Question: A patient has this finding on MRI brain (large arrow pointing to abnormality). What is the name of this sign? What underlying condition is this sign pathognomonic for?
Answer: The above image shows the “hot cross bun sign.” The hot cross bun sign refers to the MRI appearance of the pons when T2 hyperintensity forms a cross on axial images, representing selective degeneration of transverse pontocerebellar tracts and median pontine raphe nuclei. It is most classically described in multiple system atrophy, cerebellar type (MSA-C).