***Note to Andrew: I've started editing on here but I'll download this and put it on a word doc it and send it to you when it's complete. Maybe  the headings could be a set of links to the information and some words hyperlinked to the glossary of 'words you might hear'. e.g. heterogeneous

What is the corpus callosum?

The corpus callosum is a bundle of more than 200 million nerve fibres that form the major pathway connecting the two hemispheres of the brain.  Its primary function is to transfer information for motor, sensory and cognitive activity between the left and right hemispheres

The corpus callosum forms in the early part of the development of a foetus, 12 -16 weeks into a pregnancy.  The entire structure is developed at birth but continues to thicken after birth becoming more effective and efficient.  By around the age of 12, the  corpus callosum is basically functioning as it will in adulthood.

Although the corpus callosum is the major path between the hemispheres, other smaller connections do exist.  The anterior commissure has about 50 thousand nerve fibres and the posterior commmissure and hippocampal commissure are smaller again.

When looking at a side profile, cross section (sagittal) radiology image, the corpus callosum is the white, almost horse shoe shaped, piece. [PHOTOS}

What is a Corpus Callosum Disorder (CCD)?

A Corpus Callosum Disorder (CCD) is a rare, congenital, neurological condition. CCDs are highly heterogeneous in cause and presentation, with impacts ranging from mild to severe. Although research around corpus callosum function and congenital anomalies continues to discover new and more accurate information about the causes and impacts of CCDs, accurate prognosis can be difficult.

AusDoCC has adopted CCD/s (Corpus Callosum Disorder/s) as the umbrella term to describe all the conditions in which the corpus callosum fails to develop typically, in utero. The corpus callosum may be misshapen, completely or partially absent or thinner/thicker than is typical. You may also hear DCC (disorder of the corpus callosum or dysgenesis of the corpus callosum), ACC/AgCC (complete agenesis of the corpus callosum), pACC (partial agenesis of the corpus callosum), HCC (hypoplasia of the corpus callosum or hyperplasia of the corpus callosum). Terminology may vary depending on the clinician, researcher and country.

A CCD is a congenital abnormality of the brain and is not a disease or an illness.

If the Corpus Callosum  fails to develop during the first part of the pregnancy, it will not develop later.  If the Corpus Callosum has formed partially or thinly it will not regress.

Types of CCDs 

Corpus Callosum Development Descriptive terms Common abbreviations
Missing entirely/ absent

·    Agenesis of the Corpus Callosum

·   Complete Agenesis of the Corpus Callosum

·   ACC

·   C-ACC

·   AgCC

·   C-AgCC

 Incomplete/partially absent/malformed

·    Agenesis of the Corpus Callosum

·   Partial Agenesis of the Corpus Callosum

·   Hypogenesis of the Corpus Callosum

·   Dysgenesis of the Corpus Callosum

·    ACC

·   P-ACC

·   AgCC

·   P-Agcc

 Present Corpus Callosum but significantly thin ·    Hypoplasia of the Corpus Callosum ·    HCC

Agenesis of the Corpus Callosum

Agenesis of the Corpus Callosum (ACC) means that during the early weeks of in-utero development, the corpus callosum completely or partially failed to develop.  

Partial agenesis describes (pACC) missing part of the corpus callosum.

Hypoplasia of the Corpus Callosum

Hypoplasia from the Greek  – 'Hypo' meaning under and 'Plasis' meaning formation.

Hypoplasia of the corpus callosum means that during the early weeks of development the Corpus Callosum has formed but it is underdeveloped and thinner than usual.

*(ANDREW _ BOLD) Hyperplasia of the Corpus Callosum

Hyperplasia of the Corpus Callosum occurs when the corpus callosum is thicker than usual.

Dysgenesis of the the Corpus Callosum

Dysgenesis means defective or abnormal development of an organ, in this case the corpus callosum.

Corpus Callosum Dysgenesis (CCD) means that the corpus callosum has developed in some incomplete or 'abnormal' way.

Dysgensesis can also be used as a broad, general term for  the various types of Corpus Callosum Disorders (CCD) including complete, partial or hypo/hyperplasia.

There is little research available that shows the effects of the different types of disorders will have on a person.  When we refer to “disorders" and the effects we are covering all the above. The term 'disorders' refers directly to the corpus callosum and does not describe the person with the diagnosis.

What Causes a CCD?

Most CCDs are believed to be of genetic origin causing abnormalities in the structure of chromosomes or the genes within them. They may be inherited or a new mutation (de-novo). As of 2023, scientists have discovered more than 400 genes causing a congenital corpus callosum anomaly. Global research continues to examine this area. With a genetic cause, other organs may also be affected. There are many syndromes that include corpus callosum anomalies such as Aicardi syndrome or Andermann syndrome. 

Other possible (non-genetic) causes may be: 

– environmental, such exposure of the foetus to toxins or infections, for example, alcohol consumption

– a hindrance or blockage of the corpus callosum formation caused by a growth of a cyst.

For some there will never be an answer to the question, which can be frustrating for parents, researchers and clinicians. 

Over the years in discussions with other parents a variety of anecdotal suggested 'causes' has been put forward, from painting a room to taking a particular medicine to a mother’s health. While some will speculate on what has caused the disorder, research continues to give us some more accurate answers, albeit slowly. 

How is it Diagnosed?

A Corpus Callosum Disorder (CCD) may be diagnosed with neuroimaging (scans, magnetic resonance imaging (MRI) in utero or at some point after birth. For some a MRI is conducted due to developmental delays and looking for answers.  For others it could be incidentally after unexplained headaches or head injuries at any life stage. Many people diagnosed as adults often discover a diagnosis that gives perspective to unexplained past issues. 

It is also being diagnosed before during an prenatal ultrasound, where enlarged ventricles can point to other problems or a specific problem with the Corpus Callosum is seen.  This can be followed up by a MRI on the developing baby and further screening after the baby is born.

A baby who ends up in the Neonatal Intensive Care Unit will as part of their stay have a head ultrasound done and the disorder can be picked up at this point.  Further imaging will be needed to confirm the exact disorder.

How common is it?

A Disorder of the Corpus Callosum is a rare congenital birth defect.  It is hard in Australia to give any sort of figures to say how common it is, to our knowledge, no real statistics have been kept.   The statistics from the USA suggest that it could be around 1 :4000 births.

Other Issues:

– A DCC can occur alone, with other abnormalities or as part of a syndrome,

– DCCs affect individuals very differently with the range of impact being anywhere from mild (such as normal development with some difficulties in higher cognitive processes) right through to severe disability (such as intellectual disability/ cerebral palsy),

– More commonly documented difficulties and secondary conditions include; developmental delay, seizures, disorders in emotion or behaviour regulation, high pain tolerance, autism, cerebral palsy, learning impairments and social difficulties,

– Early intervention services are recommended for children diagnosed with a DCC.

Management guidelines for professionals can be found HERE

Resources for people with a CCD, parents and families can be found here