Ulcerative Colitis

Ulcerative colitis is an inflammatory bowel disease limited to the mucosa and submucosa of the colon. The disease typically begins in the rectum and continuously extends proximally to involve part of the colon or the entire colon (pancolitis). In 10-40% of cases, the distal ileum is also inflamed, which is referred to as backwash ileitis. The most severe

Table 13.2. CTC features of inflammatory bowel disease

Discrete irregular wall thickening (continuous vs. discontinuous)

Flattening or disappearance of haustra

Increased CM enhancement of wall

Stenosis

Pseudopolyps

Cobblestone pattern (Crohn)

Fibrofatty proliferation around colon (Crohn > UC)

Lymph nodes (Crohn > UC)

Abscess, fistula, pseudotumor (Crohn)

complication is the toxic megacolon, which appears in up to 5% of cases and carries the risk of perforation and peritonitis (Fig. 13.6a,b).

Although there is little experience in the evaluation of ulcerative colitis with CT colonography, the early subtle inflammatory mucosal changes, such as the granular pattern of the mucosa or tiny punctuate ulcers known from double contrast barium enema, may be beyond current spatial resolution of CT colo-nography.

Progression of the disease leads to hyperemia and submucosal edema, which then results in thickening and stratification of the wall, and is accompanied by increased paracolic vascularity. Increased ulceration and pseudopolyps appear and the mucosa becomes friable. Lymph node enlargement is only slight. The appearance of abscess or fistula formation is uncommon. In these acute stages, the benefit of CT colo-nography, in contrast to conventional colonoscopy, seems to be questionable. In case of toxic megacolon, there is an absolute contraindication to insufflation of air due to the extreme risk of perforation. In case of acute colitis without signs of toxic megacolon, CTC should be performed with caution. There are only a few reports about colonic perforations due to CTC (Sosna et al. 2005). However, in most cases, stenotic or otherwise diseased colons were affected and ulcer-ative colitis has been reported as one of these predisposing conditions (Coady-Fariborzian et al. 2004). The air distension of the colon may lead to intramural laceration or frank perforation (Fig. 13.7a-c.)

Subacute and chronic forms lead to thickening and rigidity of the wall. Narrowing of the colonic lumen and foreshortening of the colon may occur (Macari and Balthazar 2001). The bowel loses its haustral pattern, which can result in a tubular "lead pipe" appearance. Post-inflammatory polyps may be present. As a result of inflammation, there may be proliferation of the pericolic fat (Fig. 13.8a-c.).

Fig. 13.6a,b. Toxic megacolon (no colonic insufflation was performed): colonic dilatation with intraluminal air and fluid (a). The luminal contour is distorted and anhaustral. Diffuse slight wall thickening with increased CM enhancement of the whole colon and ill-defined nodular/ pseudopolypoid surface (a,b). There is an absolute contraindication for insufflation of air due to the extreme risk of perforation!

Fig. 13.6a,b. Toxic megacolon (no colonic insufflation was performed): colonic dilatation with intraluminal air and fluid (a). The luminal contour is distorted and anhaustral. Diffuse slight wall thickening with increased CM enhancement of the whole colon and ill-defined nodular/ pseudopolypoid surface (a,b). There is an absolute contraindication for insufflation of air due to the extreme risk of perforation!

Fig. 13.7a-c. Acute ulcerative colitis with perforation due to air insufflation: discrete diffuse wall thickening with increased CM enhancement of the whole colon (a). Total flattening and disappearance of the haustra with a tubular appearance of the colon (a,b). Focal paracolic air formations around the transverse colon are a sign of perforation (arrow) (a-c)

Fig. 13.7a-c. Acute ulcerative colitis with perforation due to air insufflation: discrete diffuse wall thickening with increased CM enhancement of the whole colon (a). Total flattening and disappearance of the haustra with a tubular appearance of the colon (a,b). Focal paracolic air formations around the transverse colon are a sign of perforation (arrow) (a-c)

Colonoscopy Ulcerative Colitis
Fig. 13.8a-c. Chronic ulcerative colitis: a,b narrowing of the colonic lumen and foreshortening of the colon with total flattening and disappearance of the haustra, leading to tubular appearance ("lead pipe") of the colon; c pseudopolyps (arrow)

The risk of development of colorectal cancer increases with the extent and the duration of the disease. Focal wall thickening, shoulder formation, or large polypoid lesions are suspicious for the development of colorectal cancer (Fig. 13.9. a-c). Differentiation between an inflammatory stenosis in ulcerative colitis and cancer is the domain of endoscopy with biopsy, but CTC may be used as an adjunct in patients with an endoscopically non-assessable colon.

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