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.