Antenatal diagnosis of fetal intracranial anomalies.

Defects in the central nervous system (CNS) are the most devastating of the various fetal malformations that can be sonographically diagnosed. The sonographer often initiates a decision-making process that presents the patient with difficult options. An accurate and reliable sonographic diagnosis becomes an essential part of this evolving aspect of obstetric care. In this paper, some of the major defects of the CNS that have been diagnosed sonographically are presented with a brief outline of the pathologic features, diagnostic features, the prognosis, as well as management options. Most of these malformations are serious enough so that termination of pregnancy is usually offered if the diagnosis is made prior to the age of viability and, for some malformations (ie, hydranencephaly, alobar holoprosencephaly), even later. Intrauterine treatment, principally ventriculoamniotic shunting, remains an investigational procedure. A diagnosis of a serious or lethal malformation allows the obstetrician to choose not to perform a cesarean section because of fetal distress or dystocia due to macrocephaly in such "doomed" fetuses. On the other hand, cesarean section may be the preferred route of delivery for fetuses with other malformations (eg, meningomyelocele).