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Neural tube defects

Last updated: January 20, 2021

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Neural tube defects (NTDs) are the most common congenital malformations of the central nervous system (CNS). They develop between the 3rd and 4th week of pregnancy and are often caused by folate deficiency. Most commonly, a deficiency in folate results in improper closure of the neural tube 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, 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 maternal serum or amniotic fluid. Treatment involves prophylactic administration of antibiotics and rapid surgical closure of the defect to avoid CNS infections. Supplementation with folate is an important preventative measure and should ideally be initiated 4 weeks prior to conception.

Epidemiological data refers to the US, unless otherwise specified.

Most NTDs are isolated malformations with multifactorial etiology.

Spinal defects (subtypes of spina bifida) [4]
Condition Description Clinical features

Diagnosis

Closed spinal dysraphism
Spina bifida occulta
  • Most commonly affects the lower lumbar or sacral region
  • Often asymptomatic (may be an incidental finding in imaging)
  • Possible symptoms at the level of the vertebral defect:
    • Lumbar skin dimple
    • Collection of fat
    • Patch of hair
Lipomyelomeningocele
  • Often asymptomatic
  • Subcutaneous mass in the lumbar or sacral region
  • Possibly skin dimple and/or patch of hair
Lipomeningocele
Open spinal dysraphism
Meningocele
Myelomeningocele
Myeloschisis (rachischisis)
  • Portions of the neural tube completely fail to fuse, leading to bare, exposed neural tissue without coverage of meninges, bones, or skin.
  • Most severe subtype
Myelocele

Cranial defects [4]
Condition Description Clinical features Diagnosis
Anencephaly
Encephalocele
  • Brain tissue herniates through occipital or frontal bone defect.
  • Usually covered by skin
  • Malformations and neurological deficits that vary in severity
  • Lethal in severe cases
  • Normal AFP (usually not elevated)
Acrania
  • Incompatible with life

The most common NTDs are spina bifida and anencephaly.

Prenatal period [1]

AFP is only elevated in open NTDs.

Postnatal period [1]

Tethered cord syndrome [5][6]

Congenital dermal sinus

The differential diagnoses listed here are not exhaustive.

  • Prenatal
    • Counseling for parents: individual decision about continuation or termination of the pregnancy (refer to specialized clinics)
    • Myelomeningocele: fetal surgery may be an option
  • Delivery
  • Postnatal
    • General management
      • Cover defect with sterile, wet compresses (avoid pressure on defect)
      • Prophylactic administration of broad-spectrum antibiotics
    • Surgical treatment
      • Open NTDs: Surgery should be performed within 72 hours after delivery (to reduce the risk of CNS infection).
      • Closed NTDs: monitoring and possibly elective surgery
      • Hydrocephalus: consider placement of a ventriculoperitoneal shunt
    • Longterm care

Supplementation of 400–800 μg of folate per day is recommended for all women who are planning for pregnancy.

  1. Sahni M, Ohri A. Meningomyelocele. StatPearls. 2020 .
  2. Congenital anomalies. https://www.who.int/news-room/fact-sheets/detail/congenital-anomalies. Updated: September 7, 2016. Accessed: January 14, 2020.
  3. Bibbins-Domingo et al.. Folic Acid Supplementation for the Prevention of Neural Tube Defects. JAMA. 2017; 317 (2): p.183-189. doi: 10.1001/jama.2016.19438 . | Open in Read by QxMD
  4. Tethered Cord Syndrome. https://rarediseases.org/rare-diseases/tethered-cord-syndrome/. Updated: January 1, 2010. Accessed: March 1, 2018.
  5. Tethered Spinal Cord Syndrome. https://www.aans.org/Patients/Neurosurgical-Conditions-and-Treatments/Tethered-Spinal-Cord-Syndrome. . Accessed: January 17, 2020.
  6. Tolcher M, Shazly S, Shamshirsaz A, et al. Neurological outcomes by mode of delivery for fetuses with open neural tube defects: a systematic review and meta-analysis. BJOG. 2018; 126 (3): p.322-327. doi: 10.1111/1471-0528.15342 . | Open in Read by QxMD
  7. Benjamin RH, Lopez A, Mitchell LE, et al. Mortality by mode of delivery among infants with spina bifida in Texas. Birth Defects Res. 2019; 111 (19): p.1543-1550. doi: 10.1002/bdr2.1608 . | Open in Read by QxMD
  8. Recommendations: Women & Folic Acid. https://www.cdc.gov/ncbddd/folicacid/recommendations.html. Updated: August 13, 2019. Accessed: January 17, 2020.
  9. Neural Tube Defects. http://neuropathology-web.org/chapter11/chapter11bNTD.html. Updated: March 1, 2012. Accessed: March 1, 2018.
  10. Spina bifida. http://www.mayoclinic.org/diseases-conditions/spina-bifida/basics/prevention/con-20035356. Updated: August 27, 2014. Accessed: February 17, 2017.
  11. Dukhovny S, Wilkins-Haug L. Open Neural Tube Defects: Risk Factors, Prenatal Screening and Diagnosis, and Pregnancy Management. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/open-neural-tube-defects-risk-factors-prenatal-screening-and-diagnosis-and-pregnancy-management.Last updated: August 29, 2017. Accessed: October 10, 2017.