Ulcerative Colitis and Crohn's Disease Diagnosis

Anatomical Distribution Patterns

Ulcerative Colitis typically involves the left colon, with the disease beginning in the rectum and extending proximally in a continuous fashion, commonly affecting the rectosigmoid and descending colon, according to the American Gastroenterological Association 1, 3
Crohn's Disease most commonly affects the terminal ileum and right colon, producing right lower quadrant pain, and shows patchy, discontinuous distribution with skip lesions throughout the GI tract, as noted by the Crohn's and Colitis Foundation 1, 2

Crohn's Disease patients more commonly present with right lower quadrant pain when the terminal ileum is involved, as stated by the American College of Gastroenterology 2

If left-sided pain occurs with rectal sparing on colonoscopy, strongly consider Crohn's Disease rather than Ulcerative Colitis, according to the American Gastroenterological Association 1, 4
Segmental left-sided colitis in the setting of diverticulosis may represent segmental colitis associated with diverticulosis, Crohn's Disease, or IBD-unclassified, as reported in Gastroenterology 5

Perform complete ileocolonoscopy with at least two biopsies from five different sites to differentiate Ulcerative Colitis from Crohn's Disease, as recommended by the American College of Gastroenterology 1, 4
Cross-sectional imaging is essential because approximately one-third of Crohn's Disease patients have small bowel disease not detectable by colonoscopy, according to the Crohn's and Colitis Foundation 1, 4

Ulcerative Colitis shows continuous mucosal inflammation limited to mucosa/submucosa, while Crohn's Disease demonstrates transmural inflammation with potential granulomas and focal, patchy distribution, as noted by the American Gastroenterological Association 1, 2
Crypt abscesses are more common in Ulcerative Colitis than Crohn's Disease, according to the American College of Gastroenterology 4