The term “spina bifida” comes from the latin “split spine,” which is actually
a pretty good description, because spina bifida is a birth defect where the tissue on the
left and right side of the back that normally come over the spinal cord to protect it, don’t
completely meet up to form a nice seal, leaving behind various degrees of an opening right
down the middle of the lower back.
Very early on in fetal development, the ectoderm, which is the outer layer of the fertilized
egg, starts to develop a bit of a ridge that eventually becomes the neural tube.
This neural tube goes on to become the spinal cord, the brain, as well as tissues that enclose
and protect them, called the meninges, and spina bifida occurs when a portion of this
neural tube fails to close properly, typically in the lower back.
This constitutes a defect or absence of the vertebral arches due to failure of mesoderm
to organize over the region of the defect, and it may or may not involve the underlying
meninges and neural tissue.
Alright so there are three main types of spina bifida, the first is myelomeningocele, also
called meningomyelocele, and this is the most severe of the three and occurs when the spinal
cord and the surrounding meninges protrude out of an opening in the bony vertebrae and
are held together by a sack of skin that pouches out from the back.
In really severe cases, there is no skin at all, and the nerves of the spinal cord are
therefore exposed, a condition called ‘open spina bifida, and this can cause serious damage
to the exposed nerves as well as risk an infection, resulting in symptoms like loss of sensation
or paralysis in the areas of the body below the damaged site, bladder or bowel movement
problems, seizures, as well as leg and foot deformities.
Now a myelomeningocele is typically associated with a condition called an Arnold Chiari II
malformation, which is where cerebellar and brainstem tissue slip down into the foramen
magnum—the opening at the base of the skull.
This Arnold Chiari II malformation results in a variety of symptoms related to the cerebellum
and often resulting in hydrocephalus—an abnormal accumulation of cerebrospinal fluid
in the brain.
Alright the second type of spina bifida is meningocele, sometimes called a meningeal
cyst.
In this condition, the prenatal spinal deformities result in only the meninges (and not the spinal
nerves) slipping into the gaps between the deformed vertebrae.
This one’s the least common form of spina bifida, and because the spinal cord itself
is not damaged, these individuals often do not experience the severe symptoms that are
seen in myelomeningocele.
Alright the third type and finaly type is spina bifida occulta, and this is the most
common and most mild form of spina bifida.
In fact, ‘occulta’ is latin for hidden, which is appropriate since many of the normal
prenatal tests used to diagnose spina bifida don’t catch the disorder because the deformities
in the tissues of the lower back are tiny.
In spina bifida occulta, the spinal cord and surrounding tissue don’t protrude, nor is
any of the tissue forced into the spaces in between the vertebrae.
Since the spinal nerves are undamaged, people with this form of the disorder are often asymptomatic,
and the condition is usually only found accidently later in life.
At most, people might have hair, a dimple, or birthmark on their back above the site
of the lesion.
Now, the exact cause of all three types of spina bifida isn’t known, but there are
known risk factors like folate or Vitamin B9 deficiency during fetal development.
Therefore prenatal vitamins include folic acid, which is the manufactured form of folate.
The developmental deformities, though, that cause spina bifida often take place in the
fourth week of pregnancy (which is 21-28 days) and this could be before a woman might know
she’s even pregnant, and therefore she’s not taking prenatal vitamins yet.
To help combat this, enriched grain products like breakfast cereals made with whole grains
have folic acid added to flour as a general preventative measure.
Other risk factors for having a child with spina bifida include obesity, poorly controlled
diabetes, and taking medications that interfere with folate metabolism like certain anti-seizure
medications.
Diagnosis for the most severe form of spina bifida—myelomeningocele—is often done
prenatally by looking for an increased level of alpha fetoprotein (or AFP) in the mother’s
serum, which can happen when the skin surrounding the fetus’s spine is missing and AFP leaks
into the amniotic fluid and into the mother’s bloodstream.
AFP, though, can be elevated by other conditions as well so in order to get a more exact diagnosis,
additional blood tests for Human chorionic gonadotropin (or HCG), inhibin A, and estriol,
as well as an ultrasound are usually done.
In more serious cases, amniocentesis (where a sample is taken directly from the amniotic
sac surrounding the fetus) can be performed.
For treatment, prenatal surgery is done to close a myelomeningocele, but this surgery
can be dangerous to the developing fetus as well as the mother.
In cases where postnatal surgery is chosen, it is often done within the first few days
of an infant's life in order to minimize the risk of infection like meningitis.
Even if the surgery is successful, people with this condition typically need additional
interventions such as urinary catheterization to help with urination and crutches or wheelchairs
in case of paralysis or low muscle tone, because the damaged or underdeveloped spinal nerves
can’t be repaired.
Alright, as a quick recap, the three types of spina bifida are spina bifida occulta,
which is the most common and least severe, meningocele, which is the least common and
also typically not very severe, and myelomeningocele, which is the most severe form of spina bifida.
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