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The Genome
CMECNE

Neural Tube Defects: Definitions, Key Clinical Findings and Management

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Learning Objectives and CME/Disclosure Information

This activity is intended for healthcare providers delivering care to women and their families.

After completing this activity, the participant should be better able to:

1. Describe the different types of neural tube defects
2. Discuss the recommendations for screening, diagnosis and management of fetal neural tube defects

Estimated time to complete activity: 0.5 hours

Faculty:

Susan J. Gross, MD, FRCSC, FACOG, FACMG
President and CEO, The ObG Project

Disclosure of Conflicts of Interest

Postgraduate Institute for Medicine (PIM) requires faculty, planners, and others in control of educational content to disclose all their financial relationships with ineligible companies. All identified conflicts of interest (COI) are thoroughly vetted and mitigated according to PIM policy. PIM is committed to providing its learners with high quality accredited continuing education activities and related materials that promote improvements or quality in healthcare and not a specific proprietary business interest of an ineligible company.

The PIM planners and others have nothing to disclose. The OBG Project planners and others have nothing to disclose.

Faculty: Susan J. Gross, MD, receives consulting fees from Cradle Genomics, and has financial interest in The ObG Project, Inc.

Planners and Managers: The PIM planners and managers, Trace Hutchison, PharmD, Samantha Mattiucci, PharmD, CHCP, Judi Smelker-Mitchek, MBA, MSN, RN, and Jan Schultz, MSN, RN, CHCP have nothing to disclose.

Method of Participation and Request for Credit

Fees for participating and receiving CME credit for this activity are as posted on The ObG Project website. During the period from Aug 14 2018 through Jan 25 2023, participants must read the learning objectives and faculty disclosures and study the educational activity.

If you wish to receive acknowledgment for completing this activity, please complete the post-test and evaluation. Upon registering and successfully completing the post-test with a score of 100% and the activity evaluation, your certificate will be made available immediately.

For Pharmacists: Upon successfully completing the post-test with a score of 100% and the activity evaluation form, transcript information will be sent to the NABP CPE Monitor Service within 4 weeks.

Joint Accreditation Statement

In support of improving patient care, this activity has been planned and implemented by the Postgraduate Institute for Medicine and The ObG Project. Postgraduate Institute for Medicine is jointly accredited by the Accreditation Council for Continuing Medical Education (ACCME), the Accreditation Council for Pharmacy Education (ACPE), and the American Nurses Credentialing Center (ANCC), to provide continuing education for the healthcare team.

Physician Continuing Medical Education

Postgraduate Institute for Medicine designates this enduring material for a maximum of 0.5 AMA PRA Category 1 Credit(s)™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

Continuing Nursing Education

The maximum number of hours awarded for this Continuing Nursing Education activity is 0.4 contact hours.

Read Disclaimer & Fine Print

WHAT IS IT?

Approximately 3 to 4 weeks after fertilization, the neural plate folds, creating the neural tube. There are multiple factors, environmental as well a genetic, that go in to ensuring a full closure. When this process is not fully completed, neural tube defects (NTD) result. Folic acid supplementation decreases the risk for failed closure. ACOG recommends that folic acid, 400 micrograms, should be offered to all women “capable of becoming pregnant” starting at least 1 month before pregnancy (see ‘Related ObG Topics’ for more on folic acid recommendations).

Types and Definitions

Cranial

  • Anencephaly
    • Failure of cephalic fusion
    • Abnormal clinical findings: Brain | Skull | Skin
  • Exencephaly
    • Failure of scalp/skull formation
    • Abnormal clinical findings: Exteriorization of brain
  • Encephalocele
    • Complete failure of skull formation
    • Abnormal clinical findings: Brain extrusion
  • Iniencephaly
    • Failure of cervical/upper thoracic vertebrae closure
    • Abnormal clinical findings: Brain | Thorax | Diaphragm | Lungs | Heart | Retroflexed spine

Spina Bifida – Failure of Spinal/Caudal Closure

  • Myelomeningocele
    • Abnormal clinical findings: Exposure of cord and meninges
    • Lumbosacral most common
  • Meningocele
    • Abnormal clinical findings: Exposure of meninges
  • Spina Bifida Occulta
    • Vertebral defect without spinal cord or meningeal exposure

Complex – Severe

  • Holorachischisis
    • Entire spinal cord exposed
  • Craniorachischisis
    • Anencephaly and additional NTD (usually affecting cervical-thoracic region)

KEY POINTS:

Clinical Findings

75% of infants with myelomeningocele survive to early adulthood with modern therapies

CNS

  • Ventriculomegaly (hydrocephalus)
    • Can be treated with ventriculoperitoneal shunt placement
    • Placement often in first year of life, with many requiring revisions
  • Arnold–Chiari malformation (herniation of the cerebellar tonsils and distal medulla oblongata into the foramen magnum / spinal canal
    • Risk of severe neurologic morbidity or mortality
  • Intellectual delay
    • Intelligence dependent on level/type of the NTD, Arnold-Chiari malformation, hydrocephalus

Ambulation

  • Ability to walk dependent on level of NTD
    • L4 level or lower have better function

Bladder function

  • Myelomeningocele commonly associated with neurogenic bladder
    • Not related to vertebral defect level
    • May result in chronic renal dysfunction, with related morbidity and mortality

Bowel function

  • Most patients with open (no skin covering) NTDs will have bowel dysfunction and fecal incontinence

Note: Approximately 30% of individuals with NTD will have severe, life-threatening latex allergy

