see also:

• central / periumbilical abdominal pain in the ED
• diarrhoea

• 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

• 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
    • see http://learningradiology.com/archives2009/COW%20383-Target%20sign/targetsigncorrect.htm
  • “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
• ulcerative colitis
  • 95% of cases have rectal involvmenet and only a minority have terminal ileum affected
• pseudomembranous colitis - see also Clostridium difficile
  • 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

• colorectal cancer (bowel cancer)
• diverticulitis
• trauma

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

• Crohn's disease
• tuberculosis (TB)
• Yersinia entercolitica
• cytomegalovirus (CMV)
• lymphoma

• neutropenic colitis (typhlitis)
• amoebiasis
• lymphoma
• infectious colitis such as Salmonella, shigella

• extension of stomach cancer or pancreatic cancer
• pancreatitis

• watershed ischaemic 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

• diverticulitis
  • segmental wall thickening and hyperaemia with inflammatory changes in the pericolic fat and adjacent liquid or intramural abscess
• radiation_colitis
• endometriosis
• schistosomiasis

• radiation_colitis
• infectious proctitis (eg. gonococcus, Herpes simplex virus (HSV), C. trachomatis)
• stercoral colitis (ischaemic colitis from feacal_impaction)

• 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