Age-related brain atrophy with a constant cortical thickness in the normal elderly

A study was performed to determine whether the thickness of the cerebral cortex remains unchanged during agerelated brain atrophy in the normal elderly (physiological brain atrophy of the elderly). Thirty autopsied brains from normal subjects (normal brains; patient age 65–96 years) and two from patients with Alzheimer-type dementia (ATD brains; patient age 90 and 101 years) were analyzed. Volumes of the fresh brain and intracranial cavity were measured at autopsy to estimate the degree of brain atrophy using the ratio of fresh brain volume to intracranial cavity volume (BV/ICV ratio). Each brain was then fixed, and sliced coronally at 1.0 cm intervals. Each cut surface was photographed, and input to a personal computer. Then, the cross-sectional areas of the cortex and the white matter, and the perimeter of the cortex were measured to calculate the volumes of the cortex and the white matter. For normal brains, the cortical thickness was constant (0.27 ± 0.01 cm), regardless of age and the BV/ICV ratio. In addition, the volume ratio of the cortex to the white matter remained unchanged, regardless of the brain volume or BV/ICV ratio. These results show that the cortical thickness remains constant regardless of the degree of brain atrophy or cortical atrophy. In the two ATD brains, the cortical thickness was 0.23 and 0.21 cm, being less than that of any of the normal brains. Thus, the mean cortical thickness remains unchanged in physiological brain atrophy of the elderly, and a decrease in cortical thickness can be a pathological phenomenon.