in an atrophied pons. Cerebellum and middle cerebellar peduncles are also atrophied.
Multiple system atrophy is a rare neurological disorder characterized by a combination of parkinsonism, cerebellar and pyramidal signs, and autonomic dysfunction. The term "Multiple System Atrophy" is synonymous with striatonigral degeneration (SND) when Parkinsonism predominates, olivopontocerebellar atrophy (OPCA) when cerebellar signs predominate, and Shy-Drager syndrome when autonomic failure is dominant. The incidence (new case per 100,000 person years) for ages 50 to 99 years is 3.0 (Bower et al, 1997), or about half as frequent as it's close relative, progressive supranuclear palsy (PSP). The mean age of onset is 54.
Pathophysiology: There is neuronal loss and gliosis in the inferior olives, pons, cerebellum, substantia nigra, locus ceruleus, striatum and the intermediolateral column of the spinal cord.Similar pattern of neuronal loss is seen in a patient with parkinsonism, the neuronal loss being secondary to presumed vasculitis, and proposed that the sign may reflect wallerian degeneration of transverse pontocerebellar fibers secondary to vasculitic infarction.\
MRI - On T2-weighted MR images, a hyperintense rim at the putaminal edge, putaminal atrophy, and intrinsic signal intensity change are seen. In MSA-c, the changes predominantly affect the infratentorial structures. On T2-weighted MR images, atrophy and increased signal intensity within the pons, cerebellum, and middle cerebellar peduncles are seen.
References1. Schrag A, Kingsley D, Phatouros C, et al. Clinical usefulness of magnetic resonance imaging in multiple system atrophy. J Neurol Neurosurg Psychiatry 1998;65:65–71.
2. Muqit MM, Mort D, Miskiel KA, Shakir RA. “Hot cross bun” sign in a patient with parkinsonism secondary to presumed vasculitis. J Neurol Neurosurg Psychiatry 2001;71:565–566.