Crohn Disease

Published on 18/07/2015 by admin

Filed under Radiology

Last modified 22/04/2025

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 Faster to perform, less operator dependent, more sensitive and specific

image Allow assessment of extraintestinal disease
image Distend bowel with water ± neutral contrast agent (e.g., VoLumen)
image Bolus IV contrast medium at 3-4 mL/sec
• Noncicatrizing, acute phase

image Target or double halo sign
image Hyperenhancing inner ring (mucosa)
image Low-density middle ring (submucosal edema)
image Engorged vasa recta: Comb sign
image Proliferation of mesenteric fat and lymphadenopathy
• Chronic or cicatrizing phase

image Strictures, ± dilated small bowel (SB) upstream
image Abscesses, fistulas, sinus tracts
• Barium enema, enteroclysis can depict strictures & fistulas
• Colonoscopy is best to assess colonic involvement, guide biopsy of colon and terminal ileum
• Capsule endoscopy may complement imaging studies

image Not of proven value following negative CT or MR enterography
image Contraindicated in patients with enteric strictures

TOP DIFFERENTIAL DIAGNOSES

• Ulcerative colitis (“backwash” ileitis)
• Mesenteric enteritis and adenitis
• Infectious ileitis or colitis

PATHOLOGY

• Transmural inflammation, lymphoid aggregates, noncaseating granulomas

image Predisposes to strictures, fistulas, sinus tracts, abscesses

CLINICAL ISSUES

• Crohn disease is characterized by intermittent periods of exacerbation of symptoms followed by remissions
• Complications: Fistulas, sinus tracts, toxic megacolon, obstruction, perforation

DIAGNOSTIC CHECKLIST

• Segmental, discontinuous inflammation of SB ± colon with mucosal hyperenhancement, submucosal edema, engorged vasa recta
• Consider associated findings (cholangitis, arthritis)
image
(Left) This graphic in the sagittal plane illustrates typical features of Crohn disease including, segmental small bowel (SB) wall thickening, mucosal hyperemia image, transmural inflammation with deep ulcers image, mesenteric vessel engorgement, and fibrofatty proliferation image.

image
(Right) This 19-year-old man has an acute flare of his Crohn disease. CT shows mucosal hyperenhancement, wall thickening, and luminal narrowing of the terminal ileum (TI) image.
image
(Left) CT in the same patient shows the inflamed TI image, as well as local mesenteric fibrofatty proliferation and engorged vasa recta image.

image
(Right) A spot film from a SBFT in the same patient shows diseased TI and colon with longitudinal and transverse ulcerations of the ileal mucosa (cobblestone pattern) and luminal narrowing. At least 2 sinus tracts image are opacified. Traditional barium studies remain valuable for evaluation of strictures, fistulas, and sinus tracts.

TERMINOLOGY

Synonyms

• Terminal ileitis, regional enteritis, ileocolitis

Definitions

• Disease of unknown etiology characterized by transmural inflammation of GI tract

IMAGING

General Features

• Best diagnostic clue

image Segmental, discontinuous inflammation of small bowel (SB) ± colon with mucosal hyperenhancement, submucosal edema, engorged vasa recta

– Usually accompanied by clusters of prominent mesenteric nodes
• Location

image Anywhere along GI tract, from mouth to anus

– Most common: Terminal ileum (TI) and proximal colon
image Distribution

– 80% of patients have SB involvement
– 50% have ileocolitis
– 20% have disease limited to colon

image Only 10% have rectal involvement
• Morphology

image Transmural inflammation

– Predisposes to strictures, fistulas, sinus tracts, abscesses
image Skip lesions (segmental or discontinuous)

Fluoroscopic Findings

• Barium studies: Early changes

image “Target” or bull’s-eye appearance of aphthoid ulcerations: Punctate shallow central barium collections surrounded by halo of edema
image “Cobblestoning”: Combination of longitudinal and transverse ulcers
image Deep fissuring ulcers
image Mural thickening: Transmural inflammation, fibrosis
• Barium studies: Late changes

image Skip lesions: Segmental disease with normal intervening segments
image Sacculations seen on antimesenteric border
image Postinflammatory pseudopolyps, haustral loss, intramural abscess
image String sign: Luminal narrowing and ileal stricture
image Sinus tracts, fissures, fistulas are hallmarks of disease
image Anorectal lesions: Ulcers, fissures, abscesses, hemorrhoids, stenosis

