What is the best treatment approach for an adult patient with an anal fistula, particularly those with a history of anal abscesses or inflammatory bowel disease (IBD)?

Treatment of Anal Fistula

For anal fistulas, the treatment approach depends critically on whether the patient has inflammatory bowel disease (IBD): non-IBD patients with simple fistulas should undergo fistulotomy, while IBD patients with complex fistulas require combined surgical drainage with seton placement followed by anti-TNF therapy (infliximab as first-line). 1

Initial Assessment and Sepsis Control

Before any treatment, imaging and drainage of sepsis is mandatory. 1

• Obtain pelvic MRI to define fistula anatomy, identify abscess formation, and classify complexity (simple vs. complex) 1
• If MRI unavailable, perform examination under anesthesia (EUA) with endoanal ultrasound 1
• Drain any abscess immediately before considering definitive treatment - undrained abscess is an absolute contraindication to anti-TNF therapy 1, 2
• Use intravenous antibiotics plus radiological drainage as first-line; surgical drainage only if percutaneous approach fails 1, 2

Treatment Algorithm Based on Fistula Type

Simple/Superficial Fistulas (Non-IBD Patients)

Fistulotomy (laying open the tract) is the gold standard for subcutaneous or superficial fistulas. 1, 3

• This includes submucosal, intersphincteric, or trans-sphincteric fistulas in the lower third of the anal sphincter 1
• Contraindications: active Crohn's disease (CDAI >150) or evidence of perineal Crohn's involvement 1
• Risk of incontinence is directly related to thickness of sphincter muscle divided 3

Complex Fistulas (IBD Patients)

The treatment sequence is: (1) drain abscess, (2) place loose seton, (3) start infliximab after adequate drainage. 1

Step 1: Seton Placement

• Place loose, non-cutting silastic setons to establish drainage and prevent abscess recurrence 1
• Setons should remain in place through infliximab induction (at least 5 infusions or after completing induction therapy) 1
• Exception: avoid setons in rectovaginal fistulas without abscess, as they worsen fecal discharge 1

Step 2: Medical Therapy

Infliximab is first-line biological therapy and should be started as soon as adequate sepsis drainage is achieved. 1

• Infliximab dosing: 5 mg/kg at weeks 0,2, and 6 (induction), then every 8 weeks (maintenance) 1
• Achieves complete fistula closure in 55-69% at 14 weeks 1
• Target infliximab levels >10 μg/mL for better response in perianal disease 1
• Adalimumab is an alternative but has less robust evidence for perianal fistulas 1

Step 3: Assess Rectal Inflammation

Active proctitis must be medically controlled before considering definitive surgical repair. 1

• Perform EUA to assess rectal mucosa - proctitis is associated with lower healing rates 1
• Patients with rectal involvement have 29% proctectomy rate vs. 4% without rectal involvement 1

Step 4: Maintenance Therapy

• Use thiopurines, infliximab, adalimumab, seton drainage, or combination as maintenance 1
• Clinical assessment (decreased drainage) is usually sufficient to monitor response 1
• MRI or endoanal ultrasound combined with clinical assessment can evaluate tract inflammation improvement 1

Sphincter-Preserving Surgical Options (Selected Cases Only)

These procedures should only be offered in highly selected patients after extensive counseling, as long-term results are poor, particularly with complex disease and ongoing inflammation. 1

• Advancement flap: 20% healing rate in IBD patients at 12 weeks 4
• LIFT (ligation of intersphincteric fistula tract): variable results 1
• Fibrin glue: 38% effective at 8 weeks (vs. 16% observation), better in simple fistulas 1; 0% healing in one IBD series 4
• Fistula plug: 55-75% success in IBD patients, though wide variation reported 1, 4
• VAAFT (video-assisted anal fistula treatment) with advancement flap: 82% success at 9 months 1
• Allogeneic adipose-derived stem cells (darvadstrocel): 50% complete remission at 24 weeks vs. 34% placebo; 59.2% clinical remission at 1 year 1

Refractory Disease

For patients failing medical and conservative surgical therapy, consider faecal stream diversion with ostomy. 1

• Counsel patients that rates of successful reversal are low 1
• Proctectomy is the last resort 1

Critical Pitfalls to Avoid

• Never start anti-TNF therapy before draining abscesses - this can worsen sepsis and is the most dangerous error 1, 2
• Never perform fistulotomy in complex fistulas or active proctitis - leads to incontinence and non-healing ulcers 1, 2
• Never surgically treat concomitant perianal skin tags - can lead to chronic non-healing ulcers 1
• Never perform immediate resection without stabilization - optimize nutrition, control sepsis, and balance fluids/electrolytes first 5, 2
• Avoid premature seton removal before completing infliximab induction - may result in recurrent abscess 1

Special Populations

Asymptomatic Fistulas

• Asymptomatic low anal-introital fistulae do not need surgical treatment 1

Rectovaginal Fistulas

• Symptomatic rectovaginal fistulas usually require surgery including possible diverting ostomy 1
• Control rectal inflammation medically before and after surgery to prevent recurrence 1
• Infliximab achieves 45% closure at week 14 2