Crypt abscesses, giant cells, and microgranulomas are nonspecific and can occur in both infectious colitis and inflammatory bowel disease. In contrast, crypt architecture is often abnormal in inflammatory bowel disease, with crypt distortion the most frequent finding. Inflammation of the lamina propria is present, with an increased number of both acute and chronic inflammatory cells. Ulcerative colitis affects the colon, with onset in the rectum and variable proximal colonic involvement. The inflammation is mucosal and contiguous.
Bloody diarrhea is the most common symptom.
In contrast, Crohn's disease can involve any part of the GI tract from the mouth to the anus. Segmental involvement of two or more areas is characteristic, and transmural involvement can result in fistulas and abscesses. In mild ischemic colitis, mucosal disease may lead to diarrhea, which may be bloody. In severe colitis, transmural damage and perforation can result. Sparing of the rectum is typical.