Neural Tube Defects and Spina Bifida
-
Neural tube defects can result in nerve damage, learning disabilities, paralysis, and death.
-
The diagnosis can be made before birth and is based on a blood test, an amniotic fluid test, or an ultrasound.
-
After birth, doctors do a physical examination and may do additional imaging tests.
-
Folate (folic acid) taken by the mother before conception and during the first trimester can help prevent these defects.
-
Surgery is needed to close neural tube defects.
(See also Overview of Brain and Spinal Cord Birth Defects.)
In the fetus, the brain and spinal cord develop as a groove that folds over to become a tube called the neural tube. Layers of tissue that come from this tube normally become the brain and spinal cord and the tissues that cover them, including part of the spine and the meninges. Sometimes the neural tube does not develop normally, which may affect the brain, spinal cord, and meninges.
Anencephaly is the most severe form of neural tube defect. In anencephaly, the brain tissue fails to develop. This defect is always fatal.
Chiari malformation may be present. In this abnormality, the cerebellum (the part of the brain that controls balance) protrudes through the opening in the bottom of the skull. The protruding cerebellum may put pressure on the brain stem or spinal cord. Children may develop hydrocephalus (water on the brain).
Syringomyelia, a dilation of the normally small fluid-filled central canal of the spinal cord, cord may be present.
Spina bifida
Spina bifida results when the neural tube fails to close completely and remains an open channel. In spina bifida, the bones of the spine (vertebrae) do not close over the spinal cord. It most commonly affects the spine in the lower back. One or more of the vertebrae may be involved.
Spina bifida occulta is the mildest form of spina bifida. Only the bone is affected and the spinal cord and meninges are unaffected. This common defect is called occulta because it is hidden (covered) by a layer of skin that typically appears normal except sometimes there may be a small tuft of hair or different color of the skin overlying the defect. It usually causes no symptoms, but children who have a larger defect may have symptoms such as leg weakness or bladder dysfunction.
In occult spinal dysraphism, a more severe form of spina bifida, newborns are born with visible abnormalities on their lower back. These include birthmarks, overly pigmented areas (hemangiomas and flame nevus [stork bite]), tufts of hair, openings in the skin (dermal sinus), or small lumps (masses). The underlying spinal cord may be abnormal such as having a fatty tumor (lipoma) or other problems that can lead to nerve damage.
In spina bifida cystica, the most serious form of spina bifida, tissues of the meninges and/or spinal cord protrude through the opening in the vertebrae, causing the following defects:
Damage to brain or spinal cord tissue is much more likely when the tissue protrudes than when it does not. Also, when spinal cord tissue or meninges are exposed, they may become infected by bacteria, causing meningitis.
Spina Bifida: A Defect of the Spine
Causes
There are many causes of neural tube defects. Deficiency of a B vitamin, folate, during pregnancy is a significant factor. Genetic factors and use of certain drugs during pregnancy (such as valproate) can make neural tube defects more likely. The defect often develops before the mother knows she is pregnant.
Symptoms
Many children who have minor neural tube defects have no symptoms.
Most symptoms caused by neural tube defects result from brain or spinal cord damage.
Brain damage can cause problems, including water on the brain (hydrocephalus), learning disabilities, and difficulty swallowing.
Spinal cord damage can cause severe problems, typically involving the bowels, bladder, and legs. Problems include
-
Weakness and paralysis: Walking is difficult or impossible, unused muscles shrink and stiffen up
-
Decreased sensation of the skin
-
Urinary problems: Inability to pass urine (urine retention) or urinary incontinence and frequent urinary tract infections (severe urinary problems sometimes lead to kidney failure)
-
Bowel problems: Loss of control over bowel movements or constipation
Other problems, such as clubfoot, arthrogryposis (joints, usually ankles, that become frozen and cannot bend), a dislocated hip, or an abnormally curved spine (kyphosis), may also be present at birth.
Diagnosis
Many neural tube defects can be detected before birth with prenatal screening tests. A high level of alpha-fetoprotein in a pregnant woman's blood or in amniotic fluid may indicate a neural tube defect in the fetus. So during the 2nd trimester, blood tests or amniocentesis (removing a sample of fluid from around the fetus) may be done to measure these levels.
Prenatal ultrasonography may show the defect or characteristic abnormalities.
After birth, some defects are obvious during the physical examination. If newborns have abnormalities that suggest occult spinal dysraphism, ultrasonography or magnetic resonance imaging (MRI) is done to check for defects in the spine. X-rays may also be done.
After spina bifida is diagnosed, tests to evaluate bladder function are done. They include urinalysis, urine culture, blood tests, and ultrasonography.
Prognosis
With appropriate care, most children do well. However, complications, such as loss of kidney function and problems with shunts needed to treat hydrocephalus, may occur and sometimes cause death in older children.
Prevention
All women of childbearing age who have not had an infant with a neural tube defect should consume folate (folic acid) through diet or by taking a supplement and continue doing so through the first 3 months of pregnancy.
Women who have had an infant with a neural tube defect are at high risk of having another affected infant and should take high-dose folate supplements beginning 3 months before getting pregnant and continuing through the first 3 months of pregnancy. Folate can reduce the risk of neural tube defects by as much as 75%.
Treatment
Health care practitioners, usually a team of specialists (including a neurosurgeon, a urologist, a pediatrician, a pediatric rehabilitation medicine specialist, an orthopedic surgeon, a physical therapist, a nurse practitioner, and a social worker), evaluate the type and severity of the defect and talk to the family about how treatment and care can be implemented.
Neural tube defects are usually closed surgically. Certain defects, such as a myelomeningocele, are typically repaired soon after birth.
Problems with the bladder, bones, or muscles and other problems are treated as needed.
