Multiple system atrophy (MSA)
General description
Multiple system atrophy (MSA) is a neurodegenerative disorder caused by accumulation of immobilized α-synuclein in oligodendrocytes. Those with cerebellar ataxia at first onset or in the early stages of the disease are called olivopontocerebellar atrophy (MSA-C), those with Parkinsonism are called striatonigral degeneration (MSA-P), and those with significant autonomic dysfunction, especially orthostatic hypotension, are called Shy-Drager Syndrome, according to their original names. The three major syndromes overlap as the disease progresses, and imaging findings such as atrophy of the brainstem and cerebellum and abnormalities of the striatum are also seen, and the histopathology is also common.
Early MSA-C often presents only with cerebellar ataxia. Early MSA-P may also present only with parkinsonian symptoms and may respond to antiparkinsonian drugs.
References
- Massano, João, Fernando Costa, and Goreti Nadais. "Teaching neuroImage: MRI in multiple system atrophy:“hot cross bun” sign and hyperintense rim bordering the putamina." Neurology 71.15 (2008): e38-e38.
Hot cross bun sign
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BrainstemPons
If the transverse pontine fiber degeneration is mild in the early stage of the disease, T2WI shows a linear high signal in the anterior-posterior direction. As the disease progresses, the transverse pontine fiber degeneration becomes stronger, and the abnormal signal at the pons shows a cross-shaped T2WI high signal. This is called the hot cross bun sign.
Hot cross bun sign was initially thought to be specific to MSA, but as the research progressed, it was found that the hot cross bun sign was also found in Spinocerebellar ataxia 1 (SCA1), Spinocerebellar ataxia 2 (SCA2), and Spinocerebellar ataxia 3 (SCA3).
Putaminal degeneration
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Putamen
In MSA-P, Parkinsonism often exhibits a left-right asymmetry in the early stages, with T2WI and FLAIR revealing a dorsolateral linear high signal in the putamen on the side opposite to the symptomatic side. This asymmetry indicates atrophy, typically occurring in the putamen on the side opposite to the symptomatic side.
Middle cerebellar peduncle lesion
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Middle cerebellar peduncle
While the "hot cross bun" signs are also seen in Spinocerebellar ataxia 1 (SCA1), Spinocerebellar ataxia 2 (SCA2), and Spinocerebellar ataxia 3 (SCA3), bilateral hyperintensity in the middle cerebellar peduncle is often observed in MSA, but without signal changes in SCA 1, 2, or 3.
Signal changes are frequently asymmetric, occurring on the same side as the more symptomatic side.
Atrophy of brainstem and cerebellum
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Cerebellum
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Brainstem
Neuromelanin
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Substantia nigra
Neuromelanin imaging reveals a decrease or disappearance of hyperintensity in the substantia nigra on the side opposite to the symptomatic side. This is particularly notable in MSA-P, where there are no significant findings in the putamen. Neuromelanin imaging confirms these observations, indicating an association with Parkinsonism.