Objective The aim of this study was to determine the diagnostic accuracy of magnetic resonance colonography (MRC) for the evaluation of disease activity and severity in patients with ulcerative colitis (UC) using endoscopy as the reference standard.

Methods Fifty patients with UC underwent colonoscopy and MRC for the evaluation of disease activity. All patients were prospectively and consecutively included. Endoscopic activity was evaluated globally and on a segment basis using the modified Baron score (MBS), and also classified as absent, mild to moderate (inflammation without ulcers) or severe (presence of ulceration). MRC parameters evaluated in each segment were: wall thickness, pre- and post-contrast wall signal intensity, relative contrast enhancement (RCE), mural oedema, ulcers, enlarged lymph nodes and the comb sign.

Results Independent predictors for endoscopic activity on a segment basis were RCE (p=0.006), presence of oedema (p=0.003), enlarged lymph nodes (p<0.001) and the comb sign (p<0.001). A segmental simplified MRC index (MRC-S) ≥1 detected endoscopic inflammation with high diagnostic accuracy (sensitivity 87%, specificity 88%, area under the curve (AUC) 0.95; p<0.001). MRC-S index ≥2 detected severe lesions with high sensitivity (83%) and specificity (82%) with an AUC of 0.91 (p<0.001). The MRC-S index strongly correlated with the MBS (r=0.81, p<0.001) and with the subjective assessment of the radiologists for the evaluation of disease severity (r=0.77, p<0.001).

Conclusions MRC has a high accuracy for the diagnosis of disease activity and severity in UC.