Agenesis of the Corpus Callosum (ACC)
A birth defect in which there is partial or complete absence of the corpus callosum, the bundle of nerve fibers that connects the two hemispheres of the brain.
ACC may occur as an isolated defect, but it is frequently associated with other malformations, chromosomal abnormalities (such as trisomy 18 and trisomy 8), and genetic syndromes. The outcome depends on the underlying cause and the presence of other structural defects. Isolated ACC (particularly partial ACC) is associated with no or only mild neurologic impairment in a large proportion of cases. ACC occurring as part of a syndrome may be associated with severe neurologic impairment, including significant intellectual disability and seizures. ACC does not cause death in the majority of children.
Ultrasound findings may include:
- Absence of the corpus callosum and cavum septum pellucidum.
- “Teardrop” configuration of the lateral ventricles.
- Dilatation and upward displacement of the third ventricle (interhemispheric “cyst”).
- Abnormal branching of the anterior cerebral artery.
Magnetic resonance imaging (MRI) is sometimes useful in confirming the diagnosis.
Additional abnormalities commonly associated with ACC include:
- Chiari malformations
- Schizencephaly
- Encephaloceles
- Dandy–Walker malformations
- Holoprosencephaly
- Congenital heart defects
- Gastrointestinal or genitourinary malformations
Risk of recurrence:
- Approximately 1% for sporadic cases.
- About 25% if ACC is associated with an autosomal recessive cause.
- If inherited as an X-linked recessive disorder, approximately 50% of male offspring may be affected.