Fetal central nervous system abnormalities.

The advances in the sonographic imaging of the fetus have made the detailed examination of the fetal central nervous system (CNS) a routine part of the prenatal sonogram. A logical sonographic approach to the diagnosis of fetal CNS abnormalities is presented, based on the normal sonographic anatomy and the understanding of CNS pathology. This approach results in a classification of CNS abnormalities derived from ultrasound findings. The main categories are (1) hydrocephalus, (2) entities that mimic hydrocephalus, and (3) neural tube defects. Once a disorder is classified and all ultrasound abnormalities identified, a differential diagnosis can be developed.