Metachromatic leukodystrophy, juvenile form

The characteristic MR features of MLD include symmetric confluent areas of high signal intensity on the long TR images within the periventricular and cerebellar white matter, with sparing of the subcortical U fibers until late in the disease .

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In late-onset cases (juvenile and adult forms), there is predominant involvement of the frontal white matter. The signal abnormality progresses from the anterior to the posterior direction. In the late-infantile form of MLD, the most common type, a posterior (occipital) predominance of signal abnormality, has been reported with dorsofrontal progression of disease. Involvement of the corticospinal tracts, although typically ascribed to X-linked adreno-leukodystrophy, may also be seen in the late-infantile form of MLD. High signal intensity is seen on the long TR images along the path of the corticospinal tracts in the posterior limbs of the internal capsules and brainstem. As the disease progresses, the signal abnormality becomes more extensive and confluent with associated atrophy. The corpus callosum is invariably affected, and hypointensity within the thalami on T2-weighted images may be seen. Lesions in the deep gray matter are rarely seen, and if present appear as subtle signal abnormalities. The so-called tigroid pattern of demyelination (alternating areas of normal white matter within areas of demyelination), typically described in Pelizaeus-Merzbacher disease, may also be seen in the late-infantile form of MLD. Distinguishing features of MLD include absence of contrast enhancement, frequent involvement of cerebellar white matter, and lack of involvement of deep gray matter. Proton MR spectroscopy frequently demonstrates abnormality in the metabolic peaks before conventional MR images