Current and future applications of brain magnetic resonance imaging in ARSACS

Abstract

Magnetic Resonance Imaging (MRI) is a tool with an unquestionable role in the study of neurodegenerative disorders, both for diagnostic purposes and for its ability of providing imaging-derived biomarkers with a growing central role as reliable outcomes in clinical trials. This is even more relevant when dealing with rare disorders such as the Autosomal Recessive Spastic Ataxia of Charlevoix-Saguenay (ARSACS), in which the search of diagnostic and prognostic biomarker is crucial. Due to the rarity of this condition, a comprehensive knowledge of MRI signs observed in ARSACS is lacking. Furthermore, many domains remain still unexplored in ARSACS, especially with reference to the application of advanced imaging techniques that could shed light on the pathophysiological mechanisms of brain damage in this disorder. In this review, after a brief introduction on the major conventional and advanced MRI techniques that can used for diagnostic and research purposes, we present current neuroradiological knowledge in ARSACS. Having discussed strength and weak points of conventional and advanced imaging findings, we also suggest possible future research in this neurologically complex clinical condition.

Keywords: ARSACS; Ataxia; Brain; Magnetic resonance imaging.

Fig. 1

Patterns of atrophy detectable via conventional MRI in ARSACS. A sagittal midline T1-weighted image (A) showing in an ARSACS patient the typical occurrence of superior vermis atrophy (black arrow) along with a “bulky” appearance of the pons (white star). Other imaging findings include a thinning of the mid-posterior segment of corpus callosum (white arrowhead), a mild atrophy of the upper cervical cord (white arrow) and the evidence of a posterior fossa arachnoid cyst (white asterisk), with the latter finding also visible in the axial multiplanar reconstruction in (B), where is also possible to appreciate the thickening of middle cerebellar peduncles (white arrowheads). Finally, a coronal multiplanar reconstruction (C) confirming the occurrence of a significant superior vermis atrophy (black arrows), coupled to a mild degree of cerebellar hemispheres (black arrowheads) and, more pronounced, biparietal (white arrows) atrophy

Fig. 2

Patterns of signal changes detectable via conventional MRI in ARSACS. Axial multiplanar reconstruction (A) of a 3D Fluid Attenuated Inversion Recovery (FLAIR) sequence showing in an ARSACS patient the occurrence of the “pontine stripes” (black arrows). Axial (B) image of 2D FLAIR (left panel) showing a mild hyperintensity in the lateral portion of the pons merging in middle cerebellar peduncles, confirmed evaluating the turbo spin echo T2-weighted sequence (right panel). On both images, is possible to observe the thickening of middle cerebellar peduncles (white arrows). An axial T2-weighted image (C) shows the presence of a bilateral hyperintensity of lateral thalami, described as “thalamic rim sign” (white arrowheads)

Fig. 3

An example of advanced imaging findings in ARSACS. Tractography reconstruction from a diffusion MRI sequence using a probabilistic approach of the corticospinal tract (A) and of the bundles at the level of the pontine region (B), with the latter image showing an over-representation of the latero-laterally oriented fibres that fill nearly the whole pons (red), along with thickened middle cerebellar peduncles (green) in an ARSACS patient