Asymmetry of the hippocampus and amygdala in MRI volumetric measurements of normal adults.

Multiple studies have explored the relationship between MRI-based volumetric measurements of the hippocampus and amygdala, the degree of volumetric asymmetry of these structures, and symptom manifestation. However, considerable variability exists with regard to the reported volumetric values of these structures. The present study employed meta-analytic procedures to provide a systematic analysis of the normal population parameters of hippocampal and amygdala volumetric asymmetry as well as the absolute intrahemispheric volumes of these structures in normal adults. A literature review of studies published between 1990 and 2002 resulted in a representative sample of 82 studies (N = 3,564 participants) providing volumetric information of the hippocampus and 51 studies (N = 2,000 participants) providing volumetric information of the amygdala. Results revealed that both the hippocampus and the amygdala are reliably asymmetrical structures in normal adults, with larger right hippocampal (D = 0.21, p.001) and right amygdala (D = 0.09, p.01) volumes. Additional analyses indicated that differences in MRI magnet field strength and slice thickness values might differentially contribute to volumetric asymmetry estimates. These results expand on previous volumetric normative studies and may be relevant to investigators studying the clinical correlates of hippocampal and amygdala volumes.