CT Findings

• Noncicatrizing, acute phase

image Stratified wall thickening of discontinuous SB segments

– Target or double halo sign
– Hyperenhancing inner ring (mucosa)
– Low-density middle ring (submucosal edema)
– Soft tissue density outer ring (muscularis propria and serosa)
image Comb sign: Engorged vasa recta

– Supply actively inflamed SB segments
image Proliferation of mesenteric fat and lymphadenopathy

– Nodes rarely more than 1 cm in diameter
• Chronic or cicatrizing phase

image Luminal narrowing, ± dilated SB upstream
image Mural stratification lost: Indistinct mucosa, submucosa, muscularis propria

– Alternatively, submucosal fat may proliferate, preserve stratification
image Abscesses, fistulas, sinus tracts

– Fistulas connect 2 epithelialized surfaces (e.g., bowel-to-bowel, bladder, vagina, or skin)
– Sinus tracts are blind-ending (e.g., bowel to abscess)
image Mesenteric changes: Abscess, fibrofatty proliferation, mildly enlarged nodes
image Perianal disease: Fistulas and sinus tracts

MR Findings

• Breath-holding, fat suppression, and gadolinium enhancement show extent and severity of inflammation

image Mucosal hyperenhancement, submucosal edema, engorged vasa recta in acute inflammation
• Allows real-time imaging to assess peristalsis in segments of suspected disease
• Sensitive in detecting and characterizing fistulas, sinuses, abscesses in perianal Crohn disease
• Diffusion-weighted imaging can reveal active inflammation even without IV contrast administration

Ultrasonographic Findings

• Grayscale ultrasound

image Transrectal sonography

– Mural thickening, abscesses, fistulas
– Anal sphincter heterogeneity

Other Modality Findings

• Colonoscopy is best modality to assess colon

image Often allows inspection and biopsy of terminal ileum
• Capsule endoscopy is commonly used to complement imaging studies

image Not of proven value following “negative” CT or MR
image Contraindicated in patients with enteric strictures

Imaging Recommendations

• Best imaging tool

image Multiplanar CT or MR enterography

– Distend bowel with water ± neutral contrast agent (e.g., VoLumen)
– Bolus IV contrast medium at 3-4 mL/sec
– For CT, use low-dose protocols (e.g., iterative reconstruction) to reduce radiation risk
image Barium enema, enteroclysis

– Can be useful for depiction of strictures and fistulas
image MR for perianal and rectal Crohn disease

DIFFERENTIAL DIAGNOSIS

Ulcerative Colitis (“Backwash” Ileitis)

• Lesions are usually continuous and almost always involve rectum

image Terminal ileal pathology in < 25% of cases
• Generally not transmural process

image Fistulas, abscesses, strictures are much less common
• Some 10-15% of patients have “indeterminate colitis”

image Features of Crohn disease and ulcerative colitis overlap

Mesenteric Enteritis and Adenitis

• Common cause of RLQ pain in children, adolescents
• Enlarged mesenteric nodes, ileal wall thickening
• Usually resolves spontaneously in 2-4 days

Infectious Ileitis or Colitis

• Opportunistic infections: Mycobacterial, cryptosporidiosis, Cytomegalovirus (CMV)
• Mycobacterium tuberculosis

image Ileocecal (most common): Transmural, stenosis, fistulas
image Horizontal ulcers, nodular mucosal thickening
image Cecal contraction, widely patent ileocecal valve
image Pericecal lymphadenopathy on CT
• Atypical: Mycobacterium avium-intracellulare infection (MAI)

image SB most common site
image Diffusely thickened folds, micronodular mucosa
image Mesenteric adenopathy and abscess on CT
• Cryptosporidiosis

image Most common cause of enteritis in AIDS patients
image Thickening of folds and bowel wall; ↑ fluid in lumen
image CT may show enlarged lymph nodes
image Oocysts in stool and mucosal biopsy
• CMV

image Terminal ileitis indistinguishable from Crohn

Ischemic Enteritis

• Due to vascular insufficiency
• Superior mesenteric artery clot or embolism

image Usually affects distal SB and right side colon
image Luminal narrowing, mucosal hypoenhancement, ± pneumatosis

