Encyclopedia of Health and Medicine

282 The Nervous System
medications. Surgery to interrupt electrical activity
in the brain is sometimes an option for intractable
seizures (seizures that fail to respond to medication
therapy).
Risk Factors and Preventive Measures
Neurologists do not know the cause of most
seizure disorders; thus there are no measures
known to prevent them from developing. People
who have recurrent seizures or do not experience
full suppression of seizures with treatment should
not drive or engage in other activities that can put
them or others at risk. Many states have laws that
regulate the conditions under which a person who
has a seizure disorder may obtain a driver’s
license; such laws vary among states.
See also MYOCLONUS.
spina bifida A form of neural tube defect in
which the distal (lower) portion of the neural tube
fails to close early in embryonic development. In
very mild spina bifida the defect may be unapparent
and cause no problems. Severe spina bifida
leaves the SPINAL CORD partially or completely
exposed, resulting in numerous complications that
often include deformity and PARALYSIS. Doctors
identify three forms of spina bifida:
• Spina bifida occulta is the most common and
the mildest form. Only a small portion of a single
vertebra fails to close properly. The spinal
cord and the SPINAL NERVES develop correctly.
The surface of the spine looks and feels normal,
and the person has no symptoms.
• Meningocele is when the meninges (membranes
that enclose the spinal cord) protrude
under the surface of the SKIN through the
incompletely closed vertebrae (usually two or
more). The spinal cord and spinal nerves
develop correctly, however.
• Myelomeningocele is the most severe form.
The spinal canal is open and exposed along the
lower spine. The spinal cord and meninges typically
appear as a saclike structure, which may
be under or on top of the skin. The spinal cord
and spinal nerves do not develop correctly, and
often there are deformities of the pelvis,
abdominal and pelvic organs, and lower limbs.
Meningocele and myelomeningocele are rare.
Myelomeningocele can be life threatening,
depending on its location and the extent of exposure
of the spinal cord, which presents a significant
risk for INFECTION (MENINGITIS or ENCEPHALITIS).
Symptoms and Diagnostic Path
Diagnostic prenatal ULTRASOUND detects many neural
tube defects before birth. At birth, symptoms of
meningocele and myelomeningocele are apparent
as deformities of the spine. COMPUTED TOMOGRAPHY
(CT) SCAN or MAGNETIC RESONANCE IMAGING (MRI) help
the neurosurgeon assess the extent of the damage
and plan an appropriate course of treatment.
Treatment Options and Outlook
Spina bifida occulta requires no treatment.
Surgery is necessary to repair meningocele, though
nearly always recovery is complete. Meningocele
repair often heals with minimal or no residual consequences,
and the child grows up with normal
neurologic function. Complex surgery often is necessary
to repair myelomeningocele, and residual
complications are usually extensive. Ongoing complications
include paralysis, deformity, and HYDRO-
CEPHALY (excessive CEREBROSPINAL FLUID) that
requires a shunt. Children born with myelomeningocele
require lifetime medical and supportive
care. Many have permanent URINARY
INCONTINENCE and FECAL INCONTINENCE because the
lower spinal cord, which is nonfunctional, regulates
urination and defecation. Some may learn to
walk with crutches or braces. Developmental
delays and LEARNING DISORDERS are common.
Risk Factors and Preventive Measures
Folic acid supplementation greatly reduces the risk
for neural tube defects such as spina bifida, perhaps
by 70 percent. Health experts recommend
that all women of childbearing ability and age take
daily folic acid supplement regardless of their
pregnancy plans, as the most important period of
supplementation appears to be the four to six
weeks before CONCEPTION through the first
trimester of pregnancy. Some antiseizure medications
(notably valproic acid), DIABETES, and OBESITY
increase the risk for neural tube defects. Though
most spina bifida seems to occur spontaneously,