To date, no one knows what the bowel enhancement patterns mean pathologically. Some have suggested that mural stratification represents active inflammation, whereas homogeneous, transmural enhancement represents fibrostenotic disease. Colombel et al correlated CTE findings with endoscopic severity, histology graded from 0 to 3 (based upon the greatest severity of inflammation) and C-reactive protein levels.60 They found mild to moderate correlation between bowel enhancement, comb sign, and fat density with endoscopic score (Spearman correlation coefficients 0.33 to 0.39). The correlation between wall enhancement and histologic grade was also mild to moderate (r = 0.34–0.38). C-reactive protein (CRP) was elevated when fat density was increased and not with wall hyperenhancement. Lee et al demonstrated that patients with the comb sign were sicker and had higher levels of CRP levels.61 Florie et al compared MRE using qualitative assessment as well as wall thickness and enhancement with endoscopic disease severity grading as well as Crohn's Disease Endoscopic Index of Severity (CDEIS).62 There was a moderate to strong correlation (r = 0.61 and r = 0.62 for the two radiologists) between severity rated at MRI and CDEIS. Wall thickness correlated moderately to strongly as well with CDEIS (r = 0.57 and 0.50). Enhancement correlated weakly to moderately with CDEIS (r = 0.45 and 0.42). Unfortunately, the authors did not measure wall thickness and wall enhancement was not performed; only nonparametric, qualitative assessment was performed. All of these studies show that we have very poor gold standards for measuring inflammatory activity.
