Age-related brain atrophy: a study with computed tomography.

Brain atrophy in 176 men and 205 women without neurologic disturbances was studied using x-ray computed tomography. The ages ranged from 21 to 79 years. We measured cerebrospinal fluid (CSF) space volume above the level of the tentorium cerebelli and calculated brain atrophy index (BAI): BAI (%) = (CSF space volume/cranial cavity volume). Both the CSF space volume and BAI decreased from the 20s to the 30s only in men (p less than .001), and both were minimal in the 30s in men and in the 20s in women. Although both the CSF space volume and BAI started to increase in the 40s in both sexes (p less than .001, .002), considerable atrophy of the brain started to occur in the 40s in men and in the 50s in women. Both the CSF space volume and BAI increased exponentially with age after the 30s in both sexes (p less than .001).