Magnetic resonance imaging to differentiate between Crohn's disease-associated and cryptoglandular perianal fistula.

Background: The radiological features of Crohn's disease (CD)-associated and cryptoglandular perianal fistulae (PAF) are similar, but distinguishing them is crucial for treatment decisions. Delayed CD diagnosis in PAF can worsen long-term outcomes and accurate radiological differentiation may help identify CD-associated PAF.

Methods: In a retrospective single-center study, we analyzed the pelvic MRI images of the patients with PAF. Logistic regression analysis was performed to identify MRI parameters with independent predictive value for CD-associated PAF. Statistically significant magnetic resonance imaging (MRI) parameters from the model, along with their corresponding coefficients, were used to develop the "DMC index" for differentiating between CD-associated and cryptoglandular PAF.

Results: Out of the 287 MRI screened for eligibility, 119 cases, including 32 (26.89%) patients with an established clinical diagnosis of CD, were analyzed. On multivariate logistic regression analysis, ≥ 2 internal openings of the fistula tract, rectal thickening and distance of the mucosal origin from the anal verge > 1.85 cm predicted the PAF to be associated with CD. The DMC index, with a threshold of ≥ 1.5, demonstrated strong discriminatory ability for CD-associated PAF (sensitivity 65%; specificity 94%; area under curve 0.88 [95% CI 0.81-0.95; p < 0.0001]).

Conclusion: The DMC index effectively identifies CD-associated PAF with high specificity, ensuring minimal false positives and strong diagnostic reliability. Integrating this index with additional diagnostic modalities may facilitate earlier CD diagnosis in patients presenting with PAF, potentially improving long-term clinical outcomes.