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At a glance

A neuronal migration disorder characterized by partial or complete agenesis of the corpus callosum.

Incidence

Corpus callosum agenesis (CCA) is the most common cerebral malformation. It has an estimated prevalence of approximately 1.8:10,000 in the general population and accounts for about 2 to 6% of children with developmental disabilities.

Genetic inheritance

Agenesis of the corpus callosum has been associated with several chromosomal rearrangements. These include autosomal dominant, autosomal recessive, and X-linked inherited syndromes.

Pathophysiology

Unknown. The corpus callosum is the largest fiber tract in the brain, and by connecting the two cerebral hemispheres with each other it enables the integration of neural information from either side of the brain and body. The etiology of CCA is unknown, but one theory considers an insult to the commissural plate during embryogenesis that interferes with the migration of the cells that form the corpus callosum. This insult can be a result of chromosomal abnormalities, be part of a syndrome, a migration, or a metabolic disorder. CCA may be an isolated anomaly or part of a syndrome with other, more extensive malformations or metabolic or genetic disorders. The corpus callosum is formed between the seventh and twentieth weeks of gestation. Consequently, partial or complete CCA may occur if this process is disrupted. Major parts of the cortex and cerebellum develop at the same time, therefore associated anomalies must always be excluded. As a rule, formation of the corpus callosum starts in the front and proceeds posteriorly (holoprosencephaly is the main exception to this rule), which explains why partial callosal agenesis usually involves the posterior portion of the corpus callosum.

Diagnosis

Based on the clinical findings in children undergoing extensive examination for epilepsy, cognitive impairment, or, less often, behavioral problems. CT- or MRI-imaging confirms the absence of the corpus callosum. Frequently, there is also upward displacement and enlargement of the third ventricle (because the corpus callosum normally forms the roof of the third ventricle), widely spaced dorsal horns, and possible evidence of other migration disorders. Antenatal diagnosis is possible, but ultrasound is considered a poor modality in diagnosing CCA and an in-utero MRI-scan should be performed instead.

Clinical aspects

The most common symptoms of CCA are delayed motor and cognitive functions, epilepsy, and deficits in social and language skills. Clinically and prognostically, CCA can be divided into two types. Type I is not associated with other disorders. Patients may have mild-to-moderate mental retardation and no or only mild neurologic manifestations, which may include seizure disorders and impaired visual, motor, and coordination skills. A peculiar facies with prominent forehead, macrocephaly or microcephaly, deep-set eyes, and preauricular skin tags is common. However, some patients have no clinical signs, which makes parental counseling difficult in the absence of radiologic and genetic markers allowing ...

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