What is the initial treatment for a patient with fistula in ano?

Initial Treatment of Fistula in Ano

For patients with fistula in ano, the initial treatment depends critically on whether an acute abscess is present and the relationship of the fistula tract to the anal sphincter muscle—immediate surgical drainage is required for any associated abscess, followed by either fistulotomy for simple low fistulas not involving sphincter or seton placement for fistulas involving sphincter muscle. 1, 2

Clinical Assessment and Diagnosis

The initial evaluation must identify:

• Presence of acute abscess: Look for throbbing pain, visible perianal redness/swelling, fluctuance on palpation, or signs of systemic infection/sepsis 1
• External opening location: Typically presents with drainage of blood, pus, or fecal material from perianal skin 1
• Sphincter involvement: This determines surgical approach and risk of incontinence 1, 2

For patients with systemic signs, obtain complete blood count, serum creatinine, and inflammatory markers (C-reactive protein, procalcitonin, lactates) 1. Check serum glucose, hemoglobin A1c, and urine ketones to identify undetected diabetes 1.

Imaging Considerations

Imaging is NOT routinely required for straightforward cases but should be obtained for: 1

• Atypical presentation
• Suspected occult supralevator abscess
• Complex fistula anatomy
• Suspected Crohn's disease

When imaging is indicated, use MRI, CT scan, or endosonography based on available resources 1. Note that CT has limited sensitivity (77%) for anorectal abscess and correctly classifies only 24% of perianal fistulae compared to 82% with endoanal ultrasound 1.

Surgical Management Algorithm

If Abscess is Present:

Immediate incision and drainage is mandatory 1, 2. The incision should be kept as close as possible to the anal verge to minimize potential fistula length while providing adequate drainage 2.

Timing considerations: 1, 2

• Emergent drainage for patients with sepsis, immunosuppression, diabetes, or diffuse cellulitis
• Fit, immunocompetent patients with small perianal abscess without systemic sepsis may be managed as outpatients

Concurrent Fistula Management at Time of Abscess Drainage:

For low fistulas NOT involving sphincter muscle (subcutaneous):

• Perform fistulotomy at the time of abscess drainage 1

For fistulas involving ANY sphincter muscle:

• Place a loose draining seton rather than performing immediate fistulotomy 1, 2
• This prevents incontinence while maintaining drainage

If no obvious fistula is identified:

• Do NOT probe to search for possible fistula—this risks iatrogenic complications 1

For Chronic Fistula Without Acute Abscess:

Simple intersphincteric or low transsphincteric fistulas:

• Fistulotomy is the procedure of choice with healing rates >95% 3
• Patient selection is crucial for low transsphincteric fistulas to determine if fistulotomy can be performed safely

Complex fistulas (high transsphincteric, suprasphincteric, extrasphincteric):

• Use ONLY sphincter-saving techniques 3
• Ligation of intersphincteric fistula tract (LIFT) and rectal advancement flaps provide optimal outcomes with healing rates of 60-90% 3
• Novel techniques include fistula laser closure (FiLaC) and video-assisted anal fistula treatment (VAAFT) with healing rates 65-90% 3

Antibiotic Therapy

Antibiotics are NOT routinely required after drainage alone 1

Indications for antibiotics: 1

• Presence of sepsis
• Surrounding soft tissue infection/cellulitis
• Immunosuppression or other immune disturbances
• High-risk patients or risk factors for multidrug-resistant organisms (sample drained pus for culture) 1

Critical Pitfalls to Avoid

Risk of recurrence after drainage alone can be as high as 44% 2. Factors increasing recurrence risk include: 2

• Inadequate drainage
• Loculations
• Horseshoe-type abscess
• Delayed time from disease onset to incision

Do not perform aggressive probing or fistulotomy of complex fistulas in the acute setting—this significantly increases incontinence risk 1, 4. Trading radical surgery for conservative sphincter-preserving procedures may result in more recurrences requiring repeated operations, but this is preferable to permanent fecal incontinence 4.

Wound packing after drainage: No evidence-based recommendation exists for or against packing 1.