Corpus Callosum

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Corpus callosum is a large C shape white matter that divides the cerebral cortex into the right and left hemispheres. It is an essential part of the human brain, structurally as well as functionally. It forms the floor of the longitudinal fissure that separates the left and right hemispheres.

This thick band of nerve fibers allows the communication between both hemispheres. This part is responsible for transmitting sensory, motor, and cognitive information between both halves of the brain. It is the most extensive connective pathway in the brain, with 200 million axonal projections in the middle of two hemispheres. It occupies the center of the brain and almost 10 cm in length.

In this article, we will get a deep insight into etymology, gross anatomy, histology, and function and treatment of the corpus callosum. As well as, we will discuss the clinical significance of this critical brain organ.

Etymology

The word “Corpus Callosum” comes from the Latin word corpus meaning “body” and callosum, meaning “tough or hard.”

Location

The Corpus callosum is found under the cerebrum, resides within the interhemispheric fissure at the midline of the brain. The interhemispheric fissure is a deep furrow that separates the brain into left and right hemispheres.

Anatomical
Structure

Although the corpus callosum is seen as a single large white fiber bundle however, it is composed of four individual fibers known as commissural fibers. From anterior to posterior, the corpus callosum is divided into rostrum, genu, body/trunk, and splenium.

Rostrum

The rostrum is
continuous with lamina terminals and connects the orbital surfaces of frontal
lobes. It has a resemblance to a bird's beak; that why it's called rostrum.

Genu

The genu is an outgrowth of the anterior corpus callosum. A tract called “forceps minor” extends fibers from the genu and connects the lateral and medial surfaces of frontal lobes.

Body

The long central
section is called the body, and its fibers extend to the surface of the
hemispheres through the corona radiate.

Splenium

Forceps major project fibers from the splenium and connects the occipital lobes. This tact tapers away at the posterior section. A narrowed part between splenium and trunk is known as the isthmus.

 All white matter fibers project from the body or trunk while one fiber projects from the splenium but not included in the forceps major is called “tapetum.” It extends along the temporal and occipital lobes of the lateral ventricle.

However mostly
there are two types of connections homotopic and heterotopic

  • Homotopic
    connections connect the similar areas of the left side of the brain with the
    right side.
  • Heterotopic
    connections connect the different areas of both sides of the brain hemispheres.

 Histology

The corpus callosum always needs a constant and abundant blood supply to perform its functions. Infarcts uncommonly involve it. Mostly it gets its blood supply via pericallosal, the posterior pericallosal arteries, and branches from the anterior and posterior cerebral.

Besides, if it needs extra blood, then it receives blood from the anterior communicating artery via a median callosal artery or the subcallosal artery. How different fibers of corpus callosum get blood supply is described below. Have a look to know more about the histology of corpus callosum

  • The subcallosal artery is a large version of
    the hypothalamic branch, which supplies blood to the medial portions of rostrum
    and genu.
  • The posterior pericallosal artery or splenial
    artery is supplied blood to the splenium. However, its origin point is unknown
    and arising from P3 or branches thereof.
  • The median callosal artery is an extended
    version of the subcallosal artery and supplies the blood to the rostrum and
    genu but also reaches to the body of the corpus callosum.

Functions of Corpus Callosum

The primary purpose of the corpus callosum is to integrate the information by joining both cerebral hemispheres to process motor, sensory, and cognitive signals. It connects the similar areas of the brain and transmits the information across the left and right hemispheres.

For instance, rostrum and genu connect the frontal horns of right and left hemispheres while body and splenium connect the temporal and occipital lobes of both hemispheres. Similarly, by connected similar areas brings harmonization of their functions.

Besides, corpus
callosum plays a crucial role in eye movement and vision by connecting both
halves of the hemispheres of the visual field. This white matter nerve bundle
allows us to identify and see the objects by connecting the visual cortex in
brain language centers.

Additionally, Corpus callosum process the tactile information in the parietal lobes and transmit between the brain hemispheres to identify the touch.

Likewise, it helps in maintaining the balance of attention, arousal, and play a primary role in cognition. The study suggests that the weak integrity of corpus callosum causes a decline in cognitive function in adults.

On the flip side, an increase in callosum thickness helps in those brain areas development, which correlates with intelligence, problem-solving activities, and processing speed.

Clinical Significance

Corpus Callosum is a significant part of the brain and integrates and transmits information between the left and right hemispheres. Any defect in the corpus callosum leads to distraction in brain communication, which causes severe consequences.

 Agenesis of the corpus callosum has great
significance clinically, and it occurs under different subdivisions such as

  • Acquired Form of ACC
  • Andermann syndrome
  • X-Linked Dominant Inheritance ACC e.g., ARX
  • Aicardi Syndrome

AgCC is a rare congenital disorder in which partial or complete absence of corpus callosum occurs. Usually, this disease develops between the 3rd or 12th week of gestational life because, during this period, brain development of the fetus is at its peak. 

Causes

Agenesis of
corpus callosum (AgCC) occurs due to different factors such as genetic
inheritance, chromosome mutations, and parental infections.

