#Hippocampus anatomy gyri series#

Contrast administration is only necessary if findings on the non-enhanced series need further investigation. If acquisition time is limited, at least coronal IRT1W (1.5В T) or T2W (3В T) images perpendicular to the hippocampal plane should be acquired as extra to a standard screening protocol. A tilted coronal T2-weighted (T2W) series should be acquired as well with high resolution (0.5В mm or less in-plane) to evaluate the internal hippocampal structure. In patients with medically refractory epilepsy, MRI at 3В T, if available, is preferred, and for the hippocampus, a 1-mm isotropic 3D series with T1W and FLAIR contrast with a good signal-to-noise ratio must be acquired with reconstructions along and perpendicular to the plane of the hippocampi. Indications that require tailored sequences for optimal visualization of the hippocampus are medically refractory epilepsy and dementia. The design of the imaging protocol largely depends on the clinical question. The inferolateral extension of the transverse fissure is the hippocampal fissure, which extends between the dentate gyrus and the subiculum and is often obliterated and not visible on MRI. The superolateral extension of the transverse fissure is the choroidal fissure. The transverse fissure of Bichat is the lateral extension of the ambient cistern which separates the thalamus superiorly from the parahippocampal gyrus inferiorly. The subiculum is the medial and superior edge of the parahippocampal gyrus and its site of union with the cornu ammonis.The hippocampus is surrounded by several fissures which are collectively referred to as the perihippocampal fissures. The cornu ammonis continues inferomedially in the parahippocampal gyrus, a gray matter structure that forms the transition area between the basal and mesial areas of the temporal lobe. AвЂ‰=вЂ‰alveus, AcвЂ‰=вЂ‰Ambient cistern, BвЂ‰=вЂ‰basal vein of Rosenthal, CвЂ‰=вЂ‰tail of caudate nucleus, ChFвЂ‰=вЂ‰choroid fissure, CSвЂ‰=вЂ‰collateral suclus, DGвЂ‰=вЂ‰dentate gyrus, PвЂ‰=вЂ‰posterior cerebral artery, PHGвЂ‰=вЂ‰parahippocampal gyrus, SubвЂ‰=вЂ‰subiculum, TвЂ‰=вЂ‰temporal horn of the lateral ventricle, TbвЂ‰=вЂ‰transverse fissure of BichatД«ased on its cellular composition, the cornu ammonis is divided into four parts, the so-called SommerвЂ™s sectors CA1 to CA4. A small hippocampal cyst (Hs) reflects the location of the largely obliterated hippocampal sulcus. The hippocampal formation consists of the cornu ammonis or hippocampus proper, which can histologically be divided in the four Sommer sectors CA1вЂ“CA4, and the dentate gyrus (DG). At the level of the hippocampal tail, the fimbriae continue posteriorly as the crux of the fornix (11) that slants upwards towards the splenium of the corpus callosum (9) and the hippocampal tail continues as the subsplenial gyri (10).ДЄnatomy of the hippocampal formation at the level of the hippocampal body on 3-T coronal T2. The hippocampal head is separated from the amygdala (5) by the uncal recess of the lateral ventricle (7) and is characterized by small digitations separated by small sulci, the digitationes hippocampi (6). The hippocampal head is the only portion of the hippocampus not covered by the choroid plexus (7). The head (1) is located in front of the mesencephalon, the body (2) can be found at the level of the mesencephalon and the tail (3) is posterior to the mesencephalon. To easily recognize the different portions of the hippocampus, we can use the mesencephalon (4). 1вЂ‰=вЂ‰hippocampal head, 2вЂ‰=вЂ‰hippocampal body, 3вЂ‰=вЂ‰hippocampal tail, 4вЂ‰=вЂ‰mesencephalon, 5вЂ‰=вЂ‰amygdala, 6вЂ‰=вЂ‰hippocampal digitations, 7вЂ‰=вЂ‰temporal horn of the lateral ventricle, 8вЂ‰=вЂ‰uncal recess of the lateral ventricle, 9вЂ‰=вЂ‰splenium of the corpus callosum, 10вЂ‰=вЂ‰subsplenial gyri, 11вЂ‰=вЂ‰crura of the fornices. The hippocampal body is shown in detail in Fig. Zoomed-in 3-T coronal T2-weighted images at the level of the hippocampal head ( c) and the hippocampal tail ( d). Anatomy of the hippocampal formation on 3-T axial T2 ( a) and sagittal 3D-MPRAGE images ( b).

Hippocampus anatomy gyri