Brain Ventricular System

The ventricular system of the brain consists of two lateral ventricles and the midline 3rd and 4th ventricles connected by the cerebral aqueduct. CSF, largely secreted by the choroid plexuses of the ventricles, fills these brain cavities and the subarachnoid space of the brain and spinal cord.

The ventricular system and circulation of the CSF are shown. The production of CSF is mainly by the choroid plexuses of the lateral, 3rd, and 4th ventricles. The plexuses of the lateral ventricles are the largest and most important. CSF is absorbed into the venous system through the arachnoid granulations that project into the superior sagittal sinus and its lateral lacunae.

The subarachnoid cisterns, expanded regions of the subarachnoid space, contain more substantial amounts of CSF.

The lateral ventricles, the 1st and 2nd ventricles, are the largest cavities of the ventricular system and occupy large areas of the cerebral hemispheres. Each lateral ventricle opens through an inter-ventricular foramen (foramen of Monro) into the 3rd ventricle. The 3rd ventricle, a slit-like cavity between the right and the left halves of the diencephalon, is continuous postero-inferiorly with the cerebral aqueduct, a narrow channel in the midbrain connecting the 3rd and 4th ventricles. The pyramid-shaped 4th ventricle in the posterior part of the pons and medulla extends infero-posteriorly. Inferiorly, it tapers to a narrow channel that continues into the cervical region of the spinal cord as the central canal. CSF drains into the subarachnoid space from the 4th ventricle through a single median aperture (Foramen of Magendie) and paired lateral apertures (foramina of Luschka). These apertures are the only means by which CSF enters the subarachnoid space. If they are blocked, CSF accumulates and the ventricles distend, producing compression of the substance of the cerebral hemispheres.