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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.

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Background To determine whether magnetic resonance imaging (MRI)-detected extramural vascular invasion (mrEMVI) status is associated with quantitative perfusion parameters derived from dynamic contrast-enhanced MRI (DCE-MRI) in rectal cancer. Methods Seventy-two patients with rectal adenocarcinoma who underwent curative surgery alone within 2 weeks following rectal MRI were enrolled in this retrospective study. mrEMVI status was determined based on high-resolution MRI. The quantitative perfusion parameters ( K trans , k ep and v e ) derived from DCE-MRI were calculated from all sections containing tumours. DCE-MRI parameters and clinicopathological variables in patients with different mrEMVI statuses were compared. Results For patients who were mrEMVI positive, the tumours demonstrated significantly lower k ep values ( P = 0.012) and higher v e values ( P = 0.021) than tumours of patients who were mrEMVI negative, while the K trans value displayed no significant difference ( P = 0.390). The patients who were mrEMVI positive had larger tumour size, higher pathological tumour stage and increased regional nodal metastases compared to those who were mrEMVI negative (2.9 cm vs. 3.5 cm, P = 0.011; 63.8% vs. 92.0%, P = 0.010; 36.2% vs. 76.0%, P = 0.001; respectively). Conclusions This study demonstrated for the first time that tumour microcirculation is altered in mrEMVI-positive patients with rectal adenocarcinoma, as evidenced by significantly lower k ep and higher v e values. In addition, these patients were more likely to have a larger tumour size, a higher pathological tumour stage and regional nodal metastases than mrEMVI-negative patients.

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