Frequently Asked Questions


What is the Corpus Callosum?

The Corpus Callosum is a connection between the right and left sides of the brain, which contains many brain cells (neurones). It has the shape of an arch, and is approximately 10 centimetres long in adults.

How does it develop?

The Corpus Callosum is formed between the 7th and 13th weeks of the pregnancy, but its growth and development continue until later in the pregnancy. During its formation, brain cells ‘migrate’ across the area between the two cerebral hemispheres, and form connections with brain cells on the other side.

The development of the corpus callosum takes place at a time when many other brain structures are also developing.

What does the Corpus Callosum do?

The brain cells in the Corpus Callosum send messages between the two halves of the brain (cerebral hemispheres). The Corpus Callosum is the largest such connection between the cerebral hemispheres, but there are also other connections. Learning, co-ordinated movements and memory all require connections between the cerebral hemispheres.

What causes abnormal development of the Corpus Callosum?

There are several possible causes. They are most likely to have their effect during the 7th to 13th weeks of the pregnancy when the Corpus Callosum is being formed. ‘Migrating’ brain cells may lack the chemical messengers which guide them in the right direction. This can occur because of a genetic disorder.

Migrating nerve cells may be prevented from reaching their destination. This can occur because of lack of oxygen, lack of nutrients, toxic chemicals, infection or a metabolic disturbance.

How often does it happen?

Nobody is certain. An estimate is around 1 per 20,000 births.

What do the terms ‘agenesis’ and ‘dysgenesis’ mean?

  • Agenesis = failure to grow (implying that an organ is absent)
  • Dysgenesis = abnormal growth (too small; misshapen; or with a part missing)

What other abnormalities of development can occur along with callosal agenesis?

In some individuals with agenesis of the Corpus Callosum, nothing else abnormal will happen. In others, the following can occur:

Other brain malformations (including brain cells elsewhere which have not 'migrated' to the right place). Maldevelopment of gut and kidneys. Maldevelopment of eyes, nerves, muscle.

Agenesis of the Corpus Callosum may be part of a syndrome (a number of abnormalities which occur in many different individuals in a similar fashion). In some cases it may be the result of a chromosome abnormality.

What are the consequences of Agenesis of the Corpus Callosum?

The consequences vary hugely between different individuals. The effects on any individual are very dependant on other brain abnormalities, rather than being entirely the result of not having a Corpus Callosum.

The consequences include:

  • Epilepsy
  • Learning difficulties (general or specific)
  • Impaired co-ordination and motor development
  • Behavioural difficulties
  • Abnormal temperature regulation and growth.

In one survey of 56 cases in Britain: nearly two thirds had epilepsy, half had intellectual impairment, a third had a psychiatric disorder, nine cases were apparently normal neurologically.

What can be done about it?

It is not possible to repair or replace the Corpus Callosum. Most of what can be done is directed to identifying the medical, physical and educational consequences and providing the correct treatment, therapy and education for these;

  • Treatment of epilepsy
    • Anti-epileptic drugs
    • Steroids
    • Ketogenic diet
  • Recognition and management of learning difficulties
  • Management of co-ordination and motor developmental disorders.

Is there prenatal diagnosis?

This can be done using ultrasound. The Corpus Callosum cannot be visualised before midgestation, but diagnosis of Agenesis of the Corpus Callosum is very accurate after 20 weeks.

Aicardi syndrome

  • This condition affects girls (almost exclusively)
  • There is agenesis of the Corpus Callosum (in most cases)
  • The retina of the eyes is abnormal
  • There are other brain abnormalities (cysts, collections of cells which have not migrated properly)
  • Many girls have infantile spasms (a form of epilepsy often starting at around 6 months of age)
  • Most have severe learning difficulties
  • In a Canadian survey of girls with Aicardi syndrome: 3 of the 14 girls could walk or crawl and 4 girls had some language ability.

Outline from Dr Carlos de Sousa who gave a talk to a group of parents and carers - May 1999 at Great Ormond Street Hospital for Sick Children.