on a CT scan one of the main features is thickening of the large bowel wall and one should ascertain the distribution of the colitis as this has important ramifications for likely differentials
CT scan features
thickening of the large bowel wall with submucosal oedema
less marked in ulcerative colitis than in Crohns
the “target sign”, which consists of the mucosal enhancement with submucosal oedema
“halo sign”, a low-attenuation ring in the bowel wall due to deposition of submucosal fat on iv contrast scan, is more common in ulcerative colitis than Crohn's disease
inflammatory pseudopolyp made of the confluence of healthy mucosa between ulcers in ulcerative colitis
pseudomembranous colitis gives a distinct large mucosal enhancement with fibrinous plaques and detritus, and with its polypoid-like aspect confers it a distinctive look and large amount of submucosal oedema
“accordion sign” is the entrapment of some amount of oral contrast between the folds of the thickened colon
inflammatory changes in the pericolic fat
“sign of the comb”, which is caused by the engorgement of the mesenteric vessels (esp. in Crohns)
“colon cut-off sign” may be caused by ischaemic colitis, pancreatitis or an obstructing neoplasm at the splenic flexure
pneumatosis in the colonic wall (esp. in ischaemic colitis)
air in the mesenteric vessels and portal vein, this finding confers a poor prognosis
toxic megacolon is a complication of ulcerative colitis and pseudomembranous colitis
watershed areas of the colon (the splenic flexure and rectosigmoid) are particularly susceptible to ischemia from hypotension
left colon ischaemia is typical of elderly patients with hypoperfusion, while the right colon is more characteristic of young people as a complication of hemorrhagic shock after penetrating trauma
CT may demostrate thrombus within the splanchnic vessels (eg. in patients with atrial fibrillation or invasion of vessels by tumors such as pancreatic cancer