Third Ventricle of the Brain

Overview:

All of the body’s processes occur in a systematic and sequential order, ensuring that every work of the body is completed as perfectly as possible. This necessitates precise processing and appropriate handling of the sensory input received by the organs and tissues, implying a highly functioning brain.

Because the human brain is so vital and delicate, it is entirely encased in a bony protective shell to protect it from harm. The brain is also shielded by three meningeal layers: the dura mater, the arachnoid mater, and the pia mater. Despite all of those layers, there is still a region around the brain that is vulnerable to harm.

As a consequence, this area is filled with clear fluid, suspending the brain within the cranium. The fluid known as CSF is produced by the brain’s ventricle system. CSF is contained in four voids in the brain: two lateral ventricles, a third ventricle, and a fourth ventricle.

The third ventricle of the brain is detailed in this article. Its location, anatomical formation, role within the brain area and function in brain protection is explained. This article also briefly discusses the complications associated with the third ventricle of the brain.

Summary:

• The third ventricle is a narrow brain chamber in the shape of a funnel. It is located in the centre line and, as the name implies, is a key component of the brain’s ventricular system
• The third ventricle has four sides: posterior, anterior, and two lateral walls.
• It is the place where cerebrospinal fluid is manufactured and transported from, like the rest of the ventricles of the brain
• The choroid plexus is a capillary network that generates and secretes a cerebrospinal fluid (CSF) into the ventricular system of the brain.
• The third ventricle’s roof stretches from the foramen of Monro on the anterior end to the suprapineal recess on the posterior end
• Hydrocephalus and tumours can affect the third ventricle

Location:

The third ventricle is a brain cavity that is slender and in the shape of a funnel.  It is situated in the centre line and suggestively forms the central component of the brain’s ventricular system.

The third ventricle is in the diencephalic region of the brain (Figure 1). It is a narrow pierced cavity bounded laterally by the medial nuclei of each thalamus, the hypothalamus, and anteriorly by the interthalamic binding. The fornix of the corpus callosum forms the anterior canopy of the cavity, and the splenium of the corpus callosum forms the posterior canopy.

Structure:

The choroid plexus is a specialized membrane consisting of ependymal cells that coats the ventricles that are present in the brain. Ependymal cells are glial cells that are particularly supposed to generate Cerebrospinal fluid (CSF) and are in charge of releasing the fluid into the ventricles at a consistent rate. Cerebrospinal fluid (CSF) circulates throughout the main nervous system organs and structures, including the brain and spinal cord. After passing through the ventricular system, this occurs in a narrow area between the meninges known as the subarachnoid space.

The choroid plexus is a network of capillaries that produces and secretes Cerebrospinal fluid (CSF) into the brain’s ventricular system. The blood–Cerebrospinal fluid border is made up of the choroid plexus epithelial tissue. The anterior choroidal division of the internal carotid artery and choroidal divisions of the posterior cerebral artery supplies the majority of blood to the choroid plexus. A solitary choroidal vein drains the venous blood. The choroid plexuses of the lateral and third ventricles are uninterrupted when examined in the sagittal segment.

As mentioned above, the third ventricle is reported in the diencephalic region of the brain. It is narrow and is bounded laterally by the medial nuclei from each thalamus, the hypothalamus, and is stopped anteriorly by the interthalamic bonding. The fornix of the corpus callosum forms the anterior ceiling of the cavity, while the splenium of the corpus callosum forms the posterior ceiling.

The anterior commissure and the lamina terminalis limit the area anteriorly. It proceeds inferiorly into the hypothalamic infundibular and supraoptic recesses, as well as the tuber cinereum. The cavity stretches posteriorly into the pineal recess, with the Habenular commissure making a mark in the area.

Its lateral barrier is curved on both sides by the hypothalamic sulcus, which runs from the foramen of Monro to the entrance of the cerebral aqueduct of Sylvius. It is also worth noting that the foramen of Monro allows the choroid plexus of the lateral ventricles to join the third ventricle. The plexus is then located in a groove beneath the fornix and splenium of the corpus calvarium.

As a direct consequence, the third ventricle has direct communication with the following ventricles:

• It interacts among each lateral ventricle through the Monro foramen.
• It interacts with the fourth ventricle through the Sylvius aqueduct.

The third ventricle is a cuboid framework with a roof, flooring, and four wall surfaces (anterior, posterior, and two laterals). The primary purpose of the third ventricle, like all the other brain ventricles, is to generate, excrete, and transport cerebrospinal fluid (CSF). 

The Walls of the third ventricle:

The third ventricle has four sides: posterior, anterior, and two lateral walls.

