Small bowel (small intestine)
Inflammatory disorders
Crohn's disease

Author: Hanni Gulwani, M.D. (see Authors page)

Revised: 13 February 2018, last major update August 2012

Copyright: (c) 2003-2018, PathologyOutlines.com, Inc.

PubMed Search: Crohn's disease[TI] small bowel[TI] free full text[sb]

Cite this page: Gulwani, H. Crohn's disease. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/smallbowelcrohns.html. Accessed February 19th, 2018.
Definition / general
Epidemiology
  • Affects primarily Western populations, equal gender incidence
  • 3 per 100,000, peaks in teens / twenties and 50s / 60s
  • RR: Whites 2 - 5:1, Jews 3:1
  • Associated with smoking
  • Monozygotic twins have 30 - 50% concordance
Sites
  • Small bowel only (particularly terminal ileum) in 40%, colon only in 30%
  • Rarely other sites in GI tract
Etiology
  • 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
Symptoms:
  • 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

Complications:
  • 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

Course:
  • Progressive
  • Only rarely regresses
Crohn's related carcinoma
Small bowel:
  • Mean 20 years after onset of Crohn's, usually ileum or site of active disease
  • Often in strictures, 25% in bypassed bowel loops
  • Poorly differentiated, poor prognosis
  • Dysplasia in adjacent epithelium

Colon:
  • 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
Treatment
  • Medical (immunosuppressive therapy), surgical
Clinical images

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Endoscopy

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
Gross images

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Terminal ileum:
mucosal pseudopolyps
(inflammatory
pseudopolyps)

Terminal ileum: cobblestone change

Thickened bowel wall and fat wrapping

Microscopic (histologic) description
  • Sharply delimited and typically transmural involvement of bowel by an inflammatory process with mucosal damage, noncaseating, nonconfluent, sarcoid-like granulomas (60%) in involved and noninvolved 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's may mimic ulcerative colitis involve younger patients, only mucosal involvement and with fewer major microscopic features (Mod Pathol 2012;25;295)
Microscopic (histologic) images

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Deep fissuring ulcers

Crypt abscess

Obliterative muscularization


Granulomatous enteritis

Lymphoid follicles

Differential diagnosis