CT changes associated with normal aging of the human brain.

CT was used to measure changes in cerebral gray and white matter tissue densities associated with normal aging, using a cross-sectional design, in order to provide normative data for comparisons with abnormal aging such as dementias of Alzheimer's and vascular types. Cerebral compartmental densities were measured using plain CT, and their perfusion values were recorded during stable xenon inhalation (CT-CBF), among 81 neurologically and cognitively normal volunteers of different ages. Results led to the conclusion that cortical gray matter tissue densities progressively decline (polio-araiosis) after age 60. Cortical polio-araiosis is coupled with regional hypoperfusion but not with cortical atrophy. It is speculated that the cortical hypodensity identified by CT imaging parallels declines in cortical synaptic density, as reported from autopsy studies using anti-synaptophysin staining of cerebral cortex obtained from normal people above and below age 60. The coupling of cortical hypoperfusion with polio-araiosis is believed to reflect age-related reductions of cortical metabolic demands as reported by PET. During normal aging leuko-araiosis correlates directly with cortical atrophy, suggesting that anterograde axonal degeneration resulting from cortical neuronal dearborization play a role in its causation.