Last revised by Tariq Walizai on 8 Jul 2024
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Citation, DOI, disclosures and article data
Citation:
Gaillard F, Walizai T, Moore C, et al. Hippocampus. Reference article, Radiopaedia.org (Accessed on 20 Aug 2024) https://doi.org/10.53347/rID-1454
Permalink:
https://radiopaedia.org/articles/1454
rID:
1454
Article created:
Disclosures:
At the time the article was created Frank Gaillard had no recorded disclosures.
View Frank Gaillard's current disclosures
Last revised:
8 Jul 2024, Tariq Walizai
Disclosures:
At the time the article was last revised Tariq Walizai had no financial relationships to ineligible companies to disclose.
View Tariq Walizai's current disclosures
Revisions:
33 times, by 23 contributors - see full revision history and disclosures
Systems:
Central Nervous System
Sections:
Anatomy
Tags:
anatomy rewrite
Synonyms:
- Hippocampi
- Cornu Ammonis
The hippocampus (plural: hippocampi) or historically the cornu Ammonis, is an important component of the human brain, situated in the temporal lobe.It plays a role in information processing and the reproductive cycle and is involved in Alzheimer disease.
On this page:
Article:
- Gross anatomy
- Arterial supply
- Venous drainage
- Radiographic features
- Related pathology
- Related articles
- References
Images:
- Cases and figures
Gross anatomy
Location
The hippocampus lies in the hippocampal sulcus immediately below the floor of the temporal horn of the lateral ventricle, and in cross section (coronal) has appearances that are reminiscent of a seahorse. It has a head (posterior to the amygdala), a body, and a tail (which follows the upwardly curving lateral ventricle).
Although there is a lack of consensus relating to terms describing the hippocampus and the adjacent cortex, the term hippocampal formation generally applies to the dentate gyrus, fields CA1-CA3 (CA4 is frequently called the hilusand considered part of the dentate gyrus), and the subiculum(parahippocampal gyrus). The hippocampus proper is made up of CA1, CA2 and CA3 fields (Figure 1).
NB: CA is an abbreviation of cornu Ammonis
Pathways
The majority of its output is via the alveus into the fimbria which breaks free to the hippocampus to form the fornix.Information flows through the hippocampus proceeds from the dentate gyrus to CA3 to CA1 to the subiculum, with additional input information at each stage and outputs at each of the two final stages. CA2 represents only a very small portion of the hippocampus and its presence is often ignored in accounts of hippocampal function, though it is notable that this small region seems unusually resistant to conditions that usually cause large amounts of cellular damage, such as epilepsy.
The perforant path, which brings information primarily from entorhinal cortex (but also perirhinal cortex, among others), is generally considered the main source of input to the hippocampus. Layer II of entorhinal cortex (EC) brings input to the dentate gyrus and field CA3, while EC layer III brings input to field CA1 and the subiculum. The main output pathways of the hippocampus are the cingulum bundle and the fimbria/fornix, which arise from field CA1 and the subiculum.
Perforant path input from EC layer II enters the dentate gyrus and is relayed to region CA3 (and to mossy cells, located in the hilus of the dentate gyrus, which then sends information to distant portions of the dentate gyrus where the cycle is repeated). Region CA3 combines this input with signals from EC layer II and sends extensive connections within the region and also sends connections to region CA1 through a set of fibers called the Schaffer collaterals. Region CA1 receives input from the CA3 subfield (these afferents selectively target the basal dendrites in the stratum oriens, and the apical dendrites in the stratum radiatum - this is the Schaffer collateral pathway), EC layer III and the nucleus reuniens of the thalamus (which project only to the terminal apical dendritic tufts in the stratum lacunosum-moleculare). In turn, CA1 projects to the subiculum as well as sending information along the aforementioned output paths of the hippocampus. The subiculum is the final stage in the pathway, combining information from the CA1 projection and EC layer III to also send information along the output pathways of the hippocampus.
It is widely accepted that each of these regions has a unique functional role in the information processing of the hippocampus, but to date, the specific contribution of each region is poorly understood. The hippocampus also plays a vital role in the reproductive cycle.
Arterial supply
collateral branches of the posterior cerebral arteryand anterior choroidal artery6
forming the deep intrahippocampal arteries6
Venous drainage
intrahippocampal veins, draining in the superficial hippocampal veins, forming two arches, which ultimately drain into the basilar vein6,7
posterior end: draining in the medial atrial vein6,7
anterior end: inferior ventricular vein, draining in the medial atrial vein6,7
Radiographic features
MRI
The hippocampus is best imaged in the coronal plane, angled perpendicular to the long axis of the hippocampal body. The three parts of the hippocampus (head, body and tail) can be identified based on morphology and by using local landmarks 3.
amygdala-hippocampal head junction
landmarks
anterior lobe of the pituitary to basilar artery
the posterior amygdala is located above the anterior aspect of the hippocampal head 4
hippocampal head
morphology: hippocampal digitations a.k.a. pes hippocampus
landmarks
basilar arteryto interpeduncular cistern
posterior-most extent is the first slice where the uncal apex is clearly seen 4
hippocampal body
morphology: swiss roll appearance, of two interlocking U-shaped structures (cornu ammonis and dentate gyrus)
landmark: interpeduncular cistern to the superior colliculus
hippocampal tail
morphology: smaller and harder to discern the internal structure
landmarks
from superior colliculus
from the point at which the fornixcan be seen in full profile, or is separate from the wall of the ventricle 4
Related pathology
incomplete hippocampal inversion
mesial temporal sclerosis
hippocampal calcification
hippocampal sulcus remnant cysts
Related articles: Anatomy: Brain