What imaging study is recommended to evaluate progressive supranuclear palsy (PSP)?

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Last updated: September 21, 2026 • View editorial policy

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MRI of the brain without IV contrast is the optimal imaging study for evaluating PSP

MRI of the brain without IV contrast is the first-line and most appropriate imaging modality for evaluating progressive supranuclear palsy due to its superior soft-tissue characterization and ability to demonstrate characteristic patterns of regional atrophy. 1

Primary Imaging Recommendation

The ACR Appropriateness Criteria (2020) explicitly states that MRI of the brain without IV contrast is the optimal imaging modality for Parkinsonian syndromes including PSP, based on its soft-tissue characterization and sensitivity to iron deposition. 1 Contrast is typically not needed for evaluation of PSP. 1

Key MRI Findings in PSP

On structural MRI, look for these characteristic features:

  • Midbrain atrophy - the most consistent finding
  • Midbrain-to-pons area ratio (M/P) - decreased in PSP
  • Superior cerebellar peduncle (SCP) atrophy - narrowing of the SCP width
  • "Hummingbird sign" or "penguin silhouette" - midbrain atrophy on sagittal images
  • "Morning glory sign" - concave lateral margin of midbrain on axial images

Recent research confirms midbrain surface area is the optimal single MRI marker for PSP diagnosis (AUC = 0.937; sensitivity 88.8%; specificity 84.2%). 2 Surface-based measurements outperform distance- and volume-based markers.

Quantitative MRI Indices

Magnetic Resonance Parkinsonism Index (MRPI) is highly accurate for PSP diagnosis:

  • Calculated as: (pons area/midbrain area) × (MCP width/SCP width)
  • Demonstrates 100% sensitivity and specificity in distinguishing PSP from PD and MSA 3
  • MRPI values >13.55 are highly suggestive of PSP 4

The cerebral interpeduncular angle also shows high diagnostic accuracy (100% sensitivity, 90% specificity for PSP). 4

Adjunctive Nuclear Medicine Imaging

When to Consider Additional Imaging

I-123 Ioflupane (DaTscan) SPECT/CT serves a specific but limited role:

  • Useful for differentiating Parkinsonian syndromes (PD, MSA, PSP, CBD) from essential tremor and drug-induced tremor 1
  • Shows abnormal dopaminergic depletion in PSP, but cannot distinguish PSP from PD, MSA, or CBD 1
  • A normal DaTscan essentially excludes Parkinsonian syndromes 1
  • Has low specificity and variable sensitivity specifically for PSP 5

FDG-PET/CT has limited but emerging utility:

  • Can discriminate PSP from idiopathic PD based on metabolic patterns 1
  • PSP shows characteristic hypometabolism in medial frontal cortex, anterior cingulate cortex, striatum, and midbrain 1
  • Evidence quality remains limited for routine clinical use 1

Tau PET (18F-PI-2620) shows promise but is not yet standard:

  • Improves diagnostic accuracy when combined with MRI (94% sensitivity, 100% specificity) 6
  • Particularly valuable in early disease stages and variant PSP phenotypes 6
  • Not yet widely available or FDA-approved for routine clinical use

CT Head - Not Recommended as First-Line

CT is not the preferred modality due to limited soft-tissue characterization compared to MRI. 1 While CT can demonstrate patterns of regional volume loss characteristic of PSP, it should only be used when MRI is contraindicated or unavailable. 1

Clinical Context Matters

Important caveats:

  • MRI markers are more accurate in probable PSP versus possible/suggestive PSP 2
  • PSP-Richardson syndrome shows better diagnostic accuracy than PSP variants 2
  • MRI markers remain useful even in early disease stages (≤24 months) 2
  • Midbrain atrophy correlates with disease severity and specific deficits (ocular motor, gait, bulbar) 2

Practical Algorithm

  1. Start with MRI brain without contrast - measure midbrain and pons areas, SCP width, calculate MRPI
  2. If MRPI >13.55 and clinical features consistent - diagnosis strongly supported
  3. If diagnostic uncertainty remains - consider DaTscan to exclude non-degenerative causes (essential tremor, drug-induced)
  4. If available and early/variant presentation - tau PET may provide additional diagnostic confidence
  5. Reserve FDG-PET for cases where distinguishing PSP from PD is critical and MRI is equivocal

The combination of clinical assessment with quantitative MRI measurements provides the most reliable diagnostic approach for PSP in routine clinical practice.

References

1
Guideline

acr appropriateness criteria® movement disorders and neurodegenerative diseases.

Journal of the American College of Radiology, 2020

6
Research

18F-PI-2620 Tau PET Improves the Imaging Diagnosis of Progressive Supranuclear Palsy.

Journal of nuclear medicine : official publication, Society of Nuclear Medicine, 2022

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