Recent research with computerized tomography (CT) and magnetic resonance imaging (MR) of the brain has revealed a type of tissue change for which no fitting term exists. The change appears as areas of decreased density on CT and changed signals of the white matter in MR images. Because neither a definite pathological change nor a specific clinical deficit has been linked with the CT and MR changes, a designation is required that limits itself to describing the changes themselves. We propose "leuko-araiosis". The Greek root leuko-, signifying "white", has found wide usage in modern medical terminology: e.g. leucine, leukocyte, leukorrhoea. Also several precedents exist for its application to the white matter of the central nervous system: e.g. leukoencephalitis, leukomyelitis, leukotomy. Araios is an adjective meaning "rarefield", and the suffix -osis converts the adjective to a noun meaning "rarefaction, diminution of density", a word used in the Hippocratic Collection to describe a state of excessive porosity of the lung. A descriptive term precludes premature presuppositions and encourages the search for causes.