Crohns Disease

Crohn's disease may involve segments of the whole GI tract. However, Crohn's disease most often affects the terminal ileum and the proximal colon. Unlike ulcerative colitis, Crohn's disease typically affects the GI tract in a discontinuous way (so-called skip lesions) and the inflammatory process is transmural in nature.

CT usually misses the early stages of Crohn's disease (Biancone et al. 2003). With progression of the disease, mural thickening and luminal narrowing occur. The outer contour of the colon wall is irregular. The degree of contrast enhancement of the bowel wall correlates with the severity of the disease (Gore et al. 1996). As a result of the hyperemia from the inflammatory process, the local mesenteric vessels are dilated and widely spaced, which has been described as the "comb sign." A progressive increase in higher-density pericolic fat is called fibrofatty proliferation and is an attempt by the body to contain the inflammatory process, resulting in separation of the bowel loops. Usually, multiple mesenteric lymph nodes, measuring <10 mm in the short axis diameter, are present. Extensive, intersecting linear transverse and longitudinal ulcerations can result

Colonoscopy ShortsCrohn Colonoscopy

Fig. 13.9a-c. Ulcerative colitis with stenotic cancer in the transverse colon (arrow): local flattening and disappearance of the haustra in the sigmoid and descending colon (a). Focal, stenotic, circular wall thickening with shoulder formation in the transverse colon, with soft tissue attenuation and CM enhancement (b,c). Combined 2D+3D view of the stenotic cancer (c)

Fig. 13.9a-c. Ulcerative colitis with stenotic cancer in the transverse colon (arrow): local flattening and disappearance of the haustra in the sigmoid and descending colon (a). Focal, stenotic, circular wall thickening with shoulder formation in the transverse colon, with soft tissue attenuation and CM enhancement (b,c). Combined 2D+3D view of the stenotic cancer (c)

Insane Rays

Fig. 13.10a-c. Crohn's disease: Skip lesions (arrow) in the terminal ileum and the transverse colon (a,b). Irregular wall thickening and stenosis of the transverse colon with pericolic fat stranding and flattening and disappearance of the haustra (arrow) (b). Virtual colonoscopy shows luminal narrowing and cobblestone pattern

Fig. 13.10a-c. Crohn's disease: Skip lesions (arrow) in the terminal ileum and the transverse colon (a,b). Irregular wall thickening and stenosis of the transverse colon with pericolic fat stranding and flattening and disappearance of the haustra (arrow) (b). Virtual colonoscopy shows luminal narrowing and cobblestone pattern in the so called "cobblestone pattern," which can be evaluated with virtual endoscopic images (Tarjan et al. 2000). With progression of the disease, the transmural inflammation is accompanied by irreversible fibrosis. (Fig. 13.10a-c)

Frequent complications are fistula, abscesses, adhesions, and stenosis, leading to bowel obstruction. Fistula can appear as ill-defined soft tissue bands extending into the paraintestinal fat. After colonic air insufflation, small amounts of air can sometimes be present in the fistulas, resulting in a better delineation (Tarjan et al. 2000). On endo-luminal views, the fistula opening is sometimes depicted (Fig. 13.11b). A Fistula opening may be seen at the top of a pseudopolypoid lesion of granulation tissue formation. In these cases, the combination of 3D and 2D images may provide sufficient information for complex disease. Abscesses are most frequently associated with small bowel disease or ileo colitis and may extend into adjacent tissues, bowel loops, or organs. Stenosis in Crohn's disease shows, in many cases, circular cone-shaped wall thickening with increased CM enhancement and involvement of a longer segment. In other cases, short stenoses with wall thickening and abrupt shoulders at the proximal and distal end occur, which makes differentiation from malignant stenosis impossible (Figs. 13.11a and 13.12a-c). Perforations are uncommon and usually contained. Conglomerate masses are present if there is an involvement of multiple bowel segments or a large bowel segment with fistu-lation and abscess formation (Fig. 13.11c).

There is a slightly increased risk of developing colorectal cancer and lymphoma as a complication of the disease. These neoplasms mostly affect the small bowel. The presence of lymph node enlargement >10 mm in the short axis diameter should raise suspicion for malignancy.

Colonoscopy Pictures Difrent DisesesColon Cancer With Lymph Nodes Affected
Fig. 13.11. a Crohn's disease: stenosis in the transverse colon (arrow). b Ileo-cecal fistula (arrow) and stenosis in the ascending colon. c Conglomerate mass between cecum and small bowel loops (arrow)
Bowel Cancer Effecting Lymph Nodes
Fig. 13.12a-c. Crohn's disease: various forms of stenoses (arrow) and disappearance of the haustra in three different patients

For evaluation of the small bowel involvement, CT enteroclysis is the preferred technique. There is little experience about the feasibility of CT colonography in Crohn's disease. Published results indicate that CT colonography can be helpful in the evaluation of colonic involvement, especially if conventional colonoscopy is incomplete (Biancone et al. 2003). In addition, the extracolonic extent and complications of the disease can be evaluated.

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