The Inferior Cerebellar Peduncle Sign: A Novel Imaging Marker for Differentiating Multiple System Atrophy Cerebellar Type from Spinocerebellar Ataxia.

background and purposeThe hot cross bun (HCB) sign is a hallmark feature of multiple system atrophy with predominant cerebellar ataxia (MSA-C), typically observed in advanced stages of the disease; however, it can also present in other conditions such as spinocerebellar ataxia (SCA), making the differentiation challenging. The middle cerebellar peduncle (MCP) sign may be observed in various medical conditions and in healthy individuals. We hypothesized that the inferior cerebellar peduncle (ICP), known to be affected in MSA-C, may exhibit hyperintensity on FLAIR imaging, potentially aiding in differentiating MSA-C from SCA. MATERIALS AND

methodsMedical records of 153 patients with probable MSA-C and 72 genetically confirmed SCAs from a single institution were reviewed retrospectively between January 2012 and June 2023. MRI was performed using 3T scanners. The ICP sign was deemed positive when the bilateral ICP signal intensity exceeded that of the medulla oblongata on axial FLAIR images. MCP and HCB signs were also evaluated. Two independent neuroradiologists evaluated all MRIs, and interobserver agreement was assessed using κ statistics. Univariable and multivariable logistic regression analyses identified predictive features, and diagnostic performance was assessed.

resultsThe ICP sign was more prevalent in patients with MSA-C (65%) compared with those with SCA (6.9%;

conclusionsThe ICP sign on FLAIR imaging has high specificity in distinguishing MSA-C from SCA. Integrating clinical and imaging features further enhances diagnostic accuracy, potentially improving the differential diagnosis in clinical settings of cerebellar ataxia.