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Perianal MRI Active Fistula — RACP Adult Medicine MCQ

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ModerateGastroenterology & HepatologyPerianal MRI Active FistulaRACP Adult Medicine

A 30-year-old man with known Crohn's disease presents with a painful perianal abscess. He is on adalimumab. EUA reveals a complex transphincteric fistula. After seton placement and abscess drainage, what MRI finding indicates active fistula inflammation?

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Correct answer: A — High T2 signal and gadolinium enhancement of the fistula tract

MRI pelvis is the gold standard for assessing perianal Crohn's disease. Active fistula inflammation shows high T2 signal (fluid/oedema in the tract), gadolinium enhancement (active inflammation), and perianal abscess formation. Quiescent fistulae show low T2 signal (fibrosis) and no enhancement. The Van Assche score on MRI quantifies perianal disease burden. Anti-TNF therapy (infliximab has the strongest evidence – ACCENT II) plus seton drainage is the standard combined medical-surgical approach.

Reference: eTG – 2025 – Gastrointestinal; ECCO – 2024 – Perianal Crohn's Disease