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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.
The external capsule is a series of white matter fiber tracts in the brain. These fibers run between the most lateral (toward the side of the head) segment of the lentiform nucleus (more specifically the putamen) and the claustrum. The white matter of the external capsule contains fibers known as corticocortical association fibers.
Others classify them as hippocampal, cortical, and WM lesions, [23] and finally, others give seven areas: intracortical, mixed white matter-gray matter, juxtacortical, deep gray matter, periventricular white matter, deep white matter, and infratentorial lesions. [24] The distribution of the lesions could be linked to the clinical evolution [25]
The degeneration of white matter can be seen in an MRI scan and is used to diagnose leukodystrophy. Leukodystrophy is characterized by specific symptoms, including decreased motor function, muscle rigidity , and eventual degeneration of sight and hearing.
Evidence from subcortical small infarcts suggests that motor fibers are somatotopically arranged in the human corona radiata. Following subtotal brain damage, localization of the corticofugal projection in the corona radiata and internal capsule can assist in evaluating a patient's residual motor capacity and predicting their potential for functional restitution.
In a coronal section through the middle of the lentiform nucleus, two medullary laminae are seen dividing it into three parts. The lateral and largest part is of a reddish color, and is known as the putamen, while the medial and intermediate are of a yellowish tint, and together constitute the globus pallidus; all three are marked by fine radiating white fibers, which are most distinct in the ...
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. [1] [2] On MRI, leukoaraiosis changes appear as white matter hyperintensities (WMHs) in T2 FLAIR images.
The gray matter remains normal in all characteristics while the white matter changes texture, becoming soft and gelatinous. Rarefaction of the white matter is seen through light microscopy and the small number of axons and U-fibers that were affected can also be seen. Numerous small cavities in the white matter are also apparent.