- Abscess in the perirectal area
- May be associated with fistula-in-ano
- Classification of the abscess is based on the location in relation to the levator and sphincteric muscles of the pelvic floor.
- Classification by decreasing frequency: perianal, ischioanal, intersphincteric, and supralevator
- May occur at any age
- More common in males 2:1
- In children, more common in those <2 years
- Most often originates from an occluded anal gland with subsequent bacterial overgrowth and abscess formation
- Infection from within the anal glands, penetrates through the internal sphincter, and ends in the intersphincteric space
- Chronic infection and inflammation may result in the formation of fistula-in-ano. This occurs in up to 50% as a result of persistent anal sepsis or an epithelialized tract.
- Also can be associated with transmural inflammation and fistulization of the rectosigmoid mucosa due to Crohn disease
- Nonspecific anal gland infection
- Crohn disease
- Immune deficiency (e.g., neutropenia, diabetes mellitus, AIDS)
- Perforation by a foreign body
- External trauma
- Chronic granulomatous disease (CGD)
- Tumor (e.g., carcinoma, rhabdomyosarcoma)
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