What are the possible findings on a CT scan in a patient with inflammatory bowel disease?

CT Findings in Inflammatory Bowel Disease

CT enterography demonstrates multiple characteristic findings in IBD patients, with the most reliable indicators being bowel wall thickening, mural hyperenhancement, comb sign (engorged vasa recta), and perienteric fat stranding, which collectively achieve 84-89% sensitivity for detecting active disease. 1

Mural (Bowel Wall) Findings

Wall Thickening Patterns

• Wall thickening is the most common finding, with mean thickness of 11.0 mm in Crohn's disease versus 7.8 mm in ulcerative colitis 2
• Mural stratification patterns correlate with disease activity: multilayered enhancement (Type A pattern, 60% of cases) indicates acute inflammation, while homogeneous enhancement (Type D pattern, 13% of cases) suggests quiescent disease 3
• Strong mucosal enhancement with prominent low-density submucosa (Type B pattern, 18% of cases) is highly predictive of acute inflammatory activity 3

Mucosal Changes

• Mucosal hyperenhancement after IV contrast administration is a key indicator of active inflammation (P = 0.04 for correlation with histopathology) 1
• Ulcerations visible as focal wall defects or irregularities 1
• Intramural edema appearing as low-attenuation areas within the thickened wall 1

Perienteric (Mesenteric) Findings

Vascular Changes

• Comb sign (engorged vasa recta) is the most statistically significant finding for inflammation (P < 0.0001) and predicts radiologic response to therapy (P = 0.024) 1
• Increased mesenteric vascularity correlating with mucosal inflammation (r = 0.72, P < 0.01) 1

Fat and Soft Tissue Changes

• Perienteric fat stranding indicating mesenteric inflammation 1
• Fibrofatty proliferation ("creeping fat") representing chronic inflammatory changes 1
• Enlarged mesenteric lymph nodes (P = 0.016 for correlation with inflammation) 1

Complications and Structural Changes

Strictures

• Luminal narrowing with upstream dilation (mild <4 cm, moderate-severe ≥4 cm) 1
• Strictures with inflammation show concurrent wall thickening and hyperenhancement (89% sensitivity, 94% specificity for detection) 1
• Strictures without inflammation demonstrate wall thickening alone, suggesting predominantly fibrotic disease 1

Penetrating Complications

• Fistulas (enteroenteric, enterocutaneous, enterovesical) with variable detection rates: 68-100% sensitivity overall, but only 20% for enteroenteric fistulas 4
• Abscesses with 86-100% sensitivity for detection 4
• Sinus tracts extending from inflamed bowel segments 1
• Free perforation with extraluminal air and fluid 5

Distribution Patterns

Location-Specific Features

• Terminal ileum involvement is most common in Crohn's disease with highest CT sensitivity (89%) 1
• Right colon and small bowel involvement suggests Crohn's disease or infectious colitis 2
• Continuous involvement from rectum suggests ulcerative colitis 1
• Asymmetric or segmental distribution favors Crohn's disease over ulcerative colitis 1

Additional Findings

Chronic Disease Markers

• Submucosal fat deposition present in 61% of ulcerative colitis but only 8% of Crohn's colitis (P = 0.0001), indicating chronic disease 2
• Loss of haustration and rigid bowel wall correlating with UC severity (r = 0.612) 1

Extra-intestinal Manifestations

• Sacroiliitis with erosions or subchondral edema 1
• Primary sclerosing cholangitis with biliary ductal changes 1
• Nephrolithiasis and cholelithiasis 1

Critical Diagnostic Pitfalls

Standard CT without enterography protocol misses 10-25% of active disease because inadequate bowel distention obscures inflammatory changes 4. CT enterography with neutral oral contrast (>900 mL) and IV contrast is essential for optimal sensitivity 1.

CT without IV contrast has markedly poorer performance and cannot adequately assess active inflammation, as mural hyperenhancement is a key diagnostic feature 4. Non-contrast CT should not be used for evaluating suspected IBD activity 1.

Enteroenteric fistulas have particularly poor detection (20% sensitivity), so negative CT does not exclude this complication 4. MRI or surgical exploration may be needed when clinical suspicion is high despite negative CT 1.

Early or mild mucosal disease may not produce classic CT findings of wall thickening or stratification, particularly in proximal small bowel 4. Endoscopy remains the reference standard when CT is negative but clinical suspicion persists 4.