Agenesis of the corpus callosum (ACC) is a rare birth defect in which there is a complete or partial absence of the corpus callosum. It occurs when the development of the corpus callosum, the band of white matter connecting the two hemispheres in the brain, in the embryo is disrupted. The result of this is that the fibers that would otherwise form the corpus callosum are instead longitudinally oriented along the ipsilateral ventricular wall and form structures called Probst bundles.
In addition to agenesis, other degrees of callosal defects exist, including hypoplasia (underdevelopment or thinness), hypogenesis (partial agenesis) or dysgenesis (malformation).
ACC is found in many syndromes and can often present alongside hypoplasia of the cerebellar vermis. When this is the case, there can also be an enlarged fourth ventricle or hydrocephalus; this is called Dandy–Walker malformation.
Signs and symptoms
thumb|450px|right|MRI images of three patients in the sagittal plane. A and B: Complete agenesis of the corpus callosum. C: Complete agenesis of both the corpus callosum and the [[anterior commissure.]]
Laboratory research has demonstrated that individuals with ACC have difficulty transferring more complex information from one hemisphere to the other. They also have been shown to have some cognitive disabilities (difficulty in complex problem solving) and social difficulties (missing subtle social cues), even when their intelligence quotient is normal. It has also been strongly associated with autism.
Other characteristics sometimes associated with callosal disorders include seizures, spasticity, early feeding difficulties and/or gastric reflux, hearing impairments, abnormal head and facial features, and intellectual disability.
- Aplasia of the cerebellar vermis
- Chiari malformation
- Colpocephaly
- Dandy–Walker syndrome
- Holoprosencephaly
- Hydrocephalus
- Neuronal migration disorders such as grey matter heterotopia
- Schizencephaly
Causes
Agenesis of the corpus callosum is caused by disruption to development of the fetal brain between the 3rd and 12th weeks of pregnancy.
Drug exposure
In utero exposure to cocaine, heroin, amphetamines and phenylpropanolamine can lead to agenesis of corpus callosum.
Diagnosis
Callosal disorders can be diagnosed through brain imaging studies or during autopsy. They may be diagnosed through an MRI, CT scan, Sonography, prenatal ultrasound, or prenatal MRI.