Ventricular System

David E. Scott , in Encyclopedia of the Human Brain, 2002

III.A The Lateral Cerebral Ventricular System

The lateral cerebral ventricular system is the most expansive part of the mammalian cerebral ventricular system. It consists of an anterior projection, with the anterior horns bounded by the septum pillucidum medially, the genu of the corpus callosum rostrally, and the head of the caudate nucleus laterally. It is continuous with the body of the lateral ventricle, whose medial and lateral walls are composed of the body of the caudate nucleus and the lateral aspect of the thalamus. A thick veil of overlying choroid plexus, which is derived from the germinal matrix of the choroidal fissure during the seventh week in utero, commonly obscures both of these structures. The body of the lateral cerebral ventricle is continuous, with the posterior horn and the beginning of the temporal horn, an area that is collectively referred to as the collateral trigone. The posterior horn is quite variable in mammals and particularly in the human brain. The most distinct feature of the temporal horn is the presence of the massive hippocampus, with the alveolus of the fornix arising from it as a flattened filet of fibers. Both the hippocampus and the fornix are commonly obscured by a thick felt work of chord plexus, which is highly vascularized and irrigated in large part by the anterior choroidal artery coupled with some branches of the posterior cerebral artery. The lining cells of the lateral cerebral ventricle are chiefly cuboidal ciliated ependymal cells (Figs. 1 and 2). The cilia that constitutes the surfaces of these ependymal cells beat in a metachronal fashion and are regarded as a mechanism that alters the local flow and dynamics of CSF, which is produced in large part by the choroid plexus. It should be noted, however, that cilial density alters from region to region and if a region is denuded of ciliated ependymal cells, no reepithelization will occur. Hence, ciliated ependymal cells of the lateral cerebral ventricle are regarded as postmitotic.

Figure 1. Scanning electron microgram (SEM) of ependymal surface of the head of the caudate nucleus forming the lateral wall of the anterior horn of the lateral ventricle. Both cilia (CL) and micro villi (MV) are notable in this region of the cerebral ventricular system. ×8000.

Figure 2. SEM of cerebral ventricular wall of the human hippocampus 28 days postcoitus. Ependymal cells demonstrate patchy cilia (CL) interspersed by areas devoid of any membranous modification. ×6000.

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Shunt Placement and Management

Jason J. Chang , Anthony M. Avellino , in Neurocritical Care Management of the Neurosurgical Patient, 2018

Ventricular system anatomy

The ventricular system is characterized by four large fluid-filled spaces interconnected by openings between the supratentorial and infratentorial compartments ( Fig. 40.1). The lateral ventricles are bilateral C-shaped structures that span the entire cerebrum. These spaces merge into the anterior aspect of the third ventricle via the foramen of Monro. At the posterior extent, the cerebral aqueduct serves as the connection to the fourth ventricle and is prone to obstruction by pineal region masses (Fig. 40.2, Box 40.1). CSF is able to exit the ventricular system via the foramen of Magendie and foramina of Luschka located along the medial and lateral walls of the fourth ventricle.

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Structure, Function, and Development of the Nervous System

Mish Shoykhet , Robert S.B. Clark , in Pediatric Critical Care (Fourth Edition), 2011

Ventricular system

The ventricular system arises from the hollow space within the developing neural tube and gives rise to cisterns within the CNS, from the brain to the spinal cord. In the brain, the ventricular system consists of paired lateral ventricles that connect to the midline third ventricle via bilateral foramina of Monro. The third ventricle in turn connects to the fourth ventricle located in the pons and the medulla via the aqueduct of Sylvius. The fourth ventricle terminates caudally in the central spinal canal, and continues as a miniscule midline structure through the spinal cord. The ventricles contain the choroid plexus, which produces CSF, and serve as conduits for CSF flow in the CNS. Ventricular walls are lined with ependymal cells, which are connected by tight junctions and constitute a CSF-brain barrier.

