Treatment of Rectal Abscess
All rectal abscesses require surgical incision and drainage as definitive treatment. 1, 2
Diagnostic Workup
Clinical Assessment
- Perform digital rectal examination to identify the abscess location and assess for fluctuance 1, 2
- Screen for diabetes mellitus by checking serum glucose, hemoglobin A1c, and urine ketones, as this is a critical comorbidity that affects outcomes 1, 2
Laboratory Testing Based on Clinical Presentation
- If systemic infection or sepsis is present: Order complete blood count, serum creatinine, and inflammatory markers (C-reactive protein, procalcitonin, lactate) 1, 2
- For immunocompetent patients without systemic signs, extensive laboratory workup is not mandatory 1
Imaging Indications
Imaging is not routinely required for straightforward perianal abscesses but should be obtained when: 1, 2
- Presentation is atypical
- Suspicion of occult supralevator abscess exists
- Complex anal fistula is suspected
- Perianal Crohn's disease is a consideration
- Preferred modalities: MRI, CT scan, or endosonography depending on available resources 1, 2
Surgical Management Algorithm
Timing of Surgery
Base surgical timing on sepsis severity: 1, 2
- Emergent drainage required: Patients with sepsis, immunosuppression, diabetes, or diffuse cellulitis 3
- Outpatient management acceptable: Fit, immunocompetent patients with small perianal abscesses without systemic signs 1, 2
Drainage Technique
- Incision should be as close as possible to the anal verge to minimize potential fistula length while ensuring adequate drainage 3
- For deeper or complex abscesses, multiple counter incisions may be necessary 2
- The drainage route (internal transrectal vs. external) depends on the abscess location relative to the levator ani muscle 4
Management of Concomitant Fistula
Do not probe for fistulas if none is obvious to avoid iatrogenic complications 1, 2
If a fistula is identified at the time of drainage:
- Low subcutaneous fistula (not involving sphincter): Perform fistulotomy at time of abscess drainage 1, 2, 3
- Fistula involving sphincter muscle: Place a loose draining seton rather than performing immediate fistulotomy to prevent incontinence 1, 2, 3
Antibiotic Therapy
Antibiotics are NOT routinely indicated for adequately drained anorectal abscesses in immunocompetent patients 2
Indications for Antibiotics
Administer antibiotics when: 1, 2
- Sepsis is present
- Surrounding soft tissue infection/cellulitis exists
- Patient is immunocompromised
- Diabetes or other immune disturbances are present
Antibiotic Selection
- Empiric therapy must cover Gram-positive, Gram-negative, and anaerobic bacteria 2
- Sample drained pus for culture in high-risk patients or those with risk factors for multidrug-resistant organisms 1, 2
- Adjust therapy based on culture results 5
Post-Drainage Management
Wound Care
- No definitive recommendation exists regarding wound packing after drainage based on current evidence 1, 2
Critical Follow-up
- Recurrence risk after drainage alone can be as high as 44% 3
- Risk factors for recurrence include inadequate drainage, loculations, horseshoe-type abscess, and delayed time from disease onset to incision 3
- All patients require appropriate follow-up to ensure adequacy of treatment and evaluate for fistula formation, which occurs in 25-50% of cases 6, 7
High-Risk Complications to Monitor
Necrotizing soft-tissue infection (including fasciitis and myositis) can develop from rectal abscess and carries a 40% mortality rate when present 8