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A disorder of neuronal migration characterized by
partial or complete agenesis of the corpus callosum.
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Corpus callosum agenesis (CCA) is the most common
cerebral malformation. It has been estimated that 0.05 to 0.7% of the
general population and 2.3% of children with developmental disabilities
are affected.
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Agenesis of the corpus callosum has been
associated with several chromosomal rearrangements. These include autosomal
dominant, autosomal recessive, and X-linked inherited syndromes.
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Unknown. An insult to the commissural plate during
embryogenesis interferes with 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
gestational weeks 7 and 20. Consequently, partial or complete CCA may occur
if this process is disrupted. Because major parts of the cortex and
cerebellum develop at the same time, associated anomalies must always be
excluded. As a rule, formation of the corpus callosum starts in the front
and continues to the back (holoprosencephaly is the main exception to this
rule), which explains why partial callosal agenesis usually involves the
posterior portion of the corpus callosum.
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Based on the clinical findings in children undergoing
extensive examination for epilepsy, cognitive impairment, or, less often,
behavioral problems. Computed tomography or magnetic resonance 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.
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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 determination of future asymptomatic from symptomatic disease.
Type II is associated with other migration, genetic, and chromosomal abnormalities,
usually resulting in severe neurologic manifestations, which may include
severe mental retardation, microcephaly, hemiparesis, spasticity, seizure
disorder, and failure to thrive. This condition often is accompanied by
recurrent bronchopneumonia and, in the severest cases, early death in
infancy.
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Check for associated abnormalities,
particularly metabolic disorders. Assess for complications such as seizures,
paralysis, and bronchopneumonia. Preoperative investigations should include
a chest radiograph, pulmonary function tests (if possible), and arterial
blood gas analysis. Assess for difficult airway management in case of
microcephaly. Mental retardation may affect patient cooperation. Sedative
and/or anxiolytic premedication and/or the presence of the primary caregiver
during induction of ...