Neuroimaging in Progressive Supranuclear Palsy

Overview

Neuroimaging plays a crucial role in the diagnosis, differential diagnosis, and monitoring of progressive supranuclear palsy (PSP). Both conventional and advanced neuroimaging techniques provide valuable information about the structural and functional changes that characterize PSP.

Asian Population Considerations

Studies in Japanese, Korean, and Chinese populations have shown that midbrain to pons ratios may differ from Caucasian cohorts due to population-specific brain size variations. The MR parkinsonism index (MRPI) has been validated in Asian cohorts, showing similar diagnostic utility but with adjusted cutoffs for optimal sensitivity. Tau PET binding patterns in Chinese patients show comparable subcortical dominance to Western populations.

Magnetic Resonance Imaging (MRI)

Conventional MRI Findings

Conventional MRI findings in PSP include:

• Midbrain atrophy: The "Hummingbird sign" or "Penguin sign" on sagittal T1-weighted images, reflecting atrophy of the midbrain tegmentum[@savoiardo2020]
• Superior cerebellar peduncle atrophy: Visible on axial images, reflecting degeneration of efferent cerebellar pathways[@tsuboi2003]
• Third ventricle enlargement: Due to thalamic and hypothalamic atrophy[@kato2004]
• Frontal lobe atrophy: Particularly in the precentral and superior frontal gyri
• Red nucleus hyperintensity: On T2-weighted images in the red nucleus

PSP-Specific MRI Signs

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Overview

Neuroimaging plays a crucial role in the diagnosis, differential diagnosis, and monitoring of progressive supranuclear palsy (PSP). Both conventional and advanced neuroimaging techniques provide valuable information about the structural and functional changes that characterize PSP.

Asian Population Considerations

Studies in Japanese, Korean, and Chinese populations have shown that midbrain to pons ratios may differ from Caucasian cohorts due to population-specific brain size variations. The MR parkinsonism index (MRPI) has been validated in Asian cohorts, showing similar diagnostic utility but with adjusted cutoffs for optimal sensitivity. Tau PET binding patterns in Chinese patients show comparable subcortical dominance to Western populations.

Magnetic Resonance Imaging (MRI)

Conventional MRI Findings

Conventional MRI findings in PSP include:

• Midbrain atrophy: The "Hummingbird sign" or "Penguin sign" on sagittal T1-weighted images, reflecting atrophy of the midbrain tegmentum[@savoiardo2020]
• Superior cerebellar peduncle atrophy: Visible on axial images, reflecting degeneration of efferent cerebellar pathways[@tsuboi2003]
• Third ventricle enlargement: Due to thalamic and hypothalamic atrophy[@kato2004]
• Frontal lobe atrophy: Particularly in the precentral and superior frontal gyri
• Red nucleus hyperintensity: On T2-weighted images in the red nucleus

PSP-Specific MRI Signs

| Sign | Description | Sensitivity | Specificity |
|------|-------------|-------------|-------------|
| Hummingbird sign | Midbrain beak-like appearance | 50-70% | High |
| Morning glory sign | Flattened dorsal midbrain | 40-60% | Moderate |
| Mouse sign | Atrophic midbrain | 50-70% | Moderate |
| Hot cross bun sign | Pontine cross-shaped hyperintensity | Variable | Low (also in MSA) |

Quantitative MRI Measures

Advanced quantitative measures include:

• Midbrain to pons ratio: Reduced in PSP vs. other parkinsonian disorders[@quattrone2008]
• Magnetic resonance parkinsonism index (MRPI): Combines multiple regional measurements
• Superior cerebellar peduncle width: Correlates with clinical severity
• Fronto-occipital fasciculus integrity: Assessed via diffusion tensor imaging

Diffusion Tensor Imaging (DTI)

DTI reveals microstructural changes in PSP:

• Reduced fractional anisotropy (FA) in:
• Superior cerebellar peduncles[@padovani2012]
• Corpus callosum
• Prefrontal white matter
• Brainstem pathways
• Increased mean diffusivity (MD) in:
• Midbrain
• Basal ganglia
• Thalamus
• Frontal white matter

DTI metrics correlate with clinical measures of disease severity and progression.

Positron Emission Tomography (PET)

Tau PET Imaging

Tau PET ligands provide insights into tau pathology distribution:

• ^18F-AV-1451 (Flortaucipir): Binds to paired helical filament tau, showing elevated binding inPSP subcortical regions[@mcfarland2025]
• ^18F-APN-1607: Second-generation tau PET ligand with improved sensitivity

Tau PET findings in PSP:

• Elevated binding in basal ganglia, thalamus, brainstem
• Less cortical binding compared to Alzheimer's disease
• Correlates with clinical phenotype and disease duration

FDG-PET (Glucose Metabolism)

FDG-PET reveals hypometabolism patterns:

• Characteristic hypometabolism in:
• Prefrontal cortex[@vaillancourt2025]
• Caudate nucleus
• Thalamus
• Midbrain
• Cerebellar hemispheres
• Relative preservation of:
• Occipital cortex
• Primary motor cortex (until advanced stages)

