Hippocampal commissure

Last revised by Arlene Campos on 7 Jun 2024

The hippocampal commissure, also called the commissure of the fornix, is a transversely-oriented white matter tract connecting the two hippocampi via the fornices 1. The specific function of the hippocampal commissure is unknown, although damage to the fornices has been shown to lead to memory loss 2.

Gross anatomy

Arching superiorly and medially over posterior surface of the thalamus, the fornix contains white matter fibers traveling from the hippocampus to the ipsilateral mammillary body 3,4. In the region of the fornix immediately below the splenium and body of the corpus callosum, a portion of the fibers within the fornix decussate and travel transversely to join the contralateral fornix 3. This collection of decussating fibers comprise the hippocampal commissure and form the psalterium, a thin triangular lamina spanning between the body of the left and right fornices 1.

Related pathology

Given the proximity of the hippocampal commissure to the interventricular foramen of Monro, the hippocampal commissure and the related fornices may be damaged during the endoscopic removal of a colloid cyst 4,5.

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