What are the characteristic CT enterography features of ulcerative colitis?

CT Enterography Features of Ulcerative Colitis

CT enterography demonstrates characteristic features of ulcerative colitis including colonic wall thickening (mean 7.8 mm), inhomogeneous mural enhancement with a "target" appearance, and submucosal fat deposition, which help distinguish it from other inflammatory bowel diseases. 1, 2

Key CT Enterography Findings in Ulcerative Colitis

Colonic Wall Characteristics

• Wall thickness: Mean wall thickness of 7.8 mm (compared to normal 2-3 mm thickness) 3, 1
• Pattern of thickening: More uniform and symmetric compared to Crohn's disease 1
• Mural enhancement: Inhomogeneous enhancement pattern 1
• Target sign: Layered appearance of the bowel wall with alternating densities 1
• Submucosal fat deposition: Present in 61% of ulcerative colitis cases (vs. 8% in Crohn's disease) - a distinguishing feature 2

Distribution Pattern

• Continuous involvement: Uninterrupted inflammation from rectum proximally 3
• Rectal involvement: Nearly always present with characteristic "target" appearance 1
• Proximal extension: Variable extent of proximal involvement 3
• Perirectal fat proliferation: Common finding 1

Distinguishing Features from Crohn's Disease

• Wall thickness: Thinner than in Crohn's disease (7.8 mm vs. 11.0 mm) 2
• Homogeneity: More inhomogeneous compared to the homogeneous thickening in Crohn's disease 1
• Absence of skip lesions: Continuous involvement rather than segmental 3
• Fewer extraluminal complications: Less likely to show fistulas, abscesses, or mesenteric abnormalities 1

Technical Considerations for Optimal Imaging

Protocol Recommendations

• Oral contrast: 1300-1800 cc of neutral contrast (water density) administered over 30-60 minutes before imaging 4
• IV contrast: Essential for evaluating mural enhancement patterns 4
• Slice thickness: Thin collimation (2-3 mm) with multiplanar reconstruction 4
• Timing: Imaging between enteric and portal phases (50-70 seconds after IV contrast) 4
• Coverage: Should include abdomen, pelvis, and perineum 4

Diagnostic Performance

• CT enterography has excellent diagnostic performance with sensitivity of 75-90% and specificity >90% for inflammatory bowel disease 4
• Superior to standard CT with positive oral contrast, which can obscure subtle mucosal enhancement 5

Clinical Correlation and Pitfalls

Common Pitfalls

• Inadequate bowel distention can limit evaluation of wall thickness and enhancement
• Positive oral contrast can obscure mucosal enhancement patterns 5
• Normal jejunum may demonstrate increased relative nonfocal restricted diffusion compared to ileum 5
• Colonic wall thickening is non-specific and can be found in other forms of colitis 5

Differential Considerations

• Crohn's disease: Thicker wall (mean 11.0 mm), homogeneous attenuation, skip lesions, fistulas, abscesses 1, 2
• Infectious colitis: Often associated with ascites, may have right-sided predominance 6
• Ischemic colitis: Vascular distribution pattern 6
• Pseudomembranous colitis: Marked wall thickening, often with ascites 6

By utilizing proper CT enterography technique with neutral oral contrast and IV contrast enhancement, radiologists can accurately identify the characteristic features of ulcerative colitis and distinguish it from other inflammatory bowel conditions, particularly Crohn's disease.