What is spina bifida, or myelomeningocele? (MMC)
Myelomeningocele (MMC) is the medical term for spina bifida. The term spina bifida means “split spine.” Spina bifida may also be called an open neural tube defect. One in 2,400 kids will have some form of MMC.
Spina bifida is a birth defect in which the spinal cord isn’t entirely covered with skin and bone. Spina bifida occurs 25-29 days after conception when the baby's spinal cord fails to develop or close properly and is exposed through a gap in the backbone.
What causes spina bifida?
Researchers are uncertain what causes spina bifida. In other words, it’s not a woman’s fault that this happened. Over the last few decades, research has discovered some risk factors:
Exposure to certain seizure medications (carbamazepine and valproic acid)
Low folic acid levels
Rare genetic syndromes
However, in the vast majority of cases, there are no definitive or known reasons why a baby develops MMC.
Types of spina bifida
There are three types of MMC: hidden, closed, and open.
Spina bifida occulta
Spina bifida occulta, also called hidden MMC, usually presents as a lack of bone over the spinal cord. It’s often found after a baby is born, often because a collection of thick hair over the baby’s backbone is present, which leads to an ultrasound or x-ray. The images show an area of missing bone. The spinal cord is protected by its covering (the meninges) and skin. Typically, this type of MMC does not require surgery.
Closed spina bifida
Closed spina bifida occurs when there is a covering over the spinal cord, sometimes called a “bubble” or “cele.” Closed MMC presents as a bulging area over the part of the spine that’s missing skin and bone. In some cases of closed MMC, there are no nerves from the spinal cord inside the bubble. The medical term for this is meningocele. In other cases, some of the spinal nerves are in the bubble. The medical term for this is myelomeningocele.
Open spina bifida
Open spina bifida occurs when the area without skin or bone over the spinal cord is flat and without a covering. The medical term for this is myeloschisis.
Both closed and open MMC require surgery to cover the spinal cord.
Conditions associated with spina bifida
The greatest concerns for babies born with spina bifida are hydrocephalus and loss of nerve function.
Hydrocephalus is often described as increased water of the brain. The “water” in and around the brain and spinal cord is called cerebrospinal fluid (CSF).
CSF is made on both sides of the brain. It then circulates around the entire brain and spinal cord, providing a cushion.
In the case of MMC, the CSF leaks out of the spine’s canal and into the amniotic fluid surrounding the baby. This leak reduces the cushion of CSF around the brain. The brain then lies on the bones of the head. The top of the spinal cord moves down and into the bones of the baby’s neck. The medical term for this is the Chiari 2 malformation.
When the brain settles against the bones of the baby’s head and the top of the spinal cord moves into the bones of the neck, the CSF cannot move well and collects in both sides of the brain (the lateral ventricles). This is hydrocephalus.
The treatment of hydrocephalus is referred to as shunting. The shunt is a piece of tubing (called a ventriculoperitoneal, or VP, shunt) placed in the baby’s brain, which allows the extra CSF to drain.
The placement of this shunt is done during an operation performed by a neurosurgeon. Seven of eight (85%) babies born with a myelomeningocele will need a VP shunt in their first year.
Spina bifida and nerve function
Loss of nerve function is another concern related to spina bifida.
With MMC, the nerves of the spinal cord, which do not have skin and bone covering them, may be damaged or lose function because they’re no longer protected by the spinal bones and their normal covering (the meninges).
The best-case scenario is that no nerve function loss is found at birth. The worst is that nerve function is completely lost. Most babies’ conditions will fall somewhere in between.
The loss of nerve function can affect the movement of legs (crawling and walking), bladder (being able to hold urine) and bowel (being able to hold a bowel movement). In general, the lower the MMC on the spine, the better a baby’s or child’s leg, bowel and bladder function. The higher the MMC on the spine, the worse the baby’s or child’s function of the legs, bowel and bladder.
Diagnosing spina bifida
Most pregnant women will have an ultrasound done between 18–22 weeks to look at the baby’s body, inside and out. The most common way spina bifida is diagnosed is during this ultrasound.
The shape of the baby’s head (from the lack of cushioning fluid to the increase of trapped fluid in the sides of the brain), positions of the legs, and the spine’s missing skin and bones indicate a diagnosis of MMC.
Spina bifida can also be diagnosed with a blood test, if a pregnant woman chooses to have the test done in the first months of pregnancy. An increase in the amount of alpha-fetoprotein (AFP) in her blood would prompt her doctor to order an ultrasound to look for MMC, as well as other fetal problems indicated by increased AFP in the woman’s blood.
Treating spina bifida with surgery
All babies born with MMC require surgery to cover the spinal cord. The lining of the spinal cord (the meninges), muscle and skin are repaired over the spinal cord, usually in the first day after birth. This is to both repair the MMC and to decrease the risk of infection to the spinal cord and brain.
Treatment options are available either while the baby is still in the womb (prenatal surgery) or after the baby is born (postnatal surgery).
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Spinal Differences Clinic: care for your growing child
Through Children’s Mercy’s Spinal Differences Clinic, children and adolescents with spina bifida and other spinal cord injuries or disorders have access to coordinated, team-based care. Our program bridges the gap between primary and specialty care, and provides a vital link to medical and support services available to children with these disorders.
Learn about services provided in the Spinal Differences Clinic.