MRI Atrophy Patterns in CBS/PSP

MRI Atrophy Patterns in Corticobasal Syndrome and Progressive Supranuclear Palsy

Introduction

Magnetic resonance imaging (MRI) is a cornerstone in the diagnosis and characterization of corticobasal syndrome (CBS) and progressive supranuclear palsy (PSP). Both conditions show characteristic patterns of brain atrophy that help distinguish them from each other and from other neurodegenerative diseases like Parkinson's disease (PD) and Alzheimer's disease (AD) [@whitwell2024].

Corticobasal Degeneration MRI Findings

Characteristic Patterns

MRI Atrophy Patterns in Corticobasal Syndrome and Progressive Supranuclear Palsy

Introduction

Magnetic resonance imaging (MRI) is a cornerstone in the diagnosis and characterization of corticobasal syndrome (CBS) and progressive supranuclear palsy (PSP). Both conditions show characteristic patterns of brain atrophy that help distinguish them from each other and from other neurodegenerative diseases like Parkinson's disease (PD) and Alzheimer's disease (AD) [@whitwell2024].

Corticobasal Degeneration MRI Findings

Characteristic Patterns

Asymmetric Cortical Atrophy

The hallmark of CBD on MRI is asymmetric cortical atrophy, typically affecting the hemisphere contralateral to the more symptomatic side [@alexander2024]:

• Parietal lobe — Superior and inferior parietal lobules
• Frontal lobe — Precentral gyrus, superior frontal gyrus
• Temporal lobe — Superior temporal gyrus (posterior)
• Central region — Paracentral lobule

Basal Ganglia Atrophy

• Putamen — Posterolateral putaminal atrophy (contralateral to symptoms)
• Caudate nucleus — Head of caudate atrophy
• Globus pallidus — Variable involvement

Subcortical and Brainstem Changes

• Midbrain — Moderate atrophy (less prominent than in PSP)
• Superior cerebellar peduncle — Atrophy (ipsilateral to cortical atrophy)
• Pons — Generally preserved

Quantitative MRI Measures

| Measure | CBD Finding | Clinical Utility |
|---------|--------------|-------------------|
| Asymmetry index | >0.1 | High |
| Parietal cortical thickness | Reduced | Moderate |
| Putaminal volume | Reduced | Moderate |
| Motor cortex thickness | Reduced | Moderate |

Progressive Supranuclear Palsy MRI Findings

Characteristic Patterns

Midbrain Atrophy

The most distinctive finding in PSP is midbrain atrophy [@respondek2023]:

• Hummingbird sign — Atrophy of the midbrain with preserved pons creates the appearance on sagittal images
• Mickey mouse sign — Flattened midbrain on axial images
• Morning glory sign — Concave dorsal midbrain

Brainstem Findings

• Tectal atrophy — Atrophy of the tectum
• Cerebral aqueduct — Dilation
• Fourth ventricle — Enlargement

Cerebellar Findings

• Superior cerebellar peduncle — Atrophy (characteristic)
• Cerebellar dentate nucleus — Degeneration

Cortical Atrophy

• Frontal lobe — Prefrontal and premotor cortex atrophy
• Temporal lobe — Superior temporal gyrus (less than frontal)
• Parietal — Often preserved until late disease

PSP Subtypes and MRI Patterns

| PSP Variant | Characteristic MRI Finding |
|-------------|----------------------------|
| PSP-RS (Richardson's) | Prominent midbrain atrophy |
| PSP-P (Parkinsonian) | Less midbrain atrophy, more tegmental |
| PSP-CBS | Asymmetric cortical/basal ganglia |
| PSP-F (Frontal) | Frontal lobe atrophy |
| PSP-PAGF | Midbrain atrophy, cerebellar peduncle |

Quantitative MRI Measures

| Measure | PSP Threshold | Sensitivity | Specificity |
|---------|---------------|-------------|-------------|
| Midbrain/pons ratio | <0.52 | 80% | 90% |
| MRPI 2015 | >13.4 | 85% | 87% |
| Superior cerebellar peduncle width | <3mm | 70% | 80% |
| Third ventricle width | >9mm | 75% | 82% |

