The Hot Cross Bun Sign

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 pontocerebellar 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.