Holoprosencephaly is a complex brain anomaly in which the primitive forebrain (prosencephaly) fails to properly divide into cerebral hemispheres. The frequency of holoprosencephaly has been estimated to be 1 in every 5,200 to 16,000 live births. The complex cerebral and facial anomalies that are observed in infants and fetuses with holoprosencephaly will challenge the sonographer who encounters them. Prenatal detection of the milder forms is particularly difficult; the infant with mild holoprosencephaly may live for years in a vegetative state. Knowledge of the range of malformations encountered in holoprosencephaly will help the sonographer accurately identify the findings.
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