Hot Cross Bun Sign & Hot cross bun appearance of skull

Hot cross bun sign refers to the cruciform-shaped hyperintensity on T2W axial magnetic resonance images (MRI) in multisystem atrophy (MSA), more commonly in MSA-C.

  • It is called so because of its resemblance to Hot Cross Bun.(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.  See the Images.

  • The exact cause is not known but it is mostly due to selective loss of myelinated transverse pontocerebellar fibers and neurons in the pontine raphe and sparing of the pontine tegmentum and corticospinal tracts.
  • 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. 
  • To diffrentiate between MSA, and especially MSA-P, from Parkinson's disease (PD), 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. 
  • Hot cross bun sign is a manifestation of pontine atrophy in MSA and is more commonly found in MSA-C.
Hot Cross Bun in MSA

Hot Cross Bun Appearance of Skull on the other hand is seen in cases where there is prominence of suture lines of skull and prominence of frontal and parietal eminences leading to 'bossing' of head ('hot-cross-bun appearance') in newborns. Its usually seen in
  • Congenital Syphilis
  • Rickets

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