What is the treatment for a perianal abscess?

Treatment of Perianal Abscess

Incision and drainage is the cornerstone of treatment for all perianal abscesses and should be performed promptly, ideally within 24 hours unless emergency drainage is required. 1, 2

Indications for Emergency Drainage

Emergency surgical drainage is mandatory in the following situations:

• Patients with sepsis, severe sepsis, or septic shock 1
• Immunosuppressed patients 1
• Patients with diabetes mellitus 1
• Presence of diffuse cellulitis 1

Surgical Technique

The incision should be placed as close as possible to the anal verge to minimize potential fistula length while ensuring complete drainage. 1, 2

Key Technical Points:

• Complete drainage is essential, as inadequate drainage is the primary cause of high recurrence rates (up to 44%) 2
• For larger abscesses, use multiple counter incisions rather than a single long incision to prevent step-off deformity and delayed wound healing 3, 2
• Location-specific approach: perianal and ischioanal abscesses are drained via overlying skin, while intersphincteric and supralevator abscesses are drained via the rectal lumen 1

Management of Concomitant Fistulas:

• Examine for fistula tracts during drainage 2
• If a low fistula not involving sphincter muscle is identified, perform fistulotomy at the time of abscess drainage 1, 2
• For fistulas involving any sphincter muscle, place a loose draining seton rather than performing immediate fistulotomy 1, 2
• This approach significantly reduces recurrence (RR=0.13) without statistically significant increase in incontinence 4

Setting for Procedure

• Small perianal abscesses in fit, immunocompetent patients without systemic signs can be managed in an outpatient/emergency department setting 2, 5
• Bedside drainage in the emergency department significantly shortens waiting time (2.13 vs. 10.41 hours) without increasing long-term complications in appropriately selected patients with small primary abscesses 5
• Deeper or more complex abscesses require operating room drainage 2

Antibiotic Therapy

Antibiotics are NOT routinely indicated after adequate surgical drainage in immunocompetent patients. 3, 1, 2

Indications for Antibiotic Therapy:

Antibiotics should be prescribed only when:

• Systemic signs of infection or sepsis are present 3, 2
• Patient is immunocompromised 3, 2
• Source control is incomplete 3, 2
• Significant surrounding cellulitis exists 3, 2

Antibiotic Selection When Indicated:

• Use empiric broad-spectrum coverage targeting Gram-positive, Gram-negative, and anaerobic bacteria 3, 2
• The polymicrobial nature of perirectal abscesses necessitates this broad coverage 3

Post-Operative Care

• Wound packing after drainage remains controversial and may be costly and painful without adding benefit 1
• Routine imaging after incision and drainage is not required 1, 2
• Consider follow-up imaging only for recurrence, suspected inflammatory bowel disease, or evidence of fistula/non-healing wound 1, 2

Special Considerations

Risk Factors for Recurrence:

• Inadequate drainage 1, 2
• Loculations (recurrence rate up to 44%) 1
• Horseshoe-type abscess 1
• Delayed time from disease onset to incision 1

When to Consider Imaging:

• Atypical presentation 1
• Suspected supralevator or intersphincteric abscess 1
• Suspicion of Crohn's disease 1
• CT scan offers advantages of short acquisition time and widespread availability when imaging is needed 1

Crohn's Disease Considerations:

• If perianal Crohn's disease is suspected or confirmed, perform endoscopic assessment of the rectum 1
• MRI is the gold standard for perianal fistulizing Crohn's disease with 76-100% accuracy 1
• Proctitis predicts persistent non-healed fistula tracts and higher proctectomy rates 1

Common Pitfalls

• Delaying drainage while waiting for imaging - do not delay if abscess is clinically suspected 1
• Inadequate drainage - this is the most common cause of recurrence 1, 2
• Routine antibiotic prescription - antibiotics are not needed after adequate drainage in most patients 3, 1, 2
• Missing concomitant fistulas - senior surgeon involvement improves fistula identification (consultants identify fistulas in >50% of cases vs. registrars) 6