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These small regions of high intensity are observed on T2 weighted MRI images (typically created using 3D FLAIR) within cerebral white matter (white matter lesions, white matter hyperintensities or WMH) [1] [2] or subcortical gray matter (gray matter hyperintensities or GMH). The volume and frequency is strongly associated with increasing age. [2]
The MRI of patients with VWM shows a well defined leukodystrophy. These MRIs display reversal of signal intensity of the white matter in the brain. Recovery sequences and holes in the white matter are also visible. [4] Over time, the MRI is excellent at showing rarefaction and cystic degeneration of the white matter as it is replaced by fluid.
MRI image: Leukoaraiosis in a 90-year-old patient with cerebral atrophy. Head CT showing periventricular white matter lesions. Leukoaraiosis is a particular abnormal change in appearance of white matter near the lateral ventricles. It is often seen in aged individuals, but sometimes in young adults.
The degeneration of white matter, which reflects the degeneration of myelin, can be seen in a basic MRI and used to diagnose leukodystrophies of all types. T-1 and T-2 weighted fluid-attenuated inversion recovery (FLAIR) images are the most often used approach. [25]
White matter is the tissue through which messages pass between different areas of grey matter within the central nervous system. The white matter is white because of the fatty substance (myelin) that surrounds the nerve fibers (axons). This myelin is found in almost all long nerve fibers, and acts as an electrical insulation.
White matter lesions, proposed to be a causal risk factor, are common in the elderly and are associated with age. [3] Depression and cerebrovascular risk factors are also common in later life. [3] These factors make it difficult to determine what is the causal factor and to tease apart normal functioning from abnormal in the elderly population.
Using high field MRI system, with several variants several areas show lesions, and can be spacially classified in infratentorial, callosal, juxtacortical, periventricular, and other white matter areas. [21] Other authors simplify this in three regions: intracortical, mixed gray-white matter, and juxtacortical. [22]
A fourth area called DAWM (diffusely abnormal white matter) has been proposed [116] and can help to differentiate PPMS and SPMS. [117] Abundant extracellular myelin in the meninges of patients with multiple sclerosis has been found [118] Brain tissues with MRI-hidden problems are usually named Normal Appearing.