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Practice bulletins > #187 Neural Tube Defects > Flashcards

#187 Neural Tube Defects Flashcards

1
Q

What are neural tube defects?

A

Congenital structural abnormality of the CNS and vertebral column

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2
Q

What is the second-most-common major congenital anomaly?

A

Neural tube defect (after cardiac malformations)

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3
Q

How can you primarily prevent neural tube defects?

A

Folic acid supplementation

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4
Q

What forms the neural tube?

A

Flat sheet of neuroepithelial cells (neural plate), which rolls or folds in the midline to for the neural tube

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5
Q

When does the neural tube form?

A

3-4 weeks after fertilization

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6
Q

In which direction does the neural tube close?

A

Starts at the cervical region and extends cranially and caudally

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7
Q

What is anencephaly?

A

Failure of fusion of cephalic portion of neural folds; absence of all or part of brain, skull, and skin

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8
Q

What is exencephaly?

A

Failure of scalp and skull formation; exteriorization of abnormally formed brain

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9
Q

What is encephalocele?

A

Failure of complete skull formation; extrusion of brain tissue into membranous sac

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10
Q

What is iniencephaly?

A

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

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11
Q

What is spina bifida?

A

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

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12
Q

What is meningocele?

A

Failure of fusion of caudal portion of neural tube; meninges exposed

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13
Q

What is myelomeningocele?

A

Failure of fusion of caudal portion of neural tube; meninges and neural tissue exposed

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14
Q

What is myeloschisis?

A

Failure of fusion of caudal portion of neural tube; flattened mass of neural tissue exposed

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15
Q

What is holorachischisis?

A

Failure of fusion of vertebral arches; entire spinal cord exposed

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16
Q

What is craniorachischisis?

A

Coexisting anencephaly and open neural tube defect, often in the cervical-thoracic region

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17
Q

What is the prevalence of anencephaly in the US per 10,000 live births? Per 10,000 live births, stillbirths, or terminations? (2004-2006)

A

0.55 per 10,000 live births. 2.54 per 10,000 live births, stillbirths, or terminations

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18
Q

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)

A

3.4 per 10,000 live births. 4.41 per 10,000 live births, stillbirths, or terminations

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19
Q

What is the mode of inheritence of isolated (nonsyndromic) neural tube defects?

A

Multifactorial, combo of genetic and environmental factors

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20
Q

What medications/environmental exposures are associated with increased risk of neural tube defects?

A

Those that interfere with, or deplete, folic acid (taken in first 28 days). Valproic acid, fungal toxin fumonisin, maternal hyperthermia (fever, hot tub, sauna)

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21
Q

How much does use of valproic acid increase risk of neural tube defect?

A

10- to 20-fold increased risk

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22
Q

How much does maternal febrile illness during first trimester increase risk of neural tube defect?

A

As much as 3-fold

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23
Q

How much does hot tube use during early pregnancy increase the risk of anencephaly?

A

1.7-fold increase

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24
Q

What maternal medical conditions are associated with increased risk of neural tube defects?

A

Pregestational diabetes and obesity

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25
Q

Does pregestational diabetes increase the risk of neural tube defects?

A

Yes

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26
Q

Does obesity increase the risk of neural tube defects?

A

Yes

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27
Q

What general classes of genes are implicated in neural tube closure?

A

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

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28
Q

What does the methylenetetrahydrofolate reductase (MTHFR) gene do?

A

Encodes a cytoplasmic enzyme involved in conversion of homocysteine to methionine

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29
Q

What is the risk of having a subsequent child with neural tube defect after have one previously? Having two previously?

A

3.2% and 10%

30
Q

What anatomic changes are associated with failure of fusion of the neural tube at the caudal end?

A

Meningocele, myelomeningocele. Hydrocephalus, abnormal head shape, decreased biparietal diameter or head circumference, and Arnold-Chiari or Chiari type II malformation (herniation of the hindbrain)

31
Q

What anatomic changes are commonly associated with spina bifia?

A

Talipes equinovarus (clubfoot) and scoliosis

32
Q

Polyhydramnios is associated with anencephaly, why?

A

Impaired fetal swallowing

33
Q

What characteristics of spina bifida are significant prognostic factors?

A

Size and location of the lesion and presence of hydrocephalus

34
Q

With surgical and medical management, what % of infants with myelomeningocele will survive to early adulthood

A

75%

35
Q

True or false, most patient’s with myelomeningocele have lower urinary tract dysfunction?

A

True, neurogenic bladder

36
Q

Are children with myelomeningocele at risk of renal dysfunction? What risk does this pose?

A

Yes. Approximately 30-40% eventually develop renal dysfunction, which has been associated with death in nearly one third of patients with open spina bifida

37
Q

Does a neural tube defect typically affect the gastrointestinal system, if so how?

