What is the appropriate immediate management of a perirectal (perianal) abscess?

Immediate Management of Perirectal (Perianal) Abscess

Incision and drainage is mandatory for every perirectal abscess and must be performed urgently—antibiotics alone are never sufficient. 1

Timing of Surgical Intervention

Emergency drainage (within hours) is required for:

• Sepsis, severe sepsis, or septic shock 1
• Immunosuppression or immunocompromised patients 1
• Diabetes mellitus 1
• Diffuse cellulitis or extensive soft tissue infection 1

For all other patients without these high-risk features, drainage should still occur within 24 hours. 1

Small, simple perianal abscesses in young, fit, immunocompetent patients without systemic signs may be managed in an outpatient or bedside setting under local anesthesia. 1, 2

Surgical Technique

The incision must be placed as close as possible to the anal verge to minimize potential fistula tract length while ensuring complete drainage. 1, 3

Complete drainage is the single most critical factor—inadequate drainage causes recurrence rates up to 44%, compared to only 15% with proper drainage. 1, 3 This is the primary cause of treatment failure. 1

For large abscesses, use multiple counter-incisions rather than one long incision to avoid step-off deformity and delayed healing. 3

Location-specific drainage approaches:

• Perianal and ischioanal abscesses: drain via overlying skin incision 1
• Intersphincteric abscesses: drain into the rectal lumen (may require limited internal sphincterotomy) 1
• Supralevator abscesses: drain via rectal lumen if extension of intersphincteric abscess, or externally via skin if extension of ischioanal abscess 1

Management of Concomitant Fistulas

If an obvious fistula is identified during drainage:

• Perform fistulotomy ONLY for low fistulas not involving sphincter muscle (i.e., subcutaneous fistulas) 1
• Place a loose draining seton for any fistula involving sphincter muscle 1

Do NOT probe to search for a fistula when none is obvious—this causes iatrogenic complications and does not reduce recurrence. 1 Approximately one-third of perianal abscesses have an associated fistula, but probing in the acute setting with edema and anatomical distortion is contraindicated. 1

Antibiotic Therapy

Antibiotics are NOT routinely indicated after adequate surgical drainage. 1, 4

Antibiotics ARE indicated only in these specific situations:

• Sepsis or systemic signs of infection 1
• Surrounding soft tissue infection or extensive cellulitis 1
• Immunosuppression or disturbances of immune response 1
• Incomplete source control (residual undrained collections) 3

When antibiotics are needed, use empiric broad-spectrum coverage of Gram-positive, Gram-negative, and anaerobic organisms, as these infections are polymicrobial. 1, 3

Obtain pus cultures in high-risk patients or when multidrug-resistant organisms are suspected. 1

Post-Operative Care

Wound packing after drainage is controversial and no firm recommendation can be made. 1 Recent evidence suggests packing may be costly and painful without adding benefit to healing, though an ongoing UK trial (PPAC2) may provide clarity. 1

Routine post-operative imaging is NOT required. 3 Consider imaging only for recurrence, suspected inflammatory bowel disease, or non-healing wounds. 3

Critical Pitfalls to Avoid

Never delay drainage waiting for imaging—clinical diagnosis with digital rectal examination identifies 94.6% of perirectal abscesses. 4 Imaging is reserved for atypical presentations, suspected supralevator/intersphincteric abscesses, or concern for Crohn's disease. 1

Avoid timid or overly small incisions—this is a leading cause of recurrence. 3

Do not rely on antibiotics without drainage—this leads to extension into adjacent spaces and systemic infection. 3, 4

Risk Factors for Recurrence

• Inadequate drainage and loculations (recurrence up to 44%) 1, 3
• Horseshoe-type abscess 3
• Delayed time from disease onset to incision 3
• Morbid obesity, preoperative sepsis, and dependent functional status increase reoperation risk 5
• Inflammatory bowel disease, diabetes, or malignancy significantly increase recurrence risk 6

Diagnostic Workup

Check serum glucose, hemoglobin A1c, and urine ketones to identify undetected diabetes mellitus. 1

In patients with systemic infection, obtain complete blood count, serum creatinine, and inflammatory markers (C-reactive protein, procalcitonin, lactate). 1