What is the appropriate management for a patient presenting with a rectal abscess?

Management of Rectal Abscess

Surgical incision and drainage is the definitive treatment for all rectal abscesses and should be performed urgently, with timing based on the severity of sepsis. 1, 2

Initial Assessment

Clinical Examination

• Perform a focused medical history specifically checking for:

  • Undiagnosed Crohn's disease (especially in recurrent cases) 1
  • Surgical scars, anorectal deformities, and signs of perianal Crohn's disease 1
  • External fistula openings and secondary cellulitis 1

• Complete physical examination including digital rectal examination is usually sufficient to diagnose superficial abscesses, though deeper abscesses may only reveal a tender, indurated area above the anorectal ring 1. Sedation or anesthesia may be needed due to intense pain 1.

• Maintain high clinical suspicion in high-risk populations (elderly, diabetic, immunosuppressed patients) as symptoms may be absent or diminished 1

Laboratory Testing

• Check serum glucose, hemoglobin A1c, and urine ketones in all patients to identify undetected diabetes mellitus 1, 2

• For patients with signs of systemic infection or sepsis, obtain complete blood count, serum creatinine, and inflammatory markers (C-reactive protein, procalcitonin, lactates) 1, 2

Imaging Studies

Imaging is NOT routinely required for straightforward cases 1. However, obtain MRI, CT scan, or endosonography in the following situations 1, 2:

• Atypical presentation (lower back pain, severe anal pain without fissure, urinary retention) 1
• Suspected occult supralevator or intersphincteric abscess 1, 2
• Suspicion of perianal Crohn's disease or complex anal fistula 1, 2

CT scan offers advantages of short acquisition time and widespread availability, though MRI has higher detection rates 1

Surgical Management

Timing and Setting

• Emergent drainage is required for patients with:

  • Sepsis or signs of systemic infection 1, 3
  • Immunosuppression 3
  • Diabetes 3
  • Diffuse cellulitis 3

• Outpatient management may be considered only for fit, immunocompetent patients with small perianal abscesses without systemic signs of sepsis 1, 3

Surgical Technique

• Keep the incision as close as possible to the anal verge to minimize the length of a potential fistula while ensuring adequate drainage 3, 4

• For larger abscesses, use multiple counter incisions rather than a single long incision to prevent delayed wound healing 3

• Examine for associated fistula tracts during the procedure 3

Management of Concomitant Fistulas

• For low fistulas NOT involving sphincter muscle (subcutaneous fistulas): perform fistulotomy at the time of abscess drainage 1, 2, 3

• For fistulas involving ANY sphincter muscle: place a loose draining seton rather than performing immediate fistulotomy to prevent incontinence 1, 2, 3, 4

• Do NOT probe to search for a fistula if one is not obvious, as this may cause iatrogenic complications 1, 2

Antibiotic Therapy

Antibiotics are NOT routinely indicated after adequate surgical drainage in immunocompetent patients. 1, 2, 5 However, administer antibiotics in the following situations 1, 2, 3:

• Presence of sepsis or systemic signs of infection
• Immunocompromised patients
• Surrounding soft tissue infection or significant cellulitis
• Incomplete source control

Antibiotic Selection

• When indicated, use empiric broad-spectrum coverage targeting Gram-positive, Gram-negative, and anaerobic bacteria 2, 3

• Sample drained pus in high-risk patients or those with risk factors for multidrug-resistant organisms 1, 2

• Inadequate antibiotic coverage results in a six-fold increase in readmission rates for complicated perirectal abscesses, with 28.6% recurrence versus 4% with adequate coverage 6

Post-Procedure Care

• No definitive recommendation exists regarding wound packing after drainage based on current evidence 1, 2

• Close follow-up is essential to monitor for recurrence or fistula development 3

• Recurrence rates can be as high as 44%, with risk factors including inadequate drainage, loculations, horseshoe-type abscess, and delayed time from disease onset to incision 3, 4

Critical Pitfalls to Avoid

• Do not miss necrotizing soft-tissue infection (Fournier's gangrene), which requires aggressive surgical debridement and carries high mortality 1, 7

• Do not delay drainage in high-risk patients (diabetic, immunosuppressed, elderly) who may have minimal symptoms despite severe infection 1

• Do not perform immediate fistulotomy for fistulas involving sphincter muscle, as this risks fecal incontinence 1, 2, 3