P218 Development of Magnetic Resonance Imaging based index to differentiate Crohn’s disease associated perianal fistula and cryptoglandular perianal fistula

Background Magnetic resonance imaging (MRI) is the standard for evaluating perianal fistulae. Perianal fistula can be the first manifestation of CD, and needs to be differentiated from non-CD associated perianal fistula. This study sought to identify the variations in MRI characteristics of perianal fistulas in patients with and without inflammatory bowel disease (IBD), considering the potential implications for treatment decisions. Methods This was a single-center cross-sectional analysis of patients who underwent pelvic MRI for assessment of perianal fistula between January 2021 and June 2022 at Dayanand Medical College and Hospital (DMCH), Ludhiana, India. Patients who underwent dedicated MRI fistula protocol were included. Patients with prior anal resection or anastomosis, anorectal tumor, or equivocal imaging findings that could not be definitely assessed as a fistula were excluded. The following features were assessed: anatomic type of fistula (Parks classification), luminal origin (hour clock position), anal verge distance, signs of acute inflammation, circumference of anus involved by inflammation, presence of rectal inflammation, and abscess. Results Between January 2022 and December 2022, a total of 287 MRI scans were conducted to assess for perianal fistulae. Out of these, 119 MRI scans met the eligibility criteria and 32(26.89%) were associated with an established clinical diagnosis of CD. A higher proportion of females had CD-associated perianal fistula compared to non-CD perianal fistula. A significantly greater percentage of CD-associated perianal fistulas exhibited supra-levator extension, multiple and branched fistula tracts, and ≥2 internal and external openings. Patients with CD had higher prevalence of concurrent perianal abscess, proctitis, anorectal strictures, and a greater number of clock hours of inflamed anal circumference, compared to patients with cryptoglandular fistula. (Table 1) On multivariate logistic regression analysis, female sex, ≥2 internal openings, proctitis and height of the mucosal origin of the fistula from the anal verge >1.85 cm independently predicted the perianal fistula to be associated with CD. We constructed the DMCH index as follows: DMCH index: (3xfemale sex) + (3x≥2 internal openings of the fistula tract) + (6xrectal wall thickening) + (2xheight of mucosal origin of the fistula from anal verge >1.85 cm) The DMCH index greater than 7 identified the perianal fistulae associated with CD with a sensitivity of 84% and specificity of 91% [Area under curve 0.91; 95% CI 0.85-0.97; P< 0.0001].(Figure 1) Conclusion The DMCH index identifies CD associates perianal fistula with a high level of accuracy. These findings require validation and confirmation in independent, multi-reader studies.