Degree of Creeping Fat Assessed by CT Enterography is Associated with Intestinal Fibrotic Stricture in Patients with Crohn's Disease: A Potentially Novel Mesenteric Creeping Fat Index.

Background and aims Emerging evidence points to a link between creeping fat and pathogenesis of Crohn's disease (CD). Non-invasive assessment of the severity of creeping fat on cross-sectional imaging modality has seldom been investigated. This study aimed to develop and characterize a novel mesenteric creeping fat index (MCFI) based on CT in CD patients. Methods MCFI was developed based on vascular findings on CT in retrospective cohort (n=91) and validated in prospective cohort (n=30). The severity of creeping fat was graded based on the extent to which mesenteric fat extended around the intestinal circumference using the vessels in the fat as a marker. The accuracy of MCFI was assessed by comparing it with the degree of creeping fat observed in surgical specimens. The relationship between MCFI and fibrostenosis was characterized by determining if these correlated. The accuracy of MCFI was compared with other radiographic indices (i.e. visceral to subcutaneous fat area ratio and fibrofatty proliferation score). Results In retrospective cohort, MCFI had moderate accuracy in differentiating moderate-severe from mild fibrostenosis (AUC=0.799; P=0.000). ROC analysis in retrospective cohort identified a threshold MCFI of >3 which accurately differentiated fibrostenosis severity in prospective cohort (AUC=0.756; P=0.018). Excellent correlation was shown between MCFI and the extent of fat wrapping in specimens in prospective cohort (r=0.840, P=0.000). Neither visceral to subcutaneous fat area ratio nor fibrofatty proliferation score correlated well with intestinal fibrosis degree. Conclusions MCFI can accurately characterize the extent of mesenteric fat wrapping in surgical specimens. It may become another non-invasive measure of CD fibrostenosis.