Magnetic resonance imaging for evaluation of Crohn's disease: Validation of parameters of severity and quantitative index of activity

Background: The use of magnetic resonance imaging (MRI) for assessment of Crohn's disease (CD) is expanding. The aim of this study is to define and provide an external validation of the MRI predictors of active CD, severe CD, and a quantitative Magnetic Resonance Index of Activity (MaRIA). Methods: In all, 48 patients with clinically active (n = 29) or inactive (n = 19) CD underwent ileocolonoscopy (reference standard) and MRI. T2‐weighted and pre‐ and postcontrast‐enhanced T1‐weighted sequences were acquired. Endoscopic activity was evaluated by the Crohn's Disease Endoscopic Index of Severity (CDEIS), and also classified as absent, mild (inflammation without ulcers), or severe (presence of ulceration). Results: In complete agreement with a previous derivation study, independent predictors of disease severity using CDEIS as a reference were wall thickness, relative contrast enhancement (RCE), presence of edema, and ulcers on MRI. Estimation of activity in each segment using this regression model, or another with simplified coefficients (MaRIAS = 1.5*wall thickness + 0.02*RCE + 5*edema + 10*ulceration) correlated with CDEIS (r = 0.798, P < 0.001; r = 0.80 P < 0.001, respectively). In the validation cohort both indexes had a high and equal accuracy for diagnosis of active disease: receiver operator characteristic (ROC) area 0.93, sensitivity 0.87, specificity 0.87 using a cutoff point ≥7, and for diagnosis of severe disease: ROC area 0.96, sensitivity 0.92, specificity 0.92 using a cutoff point ≥11. The total of segment values (MaRIAT) correlated with global CDEIS (r = 0.83, P < 0.001). Conclusions: The MRI variables that should be evaluated in clinical practice to diagnose active CD and severe CD are validated, as well as the quantitative index of activity for use in research studies. (Inflamm Bowel Dis 2010)