plaque
n. a small patch of abnormal tissue on or within a bodily structure, formed as the result of an accumulation of substances or as the result of localized damage. Examples of the former type include the amyloid plaques of Alzheimer’s disease, arising from clumps of beta-amyloid protein, and the atheromatous plaques of atherosclerosis, consisting of lipid deposits on the lining of arterial walls. Examples of the latter type include the demyelination plaques on the protective nerve sheaths of individuals with multiple sclerosis.