A

Nearly all patients with open NTD have innervation abnormalities of the bowel and anus resulting in bowel dysfunction, and most will have fecal incontinence

38
Q

What particular allergy is common with patient’s with a neural tube defect?

A

One third of individuals with a neural tube defect have a severe allergy to latex

39
Q

True or false, the majority of adults with spina bifida are able to live independently?

A

False. Only a minority are able to

40
Q

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?

A

400mcg folate daily. 4mg daily for high risk.

41
Q

What % of neural tube defects are not prevented by folate supplementation?

A

At least 30%

42
Q

When should folate supplementation begin in regards to pregnancy? And continue for how long?

A

At least 1 month before pregnancy and continue through 12wks of pregnancy.

43
Q

What % of neural tube defects could be prevented by folic acid supplementation?

A

16-58% of neural tube defects

44
Q

By how much (%) does folic acid supplementation decrease risk of spina bifida and anencephaly?

A

79% reduction in spina bifida, 57% in anencpehaly

45
Q

What women are high risk for pregnancy c/b neural tube defects

A

History of prior affected pregnancy, women affected by NTD themselves, partner affected by NTD, partner with previously affected child

46
Q

What folic acid regmin (dose and timing) for women at high risk of NTD?

A

4mg daily starting 3 months prior to pregnancy and continued until 12 wks gestation

47
Q

What are causes of folate-resistant neural tube defects?

A

Poor glucose control in first trimester, hyperthermia, maternal obesity, and aneuploidy or genetic disorders, antiepileptic medication (valproate)

48
Q

What is the recommended limit of vitamin A intake in a pregnant woman per day?

A

No more than 5,000 international units

49
Q

Is folic acid water or lipid soluble?

A

Water soluble

50
Q

Where is alpha-fetoprotein secreted from?

A

Fetal yolk sac and liver

51
Q

How does fetal serum concentrations of AFP compare to amniotic fluid levels?

A

150-200x higher

52
Q

When should you measure maternal serum AFP?

A

Between 15 and 18 weeks

53
Q

What is the detection rate of anencephaly with MSAFP?

A

95%

54
Q

What is the detection rate of open neural tube defects with MSAFP?

A

65-80%

55
Q

Apart from open neural tube defects, what else will cause an elevated MSAFP?

A

Inaccurate gestational dating, multiple gestation, fetal abdominal wall defects, fetal nephrosis, fetal demise, and placental conditions

56
Q

Is MSAFP increased with closed neural tube defects?

A

Not usually

57
Q

Does MSAFP or second-trimester ultrasound have a higher detection rate for neural tude defects?

A

Second-trimester ultrasound

58
Q

What ultrasound findings are seen in 2nd trimester in fetus with anencephaly?

A

absence of fetal cranium and significant facial dysmorphology

59
Q

What ultrasound findings are seen in 2nd trimester in fetus with spina bifida?

A

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

60
Q

What percent of fetuses with open spinda bifida will have ultrasound findings betwen 18-22wks?

A

More than 95%

61
Q

For patients with fetus with a NTD, what additional testing should be offered?

A

Thorough ultrasound for additional anomalies, amniocentesis for genetic testing as results would affect counseling

62
Q

Measurement of what in the amniotic fluid helps differentiate between open and closed NTD?

A

Measurement of acetylcholinesterase

63
Q

What is the next step for work up if ultrasound for fetus at 18-22wk is unclear about presence of NTD?

A

Fetal MRI

64
Q

Does in utero fetal surgery performed during pregnancy change the recommended delivery time?

A

Yes. Late-preterm to early-term because of the high risk of uterine rupture, similar to patients with prior classical cesarean section

65
Q

In general, do you recommend that patients with fetus with spina bifida deliver at term or induce early?

A

Generally, delivery at term is preferred.

66
Q

In what cases would you recommend early delivery for patient with fetus with spina bifida?

A

If had in utero fetal surgery (risk of uterine rupture) or if there were rapidly increasing ventriculomegaly (to place VP shunt)

67
Q

Should babies with spina bifida be delivered by cesarean or vaginally?

A

Remains controversial (for normal head size and cephalic presentation). Overwhelming majority of evidence suggests that vaginal does not adversely affect neonatal outcome with meningomyelocele

68
Q

Do you need any special equipment/PPE for a cesarean and vaginal delivery for a baby with spina bifida?

A

Latex-free equipment, high risk of latex allergy in patients with spina bifida

69
Q

How are outcomes for children with spina bifida if they receive in utero surgery versus postnatal?

A

Prenatal surgery: more likely to have higher level of function compared to postnatal. No differences in regard to cognitive scores

70
Q

Can a women who underwent prior fetal surgery undergo a vaginal delivery?

A

No, recommend cesarean for all subsequent deliveries.

71
Q

What are risks of fetal surgery?

A

Preterm delivery, rupture of membranes, oligohydramnios, partial or complete dehiscence of hysterotomies, transfusion at delivery, pulmonary edema

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