What is spina bifida?
Spina bifida is one of the most commonly occurring inborn disorders (birth defects) in the United States. It’s caused by the incomplete development of the fetus' spine during the first month of pregnancy. (The term spina bifida means “split spine.”) Spina bifida is usually apparent at birth.
Spina bifida happens during the first 28 days of pregnancy, often before a woman knows she’s pregnant. The condition is a type of neural tube defect (NTD).
This sounds scary and some types of spina bifida are very serious. But it’s important to know that the condition varies widely in degree. Most cases are so mild they have no symptoms and don’t even need treatment (this occurs with spina bifida occulta, or “hidden spina bifida”).
However, infants born with a more serious type of this disorder have open lesions on their spine where there’s significant damage to nerves and the spinal cord. The opening can be repaired through surgery, but the nerve damage isn’t resolved and that causes permanent disability. Spina bifida can occur anywhere along the backbone, but is most often found in the small of the back or further down.
What are the types of spina bifida?
There are three main types of spina bifida:
- Spina bifida occulta.
Spina bifida occulta
Spina bifida occulta is the mildest and most common form of this disorder. It usually only involves a minimal portion of the spine; it usually shows no symptoms, and it does not require treatment. When an infant is born with spina bifida occulta, the skin covers the deformity of the spinal bone.
Spina bifida occulta literally means "a hidden spot on the spine," and for many people with this type of spina bifida, the spot remains hidden. In some people, though, the skin overlying the bony defect will show subtle changes, such as a dimple, red or purple coloring or a tuft of hair. It has been estimated that about 10% to 20% of the U.S. population has spina bifida occulta -- and most don’t even know they have it.
Rarely, spina bifida occulta will cause problems when a child grows to adolescence. By this time in the child's life, the spinal cord has become fastened to the backbone. When the growth spurt of adolescence begins, the nerves of the spinal cord become stretched. The result can be difficulties such as weakness and numbness in the legs, bladder infections and incontinence (lack of bladder and bowel control). The more the spinal cord is stretched, the worse the symptoms become. Surgery to relieve these symptoms by reducing the tension on the spinal cord is simple and often successful.
In this least common type of spina bifida, the meninges (membrane surrounding the spinal cord) protrude through the opening causing a lump or sac on the back. More severe than spina bifida occulta, meningocele can nevertheless be repaired through surgery with little or no nerve damage resulting. The surgery is performed at any time during infancy. With meningoceles, the spinal cord has developed normally and is undamaged. The child has no neurological problems.
Myelomeningocele is the most severe form of spina bifida, occurring nearly once for every 1,000 live births. For infants born with a myelomeningocele, the spinal cord does not form properly and a portion of the undeveloped cord protrudes through the back. A sac containing cerebrospinal fluid and blood vessels surrounds the protruding cord, which is usually not covered by skin so that the nerves and tissues are exposed.
Between 70% and 90% of infants born with myelomeningocele also experience hydrocephalus due to a defect at the base of the skull (Chiari malformation). Hydrocephalus is an excess buildup of spinal fluid on the brain that will cause brain damage, seizures or blindness if it is left untreated. To avoid this, plastic shunts must be surgically inserted beneath the skin to drain off excess fluid into the abdominal cavity.
Infants born with myelomeningocele often have paralysis or weakness below the level of the spinal lesion. This affects the lower limbs along with problems with bladder and bowel function. In extreme cases, the trunk and upper extremities are involved.
What causes spina bifida?
The exact cause of the occurrence of spina bifida isn’t clear. A combination of genetics and environmental factors is thought to be the main cause.