Pediatric Crohn Disease

  • Etiology: Idiopathic inflammatory bowel disease that is transmural in nature affecting the entire gastrointestinal tract in a non-contiguous manner (skip lesions) with stricturing and penetrating complications
  • Imaging:
    — Skip lesions
    — Transmural bowel inflammation affecting anywhere in gastrointestinal tract but terminal ileum is classic location
    — Progression is wall thickening which leads to wall thickening and luminal narrowing which leads to wall thickening and luminal narrowing and upstream bowel dilation which leads to penetrating complications
  • Imaging:
    — Intestinal findings: Segmental mural hyperenchancement, wall thickening, intramural edema, ulceration, sacculations, diminished peristalsis, luminal narrowing and strictures
    — Mesenteric finding of active disease (including penetrating disease): Fistula, sinus tract, inflammatory mass (phlegmon), abscess, perienteric edema and inflammation, engorged vasa recta, mesenteric venous thrombosis
    — Extraintestinal findings: Perianal and cutaneous findings, cholelithias, primary sclerosing cholangitis, avascular necrosis, sacroiliitis, pancreatitis, nephrolithiasis, pulmonary (interstitial lung disease, bronchiectasis, organizing pneumonia, necrobiotic nodule (less than 6%))
    — Note: MRI is most sensitive to identify perianal fistula
  • Imaging AXR: See secondary signs and complications:
    — Bowel wall separation due to wall thickening and creeping fat
    — Thumb printing due to wall thickening and edema
    — Bowel dilation from obstruction due to stricture
  • Imaging Small bowel follow through: See secondary signs and complications
    — Mucosal ulceration and nodularity and cobblestone appearance
    — Luminal narrowing and or dilation
  • Imaging US:
    — Bowel wall thickening
    — Loss of normal mucosal striation
    — Increased echogenicity of perienteric fat
    — Hyperemia of mesentery
  • Imaging CT: Directly visualizes bowel lumen, bowel wall, adjacent soft tissues and depicts intestinal and extraintestinal disease
    — CT signs of active disease: Mucosal hyperenhancement, wall thickening, prominent vasa recta (comb sign), mesenteric infiltration of fat
  • Imaging MRE: Bowel wall thickening and bowel wall edema with thumbprinting, wall mucosal hyperenhancement, skip lesions, engorgement of vasa recta, enlarged lymph nodes
    — MRI signs of active disease: Mucosal hyperenhancement, wall thickening, prominent vasa recta (comb sign), mesenteric infiltration of fat, hyperintense on T2WI, hypoperistalsis, restricted diffusion
  • DDX:
    — Appendix is affected in approximately 20% of Crohn disease so look for other findings of inflammatory bowel disease to distinguish it from acute appendicitis
    — Chronic granulomatous disease can cause an inflammatory bowel disease that mimics Crohn disease
  • Complications:
    — Penetrating complications usually associated with stricturing complications
    — Stricturing of small bowel resulting in obstruction requiring resection
    — Penetrating fistula and abscess formation requiring drainage
    — Fistulas can connect to skin and bladder and pelvic organs and perineal structures
    — Cancer in 3-10%
  • Treatment: Therapy is primarily medical
  • Clinical: Often not endoscopically visible as primarily affects small bowel

Imaging MRE approach to interpretation:

  • Distribution of contrast and distension of bowel – Coronal single shot sequences, confirm distention of terminal ielum
  • Wall thickening, edema, fat – Compare between fat-suppressed and nonfat-suppressed T2WI
  • Assessment of peristalsis – Cine images assess for fold pattern and altered bowel motility
  • Disease activity – Early and delayed enhancement – early enhancement in active disease with comb sign, progressive delayed enhancement in chronic disease
  • Penetrating disease – Fistula and abscess – star-sign for interloop fistula
  • Fibrostenotic disease – Stricture and small bowel obstruction – fibrostenosing disease, upstream dilation proximal to a narrowed and aperistaltic segment
  • Colonic assessment – Colonic wall thickening, loss of fold pattern, fat deposition
  • Extraenteric assessment – Mesentery, fat, lymph nodes
  • Perianal disease – Axial T2WI images though pelvis
  • Bones and other soft tissues – Sarcroiliitis, sclerosing cholangitis

Imaging MRE findings:

  • Mural thickening of greater than 3 millimeters
  • Mural edema as increased T2WI signal
  • Mural post contrast hyperenhancement
  • Bowel wall restricted diffusion
  • Stricture – Luminal narrowing due to inflammation or fibrosis that persists throughout the exam which may or may not cause obstruction with proximal dilation and stasis
  • Skip lesion leads to 1 abnormal bowel segment separated by intervening normal bowel, classic in Crohn disease
  • Mesentery – Hypervascularity – perienteric vasa recta vascular engorgement = “comb sign” associated with increased disease activity, increased ulcerations
    — Mesenteric fat stranding due to mesenteric inflamation and edema best seen on T2WI fat sat and post contrast
    — Fibrofatty proliferation – creeping fat and fat wrapping in long standing severe Crohn disease
    — Lymphadenopathy – reactive due to regional bowel inflammation, most conspicuous on DWI
  • Abscess
    — Localized infected fluid collection with discrete wall and gas
    — More common in Crohn disease than ulcerative colitis due to penetrating disease
    — Involves mesentery and iliopsoas and retroperitoneum and abdominal wall
  • Penetrating disease
    — Sinus tract is blind ending
    — Fistulous tract communicates with second epithelial surface
    — Variable MR appearance due to gas and fluid and fecal material in tract
    — Commonly enhance
  • Perianal disease
    — Fistula frequently contains fluid and enhances
    — Abscess due to perianal penetrating disease, intersphincteric or ischiorectal fossa, rim enhance, restrict diffusion
    — Vulvar disease – variable presentation with skin thickening and erythema and draining fistula or abscess, due to cutaneous granulomatous infection, contiguous versus metastatic
  • Other
    — Sclerosing cholangits – in ulcerative colitis more commonly than in Crohn disease
    — Cholelithiasis – increased incidence in Crohn disease (13-34%), due to disrupted enterohepatic circulation of bile salts
    — Sacroilitis – inflammatory bowel disease related arthritis, MRI DWI allows for early detection

