CASE 10761 Published on 03.03.2013
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MRI findings in spinocerebellar ataxia type 7

Section

Neuroradiology

Case Type

Clinical Cases

Authors

José Boto1, Victor Cuvinciuc2
1Department of Radiology
2Department of Neuroradiology
Geneva University Hospital, Geneva, Switzerland

Geneva University Hospital, Rue Gabrielle-Perret-Gentil 4, 1205 Genève, Switzerland
Connected authors
Patient

16 years, female

Categories
Area of Interest Neuroradiology brain ; Imaging Technique MR
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Clinical History
A 16-year-old girl known for unsteadiness, recurrent falls, cognitive decline and visual problems was referred for a brain MRI. Her mother has a history of balance problems associated with retinopathy since the age of 30 and her maternal grandmother also developed balance difficulties later in life.
Imaging Findings
A noncontrast brain MRI showed marked atrophy of the pons, inferior cerebellar vermis, and middle cerebellar peduncles, moderate atrophy of the midbrain and medulla oblongata, and superior cerebellar peduncles. A small hyperintensity is seen in the pons on T2WI and FLAIR imaging due to degeneration of transverse pontine fibres. Significant ex vacuo dilatation of the fourth ventricle and the cisterna magna is evident. The cerebrum and the cerebellar hemispheres show no signs of atrophy.
Discussion
Spinocerebellar ataxia type 7 (SCA7) is also known as olivopontocerebellar atrophy type III [1] or autosomal dominant cerebellar ataxia type II [2]. The gene for SCA7, (ataxin-7 gene) was mapped to chromosome 3p12→p21.1 [3, 4, 5]. A cytosine-adenine-guanine (CAG) repeat extension in this gene is responsible for the disease [6, 7] and larger repeat extensions are associated with earlier age of onset [7, 8, 9, 10]. Increasing severity of the symptoms in consecutive generations (anticipation) is a feature of SCA7 [11]. Pathology studies show neuronal loss and gliosis in the cerebellum (vermis more affected than hemispheres), inferior olive, dentate nucleus, pontine nuclei, basal ganglia and spinal cord [12, 13, 14, 15, 16]. The hallmark of SCA7 is however degeneration of the optic pathways and retina [14].

Age of onset varies widely among the different types of SCA. Initial symptoms of SCA7 usually appear in third or fourth decades [5, 8, 10, 14, 17, 18, 19]. The presenting symptoms typically relate to cerebellar involvement when the age of onset if over thirty and ataxia, dysarthria and dysphagia become more prominent as the condition progresses. However, unlike other types of SCA, visual problems caused by retinopathy may be the earliest signs of the disease, especially when the onset is before the age of 40 [12, 20], eventually leading to blindness. The role of imaging in SCA7 is to provide additional supporting evidence for the diagnosis and to objectively assess progression of the disease.

Although the diagnosis of SCA is based on clinical findings and family history with an autosomal dominant pattern of inheritance, imaging plays an important role in objectively evaluating disease progression. MRI is the modality of choice for the assessment of SCA and typically shows atrophy of the cerebellum (especially in the superior part of the vermis) and the brainstem [21]. Pontine atrophy is however the most consistent finding in SCA7 and typically precedes cerebellar atrophy [22]. Final definitive diagnosis is achieved by genetic testing [21], as was the case in this patient.

Treatment of SCA7 is symptomatic as no specific drug therapy exists [21]. The prognosis is bleak for patients, especially those affected at an early age in which the disease tends to progress more rapidly. Visual symptoms may only appear after several decades of the onset of cerebellar ataxia. In the reverse situation however the latency period never exceeds nine years [10, 18].

This case illustrates typical MRI findings in SCA7, and although the diagnosis of this condition is not radiological, MRI substantiates the clinical diagnosis and may be helpful in assessing disease progression [22].
Differential Diagnosis List
Spinocerebellar ataxia type 7
Ataxia-telangiectasia
Ethanol toxicity
Phenytoin toxicity (usually affects cerebellar hemispheres)
Idiopathic degeneration secondary to carcinoma (usually oat cell of the lung)
Focal cerebellar atrophy due to infarction or trauma
Final Diagnosis
Spinocerebellar ataxia type 7
Case information
URL: https://www.eurorad.org/case/10761
DOI: 10.1594/EURORAD/CASE.10761
ISSN: 1563-4086
Figure 1

Sagittal 3D T1W noncontrast MR image

Sagittal 3D T1W noncontrast MR image
Marked atrophy of the pons and inferior cerebellar vermis, and moderate atrophy of the midbrain and medulla oblongata are demonstrated. There are no signs of atrophy of the cerebrum.
Figure 2

Coronal 3D T1WI non-contrast MR image

Coronal 3D T1WI non-contrast MR image
Slice through the posterior fossa shows atrophy of the inferior cerebellar vermis. The cerebrum and cerebellar hemispheres show no signs of atrophy.
Figure 3

Axial 3D T1WI non-contrast MR image

Axial 3D T1WI non-contrast MR image
Significant atrophy of the pons and middle cerebellar peduncles is further demonstrated.
Figure 4

Coronal 3D T1WI non-contrast MR image

Coronal 3D T1WI non-contrast MR image
Symmetrical atrophy of the superior cerebellar peduncles is shown.
Figure 5

Axial FLAIR non-contrast MR image

Axial FLAIR non-contrast MR image
Slice through the posterior fossa shows a small hyperintensity in the pons due to degeneration of transverse pontine fibres.