Hot cross bun sign (pons)

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 ¹.

It has been described in a variety of neurodegenerative and other conditions. Common associations include:

• multiple system atrophy, cerebellar type (MSA-C) (classic sign but not pathognomonic) ¹

• spinocerebellar ataxia (various types) ⁵

Other causes which are either very rare or in which presence of the sign is rarely reported include ¹⁷:

• autoimmune/paraneoplastic rhomboencephalitis (e.g. anti-KLHL11, anti-Ri, anti-amphiphysin, anti-Homer-3) ^{7,10,14,15,16}

• bilateral cerebellar ischemic stroke ⁶

• cerebral vasculitis (causing Wallerian degeneration of pontocerebellar tracts) ⁴

• cerebrotendinous xanthomatosis ¹²

• corticobasal degeneration ⁹

• JC virus granule cell neuronopathy ³

• neurosarcoidosis ¹³

• oculodentodigital dysplasia ¹¹

• paraneoplastic cerebellar degeneration ⁸

• variant Creutzfeldt-Jakob disease (vCJD) ²