Ulcerative colitis starts in
(A) Rectum # Pathology of ulcerative colitis: In 95%t of cases the disease starts in the rectum and spreads proximally.> When the ileocaecal valve is incompetent, retrograde (backwash) ileitis involving the last 30 cm of the ileum is likely to occur.> It is a nonspecific inflammatory disease, primarily affecting the mucosa and superficial submucosa, and only in severe disease are the deeper layers of the intestinal wall affected> There are multiple minute ulcers, and microscopic evidence proves that the ulceration is almost always more severe and extensive than the gross appearance indicates.> When the disease is chronic, inflammatory polyps (pseudopolyps) occur in up to 20 per cent of cases and may be numerous.> They result from previous episodes of ulceration heaving islands of spared mucosa which will remain prominent when the adjacent mucosa heals.> In severe fulminant colitis a section cf the colon, usually the transverse colon, may become acutely dilated and the intestinal wall then becomes extremely thin and may perforate ('toxic megacolon').> On microscopic investigation there is an increase of inflammatory cells in the lamina propia, the walls of crypts are infiltrated by inflammatory cells and there are crypt abscesses.> There is depletion of goblet cell mucin. The crypts are reduced in number and appear to be atrophic and irregularly spaced. With time these changes become severe and precancerous changes can develop (severe dysplasia or carcinoma in situ).
Rectum
Transverse colon
Caecum
Descending colon
Miscellaneous