Abstract
Using computed tomography, the authors studied brain atrophy during aging in 536 men and 529 women with no neurologic disturbances, ranging in age from 10 to 88 years. They measured cerebrospinal fluid (CSF) space volume and cranial cavity volume above the level of the tentorium cerebelli and calculated a brain atrophy index (BAI):BAI(%)=100%×(CSF space volume/cranial cavity volume). CSF space volume started to increase significantly in the group aged from 45 to 54 years, while the BAT started to increase significantly in the group aged from 35 to 44 years in both men and women. The BAT increased exponentially with the increasing age after 25 years, continuing to increase until 75 years or more in both men and women: logBAT=-0.260+0.0150×age, r=0.707, n=493, p<0.001 in men; logBAI=-0.434+0.0162×age, r=0.757, n=504, p<0.001 in women. Using the xenon-133 inhalation method, the authors studied age-related decline in regional cerebral blood flow (regional initial slope index; rISI) in 197 men and 238 women with no neurologic disturbances, ranging in age from 19 to 88 years. The rISI values in women declined almost linearly with the advancing age from the 50s to the 80s except the 70s. The rISI values in men declined with the advancing age from the 40s to the 60s, but remained unchanged thereafter until the 80s, suggesting the existence of a threshold of rISI values. We estimated the rISI values (probable threshold of brain atrophy), the frequency under which is equivalent to the volume of brain tissues atrophying in a decade, and obtained constant values as about 32 for men and about 37 for women in the 50s, 60s and 70s. If the frequency of rISI values in the brain is distributed according to a Gaussian function and mean of rISI values decreases linearly to the increasing age, then brain tissues having rISI values below the thresholds degenerate almost exponentially with the increasing age, leading to the exponential atrophy of the brain.
