Fourth Ventricle of the Brain

Overview:

We owe so much to our brain, as it is responsible for numerous functions that take place inside our bodies. Hence, it needs to be protected from injuries and damage.

The ventricular system is vital to the proper operation of the central nervous system. It protects the brain by permitting it to ‘submerge’ in a liquid bath and acts as a shock absorber in the event of a head injury.

There are four cavities inside the brain known as ventricles. The ventricular system is made up of the right and left lateral ventricles, as well as the third and fourth ventricles.

In this article, the structural components, functions, and complications involving the fourth ventricle of the brain are explained.

Summary:

• This ventricle’s primary job is to safeguard the human brain from injury (with the help of a cushioning impact) and to aid in the formation of the central canal, which spans the course of the spinal cord
• There is a roof, lateral walls, and a floor to the fourth ventricle
• The cerebellum, situated close to the back of the brain, forms the roof, and the rhomboid fossa, a depression in the brainstem, forms the floor
• The floor contains the facial colliculus, sulcus limitans, and obex.
• Tumours, medulloblastomas, hydrocephalus are some complications that involve the 4th ventricle

Location:

The fourth ventricle is located anterior/ventral to the cerebellum and posterior/dorsal to the pons and medulla that form the brainstem. It runs on the superior side from the cerebral aqueduct (also referred to as the aqueduct of Sylvius) to the central canal of the brainstem and spinal cord (Figure 1) Its base is bordered with a boundary of epithelial cells known as the ependyma and is surrounded by cerebrospinal fluid (CSF).

The fourth ventricle, like other parts of the ventricular system within the brain, originates from the central canal within the neural tube (the component in an embryo that becomes the brain and spinal cord). The ventricles form during pregnancy during the first 3 months. 

During this development stage, excess supply of cerebrospinal fluid (CSF) can restrict circulation, resulting in a disorder known as hydrocephalus.

Structure:

One of the interconnecting chambers of the human brain that are filled with fluid is the fourth ventricle. We have already mentioned that there are four of these chambers or spaces inside the brain, out of these four; three are found within the cerebrum. These are the third ventricle and the lateral ventricles. The ventricular system of the brain is made up of several chambers and their contents.

The fourth ventricle contains an anterior/ventral bottom surface with a distinctive diamond form known as the rhomboid fossa, as well as a posterior/dorsal canopy that is in a tent-like shape.  Cerebrospinal fluid (CSF) manufactured and/or entering into the fourth ventricle can escape to the subarachnoid area via lateral apertures and a singular median aperture in the roof’s inferior part.

Given below are details of the structural components that exist and help shape the fourth ventricle of the brain (Figure 2).

1) The fossa of the fourth ventricle:

As the cerebral aqueduct keeps on prolonging there is a visible structure that can be observed, and it is how the cavity or fossa of the fourth ventricle interacts on the superior end with the third ventricle. The obex is the inferior section of the hollow space that reaches into the central canal of the brainstem, which passes through the vertebral column. The fossa also connects with the subarachnoid area via the three openings or apertures that will be mentioned later on in this article. 

2) Choroid plexuses and Tela choroidea:

Additional important characteristics of the fourth ventricle are the tela choroidea and choroid plexus. Two components or layers of pia mater make up the tela choroidea. The choroid plexus is a very dense vascular tissue that resembles the lateral and third ventricles in its structural arrangement. It is found within the creases of the pia mater that make up the tela choroidea.

These structural components are in charge of producing cerebrospinal fluid (CSF), which serves numerous functions:

• provides nutrition for the brain
• occupies the subarachnoid region as well as the ventricles
• waste material from the brain is removed and collected by the arachnoid villi
•  has a neuroprotective effect on the brain

3) The bottom layer or floor surface of the fourth ventricle:

Since most of the time, the shape and appearance of a structural unit help biologists in naming them, the bottom of the fourth ventricle is known as the rhomboid fossa due to this very same reason.   The posterior median sulcus divides it into two halves, the left half and the right half, while the striae medullares divide it into a triangle type shape, which is seen as a superior and an inferior triangle.

The posterior portion of the pons forms the higher triangular section.

The bottom triangular region is made up of the upper portion of the medulla’s posterior layer and an intermediate portion at the medulla-pons intersection.

As the bottom of the lateral recess, the intermediate section is extended laterally over the inferior cerebellar peduncle. The appearance of tiny crystals on its exterior distinguishes it.

Its texture is distinguished by the presence of thin bundles of transversely running fibres known as striae medullares.

The calamus scriptorius is the bottom-most section of the floor of the fourth ventricle. Taenia is a small white elevation that runs along the inferolateral edge of the floor. The right and left taeniae converge at the floor’s lower apex to form a tiny fold.

