Montreal classification in terms of extent in ulcerative colitis (CU).
| E1: Ulcerative proctitis (rectal inflammation). | Involvement is limited to the rectum (rectum) |
| E 2: Left-sided ulcerative colitis (inflammation of the colon; distal CU). | Involvement of the rectum and left colon (large intestine; extending to the left colonic flexure). |
| E3: Extensive ulcerative colitis (pancolitis). | Involvement beyond left colonic flexure, involvement of entire colon possible |