What is the workup and management for a patient with a perianal fistula and purulent drainage?

Management of Perianal Fistula with Purulent Drainage

The initial management of perianal fistula with purulent drainage requires adequate surgical drainage of any abscess under general anesthesia, followed by appropriate medical therapy based on fistula classification and underlying etiology, with infliximab being the treatment of choice for complex fistulas in Crohn's disease. 1

Initial Diagnostic Workup

Imaging

• MRI of the pelvis: First-line imaging modality to assess fistula anatomy, identify hidden abscesses, and classify the fistula 1
• Endoanal ultrasound: Alternative if MRI unavailable or contraindicated
• Examination under anesthesia (EUA): Essential for definitive assessment of fistula anatomy and drainage of abscesses 1

Additional Evaluation

• Colonoscopy: To evaluate for underlying Crohn's disease or other inflammatory conditions
• Biopsy: If malignancy is suspected (approximately 11% of colovesical and colovaginal fistulae are caused by malignancy) 1

Management Algorithm

Step 1: Abscess Drainage

• Perform adequate surgical drainage under general anesthesia
• No routine requirement for wound packing (packing only for short-term hemostasis) 1
• Do not actively probe for fistula tracts during initial abscess drainage to avoid creating iatrogenic tracts 1

Step 2: Fistula Management Based on Classification

Simple Fistulas (Low, Superficial)

• If no active rectal inflammation:
  • Fistulotomy (laying open the tract) may be performed for low fistulas 1
  • One or two-stage approach depending on complexity

Complex Fistulas (High, Multiple Tracts, Rectovaginal)

• If obvious fistula exists without probing:

  • Place loose draining seton (soft material, avoiding bulky knots) 1
  • Do not attempt to lay open the fistula to minimize tissue disruption 1

• If active rectal inflammation present:

  • Place non-cutting seton to maintain drainage and prevent abscess formation 1
  • Initiate medical therapy (see below)

Step 3: Medical Management

For Crohn's Disease-Related Fistulas

1. First-line therapy:

   • Infliximab (5 mg/kg at weeks 0,2, and 6, then every 8 weeks) 1
   • Combined with immunomodulators (azathioprine 1.5-2.5 mg/kg/day or 6-mercaptopurine 0.75-1.5 mg/kg/day) 1, 2

2. Adjunctive therapy:

   • Antibiotics: Ciprofloxacin (500 mg twice daily) and/or metronidazole (400 mg three times daily) for 1-2 weeks 2

3. For refractory cases:

   • Consider tacrolimus or cyclosporine 1
   • Surgical options for persistent fistulas after medical optimization

For Non-Crohn's Fistulas

• Antibiotics for acute infection control
• Surgical options based on fistula anatomy and complexity

Specific Management for Special Cases

Rectovaginal Fistulas

• Medical therapy to control active luminal inflammation first
• Surgical repair only when rectosigmoid mucosa has healed 1
• Options include:
  • Transanal or transvaginal advancement flaps
  • Laparotomy with primary closure or sleeve advancement flap 1

Refractory Complex Fistulas

• Consider advanced surgical techniques after medical optimization:
  • Endorectal advancement flap (if no active rectal inflammation) 1
  • Fecal diversion or proctectomy as last resort for severe cases 1

Pitfalls and Caveats

• Over-vigorous probing during initial abscess drainage can create iatrogenic tracts and complicate management 1
• Advancement flap surgery should be reserved for patients with disabling symptoms due to risk of worsening symptoms if operation fails 1
• Despite optimal medical and surgical management, approximately 65% of patients with complex perianal Crohn's disease will eventually require surgical intervention 2
• Fistulotomy should rarely, if ever, be used for rectovaginal fistulas due to sphincter injury risk 1

Follow-up

• Regular clinical assessment for drainage and symptoms
• Repeat imaging (MRI) to assess fistula healing
• Endoscopic evaluation to monitor for rectal inflammation in Crohn's disease

By following this structured approach to perianal fistula management, clinicians can minimize morbidity, preserve anal function, and optimize quality of life outcomes for patients with this challenging condition.