Imaging MRE to distinguish active versus chronic disease:

  • Active disease
    — T2WI show bowel wall thickening and edema and mesenteric congestion
    — DWI show restricted diffusion
    — Cine images show diminished peristalsis
    — Postcontrast images show early enhancement
  • Chronic disease
    — T2WI show bowel wall fat and loss of normal fold pattern with featureless loops
    — DWI show no restricted difffusion
    — Cine images show diminished peristalsis
    — Postcontrast images show delayed and progressive enhancement

Radiology Cases of Crohn Disease

Radiology Cases of Duodenal Involvement in Crohn Disease

UGI of duodenal ulcer in Chron disease
AP spot image of the duodenum from an UGI exam shows a target sign with barium pooling centrally in a large ulceration surrounded by an edematous ring in the distal aspect of the duodenal bulb. There was also extensive inflammation of the terminal ileum shown later on the small bowel followthrough exam.

Radiology Cases of Terminal Ileum Involvement in Crohn Disease

Small bowel follow through of Crohn's disease
AXR AP from a small bowel follow through shows bowel fold thickening in the proximal ileum in the left lower quadrant and bowel lumenal narrowing in the mid ileum in the midline that continues to the terminal ileum in the right lower quadrant.
UGI and SBFT of Crohn disease
Spot images of the terminal ileum from an upper GI small bowel follow through show diffuse luminal narrowing of the terminal ileum associated with mucosal ulceration along with a nodular and cobblestone appearance to the terminal ileum.
UGI and SBFT of Crohn disease of terminal ileum
AXR AP (left) shows dilated loops of small bowel and a radiopaque coin projecting over the pelvis. AP images from an upper GI and small bowel follow through exam show the coin cannot pass through the terminal ileum (above right) because the terminal ileum is ulcerated, nodular and narrowed (below right).
CT and small bowel followthrough of Crohn disease of the terminal ileum and cecum
Axial CT with intravenous and oral contrast of the abdomen (above) shows marked thickening of the wall of the cecum and narrowing of the lumen of the cecum. Images of the terminal ileum from an upper GI and small bowel follow through exam (below) show luminal narrowing and nodularity giving a cobblestone appearance along with mucosal ulcerations.
Small bowel follow through exam of Crohn disease of the terminal ileum
AXR from a small bowel follow through exam (left) shows diffuse narrowing of the terminal ileum and separation of the loops of terminal ileum due to mesenteric fat infiltration. Spot image of the terminal ileum (right) shows a nodular and cobblestone appearance to the narrowed loops of the terminal ileum.
Small bowel followthrough of Crohn disease
Spot image from an upper GI small bowel followthrough exam (left) shows a long segment of ileum on the right of the image that has lost its normal folds, is narrowed in caliber, and has a cobblestone appearance. Spot image of the terminal ileum (right) shows it also lacks its normal folds and is narrowed in caliber. Inflammatory changes are also noted in the cecum.
CT of Crohn disease
Coronal (left) and axial (right) CT with contrast of the abdomen shows wall thickening and mucosal hyperenhancement of the terminal ileum with separation of the bowel loops due to mesenteric infiltration of fat and prominent vasa recta (comb sign).
CT of Crohn's disease with fistula and abscess
Axial CT with contrast of the abdomen shows a thick-walled mass that is filled with air and oral contrast that is located medial to the oral contrast-filled thickened ascending colon and above the right psoas muscle. An extensive amount of inflammatory change is seen in the mesenteric fat in the right lower quadrant.

Endoscopy Cases of Crohn Disease

Colonoscopy images of Crohn disease
Colonoscopy images of the terminal ileum show it to be diffusely thickened and to have a cobblestone appearance.

Surgery Cases of Crohn Disease

Surgical image of Crohn disease
Surgical image shows the terminal ileum, which is between the two forceps, to be thickened in nature, firm to palpation and to have mesenteric fat wrapped around it. The appendix is normal in appearance.

Gross Pathology Cases of Crohn Disease

Gross pathology image of Crohn disease
Gross pathological image shows the terminal ileum to be thickened with mesenteric fat surrounding it. The appendix (to the left) is normal.
Gross pathological image of Chron disease
Gross pathological image shows a normal cecum and appendix (right of image) and a stricture at the terminal ileum (middle of image), which is thickened. The terminal ileum is ulcerated with pseudopolyp formation at the stricture. Histopathology showed transmural inflammation of the terminal ileum with granuloma formation and ulceration.
Gross pathological image of Chron's disease
Gross pathological image of the terminal ileum shows markedly thickened intestinal wall and adherent pericolonic fat (“fat-wrapping”).

Histopathology Cases of Crohn Disease

Histopathology image of Crohn disease
Histopathological image of lower power H&E stained section shows transmural involvement by the inflammatory process with ulceration and fissure formation.
Histopathology image of Crohn disease
Histopathological image of higher power H&E stained section shows a loosely formed granuloma which is extremely helpful in establishing a diagnosis of Chron disease on mucosal biopsies, but only observed in some cases.