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Development of the Nervous System

W.A. Grow , in Fundamental Neuroscience for Basic and Clinical Applications (Fifth Edition), 2018

Ventricular System

The ventricular system is an elaboration of the lumen of cephalic portions of the neural tube, and its development parallels that of the brain ( Figs. 5.7 and 5.9A-D ). This process, also discussed in Chapter 6, is summarized here. The cavities of the telencephalic vesicles become the lateral ventricles; the diencephalic cavity becomes the third ventricle; and the rhombencephalic cavity becomes the fourth ventricle. The cavity of the mesencephalon becomes the narrow cerebral aqueduct (of Sylvius) connecting the third and fourth ventricles, and the openings between the lateral ventricles and the third ventricle become the intraventricular foramina (of Monro).

The ventricular system is lined with ependymal cells. Each ventricle originally has a thin roof composed of an internal layer of ependyma and an outer layer of delicate connective tissue (pia mater). In each ventricle, blood vessels invaginate this membrane to form the choroid plexus.

Openings that arise in the caudal roof of the fourth ventricle during development form a communication between the ventricular system and the subarachnoid space. These are the midline medial aperture (foramen of Magendie) and the paired lateral foramina of Luschka. Although these foramina develop slowly, they are patent by the end of the first trimester. CSF is produced mainly by the choroid plexuses of the lateral and third ventricles. It escapes the ventricular system through foramina of the fourth ventricle and passes into the subarachnoid space. From there, it is absorbed into the venous system through the arachnoid villi located primarily in the superior sagittal sinus.

If the flow of CSF through the ventricles is obstructed during prenatal development, the ventricular system can become markedly dilated, a condition called congenital hydrocephalus (Fig. 5.10). The cerebral aqueduct, only 0.5 mm in diameter, is a likely site for such a blockage. Congenital atresia (failure to form) of the aqueduct can occur as an isolated event, can be inherited, or can be associated with CNS deformities (Fig. 5.9E ). Stenosis, or total obstruction, from cellular debris associated with an infection or from an intraventricular hemorrhage may also occlude this narrow passage.

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Principles of Modern Neuroimaging

Kathleen R. Tozer Fink , James R. Fink , in Principles of Neurological Surgery (Fourth Edition), 2018

Hydrocephalus.

The ventricular system is seen well on noncontrast CT. Ventricular size depends in part on the age of the patient and the extent of cerebral parenchymal volume loss. It is important to evaluate ventricular size in relation to sulcal size. Enlarged ventricles with preserved sulci and widely patent basilar cisterns may simply reflect cerebral volume loss. Even slightly increased ventricular size in a young person with effaced sulci and cisterns is much more concerning for hydrocephalus ( Fig. 4.5). Secondary signs of hydrocephalus include Transependymal CSF flow, where pressurized CSF collects in the parenchymal interstitial space, particularly around the lateral ventricles.

Hydrocephalus can either be communicating, due to compromised CSF reabsorption, or noncommunicating, due to obstruction of CSF outflow. Communicating hydrocephalus involves the entire ventricular system, including the fourth ventricle, but noncommunicating hydrocephalus results in dilatation of only the ventricles proximal to the obstruction. If obstructive hydrocephalus is suspected, a search for the underlying cause should be undertaken. CT may be helpful in some cases, but MRI is more sensitive for subtle lesions and can provide multiplanar anatomic evaluation.

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Nervous System

Bruce M. Carlson MD, PhD , in Human Embryology and Developmental Biology (Fifth Edition), 2014

Ventricles, Meninges, and Cerebrospinal Fluid Formation

The ventricular system of the brain represents an expansion of the central canal of the neural tube. As certain parts of the brain take shape, the central canal expands into well-defined ventricles, which are connected by thinner channels ( Fig. 11.37 ). The ventricles are lined by ependymal epithelium and are filled with clear cerebrospinal fluid. Cerebrospinal fluid is formed in specialized areas called choroid plexuses, which are located in specific regions in the roof of the third, fourth, and lateral ventricles. Choroid plexuses are highly vascularized structures that project into the ventricles (see Fig. 11.32B) and secrete cerebrospinal fluid into the ventricular system.