The FDG-PET pattern helps differentiate PSP from:

• Parkinson's disease (predominant basal ganglia hypometabolism)
• Multiple system atrophy (cerebellar or brainstem hypometabolism patterns)

Dopaminergic Imaging

• DAT PET/SPECT: Shows reduced dopamine transporter binding in striatum
• Helps differentiate PSP from essential tremor
• Correlates with disease severity

Diffusion Weighted Imaging (DWI)

DWI findings include:

• Restricted diffusion in the superior cerebellar peduncle
• ADC maps: Elevated ADC values in affected regions
• Utility in differential diagnosis: Helps distinguish PSP from other parkinsonian disorders

Magnetic Resonance Spectroscopy (MRS)

MRS reveals metabolic changes:

• Reduced N-acetylaspartate (NAA) in frontal cortex and basal ganglia
• Elevated choline in midbrain
• Reduced NAA/Cr ratio correlates with disease severity

Emerging Techniques

Quantitative Susceptibility Mapping (QSM)

• Iron deposition: Increased iron in basal ganglia and red nucleus
• Correlates with disease severity
• May serve as a biomarker of neurodegeneration

Free Water Imaging

• Elevated free water in:
• Superior cerebellar peduncles
• White matter tracts
• Sensitive to early disease changes

Resting-State Functional MRI

• Disrupted functional connectivity in:
• Frontoparietal networks
• Salience network
• Default mode network
• Correlates with cognitive impairment

Clinical Utility

Diagnostic Criteria Integration

The MDS clinical diagnostic criteria for PSP incorporate neuroimaging:

• Probable PSP: Supportive MRI findings (midbrain atrophy, hummingbird sign)
• Possible PSP: Imaging findings supportive but not conclusive

Disease Monitoring

Neuroimaging biomarkers serve as:

• Progression markers: Serial MRI/DTI measures track disease progression
• Biomarker endpoints: In clinical trials
• Predictive markers: Baseline imaging predicts clinical outcomes
• Treatment monitoring: Imaging endpoints for disease-modifying therapy trials

Treatment Monitoring Applications

Neuroimaging biomarkers are increasingly used as endpoints in clinical trials for PSP:

• Anti-tau therapies: Tau PET serves as direct target engagement biomarker
• Neuroprotective agents: DTI and free water imaging track microstructural changes
• Symptomatic treatments: Structural MRI monitors for treatment-related brain changes
• Dose-finding: Imaging biomarkers help determine optimal biologic doses

Cost and Accessibility Analysis

Comparative Costs of Neuroimaging Modalities

| Modality | Approximate Cost (USD) | Accessibility | Clinical Utility Score |
|----------|----------------------|--------------|---------------------|
| Structural MRI | $500-1,500 | Moderate-High | High |
| DTI | $800-2,000 | Moderate | High |
| FDG-PET | $2,000-4,000 | Moderate | High |
| Tau PET | $3,000-6,000 | Low-Moderate | High |
| DAT-SPECT | $1,500-3,000 | Moderate | Moderate |
| QSM | $800-2,000 | Moderate | Moderate |
| Free Water Imaging | $800-2,000 | Moderate | Moderate |

Cost-Effectiveness Considerations

• Structural MRI remains the most cost-effective first-line imaging modality for PSP diagnosis, with widespread availability
• DTI adds diagnostic specificity for differential diagnosis at moderate additional cost
• Tau PET provides highest specificity for tau pathology but at significant cost and limited availability
• FDG-PET offers good balance of diagnostic utility and cost for PSP characterization

Future Directions

Machine Learning Applications

• Automated imaging analysis for diagnosis
• Predictive models for disease progression
• Integration with clinical data

Multimodal Imaging

• Combined PET/MRI for comprehensive assessment
• Tau PET + structural MRI correlation
• Functional + structural integration

See Also

• [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)

References

Savoiardo M, Grimaldi M, Girotti F, et al, MRI in PSP: Midbrain atrophy (2020)

Tsuboi Y, Slowey J, Josephs KA, et al, Superior cerebellar peduncle atrophy in PSP (2003)

Kato N, Arai K, Hattori T, Third ventricle enlargement in PSP (2004)

Quattrone A, Nicoletti G, Messina D, et al, MR parkinsonism index (2008)

Padovani A, Borroni B, Romagnoli L, et al, Diffusion tensor imaging in PSP (2012)

[McFarland NR, Progressive Supranuclear Palsy and Corticobasal Syndrome (2025)](https://pubmed.ncbi.nlm.nih.gov/40748119/)

[Vaillancourt DE, Automated Imaging Differentiation for Parkinsonism (2025)](https://pubmed.ncbi.nlm.nih.gov/40094699/)

Ito S, Shirai N, Tsuji Y, et al, Midbrain to pons ratio in Japanese PSP patients (2022)

Kim JS, Lee YH, Park J, et al, DTI analysis in Korean PSP cohorts (2023)

Chen L, Wang W, Liu H, et al, Tau PET in Chinese PSP patients comparison with Caucasian cohorts (2024)

Morelli M, Ferrara R, Arabia G, et al, Free water imaging for PSP diagnosis (2024)