LAUSR

BACKGROUND Differentiating ulcerative colitis-associated "backwash" ileitis (BWI) from Crohn's terminal ileitis (CTI) is a diagnostic challenge and highly affects patient's management. This study aimed to investigate magnetic resonance enterography (MRE) features including ileocecal valve patency index (ICPI) in patients with BWI and CTI and distinguish these entities based on MRE findings. METHODS After obtaining institutional review board approval, we reviewed 1654 MREs; 60 patients with pathologically proven BWI (n = 30) and CTI (n = 30) were enrolled. Two radiologists who were blinded to the clinical diagnosis analyzed MREs. We evaluated bowel wall thickness and enhancement pattern, ileocecal valve (ICV) diameter, and lip thickness. Ileocecal valve patency index-T and ICPI-C were calculated to normalize the ICV diameter with respect to terminal ileum (TI) and cecum, respectively. An additional group of non-BWI-UC patients (n = 30) was also included to validate indices. RESULTS Circumferential mural thickening (90% vs 1%, P < .001) and inner-wall enhancement (P < .001) of TI were more frequent in BWI patients than CTI. Serosal irregularity (53% vs 13%, P = .002), higher mural thickness (5mm vs 3mm, P < .001), and asymmetric hyperenhancement (P < .001) of TI were more prevalent in CTI than BWI. Ileocecal valve patency and lip atrophy were significantly higher in BWI than CTI and non-BWI-UC groups (both P < .001). Ileocecal valve patency indices-C and ICPI-T indices were able to accurately distinguish BWI from CTI (area under the ROC curve [AUC], 0.864 and 0.847 for ICPI-T and ICPI-C, respectively) and non-BWI-UC (AUC, 0.777 and 0.791 for ICPI-T and ICPI-C, respectively). Ileocecal valve patency indices-T  ≥31.5% were 100% specific to distinguish BWI from CTI, but sensitivity was 63%. CONCLUSIONS Magnetic resonance enterography features of ICV and TI can accurately differentiate BWI from CTI. Two practical indices introduced in this study showed high specificity to distinguish BWI from CTI.