NEURAL TUBE DEFECTS
Neural tube defects (NTDs) are congenital structural abnormalities of the central nervous system and vertebral column. Neural tube defects may occur as an isolated malformation, in combination with other malformations, as part of a genetic syndrome, or as a result of teratogenic exposure
- Neural tube defects are the second-most-common major congenital anomaly
- after cardiac malformations, and their prevalence varies by geographic region, race, and environmental factors
- Outcomes and disabilities depend on level and extent of lesion; for instance, anencephaly is incompatible with life but most infants with spina bifida will survive after surgical repair
- Importantly, and in contrast to many other congenital abnormalities, primary prevention of NTDs is possible with folic acid. In addition, prenatal screening and diagnosis are widely available, and fetal surgery has improved outcomes for some newborns. The purpose of this document is to provide information about NTDs and make management recommendations for the pregnancy complicated by a fetal NTD.
The neural tube begins from a flat sheet of neuroepithelial cells (the neural plate), which rolls or folds in the midline to form the neural tube. This occurs at 3–4 weeks after fertilization, a time when some women do not yet realize that they are pregnant. Closure of the neural tube begins at the cervical region and extends cranially and caudally. However, the closure is complex, and as in other mammals, occurs in a discontinuous process (5). Simplistically, failure of neural tube closure at the cranial end results in anencephaly, and failure of closure at the caudal end results in myelomeningocele or spina bifida. The process of neural tube closure involves multiple cellular and molecular processes that are tightly regulated (6). Mutations in any of the genes involved in this process could result in abnormal neural tube closure and NTDs. The various types of NTDs, summarized in Table 1, include malformations of the spinal cord, meninges, and vertebra.