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  • colitis is inflammation of the large bowel
  • 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



  • usually presents as severe diarrhoea
    • 95% of cases have rectal involvmenet and only a minority have terminal ileum affected
    • may affect only left or right colon
    • has the most mucosal enhancement of all causes but minimal pericolonic inflammation
  • eosinophilic intestinal graft vs host disease (GVHD) following allogeneic haematopoietic stem cell transplantation
    • acute form occurs in 1st 100 days
    • chronic form occurs after 1st 100 days
  • infectious colitis such as cytomegalovirus (CMV), E. coli

short segment


    • characterized by skip lesions with transmural bowel involvement and with the terminal ileum involved in the majority of cases

terminal ileum involved

ascending colon

transverse colon

splenic flexure

    • 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



minimal features on colonoscopy

  • collagenous colitis 1)
    • secretory watery diarrhoea, may be sudden onset and last for months affects mainly women in the 50-60s and responds well to steroids
colitis.txt · Last modified: 2019/06/15 15:18 (external edit)