The hot cross bun appearance is seen in patients with MSA-c. The sign is due to a selective loss of myelinated transverse pontocerebellar fibers and neurons in the pontine raphe with preservation of the pontine tegmentum and corticospinal tracts (1). Other investigators (2) have demonstrated a similar pattern of neuronal loss in a patient with parkinsonism, the neuronal loss being secondary to presumed vasculitis, and proposed that the sign may reflect wallerian degeneration of transverse pontocere- bellar fibers secondary to vasculitic infarction. Regardless of the mechanism, this pattern of selective neuronal depletion results in a cross-shaped hyperintensity in the pons on T2-weighted MR images. Radiology: Volume 245: Number 2—November 2007
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