Value of diffusion weighted MRI in assessment of simple and complicated perianal fistula

Abstract

Aim of the study: The aim of this study was to explore the role of the DWI in assessment of peri-anal fistula and whether it can replace post contrast study. Patients and methods: MRI examinations was done for 35 patients. Images were reviewed for the presence and number of visible fistulas, internal openings, secondary extension, horse shoe and abscess. Apparent diffusion coefficient (ADC) measurement of suspected fistula tracks and abscess cavities was done to assess activity. Comparison between TIRM, DWI and post-contrast T1-weighted fat saturated sequences was done. Surgical findings were the reference standard. Results: Contrast enhanced images were superior to DWI in detection of primary fistula and internal opening while they were equivalent in detection of secondary extensions and abscess. There was no significant difference in overall accuracy of detection of perianal fistula and its complications between combined (DWI and TIRM images) and post contrast images. There was significant difference between ADC values of active and inactive fistulae and between abscess and inflammatory reaction. Conclusion: Combined DWI and TIRM is equivalent to post contrast images in detection of primary and complicated fistula. DWI is useful in differentiation between abscess and inflammatory reaction, and assessment of disease activity. Keywords: MR, Diffusion weighted images, Peri-anal fistula, Post-contrast, Fat suppression, Turbo inversion recovery magnitude (TIRM)