Which disease primarily presents lesions that are continuous, limited to the mucosa, and are not transmural?

Ulcerative colitis is characterized by the presence of continuous lesions that are limited to the mucosal layer of the intestinal wall. Unlike Crohn's disease, which can affect any part of the gastrointestinal tract and involves transmural inflammation (inflammation that goes through all layers of the bowel wall), ulcerative colitis is restricted to the colon and rectum and does not penetrate deeper layers. The lesions in ulcerative colitis typically present as contiguous areas of inflammation, starting from the rectum and extending proximally in a continuous manner, which is a hallmark of the condition.

The distinction in the pattern of involvement—continuous mucosal lesions instead of patchy or transmural lesions—helps differentiate ulcerative colitis from other gastrointestinal conditions. For instance, diverticulitis can cause localized inflammation due to diverticula, while irritable bowel syndrome primarily involves functional gastrointestinal disturbances rather than structural lesions. Thus, the features of ulcerative colitis align best with the description provided in the question.