MRI in inflammatory bowel disease

Abstract

MR enterography is increasingly being recognized as an imaging gold standard in the detection and staging of patients with inflammatory bowel disease. Its biggest advantage as compared with CT enterography is the absence of ionizing radiation. This is vital in this patient group who may go on to have multiple imaging evaluations during the course of their disease and has prompted increasing MRI referrals in an era where radiation sequelae are in the forefront of public consciousness. Moreover its non-invasive nature, high contrast resolution, multi-planar capability and lack of requirement for iodinated contrast media to provide high quality and reproducible imaging of the small bowel confer a distinct advantage over other modalities that are used to evaluate the bowel. Moreover its ability to provide functional information by utilization of MR motility sequences and diffusion weighted imaging (DWI) are unique. There has been much work on assessing disease activity on MRI and using it as a tool to guide patient management. This review will focus on the benefits and disadvantages of MR enterography and provide specific examples of protocols that may be used to assess the small and large bowel. These protocols will need to be tailored to address the clinical areas of concern. The benefits and limitation of differing categories of oral contrast media will also be discussed in some detail, as will characteristic imaging findings in patients with IBD involving both the large and small bowel. An overall review of the performance characteristics as compared with conventional imaging and endoscopic techniques will be provided. The utility of MR scoring systems as an objective method for quantification of disease activity will be discussed as will the potential impact of DWI in disease evaluation in this patient population. In the challenging area of perianal disease MRI remains an established gold standard in providing a baseline for depiction of the presence and anatomical extent of disease. It is vital therefore not only in initial management but guiding subsequent therapeutic decision-making particularly in the utilization of immune modulating drugs. The imaging technique, efficacy, classification system and the potential complications of long standing perianal disease will be described.