HIPPOCAMPAL FORMATIONS IMAGING WITH AXIAL SECTIONS PARALLEL TO THEIR LONGITUDINAL AXIS

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 (H AP) parallel to the hippocampus long axis is able to provide a complet e and comprehensive view of the structure. HF has a rostrocaudal exten t 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 bead and the tail. At more ventr al levels, HF sections consist of parts of the CA1 field and the subic ular complex. These are completely embedded in the temporal lobe and s eparated from its medial surface by the white matter and the cortical plate of the parahippocampal gyrus. More dorsal sections allow the stu dy of the amygdala, uncus and fimbria. Functional images of HF can be accurately defined by combining magnetic resonance imaging (MRI), posi tron emission tomography (PET), or single photon emission computed tom ography (SPECT) in this plane. According to the small dorsal-ventral d imension of the structures, a few slices can cover the whole HF and pr ecise regions of interest may be outlined.