Spina Bifida

(Neural Tube Defect)

In this condition factsheet:

• The Facts
• Causes
• Symptoms and Complications
• Making the Diagnosis
• Treatment and Prevention

The Facts

Spina bifida is a type of malformation that occurs during early fetal development. It's known as a type of neural tube defect (NTD), in which either the brain and spine or only the spine fails to develop properly in the womb. There are three types of spina bifida, which vary according to the severity of the malformation:

• myelomeningocele: the most severe form; both the spinal cord and its lining (the meninges) protrude from an opening in the spine
• meningocele: only the lining protrudes
• spina bifida occulta: the mildest form; there is a breach in the spinal vertebrae but it's covered by skin

These malformations are usually in the lower back or at the level of the hips.

In Canada, around 150 babies are born each year with spina bifida.

Causes

The exact cause of spina bifida is still unknown. Something goes wrong in the first 2 months after conception but experts often don't know why. It's been shown that women who have low levels of folic acid (a B vitamin) are more likely to give birth to children with neural tube defects. The assumption is that when the genes of the fetus give the order to construct the spine, the necessary chemical building blocks are missing.

There's almost certainly no single spina bifida gene, and it can occur in any pregnancy, yet some people are predisposed to it. Women with a family history of neural tube defects are at increased risk of giving birth to a baby with such a defect. Couples who already have one child with spina bifida have a slightly higher risk of having another baby with neural tube defects.

Still, most cases of spina bifida occur in families with no history of the condition.

Other risk factors for having a child with spina bifida include obesity and uncontrolled diabetes.

Symptoms and Complications

Most people with spina bifida have some degree of paralysis, usually in the lower body, and may need wheelchairs or other aids to get around. The nature of the paralysis depends on the location and severity of the lesion in the spine. Some people with mild spina bifida occulta experience no physical problems at all. There may well be people with this condition who have never been diagnosed and will never suffer any ill effects.

Unfortunately, paralysis is common and often begins in the womb. This means that babies may already have suffered complications of long-term paralysis at the time of birth. This includes having a spine that's too curved at the base, which prevents an infant from lying normally on his or her back. Sometimes the bones of the spine (vertebrae) or other joints may become locked in position, typically in a bent position. Clubfoot and dislocated hips are other common malformations seen at birth.

The nerves that control the bowel and bladder are often damaged in spina bifida, leading to various problems such as severe constipation or incontinence and frequent infections. Over the years, this can put a massive strain on the kidneys, potentially leading to kidney failure and death.

Most people with spina bifida also have malformations high in the spinal cord or brain that lead to a dangerous buildup of cerebrospinal fluid (CSF) in the ventricles inside the brain. This is called hydrocephalus. A large percentage of people with spina bifida develop this condition at some point. In an infant, it can cause the skull to grow out of proportion to the body. This condition can be treated.

People with spina bifida are of normal intelligence, but for unknown reasons they are more likely than the general population to have learning disabilities such as difficulty with decision-making, difficulty paying attention, and problems with learning math.

Babies that are born with meningocele or myelomeningocele are at risk of developing meningitis, an infection of the lining of the brain and spinal cord. For this reason, newborns with these types of spina bifida often undergo surgery to close their spinal lesion in the first few days after birth.   There have been developments in the area of fetal spinal surgery and some specialized medical centres may perform surgery while the fetus is still in the womb to prevent further damage to the spinal cord.

Making the Diagnosis

Spina bifida can be easily diagnosed at birth. Myelomeningocele and meningocele are clearly visible, and spina bifida occulta is often suggested by a tuft of hair or skin dimple over the low end of the spine. This can be confirmed with an ultrasound or amagnetic resonance imaging(MRI) scan, which will reveal the size and location of any spinal lesions.

It's also possible to detect it before birth. This can be done using a variety of tests. A blood test can be done between Week 16 and Week 18 of pregnancy to measure levels of maternal serum alpha-fetoprotein (MSAFP). This test will show a higher level in 75% to 80% of women carrying a baby with spina bifida.

An ultrasound of the fetus may show abnormalities, such as an open spine, indicating spina bifida. If a blood test indicates that the baby has spina bifida, a test called maternal amniocentesis may be done for further confirmation. This involves using a needle to obtain a sample of fluid from the womb to measure alpha-fetoprotein levels.

Treatment and Prevention

There's no cure for spina bifida and nothing can be done to repair the damaged nerves or reconstruct the central nervous system. Although spina bifida is not a progressive condition, some of its complications, such as hydrocephalus, may get steadily worse. For most people, the lesion is closed shortly after they're born, and there is no further treatment of the condition itself.

Progressive hydrocephalus can be treated with the surgical procedure known as a shunt. A pathway is created that leads from the inside of the skull to some other part of the body (usually the abdomen) where the cerebrospinal fluid can be safely drained and reabsorbed. This procedure is often lifesaving for a child. As they get older, some children with spina bifida may no longer need their shunt, but it's impossible to tell which children, so shunts are usually left in place indefinitely. Shunts carry a risk of serious infection or blockage, however, and for adults with spina bifida, shunt complications are among the leading causes of death, along with kidney failure.

Most people with spina bifida make it to adulthood, but few live to a ripe old age. Things have improved dramatically over the past few decades, when spina bifida was usually fatal in childhood. Although the quality of life for people with spina bifida is better now, a real cure for this condition still seems a very long way off. Prevention remains the key.

Women can reduce their chances of a spina bifida pregnancy by taking an adequate dietary supply (0.4 mg a day) of folic acid. It's useless for women to wait until they're pregnant and then start on folic acid, because spina bifida occurs so early in pregnancy that it's already happened by the time a woman realizes she's pregnant. Folic acid needs to be in a woman's system at the time of conception. Therefore, women who want to become pregnant should be taking 0.4 mg per day all the time. If you are at a higher risk for giving birth to a child with spina bifida, you may be required to take a higher dose of folic acid. Talk to your doctor.

Since 1998, certain foods in Canada have been fortified with folic acid. This fortification of commercial food provides about 0.1 mg a day in the average diet, enough to reduce neural tube defects but not enough to provide the maximum protection possible. If a woman is thinking of getting pregnant, she should immediately start taking 0.4 mg daily. Folic acid is the most important of all vitamins for a healthy pregnancy.

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