Cortical atrophy in senile dementia of the Alzheimer type is mainly due to a decrease in cortical length.

A prospective study was undertaken to select mentally normal old subjects and patients with senile dementia of the Alzheimer type (SDAT). The test score of Blessed et al. (1968) (BTS) was used to determine the severity of mental impairment. A pathologic study confirmed the diagnosis of either SDAT or normal brain aging at postmortem examination in 12 cases. The cortical area and the cortical perimeter of the different cerebral lobes were measured on 1-cm-thick coronal sections using a semiautomatic image analyzer. Cortical length and thickness were calculated using perimeter and area values. BTS was significantly correlated with both the area (r = 0.7695, P = 0.003) and the length (r = 0.7421, P = 0.006) of the temporal cortex. There was no significant correlation between BTS and thickness of the temporal cortex (r = 0.559, P = 0.059). These results show that reduction of length is one of the major determinants of cortical atrophy. Although this has to be confirmed by histological study, they favor the hypothesis of a column-selective atrophy in SDAT which should be considered in the interpretation of the microscopic data.