Prenatal ultrasound diagnosis of neural tube defects. Pictorial essay.

Neural tube defects (NTD) are a heterogeneous group of malformations resulting from failure of normal neural tube closure before the fourth and fifth week of embryologic development. The three most common forms of NTD are: anencephaly, encephalocele and spinal dysraphism. Less common forms of neural tube defects include iniencephaly, amniotic bands and other types of spinal abnormalities including scoliosis/cyphosis, sacral agenesis, limb-body wall complex, diastematomyelia.