Radiation Enteritis

• Due to therapeutic or excessive abdominal irradiation
• Usually pelvic SB segments and rectum
• Bowel wall thickening, luminal narrowing
• ± strictures, sinuses, fistulas simulating Crohn disease

Lymphoma

• Non-Hodgkin lymphoma more common in GI tract

image Stomach (51%), SB (33%)
image Nodular, polypoid, infiltrating masses
image Focally infiltrating form of terminal ileum

– “Aneurysmal dilation” of lumen
– Sausage-shaped soft tissue density thickening of bowel wall
image Large (> 1 cm) mesenteric and retroperitoneal nodes

PATHOLOGY

General Features

• Etiology

image Exact etiology unknown; possible factors

– Immunologic: Antibody and cell-mediated types
– Nutritional, hormonal, vascular
– Genetic, environmental, infectious, psychologic
• Genetics

image Familial disposition
image Common in monozygotic twins and siblings
image Polygenic inheritance pattern
• Associated abnormalities

image Arthritis, gallstones, sclerosing cholangitis, uveitis, ankylosing spondylitis, arterial and venous thrombosis

Staging, Grading, & Classification

• 3 stages based on pathology

image Early: Hyperplasia of lymphoid tissue, obstructive lymphedema in submucosa → shallow mucosal erosions (aphthoid ulcers)
image Intermediate: Transmural extension in mucosa and submucosa → marked fold thickening
image Advanced: Transmural extension to serosa and beyond → deep linear clefts of ulceration/fissures

Gross Pathologic & Surgical Features

• Skip lesions are common
• Edema, inflammation, fibrosis, luminal narrowing
• Adhesions, fistulas, fissures, strictures

Microscopic Features

• Transmural inflammation, lymphoid aggregates, noncaseating granulomas

CLINICAL ISSUES

Presentation

• Most common signs/symptoms

image Diarrhea, pain, melena, weight loss, fever
image Malabsorption; fissures and fistulas (perianal area)

Demographics

• Age

image Age: 15-25 years (small peak at 50-80 years)
• Ethnicity

image More common in Caucasian and Jewish populations
• Epidemiology

image 4x increased incidence with smoking

Natural History & Prognosis

• Complications: Fistulas, sinus tracts, toxic megacolon, obstruction, perforation
• Prognosis

image Crohn disease is characterized by intermittent periods of exacerbation of symptoms followed by remissions
image 10-20% lead symptom-free lives after 1st presentation
image > 50% develop strictures &/or penetrating disease (e.g., abscess or fistula) within 10 years of onset
image 30-53% recurrence after surgical resection, usually proximal side of anastomosis
• Disease itself and treatment predispose to lymphoma in bowel

Treatment

• Endoscopic biopsy to diagnose
• Medical

image Steroids, azathioprine, mesalamine
image Metronidazole, antibody treatment
image Biological agents and immunomodulator therapy (e.g., anti-TNF)

– Effective at controlling Crohn but predispose to opportunistic infections
• Surgical

image Resection of diseased bowel, strictures, fistulas

DIAGNOSTIC CHECKLIST

Consider

• Associated findings (e.g., cholangitis, arthritis)

Image Interpretation Pearls

• SB wall thickening, mesenteric fat proliferation, hyperemia on CECT

image
(Left) This 37-year-old man has chronic and acute symptoms of abdominal pain and diarrhea. CT shows distention of some proximal jejunal segments image.
image
(Right) CT in the same patient shows a more distal segment of SB with hyperenhancement of the mucosa and submucosal edema image, along with clusters of mildly enlarged mesenteric nodes image.
image
(Left) CT in the same patient shows 2 segments of inflamed SB image that were separated by normal segments of bowel, the classic “skip lesions” of Crohn disease. Note the engorged vasa recta image supplying the more distal segment of inflamed bowel.

image
(Right) CT in the same patient shows additional segments of inflamed bowel image with mucosal enhancement, wall thickening, and luminal narrowing.
image
(Left) Coronal reformatted CT in the same patient shows separate segments of inflamed bowel image along with mesenteric lymphadenopathy and prominent vessels.

