Crohn’s Disease

Crohn’s disease is a chronic relapsing and remitting inflammatory disease characterized by areas of transmural inflammation that may occur anywhere along the GI tract. The inflammatory lesions are often multifocal (“skip lesions”) and can occur anywhere, but classically involve the terminal ileum. The incidence is highest in young adults. Patient present with cramping abdominal pain, nonbloody diarrhea (though microscopic blood is quite common), and fever. Extraintestinal manifestations (joint, eye, skin, etc) should also raise suspicion for IBD. Perianal fissures and fistulas are common complications in Crohn’s.

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Chronic Active Colitis

• Cryptitis; acute inflammation in crypts

• Well-formed non-caseating granuloma (yellow arrows), which consists of large histiocytes with abundant cytoplasm. Granulomas are a feature more commonly associated with Crohn’s than Ulcerative Colitis

NEUTROPHIL WITHIN CRYPT

GRANULOMA

Chronic Inactive Colitis

• Crypt dropout with adjacent granuloma formation

• Lack of acute inflammation

Disordered crypts that branch and do not line up perpendicular to surface of epithelium

Radiology

- Extensive involvement of right colon and terminal ileum, which is often thick walled and narrowed (string sign on barium studies). Involvement of left side alone is rare.

- Asymmetric or segmental wall thickening (skip lesions)

- Fibrofatty proliferation (“creeping fat”) in mesentery, causing separation of small bowel loops

- Transmural; therefore more abscesses and fistulas more common compared to Ulcerative Colitis

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Left: Mural thickening of cecum/terminal ileum

Right: Engorged vasa recta (“comb sign”)

Active colitis: mural stratification (target sign), engorged vasa recta

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Chronic colitis: strictures, fibrofatty proliferation