Quantitative and qualitative measures of hippocampal atrophy are not correlated in healthy older men

In neuroimaging studies of dementia and mild cognitive impairment, hippocampal atrophy (HA) is commonly assessed by qualitative ratings of hippocampal appearance, or by measuring hippocampal volumes. These estimates of HA are considered to be equivalent. However, few studies have examined their relationship, especially in healthy older individuals. We therefore examined the relationship between hippocampal qualitative atrophy scores and quantitative volumetric measurements in healthy older men.

Ninety-seven healthy community-dwelling 65-70-year-old men underwent magnetic resonance imaging scanning. Hippocampal volumes were measured and adjusted for intracranial size. A validated 4-point visual rating scale was used to assess hippocampal atrophy.

There was a wide range of unadjusted hippocampal volumes among subjects (right: 2,582 to 5,196 mm(3)[mean 3,626 mm(3); SD 465.5 mm(3)] and left: 2,111 to 4,580 mm(3)[mean 3,501 mm(3); SD 439.5 mm(3)]), which was maintained following adjustment for intracranial size. However, only 9% of subjects were rated as having moderate or severe HA. Qualitative and quantitative measures were not significantly correlated (left hippocampus: rho = .07, P= .52; right hippocampus: rho = .10, P= .34).

This study shows that qualitative and quantitative indices of hippocampal atrophy in healthy older men are not equivalent. Small hippocampal volumes do not necessarily equate to hippocampal atrophy.