What is the treatment for an anal abscess?

Treatment of Anal Abscess

Surgical incision and drainage is the definitive treatment for all anal abscesses and should be performed promptly to prevent progression to systemic infection. 1, 2

Diagnosis and Initial Assessment

• Obtain a focused medical history and perform complete physical examination including digital rectal examination to confirm the diagnosis 1, 2
• Check serum glucose, hemoglobin A1c, and urine ketones to identify undetected diabetes mellitus, which is a common comorbidity 1, 2
• In patients with systemic signs of infection or sepsis, obtain complete blood count, serum creatinine, and inflammatory markers (C-reactive protein, procalcitonin, lactate) 1, 2
• Imaging (MRI, CT, or endosonography) is not routinely required but should be obtained for atypical presentations, suspected deep supralevator abscesses, or suspected inflammatory bowel disease 2, 3

Surgical Management

The cornerstone of treatment is incision and drainage, with the incision placed as close as possible to the anal verge to minimize potential fistula length while ensuring adequate drainage. 2, 3

Timing of Surgery

• Patients with sepsis, immunosuppression, diabetes, or diffuse cellulitis require emergent drainage 4
• Fit, immunocompetent patients with small perianal abscesses without systemic signs may be managed as outpatients 4, 3

Surgical Technique

• For large abscesses, use multiple counter incisions rather than a single long incision to prevent delayed wound healing and step-off deformity 1, 3
• Examine for an associated fistula tract during the procedure, but avoid excessive probing if a fistula is not obvious, as this may cause iatrogenic fistula formation 2, 5

Management of Associated Fistulas

Approximately one-third of anal abscesses have an associated fistula 1, 6:

• If a low subcutaneous fistula not involving sphincter muscle is identified, perform fistulotomy at the time of abscess drainage 2, 3
• For fistulas involving sphincter muscle, place a loose draining seton rather than performing immediate fistulotomy to prevent incontinence 2, 4, 3

This approach is critical because primary fistulotomy of complex fistulas carries significant risk of fecal incontinence, while drainage alone results in recurrence rates as high as 44% 4, 3, 7.

Antibiotic Therapy

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

Indications for Antibiotics

Administer antibiotics only in the following situations 1, 2, 3:

• Presence of sepsis or systemic signs of infection
• Immunocompromised patients
• Incomplete source control
• Significant surrounding cellulitis

Antibiotic Selection

• When indicated, use empiric broad-spectrum coverage for Gram-positive, Gram-negative, and anaerobic bacteria 1, 2, 3
• Consider sampling drained pus in high-risk patients or those with risk factors for multidrug-resistant organisms 2

Post-Procedure Care

• Close follow-up is essential to monitor for recurrence or fistula development 3
• Routine imaging after drainage is not required unless there is recurrence, suspected inflammatory bowel disease, or evidence of fistula/non-healing wound 3
• No definitive recommendation exists regarding wound packing after drainage 2

Common Pitfalls

• Inadequate drainage, loculations, horseshoe-type abscess, and delayed time from disease onset to incision are major risk factors for recurrence 4, 3
• Excessive probing during initial drainage increases risk of iatrogenic fistula formation 2, 5
• Performing immediate fistulotomy on complex fistulas involving sphincter muscle risks permanent fecal incontinence 2, 4