Neural tube defects
- Lesion
If the neural tube does not close in the fourth week, brain or spinal cord stay open or bulge out; folate before conception lowers the risk.
What it is
Neural tube defects are the most common malformations of the CNS. Failure of closure at the head end gives anencephaly; at the tail end it gives the spina bifida spectrum, from a hidden bony gap to an open, disorganised plaque of cord. Their frequency has fallen where folate supplementation and fortified flour are in place, and they are screened in pregnancy by ultrasound and maternal serum alpha-fetoprotein.
Step by step
- The neural plate folds into a tube, closing like a zipper from the middle toward both ends.
- Low folate, some drugs, maternal diabetes or genes disturb closure at one end.
- The open neural tissue lies exposed to amniotic fluid and is damaged further during pregnancy.
- Bone and meninges fail to cover it, and the cord or brain bulges or stays flat and open.
- Downward pull and a small posterior fossa add a Chiari II malformation and hydrocephalus.
The neural tube defect spectrum
| Defect | What is open or bulging | Pathology | Outlook |
|---|---|---|---|
| Anencephaly | Cranial end: no vault, no forebrain | Area cerebrovasculosa: a flat mass of vessels and glia instead of brain | Not compatible with life |
| Encephalocele | Brain through a skull defect, usually occipital | Herniated, often disorganised brain in a meningeal sac | Depends on how much brain is in the sac |
| Myelomeningocele | Cord and meninges through open vertebral arches, usually lumbosacral | Flat, disorganised neural plaque, often ulcerated and infected | Paralysis and loss of sphincter control below the level |
| Meningocele | Meninges only | Sac of meninges and CSF, cord in place | Usually good |
| Spina bifida occulta | Bone only | Missing vertebral arch under intact skin | Usually no symptoms |
Clinical notes
- Children with myelomeningocele need care for hydrocephalus (shunts), neurogenic bladder and bowel, orthopaedic problems and latex allergy.
- In Colombia, as in most of Latin America, wheat flour is fortified with folic acid, a public-health measure to prevent these defects.
Test yourself
Think of the answer, then tap the question to see it.
Which serum marker rises in the mother when the fetus has an open neural tube defect?
Alpha-fetoprotein, which leaks from the exposed fetal tissue into amniotic fluid and maternal blood.
What does area cerebrovasculosa mean?
The flat, vascular mass of disorganised tissue that sits where the forebrain should be in anencephaly.
Which posterior fossa malformation almost always accompanies a lumbosacral myelomeningocele?
The Chiari II (Arnold-Chiari) malformation, which also causes hydrocephalus.
Elsewhere in DurgiPedia
- Neural tube defects: anencephaly, spina bifida and encephalocele
- Neurulation and closure of the neural tube
- Folic acid and neural tube defect prevention
- Spinal cord: alar and basal plates and the ascent of the cord
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Myelomeningocele (StatPearls (NCBI Bookshelf), 2026).
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Representative model, for educational purposes only.