The normal colonic mucosa has a smooth, featureless pattern. In the early stages of ulcerative colitis, this is replaced by a diffusely granular appearance. This corresponds to the endoscopic findings of edema and hyperemia, and may precede actual ulceration. The granular pattern may be fine, as in the above case, or have a coarser appearance as in Film .2 and .2Z. Tiny ulcerations may become evident; these are typically shallow i.e. less than 3 mm deep. As the disease progresses, rectal valves and colonic folds in affected areas are usually destroyed. The rectum often shows diffuse narrowing, and the presacral space may become widened.

The distribution in active ulcerative colitis tends to be characteristic. The rectum is generally involved radiographically (and always histologically). The disease may be limited to the rectum, or extend proximally into the colon for a variable distance. Colonic involvement is typically continuous with that in the rectum. At times, the rectum appears less involved than the more proximal colon, and the granularity may be quite subtle (Film .3 and .3Z). The terminal ileum is almost always normal.

In active disease, double contrast barium enema has a sensitivity of approximately 90%, though it probably underestimates the extent of the disease process. When the disease process becomes quiescent, the extent of involvement is significantly underestimated when compared to the findings at colonoscopy. Thus, barium enema is much more useful in the active phase(s) of the disease. If toxic megacolon has supervened, barium enema is contraindicated because of the risk of inducing perforation.

It is important to recognize that, while ulcerative colitis is by far the most common cause of a granular mucosa seen on barium enema, many other forms of colitis can produce a similar or identical appearance. Because these forms of colitis may be infectious and readily treatable, a routine search for bowel pathogens, including Campylobacter, Salmonella, Shigella, Amoeba, and Clostridium difficile, should be carried out in any patient with suspected ulcerative colitis.

Ulcerative colitis is one of the two main types of idiopathic inflammatory bowel disease, the other being Crohn's disease. Symptoms most commonly start in early adulthood. Typically, intermittent attacks of diarrhea and rectal bleeding occur. The disease is primarily a mucosal inflammatory process, and is frequently confined to the rectum. Mild or moderate disease is usually controlled by steroids and/or sulfasalazine. About 15% of patients have severe or fulminant disease. The most important local complications of ulcerative colitis are toxic megacolon and, in long-standing extensive disease, the development of carcinoma.