MRI-Based Methods for the Identification of Cerebellar Ataxia Types

Patients with ataxia are characterized by the inability to coordinate movements leading to gait-limb ataxia, frequent falls, dysarthria and oculomotor abnormalities such as nystagmus or saccadic dysmetria. Age of symptom-onset can vary widely from childhood to late-adulthood. Many conditions can cause ataxia, including alcohol abuse, certain medications, stroke, tumors, trauma, cerebral palsy, brain degeneration and multiple sclerosis. Symptoms are usually caused by cerebellar dysfunction, or impaired vestibular or proprioceptive afferent input to the cerebellum. Based on the anatomy of the cerebellum, lesions in any of its regions (midline cerebellum and cerebellar hemispheres) could result in a different type of ataxia. For instance, damage to the midline cerebellar structures induces gait and truncal ataxia, while damage to the unilateral cerebellar hemisphere causes ipsilateral limb cerebellar ataxia.

MR imaging is an excellent tool for assessing cerebral anatomical disturbances. It can define structural disturbances, distinguish acute from subacute, chronic, or inherited diseases, and monitor disease progression. The strength of neuroimaging in diagnostic investigations is currently partly based on a pattern-recognition approaches, similar to those used in brain tumors. Based on neuroimaging data, two distinctive patterns could be identified: either degenerative or malformative. The degenerative pattern is mainly marked by cerebellar atrophy, oftenly associated with WM or GM T2/FLAIR signal changes, whereas the malformative pattern is characterized by abnormal morphology of the brain stem and/or cerebellum. For instance, in Friedrich ataxia (FRDA), the cerebellum volume is preserved with a mild upper vermis atrophy associated with smaller dentate nuclei as well as increased iron accumulation. In ataxia-telangiectasia (AT), the vermian is predominantly atrophied and oftenly isolated in young children, while some patients demonstrated an involvement of the lateral hemispheres. In spastic ataxia of Charlevoix-Saguenay (ARSACS), a cerebellar atrophy with a predominance in the superior vermis and thickening of the middle cerebellar peduncle is observed. In ataxia with oculomotor apraxia type 1 (AOA1) and 2 (AOA2), the iron-induced signal normally observed in dentate nuclei disappears, and diffuse cerebellar atrophy that predominates the anterior vermis is observed. In ataxia with isolated vitamin E deficiency (AVED), cerebellar atrophy or MRI anomalies are absent. In the spinocerebellar ataxia type 3 (SCA3), a mild atrophy of the vermis and the cerebellum was reported along with a volume reduction of the dentate nuclei and an atrophy of the middle cerebellar peduncle. In SCA6, a marked atrophy of the vermis and cerebellar hemispheres was observed but no atrophy of middle cerebellar peduncle was reported.

This Research Topic will first review the clinical aspect of the various reported types of cerebellar ataxias based on their classification and etiologies. We are soliciting articles that cover a broad range of methodologies (e.g. pattern-based vs region-based analysis, atrophy and volume measurement using voxel-based morphology and regional volumetry assessment, structural analysis using diffusion tensor imaging, metabolic assessment using MR spectroscopy, etc.) that could identify and differentiate the types of ataxias. The various findings will be covered by either new evidence, case studies or review papers.