A 32-year-old man presents with a perineal abscess just lateral to the anus. Examination shows fluctuance in the ischiorectal fossa. This space communicates with the contralateral side through which potential space?

• A Retropubic space of Retzius
• B Deep postanal space (posterior to the anococcygeal body) ✓
• C Superficial perineal pouch
• D Pararectal fossa

Explanation

The two ischiorectal fossae (ischioanal fossae) communicate posteriorly through the deep postanal space, which lies between the posterior border of the external anal sphincter and the anococcygeal ligament (just above the anococcygeal body). This communication is the route by which horseshoe abscesses track — infection starts unilaterally and spreads to the contralateral ischiorectal fossa. Surgical drainage of horseshoe abscess requires opening the deep postanal space in addition to the lateral pockets. The superficial postanal space (below the anococcygeal body) allows more superficial spread.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.