ABSTRACT
The scanning electronmicroscope was used to study the development of anencephaly in an experimental model. Anencephaly was produced consistently, using vitamin A as the teratogen. Embryos destined to become anencephalic displayed failure of opposing sides of the rostral neural tube to fuse. Subsequently, the neural folds of the experimental embryos progressively curved laterally away from the midline, whereas the neutral folds of the control embryos fused in the midline by day 12. The anlage of the choroid plexus could be identified on the surface of the everting brain folds as early as gestational day 13. Thus, the abnormal eversion of the neural tube occurred before development of the choroid plexus. This study supports the view that anencephaly ultimately results from neural tube nonclosure.