Advances in imaging in Crohn's disease.

Radiologic evaluation plays a critical role in the assessment of patients with inflammatory bowel disease, particularly Crohn’s disease (CD). In UC, colonic mucosa is readily accessible for endoscopic evaluation; thus radiologic techniques are less useful. Traditionally, fluoroscopic studies including the small bowel series and barium enema, along with CT, were the mainstays of imaging. These modalities were used to diagnose disease, document its extent, identify complications including fistula, stricture, abscess and obstruction. CT enterography (CTe) and, more recently, MR enterography (MRe), which provide a comprehensive assessment of both luminal and extraluminal disease, have supplanted fluoroscopic studies. MRe is particularly exciting because it provides all of the information of CTe as well as additional information regarding disease activity without exposing patients to ionizing radiation. The small bowel series and barium enema are essentially historic examinations for the detection and evaluation of inflammatory bowel disease. These studies, while effective at detecting mucosal abnormalities, are poorly tolerated by sick patients, provide assessment only of the bowel lumen (particularly the mucosa) and are physician dependent, limiting their reproducibility. A properly performed and interpreted SBFT or BE is unfortunately a lost art and available only in select centers. Additionally, of course, these studies may involve significant doses of radiation. Colonoscopy remains an essential diagnostic tool to visualize and biopsy the mucosa of the large bowel and distal ileum in inflammatory bowel disease (IBD). CTe is currently the gold-standard imaging study for the evaluation of Crohn’s disease, especially non-mucosal. The fundamental difference between a traditional CT and a CTe examination is the use of “negative” or low-attenuation oral contrast (which is dark on CT) as opposed to the more commonly used “positive” or high-attenuation contrast such as barium (white on CT). Negative oral contrast yields distension of the small bowel with low-attenuation, dark, fluid. After administering IV contrast, the mucosa enhances, which is striking against the dark bowel lumen. The degree of mucosal enhancement has been correlated with disease activity in patients with Crohn’s disease. CTe also provides fast, well-tolerated and comprehensive evaluation of all bowel segments as well as evidence of extraluminal complications such as abscess formation. However, there are drawbacks and limitations inherent to this technique.