Congenital true diverticulum of small bowel, resulting from incomplete closure of vitelline duct or omphalomesenteric duct (embryonic yolk and sac); usually found within 24-36 inches of ileocecal valve. Presenting features are usually bleeding (most common cause of bright red blood per rectum in young people (or obstruction), but condition can mimic appendicitis. Diverticulum sometimes contains heterotopic gastric tissue, which is diagnosed with technetium pertechnate scan. Incidental, non-inflamed diverticula are not removed in adults.