This is another example of Crohn disease involving the small intestine. Here, the mucosal surface demonstrates an irregular nodular appearance with hyperemia and focal ulceration. The distribution of bowel involvement with Crohn disease is irregular with more normal intervening "skip" areas.

The etiology for Crohn disease is unknown, though infectious and immunologic mechanisms have been proposed. The NOD2/CARD15 gene produces a bacterial lipopolysaccharide receptor in mucosal Paneth cells, and mutations in this gene affect activation of nuclear factor kappa B that is part of an innate immune response. CD patients generally have a pANCA negative / ASCA positive serologic pattern. There is a bimodal incidence for CD and an increased incidence in women and persons of Caucasian race.