Ultrasound of the Fetal Brain

Ultrasound examination of the fetal central nervous system (CNS) distinguishes itself from the sonographic evaluation of all other organs or organ systems because during the course of pregnancy, the CNS (mainly the fetal brain) undergoes significant changes, in size and in the shape of its different anatomic regions, which follow a well-defined timeline and can be recognized sonographically. The developmental milestones of the CNS from the time of its first sonographic detection to term can, and should, be taken into consideration when a fetal neurosonogram is performed. This article describes a systematic approach to the evaluation of the fetal brain by discussing the differential diagnosis of two important sonographic findings, namely ventriculomegaly and an enlarged posterior fossa, and by touching on other important brain abnormalities.