The Role of Magnetic Resonance Enterography in Diagnosis of Crohn’s Disease

Abstract

Crohn’s disease (CD) is a chronic IBD with an unpredictable course characterized by frequent flare-ups interspersed with periods of remission of varying length. CD has a worldwide distribution but is more prevalent in Europe and North America. Prevalence in many developed countries is estimated at 0.1%. In Egypt there is marked increase in the frequency of diagnosis of both UC and CD in the last 10 years. The peak incidence of CD is in adolescents and young adults between 15 and 25 years old, a second shallow peak is seen in the 50- 8 years old age group. It affects any part of the GIT from mouth to anus with 80% small bowel involvement, most commonly the terminal ileum, with characteristic multiple discontinuous sites involvement (skip lesions) and transmural inflammation. Disease is distributed equally between the sexes, although isolated colonic disease is more common in women than men. CD is characterized by cumulative structural damage to the bowel with a progression from inflammation to penetrating disease and fibrosis over time. A large arsenal of medical treatment options are available, and the challenge is to identify patterns of disease behavior early to tailor treatment, identify complications, and use surgical options appropriately. In the past, poor contrast resolution and motion artifact precluded the use of MRE for bowel imaging. Technological advances, including the use of respiration-suspended sequences, improved coils, fat suppression, and IV gadolinium, have extended the role of MRE in the evaluation of the GIT. Since then, various MR sequences to evaluate the GIT have been advocated. However, no sole sequence can be used for comprehensive imaging of CD, as each sequence has its specific advantages and limitations. Therefore, it is essential to use a comprehensive examination protocol in which disadvantages of one sequence can be compensated by the advantages of the others. Normal bowel wall when distended is uniformly thin (not exceeding 2-3mm) and is of symmetric thickness. It is important to compare the degree of thickness of similarly distended segments to exclude disorders . As a collapsed bowel loop may obscure lesions or mimic pathologic wall thickening, bowel distension is the single most important factor for any method of choice. For this purpose, a large amount of orally administered enteric CM is used in MRE examination, to achieve SB luminal distension. Oral CM not only distend the lumen but also decrease the susceptibility to develop artifacts by displacing intraluminal air. MRE used to detect subtle mucosal disease. It can assist the treating clinician in distinguishing between inflammatory stenosis amenable to medical therapy and fibrostenotic disease requiring surgery. It can enable clear