Magnetic resonance imaging in spinocerebellar ataxias
ABSTRACT Magnetic resonance (MR) imaging is widely used to visualize atrophic processes that occur during the pathogenesis of spinocerebellar ataxias (SCAs). T1-weighted images are utilized to rate the atrophy of cerebellar vermis, cerebellar hemispheres, pons and midbrain. Signal changes in the basal ganglia and ponto-cerebellar fibers are evaluated by T2-weighted and proton density-weighted images. However, two-dimensional (2D) images do not allow a reliable quantification of the degree of atrophy. The latter is now possible through the application of three-dimensional (3D) true volumetric methods, which should be used for research purposes. Ideally, these methods should allow automated segmentation of contrast-defined boundaries by using region growing algorithms, which can be applied successfully in structures of the posterior fossa and basal ganglia. Thin slice thickness helps to minimize partial volume effects. Whereas volumetric approaches rely on predetermined anatomical boundaries, voxel-based morphometry has been developed to determine group differences between different types of SCA (cross-sectional studies) or within one SCA entity (longitudinal studies). We will review recent results and how these methods are currently used to (i) separate sporadic and dominantly inherited forms of cerebellar ataxias; (ii) identify specific SCA genotypes; (iii) correlate patho-anatomical changes with SCA disease symptoms or severity; and (iv) visualize and estimate the rate of progression in SCA.
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ABSTRACT: Spinocerebellar ataxia type 7 (SCA7) is a progressive neurodegenerative disorder characterized by cerebellar ataxia and visual loss. It is caused by a CAG repeat expansion in the gene encoding the ataxin 7 protein. Visual loss is due to a progressive atrophy of photoreceptor cells that results in macular degeneration in more advanced stages. Initial semiautomatic measures in magnetic resonance imaging (MRI) studies on the brain stem have shown a diminished volume mainly in the cerebellum and pons, while T2 images have shown hyperintensities in transverse fibers at the pons. Neuropathological research, however, has shown more widespread brain damage including loss of myelinated fibers. In this study we decided to take advantage of recent MRI methodological advances to further explore the gray and white matter changes that occur in SCA7 patients. We studied nine genetically confirmed SCA7 patients and their matched controls using voxel based morphometry and tract-based spatial statistics. As expected, we found significant bilateral gray matter volume reductions (p<0.05, corrected for multiple comparisons) in patients' cerebellar cortex. However, we also found significant bilateral gray matter reductions in pre and postcentral gyrus, inferior and medial frontal, parietal inferior, parahippocampal and occipital cortices. The analysis also showed a decrement in fractional anisotropy (p<0.05, corrected) of SCA7 patients in the cerebellum's white matter, brainstem, cerebellar and cerebral peduncles, midbrain, anterior and posterior internal capsule, external/extreme capsule, corpus callosum, corona radiata, optical radiations, and the occipital, temporal and frontal lobe's white matter. These results confirm previous evidence of widespread damage beyond the cerebellum and the pons in SCA7 patients. They also confirmed previous results that had been only detectable through neuropathological analyses and, more importantly, identified new regions affected by the disease that previous methods could not detect. These new results could help explain the symptom's spectrum that affects these patients.NeuroImage 03/2011; 55(1):1-7. DOI:10.1016/j.neuroimage.2010.12.014
Article: Cerebellar ataxias.[Show abstract] [Hide abstract]
ABSTRACT: The term 'cerebellar ataxias' encompasses the various cerebellar disorders encountered during daily practice. Patients exhibit a cerebellar syndrome and can also present with pigmentary retinopathy, extrapyramidal movement disorders, pyramidal signs, cortical symptoms (seizures, cognitive impairment/behavioural symptoms), and peripheral neuropathy. The clinical diagnosis of subtypes of ataxias is complicated by the salient overlap of the phenotypes between genetic subtypes. The identification of the causative mutations of many hereditary ataxias and the development of relevant animal models bring hope for effective therapies in neurodegenerative ataxias. We describe the current classification of cerebellar ataxias and underline the recent discoveries in molecular pathogenesis. Cerebellar disorders can be divided into sporadic forms and inherited diseases. Inherited ataxias include autosomal recessive cerebellar ataxias, autosomal dominant cerebellar ataxias/spinocerebellar ataxia) and episodic ataxias, and X-linked ataxias. From a motor control point of view, the leading theories of ataxia are based on neural representations or 'internal models' to emulate fundamental natural processes such as body motion. Recent molecular advances have direct implications for research and daily practice. We provide a framework for the diagnosis of ataxias. For the first time, the therapeutic agents under investigation are targeted to deleterious pathways.Current opinion in neurology 06/2009; 22(4):419-29. DOI:10.1097/WCO.0b013e32832b9897
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ABSTRACT: Here we report the case of a 72-year-old woman who presented with severe progressive ataxia over 32 years clinically thought to be due to a hereditary neurodegenerative disease, spinocerebellar ataxia. Magnetic resonance imaging with diffusion tensor imaging revealed a presumed arteriovenous malformation in the left cerebellar hemisphere, based on evidence of prior bleeding, resulting in asymmetrical atrophy of the cerebellum and brainstem not consistent with a primary cerebellar neurodegenerative process. This is the first report of an arteriovenous malformation insidiously mimicking a progressive spinocerebellar ataxia.European Journal of Radiology Extra 07/2009; DOI:10.1016/j.ejrex.2009.02.001