Third Ventricle

The third ventricle, the cavity of the diencephalon, is a narrow, vertically oriented midline space that communicates rostrally with the lateral ventricles and caudally with the cerebral aqueduct. The third ventricle has an elaborate profile on a sagittal view, but it is narrow in the coronal and axial planes.

The boundaries of the third ventricle are formed by a variety of structures, the most important being the dorsal thalamus and hypothalamus, and by structures that form small outpocketings called recesses. These are the supraoptic recess (above the optic chiasm), the infundibular recess (in the infundibulum, the stalk of the pituitary), the pineal recess (in the stalk of the pineal), and the suprapineal recess (above the pineal). The rostral wall of the third ventricle is formed by a short segment of the anterior commissure and a thin membrane, the lamina terminalis, that extends from the anterior commissure anteriorly (ventrally) to the rostral edge of the optic chiasm. The floor of the third ventricle is formed by the optic chiasm and infundibulum and their corresponding recesses plus a line extending caudally along the rostral aspect of the midbrain to the cerebral aqueduct. The caudal wall is formed by the posterior commissure and the recesses related to the pineal, whereas the roof is the tela choroidea, from which the choroid plexus is suspended.