The topmost part of the sulcus limitans forms the upper part a region known as the locus coeruleus, within which is a nucleus known as the nucleus coeruleus, which extends into the pontine tegmentum. The superior fovea is a groove located directly beneath the sulcus limitans. The median eminence reveals a bulge termed the face colliculus at the degree of this depression.

The median sulcus is utilized as a primary characteristic to describe the bottom surface of the fourth ventricle. The medial eminence is a longitudinal rise or protrusion on each side of the sulcus. The sulcus limits this prominence laterally. The vestibular nuclei are housed in this location, which is known as the vestibular region. As a result, the vestibular area is located in both the pons and the medulla.

The sulcus limitans are distinguished by a dip, the inferior fovea, in the medullary region of the surface. An oblique sulcus runs inferior to this inferior fovea, splitting the medial eminence into two structures that are in the shape of a triangle, and they are called the hypoglossal and vagal triangles (or referred to as the hypoglossal and vagal trigones). The hypoglossal triangle is located medially, and the vagal triangle is located laterally. 

The hypoglossal and vagal nuclei are housed in these triangles. The region postrema is defined by the vagal triangle and the gracile tubercle.

4) The top surface or the ‘roof’ of the fourth ventricle:

The ceiling or the top layer of the fourth ventricle features a tent-like peak where its superior and inferior sections meet. This peak also called the fastigium, continues into the cerebellum’s white center. The superior cerebellar peduncles and superior medullary velum constitute the superior section of the roof (thin layer of white matter).

The tela choroidea of the fourth ventricle, like the rest of the fourth ventricle, is bordered with a membrane composed of the ependyma and a double fold of the pia mater. This membrane stretches lateral to the middle line area and connects to the inferior cerebellar peduncles. The foramen of Magendie is a big orifice in the lowest section of the membrane. 

This is the fourth ventricle’s median aperture, through which the complete ventricular system interacts with its components. 

5) The Lateral walls of the fourth ventricle:

The cerebellar peduncles constitute the lateral walls of the fourth ventricle. As it can be assumed, the superior cerebellar peduncle forms the superior section of these lateral walls. The inferior cerebellar peduncle, as well as the gracile and cuneate tubercles of the brainstem, composes the inferior portion.

It features two large projections called lateral recesses, one on each side of the middle line. These lateral recesses stretch laterally between the inferior cerebellar peduncle and the peduncle of the cerebellar flocculus, opening into the subarachnoid region as the lateral apertures (foramina of Luschka).

6) The Cavity of the fourth ventricle:

As an extension of the cerebral aqueduct, the cavity or fossa of the fourth ventricle interacts superiorly with another ventricle, which is the third ventricle. The obex is the lower section of the cavity that reaches into the central canal of the brainstem, which passes through the spinal column. The cavity also connects with the subarachnoid region via the three previously stated openings.

Function:

The brain and spinal cord are unquestionably vital structures of the nervous system, and they must be safeguarded. They are encased in a clear fluid known as cerebrospinal fluid (CSF). It protects the brain and spinal cord from damage and other types of harm, and it also functions as the brain’s nutrient transfer and waste collection framework. It is produced mainly in the ventricles of the brain.

Cerebrospinal fluid (CSF) is primarily made in the ventricles of the brain.

CSF is produced in the ventricles of the brain. The lateral ventricles are the central nervous system’s biggest and most proximal ventricles (CNS). The lateral ventricle CSF enters the interventricular foramen of Monro. The Monro’s foramen interventricularis connects the lateral ventricles to the third ventricle.

Through the cerebral aqueduct of Sylvius, the third ventricle links to the fourth ventricle. CSF travels through this complete route before exiting the fourth ventricle and entering the neighbouring Central nervous system cells or the central spinal canal.

This ventricle’s primary job is to safeguard the human brain from injury (via a cushioning impact) and to aid in the formation of the central canal, which spans the course of the spinal cord.

Complications involving the ventricles of the brain:

Medulloblastoma: Medulloblastoma has to be the most frequent type of malignant brain tumour in kids, and it develops in the cerebellum, where it can harm the roof structural component of the fourth ventricle. The region postrema of the caudal part of the fourth ventricle is also clinically significant known for its role in vomiting management.

Medulloblastomas are by far the most frequent type of juvenile malignant brain tumour. They typically manifest as middle line lumps or aggregates in the roof of the fourth ventricle, with accompanying mass impact and hydrocephalus. Therapy or treatment management normally comprises of surgical resection, radiation therapy, and chemotherapeutic management, with surgical resection and the existence of Cerebrospinal fluid (CSF) metastases at the point of surgery and activation of the c-erbB-2 (HER2/neu) oncogene all having a major influence on prognosis.

