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Topic

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Cornu Ammonis 1 (CA1)

Cornu Ammonis 1 (CA1) is a key subfield of the hippocampus, critical for memory processing and spatial navigation. It forms the first segment of the hippocampal formation and acts as a major output zone to other brain regions. CA1 is highly sensitive to hypoxic-ischemic injury, making it clinically significant in various neurological disorders. Its distinct cellular arrangement and connectivity make it an essential focus in neuroimaging and neuropathology.

Synonyms

  • CA1 region

  • Sommer’s sector (especially in the context of hypoxic injury)

  • Pyramidal cell layer of CA1

Arterial Supply

  • Primarily supplied by branches of the posterior cerebral artery (PCA), specifically:

    • Hippocampal arteries (from PCA)

    • Occasionally contributions from the anterior choroidal artery

Venous Drainage

  • Drained mainly by the hippocampal veins

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

Function

  • Essential for the consolidation of long-term declarative memory

  • Plays a major role in spatial memory and navigation

  • Acts as the main output region of the hippocampus, projecting to the subiculum and entorhinal cortex

  • Integrates and transmits processed information from CA3 and dentate gyrus

MRI Appearance

  • T1-weighted imaging: CA1 is isointense to other gray matter structures; individual subfields are generally not distinguishable unless there is pathology (e.g., atrophy in mesial temporal sclerosis).

  • T2-weighted imaging: Appears as part of the hippocampal formation, may show hyperintensity in acute injury (e.g., hypoxic damage or status epilepticus).

  • FLAIR imaging: Abnormal hyperintensity in CA1 can indicate early hippocampal injury (commonly seen in transient global amnesia or hypoxic-ischemic encephalopathy).

CT Appearance

  • Typically not visible as a distinct structure on non-contrast CT due to low spatial resolution and similar density to adjacent tissues

  • Can show loss of hippocampal volume or hypoattenuation in cases of severe or chronic pathology (e.g., hippocampal sclerosis)

MRI images

Cornu Ammonis 1 (CA 1) mri 3t coronal image