The corpus callosum connects the left side of the brain to the right side, each side being known as a hemisphere. The connection allows information to pass between the two halves.

Corpus callosum is Latin for "tough body," and the corpus callosum is the largest connective pathway in the brain, being made up of more than 200 million nerve fibers.

Very occasionally, a person will be born without a corpus callosum. This is known as agenesis of the corpus callosum, and it causes a wide variety of physical and behavioral symptoms.

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The corpus callosum (red part of the brain) is the connective pathway that connects the left to the right side of the brain.

Each side of the brain controls movement and feeling in the opposite half of the body. The hemispheres also process information, such as language.

Therefore, physical coordination and taking in complex information requires both sides of the brain to work together. The corpus callosum acts as the connector.

The corpus callosum sits in the center of the brain, measures around 10 centimeters (cm) in length, and is shaped like the letter "C."

Typically, the corpus callosum will form in the brain between 12 and 16 weeks after conception and near the end of the first trimester of pregnancy.

It will continue to develop throughout childhood. By the time a child is 12 years old, their corpus callosum will have finished developing. It will then remain unchanged into adulthood and throughout the rest of their life.

Until the 1950s, the exact function of the corpus callosum was unknown. In 1955, Ronald Myers, a graduate student at the University of Chicago, proved its function was related to coordination and complex problem-solving.

Some children are born without a corpus callosum. This leads to a rare disorder known as agenesis of the corpus callosum, which is estimated to affect around 1 in 3,000 people. The corpus callosum can also be damaged.

Disruptions to the development of the corpus callosum can occur between the 5th and 16th week of pregnancy.

While there is no certain cause, possible factors include:

  • prenatal infections or viruses, such as rubella
  • genetic abnormalities, such as Andermann or Aicardi syndromes
  • toxic metabolic conditions, such as fetal alcohol syndrome (heavy drinking or alcoholism during pregnancy)
  • something preventing the corpus callosum from growing, such as a cyst in the brain

Corpus callosum problems can also be due to a recessive genetic disorder. This means that parents can be carriers of the gene that causes the disorder, but not have the disorder themselves.

A child with two carrier parents has a 25 percent chance of having problems with the corpus callosum. Also, they have a 50 percent chance of becoming a carrier themselves. Both males and females are affected equally.

However, the increased use of scanning technology, such as magnetic resonance imaging (MRI), means that more children might receive a diagnosis in the future.

While its presence is not essential for survival, those who have problems with the corpus callosum will often fall behind their peers in development.

Children with agenesis may be blind, deaf, or never learn to walk or talk, while others can be very high-functioning.

"High-functioning" is a term often associated with autism. It is used when an autistic person has strong verbal skills and a disproportionally high IQ level.

A disorder of the corpus callosum is not a disease or illness in itself. Many people with agenesis of the corpus callosum lead healthy lives.

However, it can also lead to medical problems, such as seizures, which require medical intervention.

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Fluid in the skull, which is known as hydrocephalus, can be caused by agenesis of the corpus callosum.
Image credit: Bright, R., Longman, Rees, Orme, and Green, 1827.

There are a number of conditions associated with the corpus callosum.

Agenesis of the corpus callosum can sometimes cause other brain abnormalities. These include:

  • fluid in the skull, known as hydrocephalus
  • Arnold-Chiari malformation
  • deep clefts in brain tissue
  • failure of the forebrain to divide into lobes
  • disorders of neural migration

Syndromes associated with agenesis include:

  • Aicardi
  • Andermann
  • Shapiro
  • Acrocallosal
  • Menkes
  • Mowat-Wilson
  • FG

Agenesis of the corpus callosum can also happen in conjunction with spina bifida. The condition known as spina bifida is when the spine does not fuse properly, leaving a defect in the spinal canal.

Agenesis of the corpus callosum is usually diagnosed within the first 2 years of a person's life.

An epileptic seizure is often the first sign of a brain dysfunction. In mild cases, however, the disorder can go undetected for some years.

A brain scan is required to confirm problems with the corpus callosum. These tests can include:

Research about callosal disorders is ongoing. But there are some common features of agenesis of the corpus callosum, although they vary from person to person.

They can be broken down into four categories:

Physical

Physical or health-related characteristics include:

  • vision impairments
  • low muscle tone
  • difficulty feeding
  • abnormal head and facial features
  • high tolerance to pain
  • problems sleeping
  • seizures
  • hearing impairments
  • chronic constipation

Cognitive

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Agenesis of the corpus callosum may include difficulty with problem solving.

Cognitive characteristics include:

  • problems reading facial expressions or voice tone
  • difficulty with problem-solving and complex tasks
  • lack of ability in assessing risk
  • difficulty understanding abstract concepts
  • problems understanding slang or sarcasm
  • difficulty understanding emotions
  • giving untrue information but believing it is true

Development

Developmental characteristics include:

  • delays in milestones, such as sitting, walking, riding a bike
  • delays in speech and language acquisition
  • clumsiness and poor coordination
  • delayed toilet training

Social and behavioral

Particular social and behavioral characteristics include:

  • social immaturity
  • lack of self-awareness
  • difficulty understanding social cues
  • problems understanding others' perspectives
  • finding it hard to maintaining attention
  • hyperactivity
  • lack of fear
  • obsessive or compulsive behavior

If the corpus callosum has not grown properly during fetal development, then it never will. There is no direct treatment for agenesis of the corpus callosum. Symptoms will be identified and potentially treated, as they occur.

Treatment is available for many of the medical conditions associated with agenesis of the corpus callosum, such as seizures. Therapy and counseling can also help to improve language and social skills. A doctor will be able to outline all of the treatment options available in individual cases.