Neural Tube Defects
Neural Tube Defects: Excerpt from The 5-Minute Pediatric Consult
Sabrina E. Smith, MD, PhD
Dennis J. Dlugos, MD
Neural Tube Defects - BASICS
Neural Tube Defects - description
Neural tube defects (NTD) include clinical and subclinical defects resulting from failure of neural tube closure between the 3rd and 4th weeks of gestation. NTDs include anencephaly, encephalocele, myelomeningocele, meningocele, and occult spinal dysraphism. The latter 3 are different types of spina bifida.
Neural Tube Defects - general prevention
- Folic acid supplementation in early pregnancy can reduce the incidence of NTDs by 50% in the general population and by 70% in women with a history of NTD in a previous pregnancy.
- Because many pregnancies are not discovered until after the 4th week of gestation, when neural tube closure occurs, the Centers for Disease Control and Prevention (CDC) recommend that all women of childbearing age receive a minimum of 0.4 mg of folic acid daily.
- The American Academy of Pediatrics recommends that women with a history of NTD in a previous pregnancy receive 4 mg of folic acid daily, starting 1 month before and through the 1st 3 months of pregnancy.
- Women on anticonvulsants and other medications linked to NTDs may benefit from receiving 4 mg (high-risk dose = 4000 mcg) of folic acid daily.
Neural Tube Defects - epidemiology
Neural Tube Defects - prevalence
- 1 in 1,000 live births in the US (not including occult defects, for which no accurate epidemiologic data are available)
- Anencephaly: 3.7 in 10,000
- Encephalocele: 1.4 in 10,000
- Spina bifida: 5.5 in 10,000
- Myelomeningocele: 2–4 in 10,000
Neural Tube Defects - risk factors
Neural Tube Defects - genetics
- Most cases are due to a combination of genetic, environmental, and dietary factors. However, a chromosomal or gene abnormality can be identified in ~10% of children with NTDs, and this number increases if there are multiple congenital anomalies.
- Recent studies suggest that the 677C >T mutation in the methylenetetrahydrofolate reductase gene in mother or child is associated with increased risk of NTDs.
- 5% of patients are born to a couple with a family history of NTD
- After 1 child with NTD, the recurrence rate is 2–4% for subsequent pregnancies.
Neural Tube Defects - pathophysiology
- Neural tube closure begins midway along the neural axis, spreads like a zipper in both rostral and caudal directions, and is completed in a few days.
- Failure of neural tube closure most often occurs in the lumbosacral region.
Neural Tube Defects - etiology
- Genetic
- Maternal folic acid deficiency
- Gestational diabetes
- Maternal hyperthermia during days 20–28 of gestation
- Use of valproic acid, carbamazepine, and alcohol during pregnancy
Neural Tube Defects - associated conditions
The defect itself may be only the tip of the iceberg, because the malformation may involve the entire central nervous system:
- Disorganized brainstem nuclei or brainstem herniation (Chiari II malformation)
Neural Tube Defects - DIAGNOSIS
Neural Tube Defects - signs & symptoms
Neural Tube Defects - history
- Thorough health history: NTDs are associated with maternal folic acid deficiency, gestational diabetes, maternal hyperthermia during days 20–28 of gestation, and use of valproic acid, carbamazepine, and alcohol during pregnancy.
- Activity and development:
- Occult frontal encephaloceles may come to attention because of a history of developmental delay, seizures, or focal neurologic signs.
- Occult spinal dysraphism presents with lower extremity weakness or sensory loss, gait abnormalities, bowel and bladder dysfunction, foot deformities, and (rarely) recurrent meningitis.
Neural Tube Defects - physical exam
- Plot head circumference as a marker of developing hydrocephalus.
- Evidence of dysmorphic features: May indicate a syndrome
- Integrity of the skin covering the defect, because this affects the timing of surgical intervention. A bony defect or sinus may be palpable in occult cases.
- Neurologic exam of the lower extremities in a myelomeningocele outlines the functional level of the lesion and can indicate ambulatory potential: Intact hip flexion (L1-L2) and knee extension (L3-L4) are favorable signs for future ambulation.
- Flaccid paralysis is present below the level of the lesion, and limb growth may be asymmetric:
- Sensory level may not correspond to motor level.
- Cranial neuropathies, such as strabismus, laryngeal paresis, and stridor, may be present at birth or may develop in the 1st months of life.
- Local signs of occult spinal dysraphism include a dimple, sinus, lipoma, skin pigment change, or tuft of hair in the lumbosacral area.
- Examination may show foot deformities, tight heel cords, unequal leg or foot length, decreased sphincter tone, lower extremity weakness, or sensory changes.
