- Clinical science
Neural tube defects (NTDs) are one of the most common congenital central nervous system (CNS) malformations. They develop between the 3rd and 4th week of pregnancy and are often caused by folic acid deficiency. The deficiency results in improper closure of the neural plate in the embryo, mainly at the caudal or cranial ends. The formation of defects at the caudal end is more common and is known as spina bifida. Spina bifida may occur without any apparent clinical features (spina bifida occulta), or manifest with protrusion of the meninges, and potentially also the spinal cord (myelomeningocele), through a gap in the vertebrae. Myelomeningoceles predominantly cause symptoms of sensory and motor function loss, such as bladder dysfunction and paraplegia. NTDs at the cranial end can cause cranial fissure malformations; the most severe manifestation of this, anencephaly, is incompatible with life. The diagnosis of NTDs is often established during pregnancy via ultrasound and detection of elevated alpha-fetoprotein levels in the amniotic fluid. Treatment involves prophylactic administration of antibiotics and swift surgical closure of the defect to avoid CNS infections. Supplementation with folic acid is an important preventative measure and should ideally be initiated 4 weeks prior to conception.
- NTDs occur between the 22nd and 28th day post-conception ; the neural tube in the embryo closes during this time.
- Incidence: 1–2 cases per 1000 births
Epidemiological data refers to the US, unless otherwise specified.
- Maternal folic acid deficiency during pregnancy; disorders or drug intake affecting folate metabolism
- Concomitant chromosomal aberrations (e.g., trisomy 13 and 18); genetic mutations in the folate and homocysteine metabolism pathways
- Associated maternal conditions: diabetes mellitus, obesity, fever/hyperthermia during first trimester
- Spina bifida occulta: failure of one or more vertebrae to close completely; the spinal cord, spinal meninges, and overlying skin remain intact
- Spina bifida cystica; : failure of one or more vertebrae to close completely; the meninges (meningocele) and potentially the spinal cord (myelomeningocele) may protrude through the gap
- Location: primarily in the lower lumbar to sacral region
- Spina bifida occulta: usually asymptomatic; possibly visible dimple, collection of fat, or patch of hair on the skin above the defect
Spina bifida cystica
- Symptoms of spinal cord dysfunction
- Further symptoms
- Definition: cranial cleft formation with involvement of the skull and brain
- Location: variable
- Symptoms: malformations and neurological deficits that vary in severity; in severe cases always lethal
- Definition: : mainly lumbar or lumbosacral fistulae; extend from the surface of the skin to the spinal canal and frequently end in a dermoid or epidermoid cyst
- Definition: abnormal stretching of the spinal cord caused by adhesions or obstructions that tether the cord to the base of the spinal canal
- Diagnosis: MRI shows abnormally low position of the conus medullaris.
- Treatment: removal of structure tethering the spinal cord (e.g., adhesiolysis, resection of lipomas) → prevents progressive deterioration, corrects existing conditions (e.g., urinary retention)
The differential diagnoses listed here are not exhaustive.
- The baby is usually delivered by cesarean section.
- Prophylactic administration of broad-spectrum antibiotics
- Surgical closure within 72 hours after birth ; close monitoring and possibly elective surgery for closed defects
- Placement of a ventriculoperitoneal shunt in cases of hydrocephalus