What type of Magnetic Resonance Imaging (MRI) and Magnetic Resonance Angiography (MRA) of the brain should be requested to detect Central Nervous System (CNS) vasculitis?

MRI/MRA Protocol for Detecting CNS Vasculitis

For detecting CNS vasculitis, a contrast-enhanced MRI brain with vessel wall imaging protocol plus time-of-flight MRA without contrast is the most appropriate imaging approach. 1

Recommended Imaging Protocol

Primary Imaging Components:

• MRI brain with contrast 1

  • Standard brain sequences (T1, T2, FLAIR, DWI)
  • Post-contrast T1-weighted sequences
  • Vessel wall imaging (VWI) sequences with contrast enhancement - critical for detecting inflammatory changes in vessel walls 1, 2
  • Susceptibility-weighted imaging (SWI) to detect microhemorrhages and linear/lace-like blooming patterns along small vessels 3

• MRA head without contrast (time-of-flight technique) 1

  • High-resolution 3D time-of-flight MRA to evaluate luminal changes 1, 4
  • Provides assessment of stenosis, occlusions, and vascular irregularities 1

Rationale and Evidence

MRI Findings in CNS Vasculitis

• MRI head is highly sensitive for CNS vasculitis with sensitivity approaching 100% when normal 1
• Key parenchymal findings include:
  • Multiple infarcts of variable ages (seen in up to 50% of patients) 1
  • Progressive confluent white matter lesions 1
  • Cortical and subcortical T2/FLAIR hyperintensities 1
  • Multiple microhemorrhages 1
  • Mass lesions (5%), meningeal enhancement (8%), and hemorrhage (9%) 1
  • Enhancing small vessels/perivascular spaces 1

Vessel Wall Imaging Advantages

• Contrast-enhanced vessel wall imaging significantly improves diagnostic accuracy to 89% compared to 36% with luminal imaging alone 1
• Characteristic patterns in CNS vasculitis include:
  • Concentric wall enhancement (88.3% of cases) 2, 5
  • Wall thickening with enhancement 5
  • Helps differentiate vasculitis from other cerebrovascular diseases like atherosclerosis and reversible cerebral vasoconstriction syndrome 5

MRA Evaluation

• Time-of-flight MRA shows abnormalities in 81% of patients with angiographic findings of vasculitis 1
• MRA can detect multifocal stenosis and dilatation of intracranial vessels 1
• 3D TOF-MRA is superior to contrast-enhanced MRA for detecting multiloculated segmental stenoses in non-infectious vasculitis 4

Technical Considerations

• 3D vs 2D Vessel Wall Imaging:

  • 3D vessel wall imaging provides whole-brain coverage with better evaluation of vertebral arteries and distal intracranial segments 6
  • 3D sequences show more leptomeningeal and parenchymal enhancement 6
  • 2D sequences may better visualize the intradural ICA segments 6

• SWI Sequence Value:

  • SWI can detect linear and lace-like blooming patterns along small cerebral vessels in lymphocytic CNS small vessel vasculitis 3
  • These patterns are distinct from other pathologies and may increase diagnostic specificity 3

Limitations and Caveats

• MRA has limited resolution for detecting small vessel involvement 1
• Luminal imaging (MRA/CTA) alone has considerable overlap with other cerebrovascular diseases like atherosclerosis and reversible cerebral vasoconstriction syndrome 1
• Conventional angiography (DSA) remains the historical gold standard for vessel imaging but has low specificity for vasculitis 1
• No evidence supports the use of MRA with IV contrast, MRA neck, MRI perfusion, or MRV head in the initial evaluation of suspected CNS vasculitis 1

Follow-up Imaging Considerations

• Follow-up vessel wall imaging can help monitor treatment response 2
• Patients with stable or progressive vessel wall enhancement are more likely to experience clinical relapse than those with partial or complete regression 2
• Resolution of vessel wall enhancement may indicate effective treatment 5