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Cornu ammonis

The Cornu Ammonis, commonly referred to as the hippocampus, is a critical structure located in the medial temporal lobe of the brain. It plays a central role in memory formation, spatial navigation, and emotional regulation. The term “Cornu Ammonis” originates from the resemblance of this region to the ram’s horn, and it forms a major component of the hippocampal formation. The hippocampus is essential for the consolidation of information from short-term to long-term memory and is one of the first regions affected in Alzheimer’s disease.

Synonyms

  • Hippocampus

  • Ammon’s horn

  • CA region (with CA1, CA2, CA3, CA4 subfields)

  • Hippocampal proper

  • Cornu ammonis

Arterial Supply

  • Primarily supplied by branches of the posterior cerebral artery (PCA), particularly the hippocampal branches.

  • Additional supply from the anterior choroidal artery (a branch of the internal carotid artery).

  • The middle cerebral artery (MCA) may also contribute minor branches in some individuals.

Venous Drainage

  • Venous blood from the hippocampus drains via the hippocampal veins.

  • These veins empty into the basal vein of Rosenthal and the inferior ventricular vein.

  • Ultimately, blood flows into the great cerebral vein (vein of Galen).

Function

  • Memory consolidation: Converts short-term memories into long-term memories.

  • Spatial navigation: Helps in understanding and remembering spatial relationships and navigation.

  • Emotional processing: Plays a role in emotional responses and mood regulation.

  • Learning: Critical for associative and declarative learning.

MRI Appearance

  • T2-weighted: Hippocampus appears as a gray matter structure with intermediate to slightly hyperintense signal; high water content in acute pathology (e.g., edema, inflammation) can appear hyperintense.

  • T1-weighted: Normally appears as isointense to surrounding gray matter.

  • FLAIR: Signal is similar to T2; pathological changes (gliosis, edema, sclerosis) show hyperintensity.

CT Appearance

  • The hippocampus is not well differentiated on routine CT scans due to limited contrast between gray and white matter.

  • Appears as a subtle, curved structure in the medial temporal lobe; can be visualized better in cases of gross atrophy, hemorrhage, or calcification.

  • Hypodense areas may be noted in acute ischemia; hyperdense foci may indicate hemorrhage.

MRI images

Cornu ammonis mri 3t coronal image