Cerebral embryopathy in late first trimester: possible association with swine influenza vaccine.

An infant girl was born with cerebral malformations characterized by developmental arrest late in the first trimester of gestation. These features included persistent pontine flexure, cerebellum developed only around the rhombic lip, failure of migration of inferior olive, absence of basis pontis and of corticospinal and corticopontine tracts, and agenesis of olfactory bulbs. The cerebral cortex was thin and poorly laminated, and primary and secondary sulci had failed to form. The choroid plexus contained vascular malformations, hemorrhages, and infarcts. The leptomeninges contained foci of primitive mesenchyme. The mother had received an inoculation of swine influenza vaccine six weeks after conception, followed by a 2-week illness. The temporal relation to the timing of the cerebral malformation suggests a teratogenic effect of the vaccine, but may have been coincidental.