Background & Aims: To determine accuracy of endoscopic ultrasound (EUS) and magnetic resonance imaging (MRI) for evaluation of Crohn's disease perianal fistulas. Methods: Thirty-four patients with suspected Crohn's disease perianal fistulas were prospectively enrolled in a blinded study comparing EUS, MRI, and examination under anesthesia (EUA). Fistulas were classified according to Parks' criteria, and a consensus gold standard was determined for each patient. Acceptable accuracy was defined as agreement with the consensus gold standard for ≥85% of patients. Results: Three patients did not undergo MRI; I did not undergo EUS or EUA; and consensus could not be reached for 1. Thirty-two patients had 39 fistulas (20 trans-sphincteric, 5 extra-sphincteric, 6 recto-vaginal, 8 others) and 13 abscesses. The accuracy of all 3 modalities was ≥85%: EUS 29 of 32 (91%, confidence interval [CI] 75%-98%), MRI 26 of 30 (87%, CI 69%-96%), and EUA 29 of 32 (91%, CI 75%-98%). Accuracy was 100% when any 2 tests were combined. Conclusions: EUS, MRI, and EUA are accurate tests for determining fistula anatomy in patients with perianal Crohn's disease. The optimal approach may be combining any 2 of the 3 methods.
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