Topics

Topic

design image
Cornu ammonis 4 (CA4)

Cornu Ammonis 4 (CA4) is a small, distinct subregion of the hippocampus, located in the medial temporal lobe of the brain. Although relatively less prominent compared to other Cornu Ammonis subfields (CA1-CA3), CA4 is a crucial anatomical and functional part of the hippocampal formation. It is situated at the hilus of the dentate gyrus, acting as a transitional zone between the CA3 region and the dentate gyrus. CA4 plays a significant role in synaptic integration and hippocampal circuitry, making it vital for memory formation and spatial navigation.

Synonyms:

  • Hilus of the dentate gyrus

  • Endfolial nucleus

  • Polymorphic layer of the dentate gyrus

  • CA4 region of hippocampus

Arterial Supply:

  • Primarily supplied by branches of the posterior cerebral artery (PCA), especially the hippocampal arteries

  • Contributions may also arise from the anterior choroidal artery and small branches of the posterior communicating artery

Venous Drainage:

  • Drains mainly into the inferior ventricular vein and basal vein of Rosenthal

  • Additional drainage into the internal cerebral veins via the hippocampal veins

Function:

  • Facilitates synaptic integration between dentate gyrus and other hippocampal subfields

  • Involved in memory encoding, particularly episodic memory

  • Plays a role in spatial navigation and learning processes

  • Participates in the modulation of hippocampal circuitry and neuroplasticity

MRI Appearance:

  • T2-weighted imaging:

    • CA4 appears isointense to slightly hyperintense relative to adjacent hippocampal structures

    • Clear visualization may be challenging due to small size and close proximity to the dentate gyrus

    • High-resolution scans can help delineate the polymorphic layer of the dentate gyrus (CA4)

  • T1-weighted imaging:

    • Appears isointense to the rest of the hippocampus

    • Difficult to distinguish from surrounding hippocampal tissue on routine imaging

  • FLAIR imaging:

    • No specific distinguishing features under normal conditions

    • May show hyperintensity in cases of hippocampal sclerosis, ischemia, or inflammation involving the CA4 region

CT Appearance:

  • Not well visualized on standard CT due to small size and similar density to adjacent hippocampal tissue

  • Pathological changes (e.g., calcification, hemorrhage) may be appreciated if present, but normal CA4 is not clearly distinguishable on CT

MRI images

Cornu Ammonis 4 (CA 4) mri 3t coronal image