for fistulas during acute abscess drainage to avoid iatrogenic complications 2
• Place a loose draining seton at the time of drainage for any obvious fistula involving sphincter muscle 2
• Fistulotomy can only be performed at initial drainage if the fistula is low and subcutaneous, not involving sphincter muscle 2

Definitive Surgical Management Algorithm

Seton Placement (First-Line for Complex Fistulas):

• A loose draining seton should be placed for all complex fistulas to establish drainage, prevent abscess recurrence, and allow time for medical optimization 1
• Setons can be left in place indefinitely if needed, though patients may prefer suppressive medical therapy over long-term seton placement 2
• Seton placement was the most common surgical technique in specialized centers, used in 62% of cases with complex fistulas 3

Sphincter-Sparing Procedures (After Inflammation Control):

• Once inflammation is controlled, proceed with sphincter-sparing procedures such as ligation of intersphincteric fistula tract (LIFT) 1
• Endorectal advancement flap procedures can be performed for high perianal fistulas in patients without rectal inflammation 2
• Recurrence rates following advancement flap procedures are relatively high, so reserve this for patients with disabling symptoms 2

Expected Outcomes:

• Primary fistula tract eradication occurs in approximately 61% of patients after initial treatment 3
• Minor incontinence rates range from 2.4% to 6% with appropriate surgical technique 1, 3
• Recurrence risk after drainage alone can be as high as 44%, emphasizing the need for complete drainage and appropriate definitive management 1

Medical Therapy Integration

For Crohn's Disease-Related Fistulas:

• Initiate antibiotics (metronidazole and/or ciprofloxacin) in combination with seton drainage 1
• Add thiopurines or anti-TNF therapy (infliximab or adalimumab) as second-line treatment for refractory disease 1
• Medical therapy to control inflammation is imperative before attempting definitive surgical closure 1
• Infliximab can completely close all fistula tracts in many patients with complex fistulas and is considered the initial treatment of choice by most gastroenterologists 2
• Coadminister azathioprine, 6-mercaptopurine, or methotrexate routinely with infliximab to counteract immunogenic reactions and maintain remission 2
• Maintenance therapy with thiopurines, infliximab, or adalimumab combined with seton drainage is required after surgery 1

For Cryptoglandular (Non-Crohn's) Fistulas:

• Antibiotic administration is suggested only in the presence of sepsis, surrounding soft tissue infection, or immune response disturbances 2
• Sample drained pus in high-risk patients or those with risk factors for multidrug-resistant organisms 2

Management of Treatment Failures

Stepwise Escalation:

• Patients who fail initial infliximab treatment should undergo anorectal endoscopic ultrasound or pelvic MRI plus EUA with seton placement as indicated 2
• Continue treatment with infliximab, azathioprine or 6-mercaptopurine, and antibiotics 2
• Tacrolimus or cyclosporine can be considered in patients who fail multimodality approach, though nephrotoxicity and side effects occur frequently and should be used with caution 2

Last Resort Options:

• Fecal diversion may be considered for refractory cases 2
• Proctectomy should only be undertaken as a last resort 2

Critical Pitfalls to Avoid

• Never surgically treat concomitant perianal skin tags in Crohn's patients, as this leads to chronic non-healing ulcers 1
• Do not attempt definitive surgical closure before controlling inflammation with medical therapy 1
• Avoid routine EUA and seton placement before initiating infliximab therapy, as it is not mandatory 2
• Do not delay imaging in stable patients, but ensure imaging does not delay surgical intervention in unstable patients 2

Monitoring and Follow-up

• Clinical assessment (decreased drainage) is usually sufficient for routine monitoring 1
• MRI or endoanal ultrasound combined with clinical assessment is recommended to evaluate fistula tract inflammation improvement 1
• Clinical closure does not equal MRI closure, with high risk of recurrence without complete fibrotic tract on MRI 1