Posterior wall: The posterior wall stretches from the suprapineal recess in the superior area, to the aqueduct of Sylvius in the inferior region. The pineal gland is the only structure that can be seen from the posterior aspect view of the brain. When observed inferiorly to the posterior commissure, the ventricle is continued with the cerebral aqueduct of the midbrain (of Sylvius).

When examined from the front, the posterior wall is made up of five components, which seem to be (from superior to inferior order):

• Suprapineal recess 
• Habenular commissure
• Pineal body and its recess
• Posterior commissure
• Aqueduct of Sylvius

Anterior Wall: The anterior advances inferiorly from the foramina of Monro to the optic chiasm. The foramen of Monro is situated at the intersection of the anterior wall and the third ventricle’s ceiling. Only the inferior 2/3 of the anterior wall are noticeable when the brain is portrayed at the front. The rostrum of the corpus callosum covers the superior most fraction.

The corpus callosum is a huge white matter tissue that links the brain’s two hemispheres. It is a crucial functional and structural elements of the brain. It enables human beings to interpret depth and interact between the two sections of their brain. The corpus callosum derives its term from the Latin phrase “tough body.” In between two hemispheres, it is the biggest white matter framework in the brain if the size is considered (seven hundred square millimetres for the midsagittal cross-section) and also the number of projections of axons (two hundred million).

The formations that lead to the development of the anterior wall are mentioned below, from superior to inferior order:

• Foramina of Monro
• Fornix columns
• Anterior commissure
• Terminalis lamina
• Optic recess
• Optic Chiasm

Lateral Walls: The medial sides of the thalamus and hypothalamus, divided by the hypothalamic sulcus, create the lateral walls of the third ventricle. When seen from the side, the shapes of the lateral walls resemble the profile of the head of a bird who has its beaks all opened up.  The medial portion of the thalamus makes up the major portion of the lateral wall.

The optic recess is what we can observe as the superior beak, whereas the infundibular recess can be considered as the lower beak.

Tela choroidea is the vascular pia mater that is tightly attached to the ventricle ependymal membrane (Figure 2). The tela choroidea is implanted in the ventricle’s multi-layered ceiling in the third ventricle. The choroid plexus is formed by the tela choroidea.

The roof layer of the third ventricle:

The plexus is then located in a groove beneath the corpus callosum’s fornix and splenium. Posteroinferiorly, the posterior commissure extends slightly just above the entrance of the Sylvius aqueduct.

The third ventricle’s roof stretches from the foramen of Monro on the anterior end to the suprapineal recess on the posterior end. The roof is located directly beneath the main structure of Fornix. The roof has several layers, including a neural surface.

• Choroidea tela (two layers)
• The Vascular Layer

The neural layer, created by the body and the crura of the fornix, is by far the most superficial surface.

There are two small membrane-bound layers of tela choroidea beneath this layer. The tela choroidea is a somewhat transparent two-layered framework obtained from the pia mater, and its capabilities will be discussed further in the article.

A vascular layer exists between both the layers of the tela choroidea, consisting primarily of medial posterior choroidal arteries and their divisions.

The basal layer or flooring of the third ventricle:

The third ventricle floor stretches from the optic chiasm in the anterior region to the Sylvius aqueduct in the posterior area. The hypothalamus forms the anterior segment of the base layer, whereas the midbrain forms the posterior part (mesencephalon).

When the bottom of the third ventricle is observed from the upward direction, the optic chiasm forms a prominent protrusion in the anteriormost section of the ventricle. The optic chiasm is placed at the confluence of the ventricle’s bottom layer and anterior wall. The mamillary structures form a protrusion posterior to the optic chiasm. 

The hollow of the third ventricle continues into the pituitary stalk in between two prominences, creating the infundibular recess. The posterior part of the bottom surface (next to the mammillary bodies) is smooth and ordinary, lying just above the posterior perforated component and tegmentum.

If the basal layer is observed in the anterior to posterior order, the components that make up the floor of the third ventricle are the:

• Optic chiasm
• Infundibulum of hypothalamus
• Tuber cinereum
• Mammillary bodies
• Posterior perforated substance
• The anterior part of the tegmentum of the midbrain

Function:

Cerebrospinal fluid (CSF) circulates throughout the central nervous system organs and structures of the brain and spinal cord. After passing through the ventricular system, this occurs in a tiny area between the meninges known as the subarachnoid space.

The ventricular system is required for the central nervous system to function properly. It protects the head by allowing it to “float” in a fluid bath, and it works as a shock absorber in the event of a head injury. The CSF itself contributes to the supply of nutrients to the brain as well as the maintenance of brain chemistry in the cerebral cortex.

As Cerebrospinal fluid (CSF) passes across the brain, it transfers poisonous compounds as well as other waste substances into the blood circulation, where they are then discharged by mechanisms such as the kidney’s filtration system. Regardless of pressure fluctuations within the ventricles, the rate of Cerebrospinal fluid (CSF) production in the ventricles stays constant.

