Complex perianal abscess in Crohn disease — RCPSC EM MCQ

Correct answer: C — CT pelvis with IV contrast to define abscess extent

This presentation is acute complicated perianal Crohn sepsis: fever, severe anal pain, tachycardia, borderline blood pressure, urinary retention and an examination limited by pain with perianal fluctuance. In Crohn disease, perianal abscesses are often complex, deep, horseshoe or supralevator, so the immediate priority is to define the extent and anatomy of the collection to guide urgent colorectal drainage and sepsis control. CT pelvis with IV contrast is the correct investigation here because it is rapid, available in the acute setting, and demonstrates rim-enhancing collections, deep pelvic extension and associated fistulous disease. Colonoscopy must not delay drainage in acute perianal sepsis; plain abdominal radiography does not define perianal abscess anatomy; serum amylase is irrelevant; and discharge without imaging/treatment is unsafe.

Reference: American College of Radiology (ACR) Appropriateness Criteria®: Anorectal Disease, current ACR guidance; Variant 1 states that CT pelvis with IV contrast is “Usually Appropriate” for initial imaging of suspected perianal abscess or fistula. https://acsearch.acr.org/docs/3102384/narrative