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Small bowel (small intestine)

Inflammatory disorders

Crohn disease

Reviewer: Hanni Gulwani, M.D. (see Reviewers page)
Revised: 6 June 2017, last major update August 2012
Copyright: (c) 2003-2017, PathologyOutlines.com, Inc.


● Relapsing, discontinuous, transmural granulomatous disease from oral cavity to anus, usually involves small intestine and colon (eMedicine)
● Also called terminal ileitis, regional enteritis, granulomatous colitis


● Affects primarily Western populations, equal gender incidence
● 3 per 100,000, peaks in teens/twenties and 50/60s
● RR: Whites 2-5:1, Jews 3:1
● Associated with smoking
● Monozygotic twins have 30-50% concordance


● Small bowel only (particularly terminal ileum) in 40%, colon only in 30%
● Rarely other sites in GI tract


● Cause unknown, although Yersinia DNA in 30% of cases by PCR (Am J Surg Pathol 2003;27:220)
● May be due to alteration in steady state between immune system activation by microbes, antigens, endogenous inflammatory stimuli and host defenses that maintain integrity of mucosa and down-regulate inflammation
● Unclear if mucosal pathology is primary or secondary (Inflamm Bowel Dis 2010;16:896)

Clinical features

● Variable, including episodic mild diarrhea, fever, pain
● May be precipitated by stress
● If colon affected, may have anemia
● 20% have abrupt onset, resembling acute appendicitis or bowel perforation

Extraintestinal symptoms:
● Migratory polyarthritis, sacroiliitis, ankylosing spondylitis, erythema nodosum, clubbing of fingertips, primary sclerosing cholangitis (not as common as with ulcerative colitis)
● Occasionally uveitis, pericholangitis, renal disorders secondary to periureteral fibrosis

● Fibrosing strictures (common in terminal ileum), fistulas to loops of bowel, bladder, vagina, perianal skin
● Also protein losing enteropathy, generalized malabsorption, vitamin B12 deficiency, bile salt malabsorption with steatorrhea, perforation, abscesses
● 5x risk for GI carcinoma, usually adenocarcinoma of ileum

● Progressive
● Only rarely regresses

Crohn's related carcinoma

Small bowel:
● Mean 20 years after onset of Crohn, usually ileum or site of active disease
● Often in strictures, 25% in bypassed bowel loops
● Poorly differentiated, poor prognosis
● Dysplasia in adjacent epithelium

● Mean 20 years after diagnosis, usually gross intraluminal lesion, 20% in bypassed rectum
● Better differentiated and better prognosis than small bowel carcinomas
● Dysplasia near and distant from tumor


● Medical (immunosuppressive therapy), surgical

Clinical images


Gross description

● Serosa dull and granular with creeping fat (mesenteric fat wraps around bowel surface), thick/rubbery intestinal wall (due to edema, inflammation, fibrosis, hypertrophy of muscularis propria), narrow lumen (string sign on barium enema), sharp demarcation of affected from uninvolved bowel, fistulas
● No rectal involvement
Early - aphthous mucosal ulcers that coalesce into long, serpentine linear ulcers along bowel axis with cobblestone appearance
Late - shortened and fibrotic mesentery; prominent reactive lymph nodes

Clinical images

Terminal ileum: mucosal pseudopolyps (inflammatory pseudopolyps)

Terminal ileum: cobblestone change

Thickened bowel wall and fat wrapping

Micro description

● Sharply delimited and typically transmural involvement of bowel by an inflammatory process with mucosal damage, noncaseating, non-confluent, sarcoid-like granulomas (60%) in involved and non-involved bowel, fissuring (30%) deep into muscularis propria with formation of fistulas and strictures
● Focal neutrophils in epithelium early on, particularly overlying lymphoid aggregates
● Also plasmacytosis, cryptitis, crypt abscesses
● Superficial or deep ulceration, edema, lymphatic dilation, hyperplasia / duplication of muscularis mucosa
● May have prominent nerve plexuses (submucosal, myenteric), fibrosis, muscularization (Histopathology 2012;60:1034)
● Often serositis and thickened bowel wall
Late - architectural distortion (villus blunting), crypt atrophy, particularly in colon, pyloric or Paneth cell metaplasia in distal colon, rarely cystically dilated glands (enteritis cystica profunda)
● Areas of stricture may have thick and continuous muscle layer from mucosal base to muscularis propria 1 cm or more in length, called obliterative muscularization of submucosa" (Arch Pathol Lab Med 2001;125:1331)
● Isolated colonic Crohn may mimic ulcerative colitis involve younger patients, only mucosal involvement and with fewer major microscopic features (Mod Pathol 2012;25;295)

Micro images

Deep fissuring ulcers

Crypt abscess

Obliterative muscularization

Granulomatous enteritis

Lymphoid follicles

Comparison with ulcerative colitis

Virtual slides

Small intestine

Differential diagnosis

● Ischemic bowel disease

End of Small bowel (small intestine) > Inflammatory disorders > Crohn disease

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