Small bowel MR enterography: problem solving in Crohn's disease

Magnetic resonance enterography (MRE) is fast becoming the first-line radiological investigation to evaluate the small bowel in patients with Crohn's disease. It can demonstrate both mural and extramural complications. The lack of ionizing radiation, together with high-contrast resolution, multiplanar capability and cine-imaging make it an attractive imaging modality in such patients who need prolonged follow-up. A key question in the management of such patients is the assessment of disease activity. Clinical indices, endoscopic and histological findings have traditionally been used as surrogate markers but all have limitations. MRE can help address this question. The purpose of this pictorial review is to (1) detail the MRE protocol used at our institution; (2) describe the rationale for the MR sequences used and their limitations; (3) compare MRE with other small bowel imaging techniques; (4) discuss how MRE can help distinguish between inflammatory, stricturing and penetrating disease, and thus facilitate management of this difficult condition. Main Messages • MR enterography (MRE) is the preferred imaging investigation to assess Crohn's disease. T2-weighted, post-contrast and diffusion-weighted imaging (DWI) can be used. • MRE offers no radiation exposure, high-contrast resolution, multiplanar ability and cine imaging. • MRE can help define disease activity, a key question in the management of Crohn's disease. • MRE can help distinguish between inflammatory, stricturing and penetrating disease. • MRE can demonstrate both mural and extramural complications.