Neural tube defects are the most common congenital defect of the central nervous system. The term spina bifida was first used by Nicholas Tulpius in 1652 and described failure of the posterior arch of the vertebrae to close. Prior to the 1940s, the vast majority of newborns with open neural tube defects did not survive, dying from infection, hydrocephalus, or complications of surgery. The 1940s ushered in new neurosurgical techniques to repair open neural tube defects, but it was not until the 1950s that the first one-way valve cerebrospinal fluid (CSF) shunts were introduced to manage hydrocephalus. Armed with an effective treatment for hydrocephalus, this resulted in earlier surgical repairs of open lesions and lower mortality. Introduction of clean intermittent catheterization in the 1960s allowed infants with spina bifida to survive into childhood, and today, 75% of all aggressively treated individuals with open neural tube defects are surviving into adulthood. Long-term prognosis is related to the severity of the Chiari II malformation, the presence of hydrocephalus, and the level of the defect, with higher lesions generally having worse outcomes.
PATHOGENESIS AND ETIOLOGY OF NEURAL TUBE DEFECTS
Disorders of neural tube formation can involve defects in primary neurulation, closure of the anterior or posterior neuropore, or failure in the development of the lower spinal cord, which may be present before 28 days’ gestation. This leads to defects in the spinal cord, dura, meninges, cranium, and vertebrae as well as the dermal coverings. Open neural tube defects, the most common being the myelomeningocele, are characterized by failure of the surface ectoderm to close over the neural elements leaving meninges and spinal cord exposed. However, disorders in neural tube formation include a wide array of disorders including cranioschisis (total failure of neurulation), anencephaly (defects in cranial neural tissue development), and encephalocele (herniation of brain or meninges through a cranial defect), as well as occult spinal dysraphisms (skin-covered defects of vertebrae and dermal structures with subtle or absent neural abnormalities).
The incidence of spina bifida is 2 in 10,000 worldwide, but this varies widely based on geography and ethnicity. The incidence in northern China (Shanxi Province) is reported to be 100 per 10,000, with the incidence in Mexico being 5 per 10,000 and that in Northern Ireland being 3 per 10,000. The incidence in the United States is similar to the worldwide average of 2 in 10,000. Rates in African Americans are about one-third those of Caucasians, and rates in Hispanics are 2 to 3 times those of Caucasians. The incidence of spina bifida in the United States has steadily been declining, with a peak incidence of 14 to 15 per 10,000 during the Great Depression of the 1930s.
Neural tube defects result from a combination of environmental risk factors in addition to genetic causes. Seventy to eighty percent of all cases are the result of environmental/gene interactions, with the rest being ...