Hippocampal formations imaging with axial sections parallel to their longitudinal axis

Abstract

The complex shape of hippocampal formation (HF) and its obliquity make its morphological analysis difficult using brain imaging techniques. Adapted planes of section are required. The hippocampal axial plane (HAP) parallel to the hippocampus long axis is able to provide a complete and comprehensive view of the structure. HF has a rostrocaudal extent and is divided into three parts, head, body, and tail. Histological sections in the HAP display very well the pattern of the cell layers, with their transversal folding at the head and the tail. At more ventral levels, HF sections consist of parts of the CA1 field and the subicular complex. These are completely embedded in the temporal lobe and separated from its medial surface by the white matter and the cortical plate of the para-hippocampal gyrus. More dorsal sections allow the study of the amygdala, uncus and fimbria. Functional images of HF can be accurately defined by combining magnetic resonance imaging (MRI), positron emission tomography (PET), or single photon emission computed tomography (SPECT) in this plane. According to the small dorsalventral dimension of the structures, a few slices can cover the whole HF and precise regions of interst may be outlined.