Demyelination

This contrast-enhanced T1-weighted MR image demonstrates the incomplete ring enhancement sign, which can be seen in demyelinating processes such as multiple sclerosis or acute demyelinating encephalomyelitis. When demyelinating lesions are present within the hemispheric white matter, they are typically ovoid with the long axis aligned with medullary veins (ie perpendicular to the lateral ventricles). Enhancement is highly variable, from none to ring to solid. Enhancement implies active demyelination. Diffusion restriction is also variable, with high, intermediate and low apparent diffusion coefficients often present in the same study. Lesions may show central T1 hypointensity, which may reflect oedema, necrosis or gliosis, depending on lesion age. Concentric rings may be present, often best seen on T2W images.
Reference: Osborn AG. Diagnostic Neuroradiology Mosby 1994
Credit: Dr Laughlin Dawes
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