Coexistent holoprosencephaly and Chiari II malformation

Chiari II malformations and holoprosencephaly have been considered to be br ain malformations that differ with respect to teratogenic insult, embryolog ic mechanism, and morphology. We herein describe coexistent Chiari II malfo rmation and holoprosencephaly that occurred in a viable infant. A review of the literature regarding Chiari II malformations and holoprosencephaly sug gests that a disturbance to the mesenchyme in early embryologic life may be the cause of both malformations.