MRI in perianal Crohn’s disease: STIR versus T1w postcontrast fat-sat imaging

Purpose: To evaluate the diagnostic accuracy of MRI, comparing STIR images versus T1w post-contrast fat-sat images in patients affected by perianal Crohn’s disease (CD). Material and methods: From January 2007 to July 2008, 73 patients with perianal CD underwent pelvic MRI using an external phased array coil. All studies were performed with a 1.5T MRI scanner. STIR and T1w post-contrast fat-sat images were independently analysed by two expert radiologists. Perianal fistulas were classified according to the Parks surgical classification. All patients underwent examination under anesthesia (EUA) that was considered gold standard. Results: By analysing STIR, images documented 31 simple fistulas, 58 complex fistulas, 12 perianal abscess, 4 rectovaginal fistulas and 1 enteroenterica fistula. By analysing T1w, post-contrast fat-sat images documented 33 simple fistulas, 59 complex fistulas, 12 perianal abscess, 4 rectovaginal fistulas and 1 enteroenteric fistula. Pelvic MRI clearly depicted perianal manifestations of CD in all patients with full concordance with EUA in 70 patients (96%). Conclusion: MRI can be considered an accurate technique to identify and classify perianal manifestations of CD. STIR images were almost as useful as T1w post-contrast fat-sat images to show perianal CD findings and could be used to follow-up these patients without administration of contrast-medium.