Paediatric Imaging

White matter disease

(WMD). There are many disorders which can involve the cerebral white matter, either exclusively or in combination with grey matter changes. These include inborn errors of metabolism, exogenous toxins, autoimmune disease, demyelination, radiation and chemotherapy effects. When identifying a white matter disorder it is essential that the findings are placed in context with clinical features and the results of other tests, such as biochemical, genetic or haematological. Spasticity, hyperreflexia and ataxia are clinical features suggestive of WMD. Many of the conditions resulting in white matter disease appear similar in the late stages and thus if differentiation is to be made, scans must be performed early. MRI is the best imaging modality for demonstrating WMD (Fig.1), with diffusion imaging and spectroscopy occasionally being helpful.

Diseases mainly affecting white matter produce low attenuation on CT and increased signal on T2-weighted MR images. Ventricular dilatation is a common feature. The distribution and symmetry of signal changes is helpful for identifying the underlying disease process. In a child with macrocephaly bilateral, symmetrical, frontal white matter involvement of the subcortical region suggests Alexanders disease. Diffuse, subcortical involvement suggests Canavans disease. Thalamic involvement with deep white matter changes should suggest Krabbes disease. Lack of myelination rather than destruction is seen in Pelizaeus Merzbacher disease.

Nonspecific white matter patterns are seen in the end stage of any WMD, demyelinating, collagen, vascular disorders and metabolic conditions. Occasionally, congenital infections can produce white matter changes. See leukodystrophy

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Fig.1

Extensive nonspecific white matter high signal on transverse T2-weighted MR image in a child with Down's syndrome.
White matter disease, Fig.1