Multiple System Atrophy

Multiple system atrophy (MSA)

• Adult onset fatal neurodegenerative disease, unknown etiology

• Various combination of cerebellar/pyramidal/extrapyramidal/autonomic features

3 clinical subtypes characterized by signs and symptoms

• Predominantly cerebellar (MSA-C)

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    a.k.a. sporadic olivopontocerebellar atrophy (sOPCA)

• Extrapyramidal (MSA-P)

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    a.k.a. striatonigral degeneration (SND)

• Autonomic (MSA-A)

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    a.k.a. Shy-Drager syndrome (SDS)

2 distinct imaging subtypes: MSA-C and MSA-P

Best diagnostic clue

• MSA-C: Cruciform shape of hyperintense signal in pons on T2WI; atrophy of pons, inferior olives, and cerebellum

• MSA-P: Putamen atrophy, ↓ T2 signal in dorsolateral putamen ± ↑ T2 signal in lateral rim of putamen

Location

• Striatum (mainly putamen), middle cerebellar peduncles (MCP), pons, cerebellum

Size

• Decreased (atrophy)

NECT

• Pontine atrophy, enlarged 4th ventricle (4th V)

• Cerebellar atrophy (hemispheres > vermis)

• Cortical atrophy (especially frontal and parietal lobes)

T1WI

• On sagittal images

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    ↓ size of pons and medulla with flat ventral surface of pons

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    Atrophy of cerebellar vermis and hemispheres

• On axial images

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    ↓ anteroposterior diameter of pons

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    ↓ width of MCP

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    Enlargement of 4th V and cerebellopontine angle

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    Cerebellar atrophy

• Atrophy of MCP and cerebellum is greater in MSA-C than other MSA subtypes

• Lateral putaminal T1 hyperintensity in MSA-P

• Frontal, parietal atrophy

T2WI

• MSA-C type

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    Selective atrophy of lower portion of basis pontis, medulla, MCPs, and cerebellar hemispheres

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    Corresponding ↑ T2 signal in pons, MCPs, and cerebellar white matter (WM)

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    Hyperintense signal in cruciform shape in pons (“hot cross bun” sign)

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      Reflects degeneration of pontine neurons and transverse pontocerebellar fibers (TPF)

• MSA-P type

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    Atrophy of putamen

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    ↓ signal in dorsolateral putamen ± ↑ signal in lateral rim of putamen

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    ↑ signal lateral rim putamen normal finding at 3.0 T

• Atrophy of cerebral hemispheres

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    Especially frontal and parietal lobes

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    Not significantly different in various subtypes

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    Related to higher cortical dysfunction in MSA

• All MR findings may be observed in every MSA subtype

PD/intermediate

• MSA-C: ↑ signal in TPF, MCP, and cerebellum

• MSA-P: ↓ signal in dorsolateral putamen ± hyperintense lateral rim of putamen

T2* GRE

• SWI: Severe putaminal hypointensity in MSA-P type

DWI

• ↑ ADC in MCP helps differentiating MSA-C from PD and progressive supranuclear palsy

• ↑ ADC in putamen helps differentiating MSA-P from Parkinson disease

• DWI of pons with transverse diffusion gradient

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    Normal individuals: TPF seen as low intensity bundles in base of pons on axial multishot

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    MSA-C: TPF not seen on DWI of pons

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    ADC measurements in MCPs help differentiate MSA from Parkinson disease and progressive supranuclear palsy

• Diffusion tensor MR (DTI)

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    MSA-C: ↓ FA in MCP, TPF, and cerebellum

MRS

• ¹H-MRS: Significantly ↓ pontine and cerebellar NAA/Cr, Cho/Cr ratios in MSA-C

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    Pontine NAA/Cr ratio correlates with disability

• Phosphorus MRS: ↓ phosphocreatine, ↑ phosphate

MR volumetry

• Volumetry and voxel-based morphometry show striatal and cerebellar volume loss in MSA-P compared to PD and healthy controls

• MCP width < 8 mm: In MSA compared to PD and healthy controls