colitis

Introduction

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

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

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

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