The hot cross bun sign.

Hot cross bun sign refers to the cruciform-shaped hyperintensity on T2W axial magnetic resonance images (MRI) in multisystem atrophy due to the selective loss of myelinated transverse pontocerebellar fibers and neurons in the pontine raphe and sparing of the pontine tegmentum and corticospinal tracts [Figure 1, Figure 2].[1] The name derives from a sweet spiced bun baked by the Christian church on the last Thursday before Easter and marked with a cross on the top, with the four quarters representing the four quarters of the year. Multisystem atrophy (MSA) is a sporadic progressive neurodegenerative disorder of adult onset, involving the basal ganglia and the olivopontocerebellar complex to varying degrees. It commonly presents with Parkinsonian symptoms and cerebellar ataxia and depending on which of these symptoms predominates, is classified as MSA-Parkinsonian predominant(MSA-P) and MSA-Cerebellar predominant (MSA-C) respectively. [2] MSA, and especially MSA-P, has to be differentiated from Parkinson’s disease (PD) with which its clinical features overlap but treatment may differ. Certain findings on MRI may be a useful aid to clinical diagnosis. Atrophy of the putamen and brainstem and abnormal signal in the middle cerebral peduncle are found in a significant number of patients with MSA, while they are almost never found in PD patients.[3] Other findings like hypointensity of putaminal body, slit-like hyperintensity of the lateral putaminal border and atrophy of the cerebellar vermis or hemispheres