Normal anatomy by three-dimensional ultrasound in the second and third trimesters

Fetal brain is rapidly developing and changing its appearance week by week during pregnancy. It is quite difficult to observe detailed structure of the brain by conventional transabdominal sonography. Transvaginal high-resolution ultrasound and three-dimensional (3D) ultrasound have been establishing sonoembryology in the first trimester as well as neurosonography. It is possible to observe the whole brain structure by magnetic resonance imaging in the latter half of pregnancy but transvaginal high-resolution 3D ultrasound is also a powerful modality for understanding brain anatomy. As for brain vascularization, main arteries and veins have been demonstrated and evaluated in various central nervous system conditions. Transvaginal high-resolution 3D ultrasound can demonstrate even cerebral fine vascular anatomy such as medullary vessels and it is greatly expected to estimate neurological prognosis in relation to vascular development during the fetal period.