Perianal Abscess

A perianal abscess is an acute collection of pus arising most commonly from infection of an anal gland with extension into superficial perianal tissues.

Abscess and fistula represent different phases of the same cryptoglandular process. A fistula may become apparent immediately or after the abscess has healed.

Antibiotics cannot replace drainage of a mature anorectal abscess.

Patients present with constant throbbing anal pain, swelling and local tenderness.

Pain is usually unrelated to defaecation alone and progressively worsens.

Superficial abscesses produce obvious erythema, fluctuance and induration.

Fever may be absent.

Diagnosis is usually clinical.

Imaging is unnecessary for a straightforward superficial abscess.

MRI or CT is useful for occult disease, recurrent abscesses, Crohn disease, immunosuppression or suspected deep extension.

Perform prompt incision and drainage.

Make an adequate incision close enough to the anal verge to allow dependent drainage while minimising the length of any subsequent fistula tract.

Break down obvious loculations and evacuate pus. Routine prolonged packing is unnecessary and increases postoperative discomfort.

Antibiotics are not routinely required after adequate drainage in a healthy patient with uncomplicated local disease.

Use antibiotics when there is:

• Extensive cellulitis
• Systemic infection
• Immunosuppression
• Significant diabetes with complicated infection
• Another specific high risk feature.

A practical oral regimen is:

Amoxicillin clavulanate 875 mg/125 mg orally every 12 hours for approximately 5 to 7 days.

Severe systemic infection requires IV therapy and assessment for deeper sepsis.

Do not aggressively search for or divide an uncertain fistula tract during acute drainage because unnecessary sphincter division can cause permanent continence impairment.