The role of volumetric MRI in understanding mild cognitive impairment and similar classifications

We review nineteen empirical studies of mild cognitive impairment (MCI), age-associated memory impairment (AAMI) and related classifications reporting volumetric data on the hippocampus, entorhinal cortex and amygdala. Studies varied considerably in terms of the selection of participants, sample characteristics, the definitions of regions of interest and normalization techniques. Effect sizes for differences in left hippocampal volume and right hippocampal volumes of AAMI, MCI and pre-clinical dementia groups compared with controls ranged from 0.47 to 1.34. Effect sizes for left and right hippocampal volumes for Alzheimer's disease (AD) versus control were 1.88 and 1.75 respectively. Longitudinal results confirm that initial hippocampal volume is predictive of conversion to AD. Greater standardization in methodology and the development of normative age-referenced databases of regional brain volumes is required.