How does vasculitis appear on Computed Tomography Angiography (CTA) imaging?

Vasculitis Appearance on CTA Imaging

On CTA imaging, vasculitis typically appears as circumferential mural thickening (>2-3 mm) without adjacent atheroma, associated wall enhancement, and perivascular fat stranding, with active disease showing enhancement in the outer vessel wall and a low attenuation ring in the inner aspect on delayed phase images. 1

Key CTA Findings in Vasculitis

Primary Vessel Wall Findings

• Circumferential mural thickening:

  • Typically >2-3 mm thickness
  • Occurs without adjacent atheroma (important distinguishing feature)
  • May persist even after clinical response to treatment 1

• Wall enhancement patterns:

  • Enhancement in the outer portion of the vessel wall
  • Low attenuation ring in the inner aspect on delayed phase images
  • Significant enhancement defined as >20 HU increase in attenuation 1
  • Delayed/venous phase acquisition emphasizes mural enhancement 1

• Perivascular inflammation:

  • Fat stranding around affected vessels 1

Secondary Luminal Findings

• Luminal narrowing/stenosis
• Occlusion
• Aneurysmal dilation
• Vessel wall irregularities 1

Active vs. Chronic Disease Features

Active vasculitis on CTA is characterized by:

• Wall enhancement (correlates with elevated inflammatory markers)
• Low attenuation ring on delayed images (correlates with elevated inflammatory markers) 1

Chronic changes (damage) include:

• Stenosis
• Occlusion
• Dilation
• Aneurysm formation
• Calcification 2

Note that wall thickening alone without enhancement may not correlate with active disease 1.

Diagnostic Performance of CTA

• For large vessel vasculitis (LVV) diagnosis:

  • Sensitivity: 73-95%
  • Specificity: 78-100%
  • PPV: 85%
  • NPV: 65% 1

• CTA performs particularly well for Takayasu arteritis diagnosis with sensitivity of 95% and specificity of 100% 1

• When evaluating by vessel segment rather than by patient, sensitivity drops to 61% while maintaining high specificity (98%) 1

Technical Considerations

• Multiphasic technique: Non-contrast and arterial phases help differentiate intramural hematoma from vasculitis 1
• Delayed phase imaging: Essential for evaluating mural enhancement patterns 1
• Hybrid imaging: CTA can be combined with FDG-PET for improved diagnostic accuracy 1

Cerebral Vasculitis on CTA

For central nervous system (CNS) vasculitis, CTA findings include:

• Multifocal vessel wall narrowing and dilatation
• However, these findings have considerable overlap with other cerebrovascular diseases
• Sensitivity is limited by resolution as small vessel involvement may be below detection threshold 1

Common Pitfalls

1. Persistent wall thickening: Up to 49% of patients may show persistent wall thickening despite clinical response to treatment, making CTA less reliable for monitoring treatment response 1

2. Overlap with other conditions: CTA findings may overlap with atherosclerosis or other non-inflammatory vascular conditions 1

3. Limited resolution: Small vessel vasculitis may be below the resolution threshold of CTA 1

4. Differential diagnosis challenges: Wall thickening alone is not specific for active disease and may represent chronic changes 1

CTA is most useful as an initial diagnostic tool for large vessel vasculitis, particularly when combined with clinical assessment and laboratory markers of inflammation. For suspected cerebral vasculitis, MRI of the brain with vessel wall imaging provides superior soft tissue characterization 1.