溃疡性结肠炎，严重的炎症从右下方的乙状结肠沿升结肠向上蔓延。在左下方是回肠末段的回盲瓣，不包括回肠末段。溃疡性结肠炎趋向于持续沿黏膜表面浸润和趋向于在直肠开始。黏膜遭受破坏，如图显示的仅仅是残留的岛屿状黏膜，称假息肉。
This gross appearance is characteristic for ulcerative colitis. The most intense inflammation begins at the lower right in the sigmoid colon and extends upward and around to the ascending colon. At the lower left is the ileocecal valve with a portion of terminal ileum that is not involved. Inflammation with ulcerative colitis tends to be continuous along the mucosal surface and tends to begin in the rectum. The mucosa becomes eroded, as in this photograph, which shows only remaining islands of mucosa called "pseudopolyps".
