**1. Introduction**

It has been said that the central nervous system (CNS) is the most complex among the fetal and adult systems. This is one of the most common sites of congenital malformation, both in fetuses with and without chromosomal abnormality. It is extremely difficult to diagnose structural abnormalities or mild ultrasound (US) abnormalities that have been linked to major functional problems. Just the opposite, major anatomic defects may not lead to significant malfunctioning of the system. It is extremely important to study the structure, in an attempt to understand the function of the normal and abnormal fetal central nervous system [1, 2]. The detection of CNS anomalies in fetal life is feasible using modern ultrasound equipment. Many

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

anomalies of the central nervous system develop early, and nowadays, we have the tools to detect some conditions at 11–13 weeks [3–8] or even earlier. The first-trimester detection of CNS anomalies is probably the most important advance in modern sonoembriology. Later in pregnancy, neurosonography is a powerful tool in diagnosing CNS pathology.

The following chapter is structured as follows:

