Neural Tube Defects

Spina bifida, is the most common type of NTD. It occurs when the neural tube does not close completely somewhere along the backbone/spine. Symptoms vary from person to person and can change over time. They tend to occur below the defect and may range from few or none, to partial or total lower body weakness, loss of feeling, or paralysis. Complications will also vary. Cases of spina bifida are generally classified as either “closed” where the skin covers the defect or as “open” where the skin is not intact. Variants include:

Closed Neural Tube Defects
Spina Bifida Occulta
Spina bifida occulta is often called hidden spina bifida. A small gap may exist in one or more of the bones of the spine, but the spinal cord and tissues are normal. Many people with this condition do not have any symptoms and may never know that it exists unless it is identified during testing that is done for another reason.

Closed neural tube defects are frequently grouped with spina bifida occulta. They consist of a wide variety of spinal defects with malformed bone, tissue, and/or fat deposits at the location of the defect. Often there is a visible sign on the outside of the baby’s skin. This may be a tuft of hair, a dimple, a birthmark, lump, or skin opening. Many patients with this condition will have few symptoms, but some may have nerve damage that affects normal bowel or bladder function and/or can cause lower body weakness and pain.

Open Neural Tube Defects
Meningocele
With this type of spina bifida, cerebrospinal fluid (fluid from around the brain) and meninges (membranes covering brain) have ballooned out of the spinal opening to form a bulge or sac, but the spinal cord is usually in its normal location. This bulge may or may not be covered with a layer of skin. This bulge will be noticeable on the back of the baby. Symptoms are variable.

Myelomeningocele
This is the most severe type of spina bifida. It develops when the cerebrospinal fluid, meninges, and the spinal cord protrude through the opening in the spine. It leaves the spinal cord vulnerable to damage and can cause paralysis in those parts of the body below the opening. Affected patients frequently have bowel and bladder problems. Some will require assistance to walk and others will require a wheel chair. Newborns with this condition are at an increased risk of developing meningitis.

Up to 80 to 90 percent of people with spina bifida will develop hydrocephalus. This occurs when the flow of cerebrospinal fluid is blocked and builds up in the brain. The child’s head becomes larger and there is increased pressure on the brain. Left untreated, this condition can cause mental retardation and learning disabilities and can in some cases be fatal. Hydrocephalus is usually treated by putting in a tube called a shunt that allows excess cerebrospinal fluid to drain into the abdomen (tummy).

Anencephaly is the term used for an NTD that affects the head. The result is the lack of development of a large portion of the brain and skull. Some babies affected are stillborn. Those that are born alive are usually unconscious, unable to feel pain, deaf, and blind. Most of those affected die within a few hours or days.

There are varieties of other, rarer forms of NTDs. All are associated with a lack of proper neural tube formation. Examples of these include:

• Encephalocele – protrusion of membranes and brain tissue through a bony defect of the skull; this can occur anywhere along the center of the skull, in the front or back; newborns with this condition may have microcephaly (small head) and develop hydrocephalus. Prognosis depends on the location and severity of the defect.
• Iniencephaly – severe defect where the spine joins the skull; the head is bent back at a severe angle and the baby does not usually have a neck; associated with other abnormalities and most affected infants do not survive.

Some factors that increase the risk of having a baby with an NTD include:

• Personal history—people who have an NTD or a child diagnosed with NTD
• Family history—people who have family members with an NTD
• Use of some anti-seizure medications, such as valproic acid, has been associated with an increased risk. A woman should discuss her medications with her healthcare provider before becoming pregnant.
• Certain diseases in the mother, such as diabetes or obesity
• High body temperature in the mother early in the pregnancy
• Use of opioids in the first two months of pregnancy

Risk can be reduced but not eliminated by ensuring that the mother has adequate folate, also called folic acid, at the time of conception. See the section on Prevention below.

Signs and symptoms of neural tube defects vary from person to person and can change over time. Spina bifida, one of the two most common neural tube defects, may have no symptoms or only minor disabilities but can also lead to severe physical and intellectual disabilities in some cases. Health issues will vary for each individual.

Between 20% and 50% of people with spina bifida may develop tethered cord syndrome. This occurs when the spinal cord becomes attached to bone or skin (such as scar tissue) and is unable to flex and move. The cord becomes stretched and can lead to nerve damage. In children, it can lead to spine issues such as scoliosis (curvature of the spine). Surgery to untether the cord can prevent further damage but is not likely to correct nerve or tissue damage that has already occurred.

Babies born with myelomeningocele (a form of spina bifida) may experience hydrocephalus, an accumulation of fluid in the brain. These children may also develop meningitis, an infection in the tissues surrounding the brain. Usually, a surgeon will implant a shunt to drain the fluid as needed. Children with hydrocephalus are at increased risk for developmental and learning disabilities. People with spina bifida in the upper portion of the spine may be paralyzed, but those who have a defect in the lower portion of the spine may be able to walk or stand on their own or with the aid of crutches or braces. Urinary tract dysfunction and constipation are common among people with spina bifida, and skin problems can arise due to a lack of sensitivity in the lower extremities. Children with spina bifida may also have latex allergies as well as higher rates of depression and obesity.

Life expectancy for babies born with anencephaly, a neural tube defect where the forebrain or cerebrum does not form, is typically very short.

Laboratory Tests
Laboratory tests used to screen for the presence of NTD during pregnancy may include measurement of alpha-fetoprotein (AFP) in the mother's blood. This is a protein made by the developing baby that crosses the placenta, into the mother's blood stream. Levels rise during the first half of pregnancy, but will be particularly high if an open NTD is present as higher amounts cross to the mother. The concentration of AFP in the maternal blood may also be higher than expected in a twin pregnancy, or if the pregnancy is at a later stage than estimated.

Most countries no longer recommend measuring AFP in the mother’s blood to screen for NTD in pregnancy. This is because of improvements in ultrasound scanning which means routine scans are now a more accurate method of detecting affected pregnancies.

Non-Laboratory Tests
Tests include:

• Fetal ultrasound – to help diagnose NTDs prior to birth.
• X-ray, MRI (magnetic resonance imaging), and/or CT scan (computed tomography) – of spine and vertebrae after birth to look for defects and deformities.
• X-ray or CT scans of the head to detect excess fluid when hydrocephalus is suspected.

Regular clinical examinations – to detect and address complications as they arise.

Tests offered during pregnancy vary from region to region, please discuss available tests with your doctor or midwife.

It is generally recommended that all women of childbearing age get at least 400 micrograms (mcgs) of folate a day to prevent NTDs. This helps ensure that pregnant women or women who are planning a pregnancy get enough folate (folic acid). Recent evidence suggests that folic acid supplementation could reduce the incidence of neural tube defects by up to 70%, but the protection it provides must be in place at the time of conception. Ideally, a woman should begin taking folate a month before becoming pregnant and continue throughout her pregnancy.

Women at a high risk for NTDs (such as women who have or have a child with spina bifida) should take 4,000 micrograms of folic acid each day through week 12 of pregnancy, but this is not recommended for the general population.

Since folic acid is a water-soluble vitamin, it must be constantly replenished. In addition to supplements, folic acid can be found in dark green vegetables and some fruit.