Medulloblastoma is the most frequent intracranial tumour in children; with complete treatment, five-year OS is now greater than eighty percent. Only a few pieces of research have looked into the relationship between tumour site and patient prognosis.

Even though medulloblastoma has traditionally been viewed as a singular entity, it may become abundantly evident that there are a variety of discrete genetic subgroups with clinical, morphological, and imaging characteristics that crossover. 

Tumours of the fourth ventricle: Tumours of the fourth ventricle in kids present a unique surgical difficulty due to the area’s closeness to articulate neuronal parenchyma. The dentate nuclei and superior cerebellar peduncle are major aspects of the efferent cerebellar route in the walls and ceiling of the fourth ventricle, while the bottom surface of the fourth ventricle, created by the brainstem, includes many cranial nerve nuclei.

Throughout Cushing’s time at the beginning of the twentieth century, in the 1920s to be more accurate, surgical treatment of tumours inhabiting or infiltrating the fourth ventricle has been accomplished by a direct transvermian approach. The telovelar method, initially published in 1992, takes advantage of the natural passage from the cisterna magna to the fourth ventricle along the cerebellomedullary fissure, so avoiding violation of the cerebellar vermis.

This may have a part in the growth of postoperative truncal ataxia and cerebellar mutism syndrome (CMS). Descriptions and accounts of neurological complications after fourth ventricle tumour removal are mostly limited to small paediatric or joint adult and paediatric series, and they represent patient groups that are varied in terms of preoperative comorbidities, tumour placement inside the posterior fossa, and tumor grade and its histology.

Hydrocephalus: One of the disorders that might develop from an obstruction of the median and lateral apertures is a condition known as hydrocephalus. The medulla and tonsils of the cerebellum drop down through the foramen magnum to lay in the spinal canal in Arnold Chiari malformation (Type II Chiari malformation). This disorder closes the median and lateral openings, causing Cerebrospinal fluid (CSF) flow to be obstructed. 

This results in a form of hydrocephalus known as internal hydrocephalus. Chiari II can also cause syringomyelia attributed to the generation of a Cerebrospinal fluid (CSF)-filled cyst or syrinx.

Dandy-Walker syndrome (DWM): Dandy-Walker syndrome (DWM) is distinguished by a cystic expansion of the fourth ventricle and agenesis or hypoplasia of the cerebellar vermis. The majority of people will have hydrocephalus; however, it is often medically asymptomatic for long periods. 

It can occur alone or in conjunction with Mendelian disorders, syndromic deformities, chromosomal abnormalities, and congenital illnesses. Holoprosencephaly, neural tube abnormalities, and corpus callosum dysgenesis are all CNS illnesses associated with Dandy-Walker syndrome (DWM).

Fourth ventricle outlet obstruction (FVOO): A kind of non-communicating hydrocephalus known as fourth ventricle outlet obstruction (FVOO) arises when there is a separation between the subarachnoid space and the ventricular system. Because this is the distal-most ventricle, swelling of the whole ventricular system will happen as a consequence of a tumour or cyst obstructing the lateral or median openings.

Inflammatory mechanisms following a haemorrhage, viral illness, or congenital defects of the fourth ventricle are also common causes. Additional investigations, like those on a three-dimensional constructive interface in steady-state (3D-CISS), are frequently needed to treat fourth ventricle outlet obstruction (FVOO).

Conclusion:

There is a roof, cavity, Choroid plexuses, Tela choroidea, lateral walls, and a floor to the fourth ventricle. The cerebellum, situated close to the back of the brain, forms the roof, and the rhomboid fossa, a depression in the brainstem, forms the floor. The floor contains the facial colliculus, sulcus limitans, and obex. This ventricle’s primary job is to safeguard the human brain from injury (via a cushioning impact) and to aid in the formation of the central canal, which spans the course of the spinal cord. Tumours, medulloblastomas, hydrocephalus are some complications that involve the 4th ventricle.

Further Reading

The Lateral Ventricle of the Brain

Reference list

• https://www.kenhub.com/en/library/anatomy/the-fourth-ventricle (2021), 19 July (Accessed: 19 July 2021).
• Gaillard, F. (2021) Medulloblastoma | Radiology Reference Article | Radiopaedia.org, 19 July. Available at: https://radiopaedia.org/articles/medulloblastoma (Accessed: 19 July 2021).
• Roesch, Z.K. and Tadi, P. (eds.) (2020) StatPearls [Internet]: StatPearls Publishing.
• Toescu, S.M. et al. (2020) ‘Fourth ventricle tumors in children: complications and influence of surgical approach’, Journal of Neurosurgery. Pediatrics, 27(1), pp. 1–10. doi: 10.3171/2020.6.PEDS2089