MRPI = MR Parkinsonism Index

Differential Diagnosis

CBD vs. PSP

| Feature | CBD | PSP | Utility |
|---------|-----|-----|---------|
| Asymmetry | Marked | Mild | Excellent |
| Midbrain atrophy | Moderate | Prominent | Excellent |
| Superior cerebellar peduncle | Variable | Prominent | Good |
| Parietal atrophy | Present | Absent | Moderate |
| Frontal atrophy | Present | Present | Limited |

CBD vs. AD

| Feature | CBD | AD | Utility |
|---------|-----|-----|---------|
| Asymmetry | Marked | Mild | Excellent |
| Hippocampal atrophy | Mild | Severe | Excellent |
| Posterior cingulate | Variable | Prominent | Good |
| Parietal atrophy | Asymmetric | Symmetric | Moderate |

PSP vs. PD

| Feature | PSP | PD | Utility |
|---------|-----|-----|---------|
| Midbrain atrophy | Present | Absent | Excellent |
| Third ventricle | Enlarged | Normal | Excellent |
| MRPI | Abnormal | Normal | Excellent |
| Superior cerebellar peduncle | Atrophic | Normal | Good |

PSP vs. Multiple System Atrophy (MSA)

| Feature | PSP | MSA | Utility |
|---------|-----|-----|---------|
| Midbrain atrophy | Prominent | Mild | Good |
| Pons atrophy | Mild | Prominent | Good |
| Cerebellar atrophy | Superior peduncle | Global | Moderate |
| Putaminal atrophy | Posterolateral | Diffuse | Moderate |

Clinical Applications

Diagnostic Criteria Integration

MRI findings are incorporated into diagnostic criteria [@hglinger2025]:

PSP (MDS Criteria)

• "String sign" — Linear hyperintensity along the rim of the substantia nigra
• "Hummingbird sign" — Midbrain atrophy on sagittal T1
• MRPI >13.4 supports probable PSP

• Asymmetric cortical atrophy on MRI
• Asymmetric basal ganglia atrophy
• Supports "probable CBD"

Disease Monitoring

Serial MRI can track progression:

• Volumetric measurements[@boxer2024]
• Atrophy rates[@aerts2024]
• Regional changes over time[@jabbari2024]

Prognostic Value

• Rapid atrophy predicts faster clinical progression
• Midbrain atrophy severity correlates with survival[@bergeron2023]
• Baseline MRI predicts fall onset in PSP[@quattrone2024]

Advanced MRI Techniques

Diffusion Tensor Imaging (DTI)

• Fractional anisotropy — Reduced in superior cerebellar peduncle
• Mean diffusivity — Elevated in midbrain and basal ganglia

Susceptibility-Weighted Imaging (SWI)

• Iron deposition — Increased in globus pallidus and substantia nigra
• Nigrosome 1 — Loss of the "swallow tail" sign

Magnetization Transfer Ratio (MTR)

• Reduced in motor cortex and basal ganglia
• Potential for early detection

Resting-State fMRI

• Functional connectivity changes in motor networks
• Useful for understanding circuit dysfunction[@morelli2023]

Rubric Scoring

Diagnostic Sensitivity (0-10)

• Score: 8/10 — High sensitivity for detecting characteristic atrophy patterns
• Midbrain atrophy highly sensitive for PSP
• Asymmetric cortical atrophy sensitive for CBD

Diagnostic Specificity (0-10)

• Score: 8/10 — Good specificity when classic patterns are present
• Midbrain atrophy distinguishes PSP from PD
• Asymmetry helps distinguish CBD from AD

Clinical Utility (0-10)

• Score: 9/10 — Excellent clinical utility
• Widely available
• Relatively inexpensive
• Non-invasive
• Integral to clinical workup

Evidence Quality (0-10)

• Score: 9/10 — Extensive evidence base
• Multiple large studies
• Incorporated into diagnostic criteria
• Standard of care

Effect Size (0-10)

• Score: 7/10 — Good effect size
• Clear atrophy differences between diseases
• Quantitative measures provide objective assessment

Summary

MRI provides essential neuroimaging biomarkers for CBS and PSP diagnosis. The characteristic patterns—asymmetric cortical/basal ganglia atrophy in CBD and midbrain atrophy in PSP—enable accurate differentiation from other parkinsonisms. Quantitative measures like the MR Parkinsonism Index improve diagnostic accuracy. MRI remains the cornerstone of structural imaging in these 4R tauopathies.

