Neuroimaging plays a crucial role in the diagnosis and characterization of corticobasal syndrome (CBS). Structural and functional imaging can help differentiate CBS from other parkinsonian syndromes and may provide insights into the underlying pathology. The asymmetric frontoparietal atrophy pattern is a hallmark feature that distinguishes CBS from Parkinson's disease and progressive supranuclear palsy.[^brain]
- Asymmetric cortical atrophy: The hallmark imaging finding in CBS is asymmetric frontoparietal atrophy, typically more pronounced contralateral to the most affected limb[^brain]
- Parietal lobe involvement: Superior and inferior parietal lobules show significant atrophy
- Frontal lobe atrophy: Premotor cortex and supplementary motor area (SMA) are commonly affected
- Posterior temporal involvement: Superior temporal gyrus atrophy may be present
- Asymmetry index: A left-right asymmetry ratio >10% is highly suggestive of CBS
| Region |
Typical Finding |
Clinical Correlation |
| Precentral Gyrus |
Focal atrophy |
Cortical signs, weakness |
| Superior Parietal Lobule |
Moderate-severe atrophy |
Ideomotor apraxia |
| Inferior Frontal Gyrus |
Variable atrophy |
Language dysfunction |
| Posterior Temporal |
Mild-moderate |
Alexia, agnosia |
- Basal ganglia atrophy: Putamen and globus pallidus show volume loss
- Thalamic changes: Thalamic atrophy, particularly in the ventral lateral nucleus
- Brainstem involvement: Pontine and midbrain atrophy, though less prominent than in PSP
- Corpus callosum thinning: Especially in the posterior portions
- Red nucleus involvement: May show iron deposition in advanced cases
- Periventricular white matter hyperintensities: Subcortical white matter lesions
- Asymmetric involvement: White matter changes often correspond to cortical atrophy pattern
- Centrum semiovale: Small-vessel ischemic changes may be present
- Superior longitudinal fasciculus: Tract-specific degeneration correlates with apraxia
- Fractional anisotropy reduction: In corticospinal tracts and corpus callosum
- Mean diffusivity increases: Reflecting white matter tract degeneration
- Pattern differentiation: DTI metrics can help distinguish CBS from PSP and PD
- Regional specificity: Asymmetric FA loss in premotor and parietal regions
- Network-based analysis: Disruption of frontoparietal and basal ganglia networks
- N-acetylaspartate reduction: Indicating neuronal loss
- Choline elevation: Reflecting membrane turnover and gliosis
- Creatine changes: Metabolic alterations in affected regions
- Lactate peaks: May be elevated in some cases suggesting mitochondrial dysfunction
- Iron deposition: Increased iron in basal ganglia
- Microhemorrhages: Small hemorrhagic lesions may be present
- Mineralization patterns: Distinct from other parkinsonian syndromes
- Nigrosome imaging: May show normal substantia nigra in CBS (vs. PD)
- R1 relaxation: Reduced in cortical regions affected by atrophy
- Myelin integrity: Can assess demyelination patterns
- Longitudinal monitoring: Tracks disease progression over time
- Asymmetric hypometabolism: Contralateral to the most affected side
- Parietal and frontal hypometabolism: Characteristic pattern[^lehericy2014]
- Basal ganglia hypometabolism: Including putamen and caudate
- Diagnostic utility: FDG-PET pattern helps differentiate CBS from PD and PSP
- Posterior cingulate: May show hypometabolism mimicking AD patterns
- Brainstem metabolism: Generally preserved compared to PSP
- Fluorinated tau tracers: Show increased binding in CBS
- Regional distribution: Correlates with clinical symptoms
- Differential diagnosis: Helps distinguish CBD pathology from other causes
- 18F-Flortaucipir: Approved for tau visualization in AD, shows offtarget binding in CBS
- Emerging tracers: Novel 4R-tau selective tracers in development
- Presynaptic dopaminergic function: Reduced dopamine transporter binding
- Post-synaptic dysfunction: D2 receptor binding may be reduced
- Differential from PD: Helps rule out idiopathic Parkinson's disease
- Pattern analysis: Asymmetric loss pattern distinguishes CBS
- Default mode network: Disruption correlates with cognitive impairment
- Motor network: Reduced connectivity between premotor and parietal regions
- Salience network: May show increased activity in early CBS
| Feature |
CBS |
PD |
| Asymmetry |
Marked asymmetry |
Mild asymmetry |
| Cortical atrophy |
Present |
Absent |
| Parietal hypometabolism |
Prominent |
Absent |
| Dopamine response |
Poor |
Good |
| Cortical signs |
Early |
Late/Absent |
| Tremor |
Less prominent |
Prominent |
| Feature |
CBS |
PSP |
| Midbrain atrophy |
Mild-moderate |
Severe (hummingbird sign) |
| Superior frontal atrophy |
Less prominent |
Prominent |
| Parietal involvement |
Prominent |
Less prominent |
| Asymmetry |
Marked |
Symmetric or asymmetric |
| PSP-RS criteria |
Often atypical |
Classic presentation |
| Cortical signs |
Prominent early |
Minimal |
MRI findings support CBS diagnosis when:
- Asymmetric frontoparietal atrophy is present
- Basal ganglia atrophy is demonstrated
- Other causes of parkinsonism are excluded
- Cortical signs (apraxia, alien limb) accompany imaging findings
- Pattern of atrophy correlates with clinical phenotype
- Rate of progression may be estimated from imaging
- Conversion from CBS to CBD can be monitored
- Cognitive impairment predicts with posterior cingulate hypometabolism
- Serial MRI every 6-12 months tracks atrophy progression
- FDG-PET can monitor metabolic changes
- DTI provides sensitive white matter degeneration markers