There is loss of the normal mucosal outline to the large bowel, with an irregular margin and no visible haustral markings, indicating mucosal inflammation and oedema. There is marked dilatation of the large bowel, from the caecum on the right to a loop of sigmoid seen centrally in the pelvis. The appearances and the extent thus indicate a pancolitis. The transverse colon measures more than 5.5cm across, which in the presence of colitis indicates a toxic megacolon, with the risk of imminent perforation.