Exencephaly--clinical and ultrasonic correlation to anencephaly.

The antenatal sonographic diagnosis of exencephaly in four gestations is reported. Exencephaly is an uncommon malformation of the cranium that characteristically involves a large, disorganized mass of cerebral tissue. The flat bones of the calvaria are absent, leaving the brain mass uncovered. Secondarily, anencephaly may develop as a result of prolonged exposure of the developing encephalon to amniotic fluid and trauma in utero. As in anencephaly, facial structures and the bony base of the calvarium are often preserved in exencephaly. Sonographically, the outstanding feature of exencephaly is the cerebral mass, with convolutions or "pseudo" sulcal patterns present. These findings correlate well with the pathologic examination and define a clinical entity that is incompatible with human life.