Evaluation of Crohn's disease activity by MR enterography: Derivation and histopathological comparison of an MR-based activity index.

Aims: To compose a qualitative magnetic resonance imaging (MRI) activity index showing Crohn disease (CD) activity, and to compare magnetic resonance enterography (MRE) findings with histopathology results.

Materials And Methods: Twenty-six patients (11 male and 15 female; mean age 36.7) who had MRE and colonoscopic biopsy between October 2011 and August 2012 were included in the study. On MRE the following parameters were evaluated: bowel wall thickness, bowel wall T2 signal, bowel wall contrast enhancement pattern and degree, length and number of involved bowel segments, perimural T2 signal, mesenteric inflammation, mesenteric lymph nodes and complications of CD. Each parameter was scored to calculate MRI activity index. Biopsy specimens were retrospectively evaluated, histopathologic and endoscopic acute inflammmation scores (AIS, eAIS) were calculated. Each parameter and total MRI activity index were compared with the pathology scores (AIS, eAIS) by Mann-Whitney U test and Spearman correlation.

Results: Statistically significant positive correlation was found between AIS and eAIS, mural thickness and eAIS. Moderate correlation was found between MRI activity index and eAIS, mural enhancement degree and eAIS; and poor correlation was found between mesenteric inflammation score and eAIS, MRI activity index and AIS, however they were not statistically significant.

Conclusions: In CD, bowel wall thickness measured by MRE is best correlated with the histopathologic results which are accepted as the reference standard. In cases with high MRI activity index, eAIS is also generally high. MRI activity index which is measured simply and noninvasively can be used in the follow up of CD.