Ventricles Of The Brain: Overview, Gross Anatomy, Microscopic ...

The ventricles of the brain are a communicating network of cavities filled with cerebrospinal fluid (CSF) and located within the brain parenchyma. The ventricular system is composed of two lateral ventricles (one in each cerebral hemisphere), the third ventricle (located in the diencephalon), the cerebral aqueduct, and the fourth ventricle (located in the hindbrain; see the images below). The choroid plexuses are located within the lateral, third, and fourth ventricles and produce CSF through specialized ependymal cells.

Ventricles of brain. The image represents a casting of the normally fluid-filled ventricular system of the brain. (Courtesy of Todd Hoagland, PhD) View Media Gallery

The choroid plexuses of the four ventricles filter blood plasma to form CSF, which enters the four ventricles and flows out of the fourth ventricle via three apertures — the midline median aperature (foramen of Magendie) and the paired lateral aperatures (foramina of Luschka). Once CSF flows out of the median and lateral apertures, it flows into the subarachnoid space, between the arachnoid mater and pia mater, where the CSF buoys the brain and spinal cord. CSF drains from the subarachnoid space back into the dural venous sinuses via the arachnoid villi and granulations, and capillary absorption. The CSF fills the ventricles and subarachnoid space, following a cycle of constant production and reabsorption.

This ventricular system allows the CSF to circulate in a designated path. Any impediment in its circulation and clearance may lead to abnormal accumulation of CSF, called hydrocephalus. Thus, understanding the neuroanatomy of the ventricular system can help in comprehending the finer nuances in the etiopathology of hydrocephalus such as the role of genetic mutations in congenital structural malformations and their impact on the development and proliferation of neurons and neural stem cells as well as in providing insights into the syndromic causes of hydrocephalus. [1]

Evaluating ventricular parameters can also help diagnose central nervous system (CNS) degenerative diseases (e.g., Parkinson's, Alzheimer's, Huntington's, multiple sclerosis) and certain psychiatric disorders (e.g., schizophrenia). [2]

Brain, coronal view. View Media Gallery Meninges and ventricles of the brain. View Media Gallery

Embryology

The ventricular system is embryologically derived from the central lumen of the embryonic neural tube and the cerebral vesicles to which it gives rise. [3] The three brain vesicles (the prosencephalon or forebrain, mesencephalon or midbrain, and rhombencephalon or hindbrain) form around the end of the first gestational month. The neural canal dilates within the prosencephalon, leading to the formation of the lateral ventricles and third ventricle. The cavity of the mesencephalon forms the cerebral aqueduct. The dilation of the neural canal within the rhombencephalon forms the fourth ventricle (see Table 1).

Table 1. Components of the Ventricular System Derived from Cerebral Regions (From Caudal to Rostral) [3] (Open Table in a new window)

Ventricular Component	Embryonic Cerebral Region
Fourth ventricle	Rhombencephalon (or hindbrain) Myelencephalon - Caudal part Metencephalon - Middle part of the fourth ventricle
Aqueduct	Mesencephalon (or midbrain)
Third ventricle	Prosencephalon (or forebrain) Diencephalon - Caudal part of the third ventricle Telencephalon - Rostral part of the third ventricle
Lateral ventricles	Telencephalon

Choroid plexuses: The choroid plexus forms early in development, shortly after closing of the neural tube. The ependymal cells coming in contact with the adjacent mesodermally derived tissue form pseudorosettes, which protrude within the neural tube at the sites of ventricular system formation. The differentiation of these cells with the resulting development of the choroid plexus is largely completed by 22 weeks' gestation. [4]

Tufts of capillaries invaginate the roofs of prosencephalon and rhombencephalon, forming the choroid plexuses of the ventricles. CSF is secreted by the specialized ependymal cells of the choroid plexuses, filling the ventricular system. CSF flows out of the fourth ventricle through the three apertures formed at the roof of the fourth ventricle by 12 weeks' gestation. [5] The early choroid plexuses secrete protein-rich CSF into the ventricular system, likely serving as a nutritive medium for developing epithelial neural tissues. As these tissues become more vascularized, the histochemical properties of the cuboidal cells and the CSF transition to the adult phenotype. [3]