Symptoms

Individuals with AgCC experience delay cognitive and communication development, difficulty in understanding social behaviors, chewing difficulty, hearing problem, vision impairment, low muscle tone, lack of movement coordination such as sitting or walking, seizures, spasms, and distorted head or facial features.

Diagnosis

Magnetic
resonance imaging (MRI) and Ultrasound techniques are used to diagnosis the
agenesis of the corpus callosum.

Aicardi
syndrome

Aicardi is an
x-linked inherited dominant syndrome, which occurs due to agenesis of the
corpus callosum, abnormal sys structure, and infantile spasms.  Only females affected by this disease;
however, it is a rare congenital disorder with frequent seizures, mental
retardation, abnormal choroid and retinal eye layers, and disconnection between
both hemispheres.

Andermann
syndrome

It is a genetic
disorder characterized by a combination of agenesis of the corpus callosum,
progressive sensorimotor nervous system disturbances, and mental
retardation. 

Disconnection
syndrome

If the connection between two hemispheres disrupts due to trauma, stroke, or brain surgery causes disconnection syndrome. In appearance, the patient seems perfectly normal to their family however some particular tests elicit the abnormalities

Corpus
callosum impingement syndrome

This syndrome occurs when corpus callosum impingements on the inferior end of the falx cerebri. It happens due to longstanding hydrocephalus. This syndrome results in Ischaemia and eventually causes atrophy.

 Other Disease of Corpus Callosum

  • Aside from above disorders, anterior corpus
    callosum lesions may cause akinetic mutism or anomic aphasia and other diseases
    such as
  • Septo-optic dysplasia (deMorsier syndrome)
  • Alien hand syndrome
  • Split-brain
  • Alexia without agraphia (damage to the
    splenium of corpus callosum)
  • Encephalopathy a mild form with a reversible splenial
    lesion– (A rare encephalopathy of unknown origin with a transient lesion in the
    splenium, mostly associated with infectious diseases)
  • Marchiafava–Bignami (A degenerative disease
    caused by loss of myelin and necrosis of the corpus callosum)
  • Multiple sclerosis with Dawson's fingers sign
  • Susac's syndrome ( Caused by lesions in the
    corpus callosum)

Treatment

The treatment is symptomatic and supportive therapies such as physical therapy, anti-seizure medications, and special education. When hydrocephalus is present in the patient, it may be treated by a surgical shunt which drains fluid from the brain cavity.

It lowers the increased pressure on the brain and recovers the patient. Genetic counseling is another method that helps families with this disorder.

Conclusion/Summary

The Corpus
Callosum is a white matter which connects the two halves of the hemispheres and
integrates the information between the left and right side of the brain. It
lies superficial to the fornix and deep to the cingulate gyrus. It is connected
anteriorly with fornix by septum pellucidum.

Corpus callosum
comprised of several nerve tracts that connect different parts of the
hemispheres. The central part of the corpus callosum is rostrum, genu, body,
and splenium.

It gets its blood supply from different branches, such as from the median callosal or subcallosal artery branches, from the posterior pericallosal artery, from the pericallosal artery. It involves several body functioning; most importantly, it plays a role in communication between brain hemispheres. Other functions of corpus callosum include tactile localization, maintaining the balance of arousal and attention, and controlling eye movement and vision.

Complete or
partial absence of corpus callosum causes many neural defects and affects the
child's brain development. Agenesis of the corpus callosum is a rare congenital
disorder but gives a wide range of symptoms such as impaired hearing, lack of
movement, vision loss, and seizures.

Contrastingly,
corpus callosum impingement syndrome results from long term hydrocephalus but
does not show any symptoms.

Supportive
therapies and anti-seizure medications are used to treat the agenesis of corpus
callosum and related disorders.

References

  1.  Velut, S; Destrieux, C;
    Kakou, M (May 1998). "[Morphologic anatomy of the corpus
    callosum]". Neuro-Chirurgie. 44 (1 Suppl):
    17–30. 
    PMID 9757322.
  2. ^ "Corpus
    callosum"
    . Queensland Brain
    Institute. 10 November 2017.
  3. Jump up to:a b Luders,
    Eileen; Thompson, Paul M.; Toga, Arthur W. (18 August 2010). 
    "The Development of
    the Corpus Callosum in the Healthy Human Brain"
    . Journal
    of Neuroscience. 30 (33): 10985–10990. 
    doi:10.1523/JNEUROSCI.5122-09.2010PMC 3197828PMID 20720105.
  4. Jump up to:a b c Gaillard,
    Frank. 
    "Corpus callosum |
    Radiology Reference Article | Radiopaedia.org"
    . radiopaedia.org.
  5. ^ Carpenter,
    Malcolm (1985). Core text of neuroanatomy (3rd ed.). Baltimore:
    Williams & Wilkins. pp. 26–32. 
    ISBN 978-0683014556.
  6. ^ Ropper,
    A.; Samuels, M.; Klein, J. (2014). Adams and Victor's Principles of
    Neurology(10th ed.). McGraw-Hill. p. 798. 
    ISBN 978-0071794794

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