Boundary of Amygdala and Hippocampus

To the Editor: For the last two decades, volumetric magnetic resonance imaging (MRI) studies have been widely used for clinical and research purposes in neuroscience. Recently, high-resolution MRI with thin-slice and advanced image-processing technologies have satisfied these needs. Because of its neurophysiologically important role, the hippocampus has been the main target of measurement in neuropsychological diseases such as Alzheimer’s disease, epilepsy, depression, and schizophrenia.

Many researchers have developed methods of quantifying real hippocampal volume. And there has been an advance in the methodology of MRI volumetry (1–4). Correct anatomical separation between the amygdala and hippocampus is difficult. So deciding on an anatomical boundary between the two structures is an important issue in amygdala-hippocampus volumetric MRI studies.

Michael D. De Bellis, M.D., M.P.H., et al. wrote a report (5) related to hippocampal volume measurement, but their study appeared to make a mistake in its setting of amygdala and hippocampus boundaries. In Figure 2, the trace line included both the posterior amygdala and anterior hippocampus. If the authors wanted to separate the hippocampus from the amygdala, the region of interest in Figure 2 would be obviously wrong. As a result, the normal hippocampal volume in Table 1 became relatively large compared to those in earlier reports.