The fetal head: borderlines.

After more than 20 years of using ultrasound to examine the fetal head, there are still areas of controversy. The size of the ventricular atrium or the anteroposterior measurement of the posterior fossa have been shown to be relatively stable throughout pregnancy. However, there are instances in which intracranial malformations occur with normal ventricular atrial measurements. Although there are more obvious posterior fossa defects such as Dandy-Walker malformation, there are other abnormalities such as Dandy-Walker variant that are difficult to detect. Another area of controversy surrounds dealing with the fetus with a choroid plexus cyst. Review and understanding of the current literature are needed to best manage these fetuses with choroid plexus cysts. Knowledge of central nervous system embryology and of technical pitfalls of sonography, and understanding the overlap between normal and abnormal anatomy are needed to obtain a more precise central nervous system diagnosis. This article will review some of the borderlines in examination of the fetal brain.