MR anatomy, anatomical variants and morphometry of hippocampal formation

Abstract

Nowadays the question of limbic structures involvement in different types of brain pathology is much debated in literature. However, obtained results are often contradictory. This can be explained by the insufficient knowledge of normal volume and linear measurements of brain structures responsible for human emotional and cognitive functioning including different age periods. Different anatomical variants of these structures were described in literature indistinctly, often leading to misinterpretation of neuroimaging findings. Besides, hippocampal formation, being complex structure, consists of different parts, including subregions (head, body and tail) and subfields (СА1-СА4, subiculum, presubiculum, dentate gyrus), which changes depend on different psychological and psychiatric symptoms. In our study we have analyzed MRI data of mediobasal parts of temporal lobes in healthy volunteers based on literature review and our own experience. The incidence rate of different hippocampal anatomical variants in healthy population was specified in the study. We have also determined MR voxel-based morphometry as a method permitting to define and evaluate volumes of different hippocampal subfields. In our research we found out certain significant differences in hippocampus fissure volumes, parasubiculum, molecular layer of dentate gyrus, fimbria, СА3 and СА4 Brodmann areas, demonstrating that in adulthood morphofunctional connections are not finally formed, that’s why volumes of molecular layers CA1-CA3 smaller in adulthood than in elder population. But hippocampal fissure become smaller in elder ages because of atrophic changes.

Keywords:

anatomical variants, temporal lobe epilepsy, hippocampus, MRI, segmentation