Imaging Findings of Vasculitis in the Head
MRI is the most valuable imaging modality for suspected CNS vasculitis, with a sensitivity approaching 100% when normal, while characteristic vessel imaging findings include multifocal stenosis and dilatation of intracranial vasculature with vessel wall inflammation. 1
Primary Imaging Modalities for CNS Vasculitis
MRI Head
MRI is the preferred initial imaging modality for suspected CNS vasculitis due to:
Superior soft-tissue characterization of brain parenchyma and vessel walls
Multiple parenchymal findings including:
- Multiple infarcts of variable ages (seen in up to 50% of patients)
- Progressive confluent white matter lesions
- Cortical and subcortical T2 lesions
- Multiple microhemorrhages
- Mass lesions (5% of cases)
- Meningeal enhancement (8% of cases)
- Hemorrhage (9% of cases)
- Enhancing small vessels/perivascular spaces 1
Near 100% sensitivity when normal (a normal MRI effectively rules out CNS vasculitis) 1
Advanced MRI Vessel Wall Imaging
Recent advances in MRI vessel wall imaging significantly improve diagnostic accuracy:
- Contrast-enhanced MRI vessel wall imaging combined with luminal imaging increases diagnostic accuracy to 89% compared to 36% with luminal imaging alone 1
- Helps differentiate CNS vasculitis from other cerebrovascular diseases by showing characteristic inflammatory changes of vessel walls 1
Cerebral Arteriography
- Traditional standard for imaging diagnosis due to submillimeter resolution
- Shows multifocal stenosis and dilatation of intracranial vessels
- Limited by:
- Low specificity (findings overlap with atherosclerosis and reversible cerebral vasoconstriction syndrome)
- Limited sensitivity (small vessel involvement may be below resolution threshold) 1
CTA Head
- Shows multifocal vessel wall narrowing and dilatation
- Findings on CTA for CNS vasculitis include:
- Circumferential mural thickening (>2-3mm) without adjacent atheroma
- Associated wall enhancement
- Perivascular fat stranding 2
- Limited by:
- Considerable overlap with other cerebrovascular diseases
- Resolution limitations for small vessel involvement 1
MRA Head
- Offers noninvasive, radiation-free examination
- Time-of-flight MRA abnormal in 81% of patients with angiographic findings of vasculitis
- Normal in 100% of patients with normal angiogram
- Limited by resolution and specificity (similar to CTA and arteriography) 1
Characteristic Imaging Patterns
Large Vessel Vasculitis
- Homogeneous, circumferential wall swelling
- Smoothly tapered luminal narrowing 3
- Wall enhancement patterns:
- Enhancement in outer vessel wall
- Low attenuation ring in inner aspect on delayed phase images
- Significant enhancement (>20 HU increase in attenuation) 2
Active Disease Markers
- Wall enhancement and low attenuation ring on delayed images
- Correlates with elevated inflammatory markers
- Perivascular inflammation with fat stranding around affected vessels 2
Important Diagnostic Considerations
Limitations and Pitfalls
- Persistent wall thickening may be seen in up to 49% of patients despite clinical response to treatment 2
- Wall thickening alone is not specific for active disease and may represent chronic changes
- Small vessel vasculitis may be below the resolution threshold of CTA and conventional angiography 1, 2
- Findings may overlap with atherosclerosis or other non-inflammatory vascular conditions 2
Optimal Imaging Approach
- Start with MRI head as the initial imaging study (highest sensitivity)
- Consider advanced vessel wall imaging to improve specificity
- Use cerebral angiography, CTA, or MRA for additional vessel characterization
- Consider multiphasic technique including non-contrast and arterial phases to differentiate intramural hematoma from vasculitis 2
MRI findings of CNS vasculitis have considerable overlap with other CNS diseases, but the sensitivity of a normal MRI for excluding CNS vasculitis approaches 100%, making it the most valuable initial screening tool 1.