Ischiorectal Abscess

An ischiorectal, or ischioanal, abscess occupies the fat filled space lateral to the external anal sphincter and below the levator ani.

It usually develops when cryptoglandular infection crosses the external sphincter from the intersphincteric plane.

Large collections can extend posteriorly across the midline, producing a horseshoe abscess.

Pain is deep, constant and often severe.

The superficial skin may initially appear normal because the collection lies deeper than a simple perianal abscess.

Later findings include buttock or perianal swelling, induration and tenderness.

Systemic symptoms are more common with large deep abscesses.

A horseshoe abscess can produce bilateral buttock pain and posterior midline tenderness.

CT pelvis with IV contrast: useful in acutely ill patients with deep disease.

Pelvic MRI: best for complex, recurrent or anatomically uncertain sepsis when immediate drainage is not delayed.

Prompt operative drainage is required.

Drain externally through the perianal or ischioanal skin with an incision that allows effective cavity drainage while avoiding unnecessary sphincter injury.

Large cavities require complete evacuation and disruption of loculations.

A horseshoe abscess usually requires drainage of the deep postanal space plus lateral ischioanal extensions. Multiple counter incisions with a draining seton or modified Hanley approach can achieve drainage while limiting sphincter division.

Avoid a large posterior midline sphincter division unless clearly required.

Antibiotic use follows the same principles as other anorectal abscesses and does not substitute for drainage.