Aqueductal atresia as a feature of arhinencephalic syndromes.

Two cases are presented of aqueductal atresia associated with arhinencephalic syndromes. The first case was one of semilobar holoprosencephaly with occipital encephalocele, the second one of lobar holoprosencephaly (callosal agenesis with interhemispheric cyst). Only the second case was associated with obstructive hydrocephalus. The absence of hydrocephalus in the first case may be ascribed either to the greater distensibility of the encephalocele, or to the displacement of the choroid plexuses from the intracranial portion of the common ventricle into the hernial sac.