Neuroimaging in Leukodystrophies: Conventional Brain MRI

Owing to its high sensitivity, MRI is the primary neuroimaging modality used to detect and characterize white-matter abnormalities in patients with leukodystrophies.[8,9] Several important contributions of MRI have been recognized.[7] First, MRI shows gross morphology and involvement of different brain structures or tissue classes. Typically, leukodystrophies are associated with increased T1 and T2 relaxation times owing to decreased myelin content and increased water content, leading to decreased signal intensity on T1-weighted images and increased signal intensity on T2-weighted images. Second, MRI can be used to monitor the progression of the disease or the response to therapy. Finally, the pattern of abnormal MRI findings, which can be typical for a particular entity or type of a disorder, can aid in the diagnosis.[10] As an example, MRI findings in three patients with adrenoleukodystrophy showing the three characteristic symmetric patterns of white-matter involvement in this disorder are presented in Figure 1. Other examples of leukodystrophies with characteristic patterns of involvement include metachromatic leukodystrophy,[11] Alexander’s disease,[12] and Canavan’s disease.[13] Intriguingly, in recent years, pattern recognition based on common features on brain MRIs has led to the classification and discovery of previously unrecognized (idiopathic) leukodystrophies.[10] Some examples include “megalencephalic leukoencephalopathy with sub-cortical cysts,” which was first described by van der Knaap et al.[14] (Figure 2), or “leukoencephalopathy with vanishing white matter.”[15,16]

Figure 1.

Typical patterns of involvement (T2-weighted magnetic resonance imaging [MRI]) in patients with adrenoleukodystrophy. A, Parieto-occipital and splenium of corpus callosum (approximately 66% of cases with abnormal brain MRIs who presented to our institute); B, frontal lobe and genu of corpus callosum (15%); and C, selective frontopontine corticospinal tract involvement only (12%).[57] Note the symmetric involvement of both hemispheres in all three patterns. Provided by Dr Ali Fatemi, Kennedy Krieger Institute, Baltimore, MD.

Figure 2.

T2- and T1-weighted magnetic resonance images in megalencephalic leukoencephalopathy with subcortical cysts. Subcortical cysts are apparent in the frontal and temporal lobes on T1-weighted images.

Although significant advances in the understanding and diagnosis of leukodystrophies using MRI have been made in the last decade, many problems remain. A substantial number of leukodystrophies remain unclassified despite multiple investigations using clinical, genetic, biochemical, or imaging studies. In addition, the common observation of abnormal white-matter signal on MRI (T2 hyperintensity) can reflect multiple different underlying pathologic changes, including acute or chronic demyelination, inflammation, edema, or gliosis. Therefore, conventional MRI studies might lack specificity. Because of this issue, there has been interest over the last few years in alternative advanced magnetic resonance methodologies (in particular magnetic resonance spectroscopy) that might provide more specific or complementary information regarding brain structure and composition than conventional MRI.

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