What causes the hot-cross bun sign in the pons on MRI?
Let me know in the comments.
Click to reveal the answer
The hot-cross bun sign is caused by selective degeneration of pontine neurons and transverse pontocerebellar fibers. It is most commonly associated with multiple system atrophy with cerebellar features (MSA-C), a neurodegenerative alpha-synucleinopathy that presents clinically with adult-onset sporadic cerebellar ataxia. This sign can also be seen in other conditions causing pontocerebellar degeneration or injury, such as bilateral pontine infarction with Wallerian degeneration or paraneoplastic neurological syndromes.
Why is it called so?
It is named “hot cross bun” because the axial T2-weighted MRI image of the pons shows a cruciform (cross-shaped) hyperintensity resembling the traditional hot cross bun pastry, which has a cross pattern on top.
Pathophysiology
The sign develops due to degeneration and loss of myelinated transverse pontocerebellar fibers and median raphe pontine neurons in the base of the pons. This neuronal loss leads to gliosis and increased water content, producing the characteristic T2 hyperintense cruciform pattern on MRI.
Alternative names: None
Other associated named signs: Middle cerebellar peduncle hyperintensity often accompanies the hot cross bun sign in MSA-C.
Improve Content And Help Your Colleagues!
Found an error in the post? Please let us know using our contact page and we will update it with due credits!
If you wish to contribute radiological images for this case (or any other article on the website), you can submit them here and you will be duly credited: Submit radiology case