Sonographic Evaluation of Normal Anatomy of Fetal Central Nervous System in Mid-Trimester

Abstract

The central nervous system is a common site for congenital anomalies. Neural tube defects (NTDs) such as anencephaly, encephalocele and spina bifida are among the most common central nervous system congenital anomalies. They result from failure of closure of the neural tube during embryonic development. The neural tube formation starts during the fourth week (22 - 23 days) after fertilization and fuses approximately between the days 25th and 27th. Most of NTDs result from genetic factors and environmental factors which are poorly understood. Diagnostic sonography can show a detailed visualization of the fetal intracranial anatomy such as the cerebral hemispheres, midbrain, thalami, and lateral ventricles. They also can measure the ratio between lateral ventricular and cerebral hemispheric width. It might show as well, the ratio between gestation, the rapid growth of the cerebral hemispheres and the expansion of the cerebral ventricles. The ultrasound during pregnancy plays a prominent and influential role in the prenatal evaluation of the central nervous system. It gives an excellent window for viewing and evaluating the fetal central nervous system during the second trimester through the lateral ventricles and transthalamic view, thus effectively contributing in the diagnosis and treatment of its congenital anomalies.