During early development of the brain (equivalent to the third and fourth weeks of human development), cerebrospinal fluid plays an important role in overall growth and development of the brain. As the amount of cerebrospinal fluid increases through an osmotic mechanism, its pressure increases on the inner surfaces of the brain. This change, along with the possible effect of growth factors in the fluid, results in increased mitotic activity within the neuroepithelium and a considerable increase in the mass of the brain. If the cerebrospinal fluid is shunted away from the ventricular cavities, overall growth of the brain is considerably reduced.

In the fetus, cerebrospinal fluid has a well-characterized circulatory path. As it forms, it flows from the lateral ventricles into the third ventricle and, ultimately, the fourth ventricle. Much of it then escapes through three small holes in the roof of the fourth ventricle and enters the subarachnoid space between two layers of meninges. A significant portion of the fluid leaves the skull and bathes the spinal cord as a protective layer.

If an imbalance exists between the production and resorption of cerebrospinal fluid, or if its circulation is blocked, the fluid may accumulate within the ventricular system of the brain and, through increased mechanical pressure, result in massive enlargement of the ventricular system. This condition causes thinning of the walls of the brain and a pronounced increase in the diameter of the skull, a condition known as hydrocephalus ( Fig. 11.38 ). The blockage of fluid can result from congenital stenosis (narrowing) of the narrow parts of the ventricular system, or it can be the result of certain fetal viral infections.

A specific malformation leading to hydrocephalus is the Arnold-Chiari malformation, in which parts of the cerebellum herniate into the foramen magnum and mechanically prevent the escape of cerebrospinal fluid from the skull. This condition can be associated with some form of closure defect of the spinal cord or vertebral column. The underlying cause of the several anatomical forms of Arnold-Chiari malformation remains unknown.

In the early fetal period, two layers of mesenchyme appear around the brain and spinal cord. The thick outer layer, which is of mesodermal origin, forms the tough dura mater and the membrane bones of the calvarium. A thin inner layer of neural crest origin later subdivides into a thin pia mater, which is closely apposed to the neural tissue, and a middle arachnoid layer. Spaces that form within the pia-arachnoid layer fill with cerebrospinal fluid.

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Nervous System, Neuroembryology of

H.B Sarnat , L. Flores-Sarnat , in Encyclopedia of the Neurological Sciences (Second Edition), 2014

Development of the Ventricular System

The ventricular system begins with closure of the neural folds to form the neural tube, leaving a lumen within a cylinder. In the spinal cord, this lumen becomes the central canal (see Neurulation). The brain initially forms three vesicles: the pros-, mes-, and rhombencephalon. The third ventricle is the diencephalic or caudal portion of the primitive rostral vesicle and, after cleavage to form an interhemispheric fissure and two cerebral hemispheres, the lateral ventricles are continuous with it; this connection becomes narrowed with further tissue growth to become the foramina of Monro. Before the telencephalic flexure begins, the telencephalic lateral ventricles are straight, simple cavities. With the bending of the telencephalon, the posterior pole of the primitive lateral ventricle becomes the temporal horn. The occipital horn forms afterward, as the newest part of the ventricular system, hence the most variable. Occipital horns are symmetrical in only 25% of normal subjects. Transitory extensions of the rostral lateral ventricles into the olfactory bulbs are seen in the late first and early second trimesters, but become obliterated and sometimes leave residual ependymal cell rests.

The cerebral aqueduct (of Sylvius) forms by narrowing of the mesencephalic ventricle, and its dorsal extensions into the tectal plate (future colliculi) are transitory and become obliterated with growth of the parenchyma. The fourth ventricle forms with growth dorsally of the rhombic lips of His and the membranous anterior and posterior vela of the cerebellum.

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Biomechanical Modeling of Brain Soft Tissues for Medical Applications

Fanny Morin , ... Yohan Payan , in Biomechanics of Living Organs, 2017

2.2 Ventricular System and Cerebrospinal Fluid

The ventricular system, located in the middle of the telencephalon, is mainly composed of four cavities: the two lateral (left and right), third and fourth ventricles (see Fig. 1B). The cerebrospinal fluid (CSF), which immerses all the CNS, is produced and dispatched by these ventricles (mostly the lateral ones). This liquid is composed of 99% water. Its total volume is approximately 120–150   mL for an adult and is renewed three to four times per day. Several roles are handled by the CSF. First, it protects the brain against infections (thanks to its biochemical composition), and it mechanically protects against impacts. Next, hormones and biological agents are transmitted to the different parts of the brain through this fluid.

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Tumors of the Central Nervous System

Raviteja Suryadevara , ... Prahlad Parajuli , in Nanotechnology-Based Targeted Drug Delivery Systems for Brain Tumors, 2018

1.3.6 Ventricular System

The ventricular system is primarily responsible for circulating CSF throughout the CNS. This system consists of seven components: choroid plexus, two symmetrical positioned lateral ventricles, third ventricle, cerebral aqueduct, fourth ventricle, and the central canal of the spinal cord.

First, cells of the specialized choroid plexus epithelia create the CSF. The choroid plexus is located in the lateral ventricle (except the occipital and frontal horns), the roof of the third ventricle, and the roof of the fourth ventricle. To understand the flow of CSF, we will assume the case in which CSF is produced in the lateral ventricles. After production, the CSF moves from the lateral ventricles into the third ventricle through the two intraventricular foramina of Munro. From the third ventricle, the CSF flows into the fourth ventricle through the cerebral aqueduct. From the fourth ventricle, the CSF exits the cranium and enters the subarachnoid space of the spinal cord and the brain through two lateral apertures (foramina of Luschka) and a single median aperture (foramen of Magendie). The fourth ventricle is also continuous with the central canal of the spinal cord, the last component of the ventricular system. Because it is a location where the majority of CSF is evenly distributed, tumors in the fourth ventricle, such as ependymomas, medulloblastomas, and choroid plexus tumors, can cause complications with the flow of CSF, resulting in a condition known as obstructive or communicating hydrocephalus. After its journey through the respective subarachnoid regions of the CNS, the CSF is reabsorbed into the venous system at the superior sagittal sinus, located at the margin of the falx cerebri, through structures known as arachnoid granulations. Complications that arise with CSF reabsorption generally cause a condition known as nonobstructive or communicating hydrocephalus.

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The Organization of the Nervous System II

Russell J. Love Ph.D. , Wanda G. Webb Ph.D. , in Neurology for the Speech-Language Pathologist, 1992

The Ventricular System

The ventricular system of the brain has three parts: the lateral ventricles, the third ventricle, and the fourth ventricle. These are actually small cavities within the brain and are joined to each other by small ducts and canals ( Figure 3-4). Each ventricle contains a tuftlike structure called the choroid plexus, which is concerned mainly with the production of cerebrospinal fluid.

Figure 3-4. The ventricular system.

The lateral ventricles are paired, one in each hemisphere. Each is a C-shaped cavity and can be divided into a body located in the parietal lobe and anterior, posterior, and inferior horns, extending into the frontal, occipital, and temporal lobes, respectively. The lateral ventricle is connected to the third ventricle by an opening called the intraventricular foramen or the foramen of Munro. The choroid plexus of the lateral ventricle projects into the cavity on its medial aspect.

The third ventricle is a small slit between the thalami. It is connected also to the fourth ventricle, through the cerebral aqueduct or the aqueduct of Sylvius. The choroid plexuses are situated above the roof of the ventricle.

The fourth ventricle sits anterior to the cerebellum and posterior to the pons and the superior half of the medulla. It is continuous superiorly with the cerebral aqueduct and the central canal below. The fourth ventricle has a tent-shaped roof, two lateral walls, and a floor. There are three small openings in the fourth ventricle, the two lateral foramina of Luschkea and the median foramen of Magendie. Through these openings the cerebrospinal fluid enters the subarachnoid space. The choroid plexus of the fourth ventricle has a T-shape. The ventricular system serves as a pathway for the circulation of the cerebrospinal fluid (Figure 3-4). The choroid plexuses of the ventricles appear to secrete the cerebrospinal fluid actively, although some of the fluid may originate as tissue fluid formed in the brain substance.

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