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Agenesis Corpus Callosum - spina bifida and hydrocephalus

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What is the corpus callosum?

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 fibres.

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 centre of the brain, measures around 10 centimetres (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.

What is Agenesis of the corpus callosum (ACC)

ACC is partial or complete absence of the corpus callosum. ACC can be found in a significant portion of people who have spinal open neural tube defects – i.e. those living with spina bifida myelomeningocele.

It was first recognized and documented in 1887 by John Langdon Down, a British physician best known for his description of the common genetic disorder that is now called Down Syndrome

What Causes Agenesis of the Corpus Callosum?

In many cases, the cause of agenesis of the corpus callosum cannot be identified. Known causes include:

• Chromosomal defects that affect fetal brain development

• Certain viral infections in the mother that pass to the developing baby

• Exposure of the unborn baby to certain toxins or medications

• Abnormal brain development caused by cysts

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

Symptoms of Agenesis of the Corpus Callosum

If there are no other brain development abnormalities, infants may have few, if any, significant difficulties in later life. New-borns with agenesis of the corpus callosum may not show symptoms right away, especially if they have no other associated conditions.

Common symptoms that may become more apparent during infancy and childhood can include an epileptic seizure, this is often the first sign of a brain dysfunction. In mild cases, however, the disorder can go undetected for some years.

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

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

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 behavioural

Particular social and behavioural 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 behaviour

ACC can occur as an isolated condition or in combination with other cerebral abnormalities, including Arnold-Chiari malformation, Dandy-Walker syndrome, schizencephaly (clefts or deep divisions in brain tissue), and holoprosencephaly (failure of the forebrain to divide into lobes.)

Girls may have a gender-specific condition called Aicardi syndrome, which causes severe cognitive impairment and developmental delays, seizures, abnormalities in the vertebra of the spine, and lesions on the retina of the eye.

ACC can also be associated with malformations in other parts of the body, such as midline facial defects.

The effects of the disorder range from subtle or mild to severe, depending on associated brain abnormalities. Children with the most severe brain malformations may have intellectual impairment, seizures, and hydrocephalus.

Other disorders of the corpus callosum include dysgenesis, in which the corpus callosum is developed in a malformed or incomplete way, and hypoplasia, in which the corpus callosum is thinner than usual.

Individuals with these disorders have a higher risk of hearing deficits and cardiac abnormalities than individuals with the normal structure.

Some people may have the following:

• deep-set eyes and a prominent forehead. An abnormally small head (microcephaly), or sometimes an unusually large head (macrocephaly), may be present

• tags of skin in front of the ears (pre-auricular skin tags)

• one or more bent fingers (camptodactyly)

• delayed growth has also been associated with some cases of agenesis of corpus callosum

• wide-set eyes (tele canthus)

• a small nose with upturned (anteverted) nostrils

• abnormally shaped ears

• excessive neck skin

• short hands

• diminished muscle tone (hypotonia)

• abnormalities of the larynx

• heart defects

• symptoms of Pierre-Robin syndrome may be present (a smaller than normal lower jaw, a tongue that falls back in the throat, and difficulty breathing)

Diagnosis of Agenesis Corpus Callosum ACC

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

• prenatal ultrasound

• computerized tomography (CT scan)

• MRI scan

Treatment of Agenesis Corpus Callosum ACC

There is no standard course of treatment for ACC. Treatment usually involves management of symptoms and seizures if they occur.

Associated difficulties are much more manageable with early intervention and therapy, especially therapies focusing on left/right coordination.

Early diagnosis and interventions are currently the best treatments to improve social and developmental outcomes.

Agenesis Corpus Callosum - spina bifida and hydrocephalus

Agenesis of corpus callosum can occur in conjunction with spina bifida - it is a related disorder. People with spina bifida myelomeningocele sustain a disruption of neuroembryogenesis (neural system development) that initiates a cascade of brain events that includes primary central nervous system (CNS) malformations such as agenesis corpus callosum and a secondary destructive process hydrocephalus (Detrait et al., 2005).

There are several conditions associated with the corpus callosum.

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

• fluid in the brain - hydrocephalus

• Chiari malformation

• deep clefts in brain tissue

• failure of the forebrain to divide into lobes

• disorders of neural migration – spina bifida myelomeningocele


To download this guide as a pdf, please click here.