 Crohn's ileitis, manifest in the ileum only, accounts for thirty percent of cases, while Crohn's colitis, of the large intestine, accounts for the remaining twenty percent of cases and may be particularly difficult to distinguish from ulcerative colitis.Gastroduodenal Crohn's disease causes inflammation in the stomach and first part of the small intestine called the duodenum.Jejunoileitis causes spotty patches of inflammation in the top half of the small intestine, called the jejunum.