Multiple-System Atrophy

Multiple-system atrophy is a neurodegenerative disorder that involves the basal ganglia, olivopontocerebellar system, and the autonomic system to varying degrees. Differentiation from idiopathic Parkinson disease is often difficult, especially early in the disease. Different subtypes have been defined based on the dominant symptoms:

• MSA-p (striatonigral degeneration): Parkinsonism predominates, but with less evidence of rigidity and resistance to levodopa. The basal ganglia, particularly the putamen, are affected. MRI may show putaminal atrophy and hyperintensity (T2-hyperintense rim at the putaminal edge).
• MSA-c (olivopontocerebellar atrophy): Atrophy and increased signal intensity are seen within the pons, cerebellum, and middle cerebellar peduncles. On MRI, the olivary nuclei and medulla are small. There is atrophy of the pons and the cerebellar hemispheres with relative sparing of the vermis. The transverse pontine fibers, brachium pontis, middle cerebellar peduncles, and bulbar olives may be T2-hyperintense. The putamen, globus pallidus, and substantia nigra may be T2-hypointense. The hot cross bun sign may be seen on T2-weighted images as a T2-hyperintense cross in the pons due to loss of myelinated transverse pontocerebellar fibers and neurons in the pontine raphe.
• MSA-a (Shy-Drager syndrome): Autonomic failure is dominant, with orthostatic hypotension, urinary incontinence, inability to sweat, and extrapyramidal and cerebellar disturbances. As with MSA-p, there is T2-hyperintensity with the putamen.

References

• Gallucci M, Limbucci N, Catalucci A, Caulo M. Neurodegenerative diseases. Radiol Clin North Am. 2008 Jul;46(4):799-817, vii.
• Schrag A, Kingsley D, Phatouros C, Mathias CJ, Lees AJ, Daniel SE, Quinn NP. Clinical usefulness of magnetic resonance imaging in multiple system atrophy. J Neurol Neurosurg Psychiatry. 1998 Jul;65(1):65-71.
• Shrivastava A. The hot cross bun sign. Radiology. 2007 Nov;245(2):606-7