Collection of pus within the subcutaenous tissue of the anus that has tracked from the tissue surrounding the anal sphincter

Epidemiology

• They are the most common form of anorectal abscess, making up around 60% of cases
• They are more common in men (M:F 2:1);
• The average age of patients is around 40 years.

Causes

• They are generally colonised by gut flora such as E. coli;
• Those caused by organisms such as Staph. aureus are more likely to be an infection of the skin rather than originating from the digestive tract.

Associated conditions:

• Any anorectal abscess can be caused by an underlying inflammatory bowel disorder, especially Crohn's;
• Diabetes mellitus is a risk factor due to its ability to affect wound healing;
• Underlying malignancy can cause these abscesses as well as other anorectal lesions due to the risk of bowel perforation.

PC

• Patients may describe pain around the anus, which may be worse on sitting
• They may have also discovered some hardened tissue in the anal region
• There may be pus-like discharge from the anus
• If the abscess is longstanding, the patient may have features of systemic infection