Spinal Cord Defects
Various malformations of the spineincluding spina bifida, meningocele, and myelomeningocele - result from defective embryonic neural tube closure during the first trimester of pregnancy. Generally, these defects occur in the lumbosacral area, but they are occasionally found in the sacral, thoracic, and cervical areas.
Spina bifida occulta is the most common and least severe spinal cord defect. It's characterized by incomplete closure of one or more vertebrae without protrusion of the spinal cord or meninges.
However, in more severe forms of spina bifida, incomplete closure of one or more vertebrae causes protrusion of the spinal contents in an external sac or cystic lesion.
In spina bifida with meningocele, this sac contains meninges and cerebrospinal fluid (CSF). In spina bifida with myelomeningocele (meningomyelocele), this sac contains meninges, CSF, and a portion of the spinal cord or nerve roots distal to the conus medullaris.
Spina bifida is relatively common and affects about 5% of the population. In the United States, about 12,000 neonates each year are born with some form of spina bifida; spina bifida with myelomeningocele is less common than spina bifida occulta and spina bifida with meningocele. Incidence is highest in persons of Welsh or Irish ancestry.
The prognosis varies with the degree of accompanying neurologic deficit. It's worst in patients with large open lesions, neurogenic bladders (which predispose to infection and renal failure), or total paralysis of the legs.
Normally, about 20 days after conception, the embryo develops a neural groove in the dorsal ectoderm. This groove rapidly deepens, and the two edges fuse to form the neural tube.
By about day 23, this tube is completely closed except for an opening at each end. Theoretically, if the posterior portion of this neural tube fails to close by the fourth week of gestation, or if it closes but then splits open from a cause such as an abnormal increase in CSF later in the first trimester, a spinal defect results.
Viruses, radiation, and other environmental factors may be responsible for such defects. However, spinal cord defects occur more often in offspring of women who have previously had children with similar defects, so genetic factors may also be responsible.
Signs and symptoms
The symptoms vary as to the level of the condition. In some cases, the spinal cord may protrude through the back and be covered by skin or a thin membrane.
Children with spina bifida may also have hydrocephalus, syringomyelia and chiari malformations. They may suffer physical problems related to the spinal cord including muscle paralysis, bowel and bladder complications, respiratory difficulties and swallowing problems. They can have secondary conditions such as learning problems, latex allergies, tendinitis, obesity, skin breakdown, gastrointestinal disorders, depression and social issues.
The diagnosis varies with the type of defect.
Spina bifida occulta
Although often overlooked, spina bifida occulta is occasionally palpable, and a spinal X-ray can show the bone defect. Myelography can differentiate it from other spinal abnormalities, especially spinal cord tumors.
Meningocele and myelomeningocele
Meningocele and myelomeningocele are obvious on examination; transillumination of the protruding sac can sometimes distinguish between them. (In meningocele, it typically transilluminates; in myelomeningocele, it does not.)
In myelomeningocele, a pinprick examination of the legs and trunk shows the level of sensory and motor involvement; skull X-rays, cephalic measurements, and a computed tomography scan demonstrate associated hydrocephalus.
Other appropriate laboratory tests in patients with myelomeningocele include urinalysis, urine cultures, and tests for renal function starting in the neonatal period and continuing at regular intervals.
Although amniocentesis can detect only open defects, such as myelomeningocele and meningocele, this procedure is recommended for all pregnant women who have previously had children with spinal cord defects; these women are at an increased risk for having children with similar defects. If these defects are present, amniocentesis shows increased alpha-fetoprotein levels by 14 weeks' gestation.
Ultrasonography can also detect or confirm the presence and extent of neural tube defects.
Spina bifida occulta usually requires no treatment. Treatment of meningocele consists of surgical closure of the protruding sac and continual assessment of growth and development.
Treatment of myelomeningocele requires repair of the sac and supportive measures to promote independence and prevent further complications. Surgery doesn't reverse neurologic deficits. A shunt may be needed to relieve associated hydrocephalus.
If the patient has a severe spinal defect, short- and long-term treatment will require a team approach, including a neurosurgeon, orthopedist, urologist, nurse, social worker, occupational and physical therapists, and parents.
In children or adults, rehabilitation measures may include:
Folic acid supplements may be effective at reducing the risk of neural tube defects such as myelomeningocele. Folic acid ( folate ) deficiencies must be corrected BEFORE becoming pregnant as the defects develop very early. Prospective mothers may be screened to determine their serum folate level . It is recommended that any woman considering becoming pregnant take 0.4mg of folic acid a day. Pregnant women need 1 mg per day.
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