Diffusion‐weighted MRI: A new tool for the diagnosis of fistula in ano

Purpose: To retrospectively determine the additional value of diffusion‐weighted magnetic resonance imaging (MRI) to T2‐weighted imaging in the evaluation of anal fistulae in comparison with gadolinium (Gd)‐enhanced imaging. Materials and Methods: Thirteen patients (mean age, 35.2 years) with 20 anal fistulae were included. The protocol consisted of fat‐suppressed T2‐weighted fast spin‐echo, diffusion‐weighted single‐shot echo‐planar (b factors 0 and 800 s/mm 2 ), and fat‐suppressed Gd‐enhanced T1‐weighted gradient echo sequences. Two radiologists evaluated images in consensus. Results: Eighteen (90%) fistulae were detected on T2‐weighted images, and 19 (95%) and 19 (95%) were detected on diffusion‐weighted and T2‐weighted images combined and on Gd‐enhanced and T2‐weighted images combined, respectively. There was no statistically significant difference in sensitivity of the techniques ( P > 0.5 for all comparison pairs). Confidence scores with diffusion‐weighted and T2‐weighted images combined or those with Gd‐enhanced and T2‐weighted images combined were significantly greater than those with T2‐weighted images alone ( P = 0.0047 and 0.014, respectively). Conclusion: Diffusion‐weighted MRI of anal fistulae is a useful sequence and can be a helpful adjunct to T2‐weighted imaging, especially in patients with risk factors for contrast agents. J. Magn. Reson. Imaging 2009;30:1021–1026. © 2009 Wiley‐Liss, Inc.