Pediatric Crohn Disease

  • Etiology: idiopathic inflammatory bowel disease that is transmural in nature affecting anywhere in gastrointestinal tract in a non-contiguous manner
  • AXR: 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
  • UGI SBFT: secondary signs and complications – mucosal ulceration, nodularity, cobblestone appearance, luminal narrowing and or dilation
  • US: bowel wall thickening, loss of normal mucosal striation, increased echogenicity of perienteric fat, hyperemia of mesentery
  • CT: directly visualize bowel lumen, bowel wall, adjacent soft tissues, depicts intestinal and extraintestinal disease
  • CT + MRI signs of active disease: mucosal hyperenhancement, wall thickening, prominent vasa recta (comb sign), mesenteric infiltration of fat, hyperintense on T2, hypoperistalsis, restricted diffusion
  • Imaging: skip lesions, transmural bowel inflammation affecting anywhere in gastrointestinal tract but terminal ileum is classic location, progression is wall thickening -> wall thickening and luminal narrowing -> wall thickening and luminal narrowing and upstream bowel dilation -> penetrating complications
  • Imaging:
    — Intestinal findings: segmental mural hyperenchancement, wall thickening, intramural edema, ulceration, sacculations, diminished peristalsis, luminal narrowing / strictures
    — Mesenteric finding of active disease (including penetrating diseaese): fistula, sinus tract, inflammatory mass (phlegmon), abscess, perienteric edema / inflammation, engorged vasa recta, mesenteric venous thrombosis
    — Extraintestinal findings – sacroiliitis, sclerosing cholangitis, avascular necrosis, pancreatitis, nephrolithiasis, cholelithias, perianal / cutaneous findings
  • Complications: stricturing of small bowel resulting in obstruction requiring resection, penetrating fistula + abscess formation requiring drainage, sacroiliitis, primary sclerosing cholangitis, avascular necrosis, pancreatitis, nephrolithiasis, cholelithiasis
  • Clinical: often not endoscopically visible as primarily affects small bowel, therapy is primarily medical

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

MRE findings:

  • Mural thickening of > 3 mm
  • Mural edema increased T2WI signal
  • Mural post contrast hyperenhancement
  • Bowel wall restricted diffusion
  • Stricture – luminal narrowing due to inflammation or fibrosis that persists througout the exam which may or may not cause obstruction with proximal dilation and stasis
  • Skip lesion – > 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 / edema best seen on T2WI fat sat + post contrast
    — fibrofatty proliferation – creeping fat / 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 / iliopsoas and retroperitoneum / abdominal wall
  • Penetrating disease
    — sinus tract is blind ending,
    — fistulous tract communicates with second epithelial surface
    — variable MR appearance due to gas / fluid / 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 / erythema / draining fistula / abscess, due to cutaneous granulomatous infection, contiguous vs. metastatic
  • Other
    — sclerosing cholangits – ulcerative colitis >>> Crohn disease
    — cholelithiasis – increased incidence in Crohn (13-34%), due to disrupted enterohepatic circulation of bile salts
    — sacroilitis – IBD related arthritis, MRI DWI allows for early detection

MRE to distinguish active vs. 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

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.
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.

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 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”).