Where is the 4th ventricle of the brain located?

The fourth ventricle is one of the components of the ventricular system in the brain, along with the lateral and third ventricles. It extends from the cerebral aqueduct (of Sylvius) rostrally to the obex caudally and is filled with CSF.

CSF enters the ventricle via the cerebral aqueduct and leaves via one of four routes:

• via the obex and into the central canal
• via the median aperture (of Magendie) into the cisterna magna
• via one of the two lateral apertures (of Luschka) into the cerebellopontine cistern

It is characteristically diamond-shaped in sagittal cross-section and located dorsal to the pons or upper part of the medulla oblongata. The roof, located dorsally is formed by the superior medullary velum and inferior medullary velum overlying the cerebellum. The floor, located ventrally, is formed by the rhomboid fossa, a diamond-shaped depression on the dorsal surface of the pons and upper half of the medulla. The sidewalls are formed by the vela and cerebellar peduncles. The peak of the fourth ventricle within the cerebellum is the fastigium and it underlies the fastigial nucleus. It is widest at the level of the pontomedullary junction. The obex is the most caudal tip of the fourth ventricle.

The fourth ventricle contains choroid plexus along its roof along the tela choroidea which may protrude out the lateral foramina of Luschka.

When observing the interior of the brain, the four follow ventricles stand out in contrast to the rest of the brain, which is mostly composed of grey matter.

The distinct appearance may be part of the reason why the ventricles were believed to have extraordinary roles. In ancient times, they were thought to house the ‘animal spirit’, a substance which allows the soul to exert control over the physical body.

The types of ventricles 

The ventricles of the brain are cavities which produce and store a substance known as cerebrospinal fluid (CSF). The brain’s ventricular system is comprised of four ventricles as well as small structures which connect each ventricle called foramina.

In this way, the ventricles are linked to each other to function as they should. The ventricles are essential for maintaining the central nervous system (CNS). 

There are four ventricles of the brain: the 2 lateral ventricles, third ventricle, and fourth ventricle. The ventricles are lined with a specialised membrane called the choroid plexus, which is made up of ependymal cells.

• 1 Functions of Cerebrospinal Fluid
• 2 Ventricles of the Brain
• 3 Production and Reabsorption of Cerebrospinal Fluid
• 4 Clinical Relevance: Hydrocephalus

The ventricular system is a set of communicating cavities within the brain. These structures are responsible for the production, transport and removal of cerebrospinal fluid, which bathes the central nervous system.

In this article, we shall look at the functions and production of cerebrospinal fluid, and the anatomy of the ventricles that contains it.

Functions of Cerebrospinal Fluid

Cerebrospinal fluid is an ultrafiltrate of plasma that surrounds the brain and spinal cord.

It serves three main functions:

• Protection – acts as a cushion for the brain, limiting neural damage in cranial injuries.
• Buoyancy – by being immersed in CSF, the net weight of the brain is reduced to approximately 25 grams. This prevents excessive pressure on the base of the brain.
• Chemical stability – the CSF creates an environment to allow for proper functioning of the brain, e.g. maintaining low extracellular K+ for synaptic transmission.

By TeachMeSeries Ltd (2022)

Fig 1 – Overview of the cerebrospinal fluid distribution in the brain

Ventricles of the Brain

The ventricles are structures that produce cerebrospinal fluid, and transport it around the cranial cavity. They are lined by ependymal cells, which form a structure called the choroid plexus. It is within the choroid plexus that CSF is produced.

Embryologically, the ventricular system is derived from the lumen of the neural tube.

In total, there are four ventricles; right and left lateral ventricles, third ventricle and fourth ventricle.

Lateral Ventricles

The left and right lateral ventricles are located within their respective hemispheres of the cerebrum. They have ‘horns’ which project into the frontal, occipital and temporal lobes. The volume of the lateral ventricles increases with age.

By TeachMeSeries Ltd (2022)

Fig 2 – Bird’s eye view of a cast of the ventricular system of the brain.

Third Ventricle

The lateral ventricles are connected to the third ventricle by the foramen of Monro. The third ventricle is situated in between the right and the left thalamus. The anterior surface of the ventricle contains two protrusions:

• Supra-optic recess – located above the optic chiasm.
• Infundibular recess – located above the optic stalk.

Fourth Ventricle

The fourth ventricle is the last in the system – it receives CSF from the third ventricle via the cerebral aqueduct. It lies within the brainstem, at the junction between the pons and medulla oblongata.

From the 4th ventricle, the fluid drains into two places:

• Central spinal canal – bathes the spinal cord
• Subarachnoid cisterns – bathes the brain, between arachnoid mater and pia mater. Here the CSF is reabsorbed back into the circulation.

By TeachMeSeries Ltd (2022)

Fig 3 – The anatomical positioning of the ventricles of the brain.

Production and Reabsorption of Cerebrospinal Fluid

Cerebrospinal fluid is produced by the choroid plexus, located in the lining of the ventricles. It consists of capillaries and loose connective tissue, surrounded by cuboidal epithelial cells. Plasma is filtered from the blood by the epithelial cells to produce CSF. In this way, the exact chemical composition of the fluid can be controlled.

Drainage of the CSF occurs in the subarachnoid cisterns (or space). Small projections of arachnoid mater (arachnoid granulations) protrude into the dura mater. They allow the fluid to drain into the dural venous sinuses.

Learn more about the production and reabsorption of cerebrospinal fluid here.

By TeachMeSeries Ltd (2022)

Fig 4 – Coronal section of the skull, meninges and cerebrum. An arachnoid granulation is visible in the centre.

Clinical Relevance: Hydrocephalus

Hydrocephalus is defined as an abnormal collection of cerebrospinal fluid within the ventricles of the brain. It is a serious condition, with chronic hydrocephalus causing raised intracranial pressure, and consequently cerebral atrophy.

Based on the underlying cause, there are two clinical classifications:

• Communicating (Non-obstructive) Hydrocephalus – Abnormal collection of CSF in the absence of any flow obstruction in the ventricles. Common causes usually involve the functional impairment of the arachnoid granulations, such as fibrosis of the subarachnoid space following a haemorrhage.

• Non-communicating (Obstructive) Hydrocephalus – Abnormal collection of CSF, with flow obstructed within the ventricular system. The most common site of obstruction is the cerebral aqueduct, connecting the third and fourth ventricles.

  By Lucien Monfils [CC-BY-SA-3.0-2.5-2.0-1.0], via Wikimedia Commons

  

  Fig 5 – Hydrocephalus on a CT scan.

There is also a third classification, hydrocephalus ex vacuo – this refers to ventricular expansion, secondary to brain atrophy. This is often seen in patients with neurodegenerative conditions, such as Alzheimer’s disease.

Treatment of hydrocephalus primarily involves reversing the cause.  Whilst treating the cause, a shunt can be inserted, which drains the fluid into the right atrium or the peritoneum.

What does the 4th ventricle of the brain control?

Is the fourth ventricle in the midbrain?