#187 Neural Tube Defects Flashcards
What are neural tube defects?
Congenital structural abnormality of the CNS and vertebral column
What is the second-most-common major congenital anomaly?
Neural tube defect (after cardiac malformations)
How can you primarily prevent neural tube defects?
Folic acid supplementation
What forms the neural tube?
Flat sheet of neuroepithelial cells (neural plate), which rolls or folds in the midline to for the neural tube
When does the neural tube form?
3-4 weeks after fertilization
In which direction does the neural tube close?
Starts at the cervical region and extends cranially and caudally
What is anencephaly?
Failure of fusion of cephalic portion of neural folds; absence of all or part of brain, skull, and skin
What is exencephaly?
Failure of scalp and skull formation; exteriorization of abnormally formed brain
What is encephalocele?
Failure of complete skull formation; extrusion of brain tissue into membranous sac
What is iniencephaly?
Defect of cervical and upper thoracic vertebrae; abnormally formed brain tissue and extreme retroflexion of upper spine. Abnormalities in development of diaphragm, lungs, and heart
What is spina bifida?
Failure of fusion of caudal portion of neural tube, usually of 3-5 continguous vertebrae; spinal cord or meninges, or both, exposed to amniotic fluid
What is meningocele?
Failure of fusion of caudal portion of neural tube; meninges exposed
What is myelomeningocele?
Failure of fusion of caudal portion of neural tube; meninges and neural tissue exposed
What is myeloschisis?
Failure of fusion of caudal portion of neural tube; flattened mass of neural tissue exposed
What is holorachischisis?
Failure of fusion of vertebral arches; entire spinal cord exposed
What is craniorachischisis?
Coexisting anencephaly and open neural tube defect, often in the cervical-thoracic region
What is the prevalence of anencephaly in the US per 10,000 live births? Per 10,000 live births, stillbirths, or terminations? (2004-2006)
0.55 per 10,000 live births. 2.54 per 10,000 live births, stillbirths, or terminations
What is the prevalence of spina bifida in the US per 10,000 live births? Per 10,000 live births, stillbirths, or terminations? (2004-2006)
3.4 per 10,000 live births. 4.41 per 10,000 live births, stillbirths, or terminations
What is the mode of inheritence of isolated (nonsyndromic) neural tube defects?
Multifactorial, combo of genetic and environmental factors
What medications/environmental exposures are associated with increased risk of neural tube defects?
Those that interfere with, or deplete, folic acid (taken in first 28 days). Valproic acid, fungal toxin fumonisin, maternal hyperthermia (fever, hot tub, sauna)
How much does use of valproic acid increase risk of neural tube defect?
10- to 20-fold increased risk
How much does maternal febrile illness during first trimester increase risk of neural tube defect?
As much as 3-fold
How much does hot tube use during early pregnancy increase the risk of anencephaly?
1.7-fold increase
What maternal medical conditions are associated with increased risk of neural tube defects?
Pregestational diabetes and obesity
Does pregestational diabetes increase the risk of neural tube defects?
Yes
Does obesity increase the risk of neural tube defects?
Yes
What general classes of genes are implicated in neural tube closure?
Genes related to folate metabolism; planar cell polarity genes (involved in cell movement during closure); and genes involved in development of cilia that are essential for cell signaling
What does the methylenetetrahydrofolate reductase (MTHFR) gene do?
Encodes a cytoplasmic enzyme involved in conversion of homocysteine to methionine
What is the risk of having a subsequent child with neural tube defect after have one previously? Having two previously?
3.2% and 10%
What anatomic changes are associated with failure of fusion of the neural tube at the caudal end?
Meningocele, myelomeningocele. Hydrocephalus, abnormal head shape, decreased biparietal diameter or head circumference, and Arnold-Chiari or Chiari type II malformation (herniation of the hindbrain)
What anatomic changes are commonly associated with spina bifia?
Talipes equinovarus (clubfoot) and scoliosis
Polyhydramnios is associated with anencephaly, why?
Impaired fetal swallowing
What characteristics of spina bifida are significant prognostic factors?
Size and location of the lesion and presence of hydrocephalus
With surgical and medical management, what % of infants with myelomeningocele will survive to early adulthood
75%
True or false, most patient’s with myelomeningocele have lower urinary tract dysfunction?
True, neurogenic bladder
Are children with myelomeningocele at risk of renal dysfunction? What risk does this pose?
Yes. Approximately 30-40% eventually develop renal dysfunction, which has been associated with death in nearly one third of patients with open spina bifida
Does a neural tube defect typically affect the gastrointestinal system, if so how?
