Birth Defects Brain Nervous System Neural Tube

The neural tube is the embryonic structure, formed in the first six weeks of pregnancy, which eventually develops into the brain and spinal cord. A “neural tube defect” (NTD) is a collective term for congenital conditions that occur when the brain and spinal cord and/or surrounding structures do not develop properly. These conditions are present from birth, and occur in the earliest stages of fetal development.

Neural Tube Defect Types

There are many types of neural tube defect, each affecting different parts of the brain and spinal cord. Some common neural tube defect types include:

  • Anencephaly involves minimal brain and skull development, and often, complete absence of the cerebrum (cortex). Anencephaly is always fatal; often before birth, and sometimes days or weeks after.
  • Chiari malformation is a neural tube development defect in which the cerebellum and spinal cord are pushed into the spinal canal.
  • Encephalocele is a protrusion of the meninges (coverings of the brain) through openings in the skull. An encephalocele may contain cerebrospinal fluid (meningocele) and/or brain matter (encephalomeningocele). Prognosis depends on site of lesion and severity.
  • Hydranencephaly occurs when the brain does not form properly and is replaced by sacs filled by cerebrospinal fluid. Babies with this neural tube development defect usually have a poor prognosis.
  • Spina bifida is the most common type of neural tube defect. Babies with spina bifida have neural tubes that don’t form or close properly somewhere along the spine. Spina bifida may have varying degrees of severity, and is often characterized by weakness, paralysis and/or sensory loss below the site of the lesion.

Other, rarer neural tube defect types may also occur, along with associated conditions, such as tethered spinal cord syndrome. This condition, often seen with spina bifida, causes limited spinal cord movement, stretching the spinal cord and eventually causing weakness in the lower extremities.

Neural Tube Defect Development, Diagnosis and Treatment

Neural tube development occurs during the first trimester, particularly during the first four weeks of pregnancy. The neural tube, which will develop into the central nervous system (brain and spinal cord), develops very early. Exposure to toxic substances or inadequate nutrition can interact with genetics to cause problems with neural tube development.

A neural tube defect can be diagnosed before birth, through amniocentesis or ultrasound, or after birth. A tuft of hair can usually be seen at the lower midline back. Neural tube defect treatment options vary widely, depending on the structures affected and the severity. Some NTDs can cause very severe disabilities, while others are fatal; these are often the NTDs that affect the brain. Others, such as encephalocele or spina bifida, can be treated or managed.

Neural Tube Defect Prevention

As these defects occur in very early stages of neural tube development, you’ll want to begin caring for yourself properly as soon as you begin trying to conceive. This will ensure that your baby will be safe from the point of conception, even before you know you are pregnant.

The most important step in prevention is to get enough folic acid, a vitamin important for healthy fetal development. This can be achieved via multivitamins or prenatal vitamins, and also through foods such as leafy vegetables and legumes. Adequate folic acid consumption is particularly important for women who have already had a child with a neural tube defect.

Resources

Centers for Disease Control and Prevention. (2005). Reducing the risk of a neural tube birth defect. Retrieved April 8, 2010, from: http://www.nbdpn.org/archives/2005/2005pdf/recurrence.pdf.

Children’s Hospital Boston. (n.d.). Anencephaly. Retrieved April 8, 2010, from: http://www.childrenshospital.org/az/Site578/mainpageS578P0.html.

Children’s Hospital Boston (n.d.). Encephaloceles. Retrieved April 8, 2010, from: http://www.childrenshospital.org/az/Site833/mainpageS833P0.html.

Medline Plus. (n.d.). Neural tube defects.Retrieved April 8, 2010, from: http://www.nlm.nih.gov/medlineplus/neuraltubedefects.html#cat1.

National Institute of Neurological Disorders and Stroke. (n.d.). NINDS hydranencephaly information page.Retrieved April 8, 2010, from: (http://www.ninds.nih.gov/disorders/hydranencephaly/hydranencephaly.htm.

Neurosurgery Today. (2005). Tethered spinal cord syndrome. Retrieved April 8, 2010, from: http://www.neurosurgerytoday.org/what/patient_e/tethered_syndrome.asp.