image
(Right) Coronal CT in the same patient shows inflamed bowel image and mesenteric lymphadenopathy image. The diagnosis of Crohn disease was confirmed on colonoscopy with biopsy of the terminal ileum.

image
(Left) This patient had prior ileocecal resection for CD and has recurrent symptoms. Coronal T2WI MR shows mural thickening of a SB segment image representing the neoterminal ileum, where recurrent disease often occurs.
image
(Right) Coronal T1 C+ FS MR in the same patient shows vivid mucosal enhancement of the affected segment image. The adjacent small bowel and colon do not enhance with the same intensity.
image
(Left) This 52-year-old woman has chronic Crohn colitis with recent recurrent urinary tract infections. CT shows markedly inflamed sigmoid colon image and mesentery.

image
(Right) CT in the same patient shows an extraluminal collection of gas and fluid image interposed between the colon, uterus image, and top of the bladder image.
image
(Left) CT in the same patient shows a markedly thickened wall of bladder image along with gas image and debris within the bladder.

image
(Right) Retrograde injection of contrast material into the bladder image opacifies the sigmoid colon image through a fistulous tract image. Fistulas are a key feature of the transmural inflammation caused by Crohn disease.

image
(Left) Film from a SBFT in a 26-year-old woman with chronic Crohn disease shows severe SB strictures, fistulas image, and ulceration with skip areas image.
image
(Right) Spot film from a SBFT in a 37-year-old patient with known Crohn disease shows the string sign, a severe luminal narrowing of the terminal ileum and the ascending colon. Note the sinus tract image and indirect evidence of mesenteric fibrofatty proliferation separating the TI from other bowel segments.
image
(Left) Axial CECT in a 48-year-old woman presenting with recent weight loss and diarrhea shows segmental small bowel wall thickening characterized by excessive submucosal fat deposition image, indicative of chronic inflammation. The nonepithelialized fistulas image extend from 1 bowel segment to the others.

image
(Right) Coronal CECT in the same patient again demonstrates the extension of the nonepithelialized fistulas image between the bowel segments.
image
(Left) This man has chronic, recurrent CD but has new symptoms of weight loss and fever. Coronal CT shows a short segment of actively inflamed SB image with enhancing mucosa and submucosal edema.

image
(Right) CT in the same patient shows a separate segment of SB that has sausage-like, soft tissue density wall thickening image felt to be concerning for neoplasm. Surgical resection confirmed lymphoma of the SB, a rare but recognized complication of CD or its medical therapy (steroids and immunomodulator drugs).
image
Small bowel follow-through shows chronic Crohn disease. Note the mucosal “cobblestoning” image and wide separation of the loops from creeping fat image.

image
Small bowel follow-through shows acute and chronic Crohn disease. Note the submucosal thickening of the ileum in acute disease image and the featureless mucosa of terminal ileum in chronic disease image.
image
Axial CECT shows mural thickening of the terminal ileum image and luminal narrowing. Note the hyperemia of the mesenteric blood vessels supplying the inflamed bowel image.
image
Small bowel follow-through shows longitudinal and transverse ulcerations of the ileal mucosa (“cobblestoning”) and luminal narrowing. The opacified sinus tract image is also seen.
image
Axial CECT shows extensive bowel wall thickening image of the distal ileum and marked inflammatory infiltration of the adjacent mesentery. Note the extraluminal bubbles of gas and the presence of small abscess image.
image
Axial CECT in the same patient demonstrates an enlarged mesenteric node image.
image
Axial CECT shows mural thickening of the ileum with submucosal edema and mesenteric hypervascularity (“comb” sign), indicating active disease.
image
Axial CECT shows a pelvic small bowel segment with submucosal edema and a “comb” sign of active inflammation.
image
Air-contrast BE shows Crohn (granulomatous) colitis with multiple aphthous ulcerations image throughout the colon.
image
SBFT shows a cobblestone appearance of a terminal ileum due to longitudinal, transverse ulcerations image.
image
Axial CECT shows recurrent Crohn disease several years following resection. Note the mural thickening and mesenteric fibrofatty proliferation.
image
Axial CECT shows rectovaginal fistula image due to Crohn disease.

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