MRI Aspects: Conventional, SWI, and DTI

Abstract

This chapter will focus on structural magnetic resonance imaging (MRI) in degenerative cerebellar ataxias. First, we will briefly introduce MRI pulse sequences, which are routinely used for brain imaging in clinical practice and biomedical research. Next, we will describe characteristic MRI findings in the most common forms of degenerative ataxias. Many of the degenerative cerebellar ataxias are disorders of the gray matter, and much of the pathology is seen on T1-weighted MRI images. Three main patterns of cerebellar degeneration are distinguished: (i) “pure” cerebellar degeneration (e.g., in spinocerebellar ataxia type 6 (SCA6)), (ii) olivopontocerebellar atrophy (e.g., in the cerebellar type of multiple system atrophy (MSA-C)), and (iii) predominant atrophy of the spinal cord (e.g., in Friedreich’s ataxia). There is a subset of cerebellar ataxias, which are accompanied by white matter abnormalities. White matter abnormalities are seen as hyperintensities in T2-weighted, proton density-weighted (PD), and fluid-attenuated inversion recovery (FLAIR) images. Some patterns of white matter disease are suggestive of certain types of ataxias, e.g., hyperintensities in the pons (“hot cross bun” sign) and the middle cerebellar peduncles in MSA-C. Susceptibility-weighted imaging (SWI) and quantitative susceptibility mapping (QSM) are not only helpful to show abnormal brain iron deposition (e.g., in superficial siderosis), but also accompanying atrophy of the iron-rich cerebellar nuclei (e.g., in SCA6). Diffusion tensor imaging (DTI) is helpful to show changes in the integrity of cerebellar white matter and cerebellar peduncles.