P2-297: Heterogeneous atrophy of medial temporal lobe structures in patients with amnesic mild cognitive impairment

Abstract

Recent MRI volumetric studies of Medial Temporal Lobe (MTL) in patients with amnestic MCI (aMCI) have shown that atrophy of the entorhinal cortex (ERC) could predict future conversion to Alzheimer's disease (AD). The aim of this study was to evaluate the volume of different MTL structures in aMCI patients and determine if volume loss of the subcomponents of the MTL is homogenous. We included 25 patients with aMCI (mean age = 68.5 ± 8.1, MMSE = 27.4 ± 1.4) and 27 healthy elderly normal control subjects matched for age. The MRI scans were acquired with a 1.5 T Siemens imager using an MP–RAGE sequence (TR/TE/TI: 9.7/4/250 ms, FOV 256mm*256mm, flip angle12°, matrix 230*256). Segmentation was performed according to previously developed protocols. Quantitative volumes were obtained with a manual ROI method on coronal images. We measured volumes of the ERC, the perirhinal cortex (PRC), the parahippocampal cortex, and the hippocampal formation (HP). Two independent operators (C.Y., A.S.), blinded to clinical data, obtained the ROI volumetric measurements independently. The inter–rater variability was 0.4% for the HP, 1.8% for the PRC, and 2.25% for the ERC. Statistical analyses were performed using ANCOVA. Comparing aMCI subjects to normal controls, we found a volume loss of the ERC (p<0.05), which was more important on the left side (p< 0.01). The posterior HP was also significantly atrophied in the aMCI group (p<0.05), while there was no difference for the anterior HP. Within the aMCI group, we identified two subgroups. One group had no ERC or PRC atrophy. The second group had significant ERC and PRC atrophy, which was in some cases associated with atrophy of the HP. This study confirms atrophy of the ERC in a group of patients with aMCI. Moreover, concerning the HP, the posterior part is more atrophied in patients with aMCI. Our results furthermore suggest a heterogeneity concerning rhinal cortices, with preservation in one patient subgroup and atrophy in another.