• Information
  1. Characteristics
  2. Epidemiology
  3. Etiology and Risks
  4. Types
  5. Diagnosis
  6. Treatment
  7. Prevention

A. Characteristics

1. Congenital anomaly of the spinal cord
2. Spina bifida
   1. Nonfusion of the embryonic halves of the vertebral arches
   2. Also described as failure of fusion of caudal neural tube
3. Occurs during the fourth week of fetal development
4. Considered a "dysraphic" disease
5. Sometimes allows the brain or spinal cord to herniate through the opening

B. Epidemiology

1. Most common major birth defect among live born infants in the United States
2. Incidence 0.15% among whites and 0.04% among blacks
3. Half of cases attributed to nutritional deficiencies
4. Remaining cases have a multi-factorial inheritance pattern

C. Etiology and Risks

1. Most cases are idiopathic
2. Chromomsal abnormalities
3. Single gene disorders - likely folate pathway gene disorders
4. Teratogenic exposures
5. About 70% of spina bifida is prevented by maternal preiconceptional folic acid supplements
   1. Mechanism of protection unclear
   2. Likely that genes regulating folate transport and metabolism involved
6. Risk Factors
   1. History of previous affected pregnancy with same partner: 30X risk
   2. Inadequate maternal folic acid intake: ~4X risk
   3. Pregestational maternal diabetes: ~6X risk
   4. Valproic acid or carbamazepine: ~15X risk

D. Types

1. Spina Bifida Occulta
   1. Failure of the L5 or S1 vertebrae to fuse
   2. In minor form seen as a small dimple with a tuft of hair on the back
   3. Rarely causes significant defects of spinal cord and roots
   4. Present in 10% of otherwise normal people
2. Spina Bifida Cystica
   1. Severe type of spina bifida
   2. Spinal cord and or meninges protrude through defect in the vertebral arch
   3. Most commonly seen in lumbar region
   4. Occurs in once in every 1000 births
3. Spina Bifida Cystica Subtypes
   1. Meningocoele
   2. Meningomyelocoele
   3. Myeloschisis
4. Meningocoele
   1. Sac contains meninges and CSF
   2. Spinal cord and roots in normal positions
5. Meningomyelocele
   1. Spinal cord and nerve roots are in the hernia sac
   2. Nervous tissue incorporated into wall of sac impairing nerve fiber development
   3. Associated with marked neurologic deficit below the level of the herniation
   4. Deficits include dermatomal sensation loss with complete or partial muscle paralysis
   5. Bowel and bladder spincter paralysis common
   6. Latex allergies common
6. Myeloschisis
   1. Neural fold fails to fold during fourth week leaving spinal cord open
   2. The affected spinal cord is a flattened mass of nervous tissue
   3. Severe neurologic defects associated

E. Diagnosis

1. Elevated levels of maternal and amniotic AFP raise suspicion for all neural tube defects
2. Ultrasound at 10 to 12 weeks to look for a cystic mass adjacent to the vertebral column

F. Treatment [1,2]

1. Termination sometimes elected for severe neural tube defects detected in utero
2. Neurosurgical Interventions
   1. Initial sac closure within 48 hours of life to prevent CNS infections
   2. Ventriculoperitoneal shunt placement in perinatal period
   3. Late tethered cord syndrome requires surgical freeing up of tight roots
   4. In utero neurosurgical repair - over 200 cases reported with apparent benefits
3. Orthopedic Interventions
   1. Splinting or casting for foot deformities begun in perinatal period
   2. Corrective foot surgery between 12 to 15 months
   3. Hip surgical releases necessary for major contractures
   4. Surgical hip dislocation correction in ambulatory patients
   5. Scoliosis complicates 50% of cases and requires braces or surgery
4. Urologic corrections to attempt bowel and bladder continence
5. Agressive physical rehabilitation

F. Prevention [2,3]

1. Vitamins and folic acid prior to conception reduce incidence of spina bifida
   1. Mothers of infants with neural tube defects noted to have low blood folic acid levels
   2. Trials of folic acid supplements in the first 6 weeks of pregnancy were completed
   3. These trials showed a 2 to 4-fold reduction in neural tube defects
   4. Folic acid shown to reduce recurrence by 70% with one prior affected child
   5. Dose of 400µg (mcg) or more of folic acid appears to reduce excess risk
   6. Ongoing consideration of supplementing flour or grains with folate
2. Various Drugs increase risk of spina bifida
3. Valproic acid and other antiepileptics in early pregnancy increases risk
4. May be as high as 1-2% of pregnancies with some antiepileptics
5. High vitamin A levels shown in animals to increase risk of neural tube defects

References

1. Mitchell LE, Adzick NS, Melchionne J, et al. 2004. Lancet. 364:1885
2. Botto LD, Moore CA, Khoury MJ, Erickson JD. 1999. NEJM. 341(20):1509
3. Berry RJ, Li Z, Erickson JD, et al. 1999. NEJM. 341(20):1485