Colorectal SurgeryPending review

Perianal Abscess and Fistula

Blockage of a mucus-secreting anal gland lets bacteria multiply into a walled-off abscess, and if that pus tracks a path to the skin before it is drained, the epithelialised tunnel it leaves behind becomes a persistent fistula-in-ano.

In a nutshell

A blocked cryptoglandular anal gland becomes infected and forms an abscess; where the pus tracks (perianal, ischiorectal, supralevator) determines the clinical picture. If the tract persists after drainage it becomes a fistula-in-ano, and how much sphincter it crosses determines whether it can be laid open or needs a seton.

Classic presentation

Acute throbbing perianal pain with a tender fluctuant swelling and fever (abscess), or chronic intermittent perianal discharge with a history of a previously drained abscess (fistula).

Key points

Perianal sepsis begins as a blocked, infected anal gland in the intersphincteric space, not as a primary skin infection.

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Educational content pending clinical review. Not medical advice.