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Topic

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Cornu ammonis 3 (CA3)

Cornu Ammonis 3 (CA3) is a critical subfield of the hippocampus, situated between CA2 and CA4. It is recognized for its distinct pyramidal neurons and plays a pivotal role in memory processing and information flow within the hippocampal formation. CA3 is essential for pattern completion and associative memory, and its structure and vascular supply make it unique among hippocampal regions. Imaging of CA3 is vital in the assessment of hippocampal pathologies, especially in epilepsy and neurodegenerative diseases.

Synonyms

  • Hippocampal field CA3

  • Hippocampus CA3 region

  • Ammon’s horn CA3

  • CA3 sector

Arterial Supply

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

  • Minor contributions may come from the anterior choroidal artery.

  • The CA3 region receives its blood supply predominantly via the middle and posterior hippocampal arteries, entering from the subiculum and adjacent parahippocampal areas.

Venous Drainage

  • Drained by the hippocampal veins, which converge into the inferior ventricular vein.

  • These veins ultimately drain into the basal vein of Rosenthal and then into the great cerebral vein (of Galen).

Function

  • Key role in pattern completion—retrieving complete memories from partial cues.

  • Involved in associative memory and spatial information processing.

  • Acts as a relay station between the dentate gyrus (via mossy fibers) and CA1.

  • Contains abundant recurrent collaterals, facilitating rapid information processing and memory encoding.

  • Vital in seizure propagation in temporal lobe epilepsy.

MRI Appearance

  • T2-weighted: CA3 is typically isointense to slightly hyperintense compared to the surrounding white matter; pathological changes (e.g., sclerosis) may show as hyperintensity.

  • T1-weighted: CA3 appears as a thin, intermediate-signal-intensity band within the hippocampus. Atrophy or sclerosis can be seen as loss of normal volume and increased signal.

  • FLAIR: Normally, CA3 has intermediate signal intensity. In pathological conditions (like mesial temporal sclerosis), CA3 may show increased signal due to gliosis or tissue loss.

CT Appearance

  • On non-contrast CT, CA3 is not separately distinguishable due to poor soft tissue contrast; it forms part of the hippocampal head and body.

  • In cases of severe hippocampal sclerosis or atrophy, loss of bulk or asymmetry of the hippocampal formation may be appreciated.

  • No specific calcifications or intrinsic hyperdensities are associated with normal CA3.

MRI images

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