Neural Tube Defects - tests
Neural Tube Defects - lab
Maternal serum α-fetoprotein (MSAFP) testing, done at 16–18 weeks’ gestation, can identify 88% of cases of anencephaly and 79% of cases of myelomeningocele.
Neural Tube Defects - imaging
- Ultrasonography:
- Reveals >99% of cases of anencephaly and 90% of cases of myelomeningocele
- Encephaloceles is more likely to be detected by ultrasound than by MSAFP testing.
- Serial cranial ultrasounds or CT scans can evaluate hydrocephalus, which can occur without rapid head growth in patients with NTDs.
- MRI for other brain anomalies, including areas of cortical dysplasia, found in 92% of patients in one neuropathologic study
- Suspected occult spinal dysraphism (often asymptomatic):
- Incidentally noted on spine radiographs
- Ultrasound (in the newborn period)
- CT scan provides more detail of bony anatomy and MRI more detail of spinal cord anatomy.
Neural Tube Defects - diag proced-surgery
- EEG for suspected seizures
- Urodynamic evaluation should be performed in all children with myelomeningocele to anticipate/prevent renal damage owing to reflux.
Neural Tube Defects - differencial diagnosis
Diagnosis reflects the embryogenesis and anatomy of each defect:
- Anencephaly results from failure of anterior neural tube closure:
- The diagnosis is obvious at birth.
- The cerebral hemispheres, basal ganglia, and variable amounts of the upper brainstem are absent.
- 75% are stillborn; the remainder die in the neonatal period
- Encephalocele reflects partial failure of anterior neural tube closure:
- Abnormal brain tissue protrudes through a skull defect usually covered by skin.
- 70–80% are occipital, 20% are frontal
- 10–20% of occipital defects are meningoceles and contain no brain tissue
- Frontal encephaloceles, unless accompanied by craniofacial abnormalities, may not be identified unless a neuroimaging study is performed for an associated symptom (such as developmental delay or seizures).
- Myelomeningocele is a failure of posterior neural tube closure:
- Abnormal neural tissue protrudes through a vertebral column defect.
- 80% are thoracolumbar, lumbar, or lumbosacral.
- By definition, this is an open defect, and the diagnosis is obvious at birth.
- Occult spinal dysraphism: Intact skin over the defect:
- Wide spectrum of defects includes dermal sinus tracts, cysts, lipomas, other tumors, diastematomyelia (bifid spinal cord), and tethered spinal cord.
- A syndromic basis for dysraphism is considered when non-neural congenital defects are present (e.g., telecanthus [Waardenburg syndrome]; conotruncal heart defect [chromosome 22q11 deletion]).
Neural Tube Defects - TREATMENT
Neural Tube Defects - initial stabilization
Urgent stabilization in the newborn period, followed by prompt neurosurgical closure:
- Acute hydrocephalus from shunt failure or tethered spinal cord from occult spinal dysraphism may arise later in life.
Neural Tube Defects - general measures
- Route of delivery:
- For most patients with NTDs and vertex presentation, no clear benefit of cesarean delivery
- One study demonstrated improved neurologic outcome in patients delivered via cesarean.
- Infants with high bladder pressure typically are treated initially with anticholinergics and clean intermittent catheterization.
Neural Tube Defects - surgery
- Neurosurgical closure of a myelomeningocele within the 1st few days of life to prevent infection and for cosmetic reasons. Closure of the defect in the 1st hours of life is not necessary; keep defect clean and moist:
- An encephalocele with adequate skin covering can be repaired less urgently.
- Promising results are reported for fetal surgery closures.
- Ventriculoperitoneal shunts should be placed in infants with hydrocephalus, because early treatment of hydrocephalus may improve cognitive outcome.
Neural Tube Defects - FOLLOW UP
- Multidisciplinary approach may include primary pediatrician, neurosurgeon, urologist, orthopedist, neurologist, physiatrist, and others.
- Anticipation of skin breakdown, decubitus ulcers, and leg injuries is important.
- In an older child with a myelomeningocele, loss of motor function in the legs, increased spasticity, gait difficulties, pain, bladder dysfunction, and scoliosis may be signs of a tethered cord.
Neural Tube Defects - disposition
Neural Tube Defects - issues for referral
Occult spinal dysraphism is most often benign/asymptomatic, but if there are possible neurologic signs or symptoms patient should be referred to neurosurgery for evaluation.
Neural Tube Defects - prognosis
- Anencephaly is uniformly fatal.
- Encephalocele: Prognosis is largely dependent on the size of the defect, the amount of brain tissue contained within the sac, and any associated brain malformations.
- Myelomeningocele:
- Prognosis for ambulation depends on the location of the lesion: The lower the lesion, the more likely the patient will ambulate:
- Virtually all children with sacral lesions are able to ambulate; 95% of adolescents and 40% of younger children with low lumbar lesions will ambulate; 30% of adolescents with high lumbar or thoracic lesions will ambulate.
