Multiple system atrophy (MSA) is a adult onset, sporadic, progressive neurodegenerative disease of unknown etiology, characterized clinically by parkinsonism, ataxia, cerebellar signs, and autonomic failure in any combination. In central nervous system imaging, hallmarks of multiple system atrophy occur due to selective loss of myelinated transverse pontocerebellar fibers and neurons in the pontine raphe with relative sparing of the cortico-spinal tracts and the pontine tegmentum. This appears on MRI as hot cross bun sign and is seen in the pons. This sign has also seen described with other neurodegenerative diseases such as spinocerebellar atrophy and parkinsonism. In a compatible clinical setting, detection of these changes on MRI is useful to confirm a diagnosis of MSA. 

Contributed by Dr. Aruna Pallewatte, Dr. Madhavi Jayachandra