Regardless of pressure fluctuations within the ventricles, the rate of Cerebrospinal fluid (CSF) production in the ventricles stays constant (i.e. interventricular pressure). If the flow of Cerebrospinal fluid (CSF) is impeded at any point or site in the ventricular system, it might be a problem. Cerebrospinal Fluid (CSF) will continue to be available and manufactured however there will be a decrease in production.

The third ventricle’s job is to create and release Cerebrospinal fluid (CSF) as well as assist in the continuous movement of Cerebrospinal fluid (CSF) through the ventricular system. In this manner, the ventricle contributes to the padding and protection of the brain, and also the transfer of nutrition and waste into and out of neural cells. 

If the circulation of Cerebrospinal fluid (CSF) via the ventricles is hindered for any cause (for example, a tumour that clogs the foramina through which the ventricles communicate), Cerebrospinal fluid (CSF) begins to build, resulting in hydrocephalus.

Complications involving the ventricles of the brain:

Third Ventricular Tumours: 

Third ventricle tumours are rare, accounting for approximately 0.6 to 0.9 per cent of all brain tumours. Primary tumours (such as colloid cysts, choroid plexus papillomas, and ependymomas) and secondary tumours can be distinguished (e.g., craniopharyngiomas, optic nerve gliomas, pineal tumours, and meningiomas).

Third ventricle cancers are further classified as lesions impacting the anterior side, posterior portion, or the entire third ventricle. A hypothetical line joining the foramen of Monro and the aqueduct divides the anterior and posterior halves of the third ventricle. Choroid plexus papillomas, ependymomas, teratomas, and germinoma are the most frequent intraventricular tumours in kids.

Craniopharyngiomas, Colloid cysts, Choroid plexus papilloma (CPP) and Ependymomas are some common types of tumours.

Colloid cysts are the well-documented of the four main tumours of the third ventricle mentioned. They have superior surgical success and a variety of options for establishing remission using safe treatments. There was just a minor indication of postoperative problems.

Choroid plexus papilloma (CPP) is another common tumour that has been described, and its management is primarily centred on surgical resection. With new developments in imaging and surgical methods, its success rate has grown to a hundred per cent, resulting in a full cure with few postoperative problems. As per the published data, there are several treatments available for craniopharyngiomas, with drastic surgery being the most popular.

Short-term side effects of radiotherapy include nausea, exhaustion, and minor skin reactions. Finally, ependymomas have few treatment options, with surgical excision being the first line of defence. When compared to other brain tumours, the prognosis for individuals with ependymomas is relatively bad, with a significant number of patients dying from the disease and a few seriously damaged patients.

Hydrocephalus: 

Hydrocephalus is a condition characterized by an excessive amount of Cerebrospinal fluid (CSF) in the central nervous system (CNS) as a result of a disruption in CSF flow or absorption. This causes an upsurge of Cerebrospinal fluid in the Central nervous system, resulting in greater pressure in the intracranial region. 

If it takes place in children, it could also cause progressive expansion of the head, possibly resulting in spasm, tunnel vision, hindering of brain ability, cognitive deterioration, aches and pains in the head, aching and discomfort in the neck region suggesting herniation of the tonsils, puking, slurred vision or double vision, poor mobility secondary to spasticity, dizziness, and other forms of mental disorders, among other side effects.

Conclusion:

The third ventricle is a narrow brain chamber in the shape of a funnel. It is located in the centre line and, as the name implies, is a key component of the brain’s ventricular system. The third ventricle has four sides: posterior, anterior, and two lateral walls. The third ventricle is a cuboid framework that includes a ceiling, floors, and four wall surfaces (anterior, posterior, and two laterals). The major function of the third ventricle, as with the other brain ventricles, is to produce, expel, and transport cerebrospinal fluid (CSF). Hydrocephalus and tumours can affect the third ventricle.

Reference list

• Ahmed, S.I. et al. (2018) ‘Third Ventricular Tumors: A Comprehensive Literature Review’, Cureus, 10(10). doi: 10.7759/cureus.3417
• Janghu, P.K. (2021) Third Ventricle, Location, boundaries, recesses and choroid plexus, Anatomy QA, 18 July. Available at: https://anatomyqa.com/third-ventricle-anatomy/ (Accessed: 18 July 2021).
• Neuroscientifically Challenged (2021) ‘Third ventricle’, 17 January. Available at: https://www.neuroscientificallychallenged.com/glossary/third-ventricle (Accessed: 18 July 2021).
• https://www.kenhub.com/en/library/anatomy/third-ventricle (2021), 18 July (Accessed: 18 July 2021).