Memory Part 3: The Role of the Fornix and Clinical Cases

High-resolution coronal T2-weighted image of the right hippocampal formation showing the dark signal of the white matter fibers of the alveus (red arrow) positioned on top of Ammon's horn (CA) of the hippocampus and below the CSF of the temporal horn of the lateral ventricle, which also contains the choroid plexus (not labeled). The dentate gyrus (DG) is shown. The alveus thickens at its medial margin to form the fimbria (yellow arrow).

Schematic overview of the fornix from the side. The fimbria forms the crus of the fornix, which is joined to the opposite fornix across the midline by the commissure of the fornix (hippocampal commissure, psalterium). The body of the fornix (B) at the top of the fornical arch is connected to the inferior surface of the body of the corpus callosum by the septum pellucidum. The column of the fornix (C) has a more superoinferior orientation and is connected to the posterior margin of the genu of the corpus callosum by the septum pellucidum. The columns of the fornix are split at the level of the anterior commissure with most the fibers (postcommissural fibers) projecting to the mammillary bodies. Published with permission from the estate of David L. Daniels.

A, Coronal anatomic specimen with a schematic reference image. The white matter fibers of the crus of the fornix can be seen forming the inferior medial margin of the posterior aspect of the body of the lateral ventricles at the level of the splenium of the corpus callosum. B, Coronal T2-weighted image shows the dark signal of the crura of the fornices (yellow arrows) forming the inferior medial margin of the posterior lateral ventricles at the level of the posterior aspect of the body of the corpus callosum (CC).

A, Coronal T2-weighted image shows the body of the fornices (yellow arrows) attached to the inferior margin of the body of the corpus callosum (CC) via the septum pellucidum (black arrow). The body of the fornices are at the upper aspect of the velum interpositum, which is traversed by the internal cerebral veins (green arrow), situated above the third ventricle but inferomedial to the body of the lateral ventricles. B, Sagittal schematic shows the position of the fornix relative to the velum interpositum. The foramen of Monro (green arrow) forms the anterior border of the velum interpositum, while the posterior border opens between the splenium of the corpus callosum above and the pineal gland below into the quadrigeminal plate cistern. The choroid plexus (red) is indicated at the roof of the third ventricle below but not within the velum interpositum. Published with permission from the estate of David L. Daniels.

A, Axial T2-weighted image shows the postcommissural fibers of the fornix (yellow arrows) coursing posterior to the anterior commissure (green arrow). B, Coronal T2-weighted image shows the superoinferior orientation of the columns of the fornix (yellow arrows).

Drawing showing verbal memory information carried primarily by the left fornix (orange), while the visuospatial memory information is primarily transmitted by the right fornix (light purple).

Drawing shows the medial aspect of the fornix (light blue) carrying fibers from the posterior hippocampus for processing of exteroceptive information for scene learning. The more lateral fibers (light red), meanwhile, carry fibers from the more rostral portions of the hippocampus for processing of interceptive signals for emotional and motivational memory and learning.

A, T2-weighted axial image shows a glioneuronal tumor (red arrow) within the right lateral ventricle near the foramen of Monro displacing and distorting the septum pellucidum and columns of the fornices (yellow arrow). B, The intraventricular glioneuronal tumor (red arrow) is better visualized on the axial FLAIR image. C, Postoperative coronal T2-weighted image shows the intraventricular neoplasm still distorting the columns of the fornix and septum pellucidum.

A, Gradient recalled-echo image shows hemorrhage (red arrow) in the cistern of the velum interpositum involving the bodies of the fornices. B, Coronal T1-weighted image 5 months later without treatment shows atrophy of the mammillary bodies, worse on the left (yellow arrow).