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Crohn Disease : Gross Pathology

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Gross Pathology of Crohn Disease:
Sites of Involvement: Any part of the GI tract may be involved. The most commonly affected sites are terminal ileum, ileocecal valve, and cecum. The frequency of involvement is as follows: small intestine alone, 40% of cases; both small intestine and colon, 30% of cases; and colon alone, 30% of cases.

Gross Morphology: Unlike ulcerative colitis, the bowel involvement in Crohn disease is not continuous but shows segmental distribution of lesions with “skip” areas. There is sharp demarcation between affected and unaffected foci. Strictures are commonly present.

The bowel involvement begins with shallow aphthous ulcers which coalesce to form long, serpentine ulcers along the length of the bowel. The longitudinal ulcers are connected by short transverse ulcers. The mucosa may be edematous or covered with hemorrhage and exudate. Bulging uninvolved mucosa adjacent to depressed ulcerated areas can create pseudopolyps or a cobblestone appearance.

The inflammation is transmural. Deep fissures develop between mucosal folds leading to perforation or formation of fistula tracts. In long standing cases, progressive inflammation, fibrosis, and hypertrophy of muscularis propria cause thickening of the intestinal wall and narrowing of the lumen with strictures. With extensive transmural involvement, mesenteric fat may be seen wrapping around the serosal surface (creeping fat).

This specimen shows Crohn's colitis with deep ulcers and fissures covered with exudate. The mucosa has cobblestone appearance. Image courtesy of Dr. Jean-Christophe Fournet, Paris, France; humpath.com; Used with permission

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