Hyperintense lesions of the middle cerebellar peduncle and beyond: a pictorial essay.

The middle cerebellar peduncle (MCP) is the largest afferent system of the cerebellum and consists of fibres from the cortico-ponto-cerebellar tract. Specifically, several relevant diseases can present with hyperintensity in the MCP on T2-weighted/fluid-attenuated inversion recovery (T2/FLAIR) magnetic resonance imaging sequences, including multiple sclerosis; acute disseminated encephalomyelitis; neuromyelitis optica spectrum disorder; progressive multifocal leucoencephalopathy; hepatic encephalopathy; osmotic demyelination syndrome; multiple system atrophy; fragile X-associated tremor/ataxia syndrome; megalencephalic leucoencephalopathy with subcortical cysts; spinocerebellar ataxias; hemi-pontine infarct with trans-axonal degeneration; and diffuse midline glioma with the histone H3K27M mutation. The aim of this pictorial review is to discuss the imaging findings that are relevant for the differential diagnosis of diseases presenting with MCP hyperintensity on T2/FLAIR sequences. Such knowledge is of utmost importance for the practicing radiologist.