**Part 2**

**Advances in Diagnosis of Inflammatory Bowel Disease** 

134 Inflammatory Bowel Disease – Advances in Pathogenesis and Management

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**7** 

*USA* 

**The Role of Imaging in Inflammatory** 

*Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts* 

The evaluation of the digestive tract through radiologic techniques represents a cornerstone in the management of patients with inflammatory bowel disease (IBD). Historically, a central facet in the diagnostic evaluation for IBD was the double contrast barium enema, which provided a non-invasive method for assessing the mucosal pattern of the large bowel. In the modern era, this approach has been supplanted by endoscopic procedures such as colonoscopy that offer direct mucosal inspection and biopsy capabilities. However, while endoscopy offers unparalleled visualization of the large bowel lumen, the small bowel remains essentially wholly inaccessible by conventional endoscopic techniques (D. D. T. Maglinte, 2006). Thus, one important role that imaging plays in the care of patients with IBD is the evaluation of the small bowel, both to help discriminate between ulcerative colitis

(UC) and Crohn's disease (CD), as well as to identify active versus inactive disease.

Moreover, the role of imaging has greatly expanded with the advancement of cross-sectional imaging techniques such as computed tomography (CT) and magnetic resonance imaging (MRI) that can assess the extramural manifestations of IBD. For example, UC almost always affects the colon in a stereotyped way, extending from the rectum proximally in a continuous manner, without skip areas. The superficial erosions in early or mild UC are below the resolution of CT and MRI. However, one severe complication of UC, and a leading cause of death, is toxic megacolon, in which inflammation leads to destruction of ganglion cells and consequent colonic dilation (Elsayes et al., 2010). In these acutely ill patients, non-invasive methods are preferred to endoscopy. Likewise, the urgent and emergent sequelae of CD such as abscesses, fistulae, perforations, and strictures are best identified by radiologic modalities. Additionally, the pre-surgical delineation of disease extent and the post-surgical investigation for operative complications revolve around crosssectional imaging. Finally, techniques such as MRI that provide superior soft tissue contrast allow for both the improved visualization of the perianal disease manifestations of CD such as fistulae and abscesses, as well as the precise anatomic localization for treatment planning

Multiple radiologic modalities, including fluoroscopy, CT, MRI, ultrasound, and nuclear medicine techniques, have been applied towards imaging IBD. In this chapter, we will discuss technical considerations, appropriate indications, and key imaging findings for each imaging modality. We will also discuss special considerations in pediatric patients, in

particular the risks of recurrent exposure to ionizing radiation.

**1. Introduction** 

(Schreyer et al., 2004).

**Bowel Disease Evaluation** 

Rahul A. Sheth and Michael S. Gee
