Usually involves the small intestine, almost always the terminal ileum. The colon is also commonly involved. If the stomach is involved, ty...
Usually involves the small intestine, almost always the terminal ileum. The colon is also commonly involved. If the stomach is involved, typically the distal stomach is affected first (it can resemble a linitis plastica). The hallmark is skip lesions; these begin as superficial ulcers, progressing to full-thickness ulcers resulting in sinuses, fistulae and abscesses. Chronically, there is fibrofatty proliferation adjacent to the affected bowel, which causes a stricture with or without upstream obstruction.
BARIUM FOLLOW-THROUGH
• Aphthous ulcers (small barium-filled pits surrounded by oedema).
• Linear ulcers on the mesenteric border are nearly pathognomonic.
• ‘Cobblestone’ appearance (a combination of longitudinal and transverse ulceration).
• Solitary strictures.
• Bowel wall thickening.
• Pseudodiverticula (islands of normal mucosa surrounded by ulceration).
CT
• Especially useful to assess an acute Crohn presentation (e.g. obstruction, perforation, abscess).• Bowel wall thickening (>10 mm) and vascular engorgement (‘comb sign’).• Fat stranding.• Circumferential submucosal hypoattenuation, surrounded by higher attenuation (‘halo sign’).• Bones: spondylitis, sacroiliitis, complications of steroid use.• Check for gallstones and renal stones.
MRI
• Very useful for monitoring disease activity (no radiation) and depicts Crohn pathology well—MRI is also specific in Crohn.• Wall thickening (5-10 mm), enhancement and oedema.• Fold thickening (‘picket fence’ appearance).• Fistulae are best highlighted as high signal tracts on fat-suppressed axial/coronal T2, their origin is in an ulcer/fissure, sign of advanced Crohn.• Fistulae enhance post-contrast.• Strictures—these are considered significant if the upstream bowel is dilated (i.e. >3 cm for small bowel).• Intramural fat—low signal in the bowel wall demonstrated on fat-suppressed images.• Lymph node enhancement.
US
• Limited role for monitoring disease activity in those not suitable for MRI/assessing for a fluid collection.• Overview of the abdomen performed with a standard low-frequency probe, then focused scan of the right iliac fossa with a high-frequency linear probe to assess the terminal ileum.• Look for bowel thickening, hyperaemia on Doppler or enhancement after contrast.
Crohn disease. Fistulogram demonstrating a long, ulcerated segment of terminal ileum with a stricture.
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