Imaging description

Inherited leukodystrophies (IL) comprise a broad group of progressive disorders caused by cellular enzyme deficiency, resulting in abnormal formation, metabolism, or destruction of myelin. The clinical and imaging features of IL are diverse, with overlapping features, often causing delay in diagnosis.

White matter signal abnormalities are the most common imaging findings in IL, which often help to confirm the clinical suspicion of IL but often lack specificity to establish the diagnosis [1,2]. One significant exception is adrenoleukodystrophy (ALD), in which MRI findings follow a distinctive pattern. The classic form, X-linked ALD, which accounts for 50–60% of the cases, can be a result of any of the 300 different mutations of the ABCD1 gene, mapped to chromosome Xq28. It presents between the ages of 2 and 12 years. The most common pattern of involvement in the initial stages is involvement of splenium of corpus callosum (Fig. 43.1). It then spreads to peritrigonal white matter, fornix, visual and auditory pathways, and corticospinal tracts. It typically spares the subcortical U-fibers (Fig. 43.2). The demyelination then spreads anteriorly and laterally, involving a large amount of cerebral white matter, especially in the most severe childhood phenotypes. When demyelination is active, the leading edge of demyelination enhances intensely. On MR spectroscopy, there is decreased NAA resonance, even in normal-appearing white matter, with increased choline and myoinositol resonances and lactate peak [2]. There may be diffusion restriction in the active inflammatory phase with decreased fractional anisotropy on diffusion tensor imaging, even in asymptomatic white matter.