Nearly all patients with open NTD have innervation abnormalities of the bowel and anus resulting in bowel dysfunction, and most will have fecal incontinence
What particular allergy is common with patient’s with a neural tube defect?
One third of individuals with a neural tube defect have a severe allergy to latex
True or false, the majority of adults with spina bifida are able to live independently?
False. Only a minority are able to
What is the daily recommended amount of folic acid that a pregnant woman should take? What about women at high risk of pregnancy affected by neural tube defect?
400mcg folate daily. 4mg daily for high risk.
What % of neural tube defects are not prevented by folate supplementation?
At least 30%
When should folate supplementation begin in regards to pregnancy? And continue for how long?
At least 1 month before pregnancy and continue through 12wks of pregnancy.
What % of neural tube defects could be prevented by folic acid supplementation?
16-58% of neural tube defects
By how much (%) does folic acid supplementation decrease risk of spina bifida and anencephaly?
79% reduction in spina bifida, 57% in anencpehaly
What women are high risk for pregnancy c/b neural tube defects
History of prior affected pregnancy, women affected by NTD themselves, partner affected by NTD, partner with previously affected child
What folic acid regmin (dose and timing) for women at high risk of NTD?
4mg daily starting 3 months prior to pregnancy and continued until 12 wks gestation
What are causes of folate-resistant neural tube defects?
Poor glucose control in first trimester, hyperthermia, maternal obesity, and aneuploidy or genetic disorders, antiepileptic medication (valproate)
What is the recommended limit of vitamin A intake in a pregnant woman per day?
No more than 5,000 international units
Is folic acid water or lipid soluble?
Water soluble
Where is alpha-fetoprotein secreted from?
Fetal yolk sac and liver
How does fetal serum concentrations of AFP compare to amniotic fluid levels?
150-200x higher
When should you measure maternal serum AFP?
Between 15 and 18 weeks
What is the detection rate of anencephaly with MSAFP?
95%
What is the detection rate of open neural tube defects with MSAFP?
65-80%
Apart from open neural tube defects, what else will cause an elevated MSAFP?
Inaccurate gestational dating, multiple gestation, fetal abdominal wall defects, fetal nephrosis, fetal demise, and placental conditions
Is MSAFP increased with closed neural tube defects?
Not usually
Does MSAFP or second-trimester ultrasound have a higher detection rate for neural tude defects?
Second-trimester ultrasound
What ultrasound findings are seen in 2nd trimester in fetus with anencephaly?
absence of fetal cranium and significant facial dysmorphology
What ultrasound findings are seen in 2nd trimester in fetus with spina bifida?
abnormal posterior vertebral arches and a protuberant myelomeningocele sac for open and closed NTD, although these may not be as evident with closed spinal abnormalities. Lemon sign and banana sign and ventriculomegaly
What percent of fetuses with open spinda bifida will have ultrasound findings betwen 18-22wks?
More than 95%
For patients with fetus with a NTD, what additional testing should be offered?
Thorough ultrasound for additional anomalies, amniocentesis for genetic testing as results would affect counseling
Measurement of what in the amniotic fluid helps differentiate between open and closed NTD?
Measurement of acetylcholinesterase
What is the next step for work up if ultrasound for fetus at 18-22wk is unclear about presence of NTD?
Fetal MRI
Does in utero fetal surgery performed during pregnancy change the recommended delivery time?
Yes. Late-preterm to early-term because of the high risk of uterine rupture, similar to patients with prior classical cesarean section
In general, do you recommend that patients with fetus with spina bifida deliver at term or induce early?
Generally, delivery at term is preferred.
In what cases would you recommend early delivery for patient with fetus with spina bifida?
If had in utero fetal surgery (risk of uterine rupture) or if there were rapidly increasing ventriculomegaly (to place VP shunt)
Should babies with spina bifida be delivered by cesarean or vaginally?
Remains controversial (for normal head size and cephalic presentation). Overwhelming majority of evidence suggests that vaginal does not adversely affect neonatal outcome with meningomyelocele
Do you need any special equipment/PPE for a cesarean and vaginal delivery for a baby with spina bifida?
Latex-free equipment, high risk of latex allergy in patients with spina bifida
How are outcomes for children with spina bifida if they receive in utero surgery versus postnatal?
Prenatal surgery: more likely to have higher level of function compared to postnatal. No differences in regard to cognitive scores
Can a women who underwent prior fetal surgery undergo a vaginal delivery?
No, recommend cesarean for all subsequent deliveries.
What are risks of fetal surgery?
Preterm delivery, rupture of membranes, oligohydramnios, partial or complete dehiscence of hysterotomies, transfusion at delivery, pulmonary edema
