Defects in primary neurulation result in open neural tube defects, such as a myelomeningocele, in which the spinal cord and meninges protrude through a vertebral arch defect. Findings typically include an elevated maternal alpha fetoprotein and a complex cystic mass overlying the lower spine.
Open NTD
Closed NTD
The notochord is a major regulator of embryonic patterning and disruption to its development may affect the CNS, gastrointestinal, or genitourinary tract. CNS structures related to notochord development include the spinal cord and vertebral column
Failure of anterior (rostral) neuropore closure results in anencephaly
Failure of prosencephalon division leads to holoprosencephaly, in which the brain does not separate normally into 2 hemispheres. A spectrum of findings may be present, including hypotelorism, a single nostril or proboscis, and/or a single central incisor.
In addition to insufficient dietary folate, first trimester use of medications that impair folate metabolism are associated with a 10- to 20-fold increased risk of NTDs. These medications include valproate (typically prescribed for bipolar disorder or epilepsy), phenytoin, carbamazepine, methotrexate and trimethoprim-sulfamethoxazole. These medications are contraindicated in pregnancy.