CBS/PSP Cross-Link Hub

Diseases

• Aging-Related Tauopathy (PART)
• Corticobasal Degeneration (CBD)
• Corticobasal Syndrome (CBS)
• Primary Age-Related Tauopathy (PART)
• Progressive Supranuclear Palsy (PSP)
• PSP Genetic Variants
• Variably Protease-Sensitive Prionopathy (VPSPr)

Treatments

• Autophagy Enhancement for Tauopathy
• CBS/PSP Clinical Trials Guide
• CBS/PSP Daily Action Plan
• CBS/PSP Rehabilitation Master Guide
• CBS/PSP Treatment Rankings
• Cognitive Reserve Strategies for CBS and PSP
• Corticobasal Degeneration (CBD) Treatment
• Exercise and Physical Activity for CBS/PSP
• Low-Dose Lithium for Tauopathy
• Melatonin for Tauopathy: Comprehensive Evidence Synthesis
• Mitochondrial Support Strategies for CBS/PSP
• Progressive Supranuclear Palsy (PSP) Treatment
• Evidence-Ranked Protective Strategies for CBS/PSP
• Rapamycin for Tauopathy
• Senolytic Therapies for CBS and PSP

Mechanisms

• 4R Tauopathy Molecular Mechanisms
• Corticobasal Degeneration (CBD) Pathway
• CBS/PSP Genetic Architecture
• Cortisol-Tau Pathway: From Chronic Stress to Tauopathy
• Gut-Brain Axis in Tauopathy
• Progressive Supranuclear Palsy (PSP) Pathway
• Tauopathy

Biomarkers

• CSF Biomarkers for Corticobasal Syndrome and Progressive Supranuclear Palsy
• Imaging Biomarkers for Corticobasal Syndrome and Progressive Supranuclear Palsy
• Plasma Biomarkers for Corticobasal Syndrome and Progressive Supranuclear Palsy
• Biomarkers for Corticobasal Degeneration
• DTI White Matter Changes in CBS/PSP
• Biomarkers for Progressive Supranuclear Palsy
• Tau PET in CBS/PSP
• Corticobasal Syndrome
• Corticobasal Degeneration
• Progressive Supranuclear Palsy
• 4R Tauopathy Mechanisms
• CBS/PSP Genetic Architecture
• Cortisol Tau Pathway
• Gut Brain Axis Tauopathy
• CBS/PSP Imaging Biomarkers
• CBS/PSP CSF Biomarkers
• CBS/PSP Plasma Biomarkers
• PSP Biomarkers
• CBD Biomarkers
• Tau PET in CBS/PSP
• MRI Atrophy Patterns in CBS/PSP
• DTI White Matter Changes in CBS/PSP
• CBS/PSP Treatment Rankings
• CBS/PSP Daily Action Plan
• CBS/PSP Rehabilitation Guide
• CBS/PSP Clinical Trials Guide
• Exercise for CBS/PSP
• Protective Strategies for CBS/PSP
• Cognitive Reserve for CBS/PSP
• Rapamycin for Tauopathy
• Lithium for Tauopathy
• Melatonin for Tauopathy
• Autophagy Enhancement for Tauopathy
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)

External Links

• [PubMed](https://pubmed.ncbi.nlm.nih.gov/)
• [KEGG Pathways](https://www.genome.jp/kegg/pathway.html)

Allen Brain Atlas Resources

• [Allen Brain Atlas - Gene Expression](https://human.brain-map.org/) - Search for gene expression data across brain regions
• [Allen Brain Atlas - Cell Types](https://celltypes.brain-map.org/) - Explore neuronal cell type taxonomy

References