Evaluation of the anal canal using diffusion tensor imaging (DTI) with fiber tractography: prospective study of treated perianal fistula

Background: To prospectively evaluate the post-therapeutic aspects of the anal canal on MRI using diffusion tensor imaging (DTI) with tractography in healed perianal fistula. Methods: : From September 2019 to August 2021, we included 21 patients referred for follow-up MRI of post-therapeutic anal fistulas. All patients were imaged at 3T including an additional DTI sequence. Our cohort was divided between normal and abnormal sphincters based on T2-weighted images. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values were measured for four different muscular components. For the qualitative data, interobserver concordance was determined using quadratic Cohen weighted kappa statistics. For quantitative data we used the Mann-Whitney test for two independent groups and Kruskall-Wallis for several independent groups, with a significance level p<0.05. Results: : The quality score of the 3D representation was satisfying with a substantial interobserver concordance. On the 3D color coded representation, we did not observe any disruption of fibers in the abnormal group. The circular configuration of the internal sphincter and puborectalis was clearly demonstrated. In both groups, there was no significant different between internal sphincter and puborectalis/external sphincters, (ADC values (p=0.38 and p=0.24; FA values (p=0.73 and p=0.27), respectively. Similarly, there was no statistically significant difference in terms of DTI values between the normal and abnormal segments. Conclusion: In healed perianal fistula, minor sequalae (on T2-weighted images) did not appear to modify the DTI parameters or the 3D tractography. However, further studies with larger cohorts are required to confirm the potential clinical impact of this new noninvasive imaging method. Trial registration : This study was approved by the National Ethical Committee (CPP 19 04) and the Institutional Review Board of the US National Library of Medicine -ClinicalTrials.gov Identifier : NCT03881436 ; first posted registration date : 19/03/2019