- Cognitive outcome depends in part on associated brain malformations and treatment of hydrocephalus.
- ~80% of children with myelomeningocele will have a neurogenic bladder (urodynamic testing). The goal of therapy is urinary continence and control of high bladder pressure.
- Many children can ultimately achieve bowel control with bowel programs involving high-fiber, low-fat foods; enemas; stool softeners; and biofeedback.
- ~60% of children with encephalocele and 80–85% with myelomeningocele are of normal intelligence.
- Risk of epilepsy corresponds to degree of mental retardation; high with frontal encephaloceles.
Neural Tube Defects - complications
- Encephalocele:
- Hydrocephalus (50%)
- Intellectual deficits (40%)
- Motor and cognitive deficits
- Seizures likely owing to dysplastic cortex surrounding the encephalocele
- Myelomeningocele:
- Hydrocephalus (80%)
- Chiari II malformation (80%), potential feeding difficulties, stridor, and apnea due to lower cranial nerve dysfunction
- Neurogenic bladder (80%): Risk of renal damage
- Orthopedic deformities; seizures (25%)
- Below-average intelligence (15–20%)
- Tethered spinal cord later in childhood
- Occult dysraphism:
- Progressive lower extremity motor or sensory deficit
- Gait dysfunction
- Sphincter dysfunction
- Foot deformities
- Scoliosis
Neural Tube Defects - patient monitoring
- The neurologic status of a patient with a repaired NTD should remain stable overall. Have a high index of suspicion for worsening hydrocephalus, syringomyelia, and tethered spinal cord—all treatable conditions that may develop over time.
- Tethered cord may accompany occult dysraphism and is a surgically treatable cause of acquired neurogenic bladder/cauda equina syndrome in young children.
- Vocal cord paralysis may appear episodically, resembling croup, in children with myelomeningocele.
Neural Tube Defects - bibliography
- Adzick NS, Walsh DS. Myelomeningocele: Prenatal diagnosis, pathophysiology and management. Semin Pediatr Surg. 2003;12:168–174.
- Blom HJ, Shaw GM, den Heijer M, et al. Neural tube defects and folate: Case far from closed. Nat Rev Neurosci. 2006;7(9):724–731.
- Botto LD, Moore CA, Khoury MJ, et al. Neural-tube defects. N Engl J Med. 1999;341:1509–1519.
- Drolet B. Birthmarks to worry about: Cutaneous markers of dysraphism. Dermatol Clin. 1998;16:447–453.
- Rowland CA, Correa A, Cragan JD, et al. Are encephaloceles neural tube defects? Pediatrics. 2006;118(3):916–923.
Neural Tube Defects - OTHER
Patient Information:
Spina Bifida Association of America Web site: http://www.sbaa.org
Neural Tube Defects - CODES
Neural Tube Defects - icd9
- 740.0 Anencephaly
- 741.9 Myelomeningocele
Neural Tube Defects - FAQ
- Q: Will my child have learning problems?
- A: At least 80% of those with myelomeningocele have normal intelligence. Cognitive outcome appears improved with early shunting of hydrocephalus.
- Q: Could my baby have other problems besides neurologic problems?
- A: Infants with NTDs need to be checked periodically for signs of bladder problems. Some develop problems with control of eye movements (strabismus), but this is often correctable.
- Q: Should I stop taking anticonvulsants during pregnancy to reduce my risk of NTDs?
- A: Not unless your doctor recommends doing so. In general, continuing the lowest dose of the medicine that best controls your seizures is recommended during pregnancy. There are risks to the fetus from poorly controlled seizures during pregnancy. The overall risks and benefits of medications must be weighed. Any woman of childbearing age who is taking anticonvulsants should receive folic acid supplementation.
Book Source Details
- Book Title: The 5-Minute Pediatric Consult
- Author(s): M. William Schwartz MD; et al.
- Year of Publication: 2008
- Copyright Details: The 5-Minute Pediatric Consult, Copyright © 2008 Lippincott Williams & Wilkins.
More About Neural tube defect
More Medical Textbooks Online about Neural tube defect
Review other book chapters online related to Neural tube defect:
Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
|
|
More About This Book:
Title: The 5-Minute Pediatric Consult
Authors: M. William Schwartz MD; et al.
Publisher: Lippincott Williams & Wilkins
Copyright: 2008
ISBN: 0-7817-7577-9
|
|
» Next page: Surveys relating to Neural tube defect
Rate This Website
What do you think about the features of this website?
Take our user survey and have your say:
Website User Survey
Medical Tools & Articles:
Next articles:
Tools & Services:
Medical Articles:
Forums & Message Boards
- Ask or answer a question at the Boards:
