What is the management of a peri-rectal abscess?

Management of Perirectal Abscess

Primary Treatment: Surgical Drainage

Incision and drainage is the cornerstone of treatment for all perirectal abscesses and should be performed promptly once diagnosed. 1, 2 An undrained perirectal abscess can expand into adjacent spaces and progress to generalized systemic infection. 1

Timing of Surgical Intervention

The urgency of drainage depends on clinical presentation:

• Emergency drainage (immediate) is required for patients with:

  • Sepsis, severe sepsis, or septic shock 2
  • Immunosuppression 2
  • Diabetes mellitus 2
  • Diffuse cellulitis 2

• Urgent drainage (within 24 hours) for stable patients without the above risk factors 1, 2

Surgical Technique

The incision should be placed as close as possible to the anal verge to minimize potential fistula length while ensuring adequate drainage. 1, 2 This is critical because inadequate drainage is a major risk factor for recurrence. 1

Specific approach based on abscess location:

• Perianal and ischiorectal abscesses: drain via overlying skin 1, 2
• Intersphincteric abscesses: drain into the rectal lumen 1, 2
• Supralevator abscesses: drain via rectal lumen or externally through skin 2

For large abscesses, use multiple counter incisions rather than a single long incision to avoid step-off deformity and delayed wound healing. 1

Management of Concomitant Fistulas

During abscess drainage, if a fistula tract is identified:

• Perform primary fistulotomy ONLY for low fistulas not involving sphincter muscle 2
• Place a loose draining seton for any fistula involving sphincter muscle 2

This approach balances recurrence prevention (fistulotomy reduces recurrence from 44% to as low as 15% 1) against the risk of incontinence from sphincter damage.

Antibiotic Therapy

Antibiotics are NOT routinely indicated after adequate surgical drainage. 2, 3 However, antibiotics should be administered in specific circumstances:

Indications for Antibiotics

Add broad-spectrum antibiotics covering gram-positive, gram-negative, and anaerobic organisms when: 1

• Systemic signs of infection or sepsis are present 1, 2
• Patient is immunocompromised 1
• Source control is incomplete 1
• Significant surrounding cellulitis extends beyond abscess borders 1

Inadequate antibiotic coverage after drainage of complicated perirectal abscess results in a six-fold increase in readmission rates (28.6% vs 4%). 4 When antibiotics are indicated, ensure coverage matches the polymicrobial nature of these infections (mixed aerobic/anaerobic organisms in 37% of cases, mixed aerobic in 33%). 4

Outpatient vs Inpatient Management

Young, fit, immunocompetent patients with small perianal abscesses and no systemic signs of sepsis may be managed as outpatients. 1, 2 Small simple perianal abscesses can be treated under local anesthesia in an ambulatory setting. 1

Approximately 35% of patients require hospital admission, with risk factors including: 5

• Preoperative sepsis
• Bleeding disorders
• Non-Hispanic black or Hispanic race
• Morbid obesity
• Dependent functional status

Diagnostic Imaging

Clinical diagnosis based on history and physical examination is usually sufficient. 1, 2 The most common symptom is perirectal pain (present in 98.9% of cases), and external perianal plus digital rectal examination identifies the abscess in 94.6% of patients. 3

Consider imaging when:

• Atypical presentation 2
• Suspected supralevator or intersphincteric abscess 2
• Suspicion of Crohn's disease 2
• Do not delay drainage if imaging is unavailable when abscess is clinically suspected 2

When imaging is needed, CT scan offers advantages of short acquisition time and widespread availability, though MRI is the gold standard for perianal fistulizing Crohn's disease (76-100% accuracy). 2

Post-Operative Care and Follow-Up

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

Common Pitfalls and Risk Factors for Recurrence

Recurrence rates can be as high as 44% after drainage alone. 1 Key risk factors include:

• Inadequate drainage (most important) 1, 2
• Loculations 1, 2
• Horseshoe-type abscess 1, 2
• Delayed time from disease onset to incision 1, 2

Complete and accurate drainage at the initial procedure is essential to prevent recurrence. 1 Needle aspiration has a 41% recurrence rate compared to 15% with proper incision and drainage. 1

Reoperations occur in 3.4% of cases (median 15.5 days later), with 79.7% performed for additional drainage, and readmissions occur in 3.0% (median 10.5 days later), most commonly for recurrent/persistent abscess (41.4%). 5