Hippocampal Subfield Volumetry and 3D Surface Mapping in Subjective Cognitive Decline

Subjective cognitive decline (SCD) may be the first clinical sign of Alzheimer's disease (AD). SCD individuals with normal cognition may already have significant hippocampal atrophy, a well-known feature of AD.

To test the hypothesis that SCD, compared to healthy individuals without SCD, have a pattern of hippocampal subfield atrophy similar to that measured in the AD pathology.

17 SCD, 21 AD, and 40 matched controls underwent a standard T1-weighted MRI and a dedicated high-resolution MRI proton-density hippocampal sequence. For each participant, three hippocampal regions-of-interest were manually delineated on the proton-density hippocampal sequence corresponding to the CA1, subiculum, and other (including CA2-3-4 and dentate gyrus) subfields. Total intracranial volume (TIV)-normalized subfield volumes were compared between-group. Voxelwise group comparisons assessed from the standard T1 MRI were also projected on 3D hippocampal surface views.

Both patient groups showed significant TIV-normalized volume decrease in hippocampus global volume and in CA1 and subiculum subfields as well as in the other subfield in AD compared to controls. Significant differences were observed between SCD and AD in hippocampus global TIV-normalized volume. Atrophy maps on hippocampal surface showed major involvement of the lateral part (CA1) in both SCD and AD, with larger overlap of other regions in AD.

The findings indicate topographically similar hippocampal subfield changes in SCD individuals as those found in AD. This further highlights the relevance of SCD recruited from a memory clinic in assessing pre-dementia AD stages.