Neural Tube Defect

• Neural tube defect is a spectrum of congenital anomalies resulting from defective closure of the neural tube.
• Spinal component = spinal dysraphism or spina bifida
• Cranial component = cranium bifidum / Encephalocele

• Any developmental abnormality involving the tubulation of the central nervous system is a neural tube defect, also termed a neurulation defect.
• Occurs in the 3rd and 4th week of intrauterine life (IUL)
• Most defects occur between day 18 and 21 of gestation.
• Fusion begins in the cervical region and progresses to both ends.
• The cranial/ventral neuropore closes by the 25th day.
• The caudal/dorsal neuropore closes by the 27th day.
• The neural tube forms the brain (proximal 2/3) and spinal cord (distal 1/3).

Spina Bifida Occulta

• Spina bifida occulta
• Diastematomyelia (Split Cord Malformation)
• Hypertrophied filum terminale
• Lipomyelomeningocele
• Congenital dermal sinus
• Anterior sacral meningocele
• Myelocystocele (Cystic dilatation at the cord’s end)

Spina Bifida Cystica

• Meningocele
• Myelomeningocele (most common)

Myelomeningocele

• 1 in 1000 live births (US)
• 9 in 1000 live births (Ireland)
• 10 in 1000 live births (Northern China)
• Incidence falling since the 1980s in developed countries
• 10-20% of the adult population has spina bifida occulta

Theories

• The theories that explain neurulation defect are broadly grouped into two:
  • The neural tube fails to close properly.
  • The once-closed neural tube ruptures.
• Can occur anywhere along the length of the spine but is most common at the lumbosacral region.

Aetiology is unknown

RISK FACTORS

Maternal/Environmental

• Maternal age ≥ 35 years
• Folate deficiency
• Metabolic diseases (e.g., diabetes mellitus, obesity)
• Maternal infections (TORCHES)
• Anticonvulsants: valproate, carbamazepine
• Hypervitaminosis A

Race/Ethnicity

• White women > Black women
• Hispanic women > non-Hispanic women

Familial/Heredity

• Enhanced recurrence risk among siblings (8% increased chance if previous spina bifida)
• Higher frequency in twins
• A mother with spina bifida has a 1-5% chance of having a child with spina bifida. This increases to 15% where both parents have spina bifida.

Genes

• Recently, specific genes have been discovered which seem to be linked to neural tube defects (NTDs):
  • VANGL1 mutation
  • MTHFR (Methyl-tetrahydrofolate Receptor)
  • SHMT1 (Serine-hydroxymethyltransferase)

• Overall mortality is 15% from:
• Apnoeic spell and aspiration (Chiari malformation)
• Shunt malfunction and CNS infection
• About 75% are ambulant; some may require walking aids
• About 75% have normal intelligence

Classification

• Occipital
  • Supratorcular
  • Infratorcular
• Cranial Vault
  • Interfrontal
  • Anterior fontanelle
  • Interparietal
  • Temporal
  • Posterior fontanelle
• Anterior (Fronto-ethmoidal)
  • Naso-frontal
  • Naso-ethmoidal
  • Naso-orbital
• Basal
  • Transethmoidal
  • Spheno-ethmoidal
  • Transphenoidal
  • Fronto-sphenoidal

Investigation

• BRAIN MRI
• Others... To prepare for surgery

Management

Encephalocele Repair

• Excise the sac and non-functioning brain tissue
• Perform a watertight dural closure

• All women of reproductive age group should take 400 µg of folic acid daily
• High-risk women should take 4 mg of folic acid daily
• 50% to 70% of cases could be prevented by the appropriate consumption of folic acid before conception and during early pregnancy

• Neural tube defects are a group of congenital anomalies which can coexist with other anomalies
• Occurs early in pregnancy
• Is better prevented
• Neurologic deficits may remain with the patients for the rest of their lives