Screening and Diagnosis

Elevated MSAFP 

  • Screening test only
  • Differential diagnosis
    • Incorrect dating | Multiple Gestation | Fetal demise
  • ≥2.5 MoM (15 to 20 weeks): Detection rates as follows (1to 3% false positive rate)
    • Anencephaly: >95%
    • Open NTD: 65% to 80%
  • Increased risk for adverse events like IUGR and fetal demise
  • According to the ACOG guideline, with modern ultrasound and recommendation for universal second trimester anatomy exam, MSAFP screening “is less important”
  • ACMG released an updated guideline on open neural tube defects that includes the role of MSAFP in prenatal care that includes the following points
    • Since quality ultrasound and prenatal care are not uniform, there is still a role for MSAFP screening
    • MSAFP screening can identify
      • Incorrectly dated pregnancies | Multiple gestations | Other anatomic abnormalities | Rare maternal conditions (e.g., liver cancer)
    • Follow up recommendations for elevated MSAFP are consistent with management guidelines below
    • It is important to consider a priori risk for NTD that may be elevated due to factors such as
      • Personal or family history of NTD use | Diabetes | Medications (e.g., valproate)

Ultrasound

  • 2D ultrasound can be considered diagnostic
    • 3D ultrasound not superior for diagnosis but may provide further anatomic detail
  • Optimal timing: 18 to 22 weeks, but earlier if indicated due to high risk or abnormal MSAFP
  • First-trimester
    • NTD can be diagnosed in the first trimester but less sensitive and should not replace standard second trimester ultrasound

Fetal MRI

  • To be used in conjunction with ultrasonography as indicated, particularly for diagnostic confirmation
  • MRI should not be used for
    • Routine NTD screening following ultrasound diagnosis
    • Primary NTD screening modality

Amniocentesis

  • Specifically for NTD Diagnosis
    • Reserve for acetylcholinesterase measurement if closed vs open NTD is inconclusive on ultrasound
  • ACOG recommends amniocentesis using microarray in the setting of fetal anomalies

Antepartum and Intrapartum Management

  • Refer to MFM unit with additional multidisciplinary support including genetics, pediatric neurosurgical and neonatology expertise
    • Outcomes likely superior if delivery occurs in high-risk, tertiary centers
  • Offer detailed sonography including fetal echocardiography
  • Individualize counseling
  • Increased antenatal fetal surveillance is not recommended
  • Delivery
    • Plan for term delivery but individualize (e.g., increasing hydrocephalus)
    • Cesarean section for breech presentation
    • ACOG states “Because it is not clear whether or how significantly the neurologic outcome is affected by the method of delivery in these infants, decisions about the timing and route of delivery should be made individually in consultation with personnel with experience and knowledge of NTDs”

Fetal Surgery

ACOG recommends that “utero repair is an option for women who meet appropriate criteria… only in an established fetal therapy center”

Benefits

  • Management of Myelomeningocele Study (MOMS) RCT
  • Participants
    • 19w0d to 25w6d
    • Upper border T1-S1 with Arnold–Chiari malformation
  • 12-month follow-up
  • Results
    • 158 patients
    • Lower incidence of composite outcome of fetal or neonatal death or need for shunt placement
      • 68% vs 98% | RR, 0.70; 97.7% CI, 0.58 to 0.84
    • Lower incidence of hindbrain herniation
      • 64% vs 96% | RR, 0.67; 95% CI, 0.56 to 0.81
    • Higher level of function, two or more levels better than expected, including ambulation without devices or orthotics
    • No difference in cognitive test scores

Maternal and neonatal risks

  • Planned cesarean required due to uterine rupture risk
  • Preterm birth
    • <35 weeks: 50%
    • <30 weeks: 11%
  • Other risks include
    • PROM | Oligohydramnios | Dehiscence | Transfusion
  • Endoscopic repair has been reported and may improve outcomes

Learn More – Primary Sources:

ACOG Practice Bulletin 187: Neural Tube Defects

ACMG Policy Statement on folic acid and neural tube defects

Laboratory screening and diagnosis of open neural tube defects, 2019 revision: a technical standard of the American College of Medical Genetics and Genomics (ACMG)

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Related ObG Topics:

NTDs and Pregnancy – Folic Acid Recommendations
NICHD Study Update: Does Prenatal Surgery of Myelomeningocele Improve Motor Development Beyond 2 Years Follow-Up?
Antiepileptic Drugs: What is the Impact on Risk for Birth Defects

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OBG Project CME requires a modern web browser (Internet Explorer 10+, Mozilla Firefox, Apple Safari, Google Chrome, Microsoft Edge). Certain educational activities may require additional software to view multimedia, presentation, or printable versions of their content. These activities will be marked as such and will provide links to the required software. That software may be: Adobe Flash, Apple QuickTime, Adobe Acrobat, Microsoft PowerPoint, Windows Media Player, or Real Networks Real One Player.

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This educational activity may contain discussion of published and/or investigational uses of agents that are not indicated by the FDA. The planners of this activity do not recommend the use of any agent outside of the labeled indications.

The opinions expressed in the educational activity are those of the faculty and do not necessarily represent the views of the planners. Please refer to the official prescribing information for each product for discussion of approved indications, contraindications, and warnings.

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Participants have an implied responsibility to use the newly acquired information to enhance patient outcomes and their own professional development. The information
presented in this activity is not meant to serve as a guideline for patient management. Any procedures, medications, or other courses of diagnosis or treatment discussed or suggested in this activity should not be used by clinicians without evaluation of their patient’s conditions and possible contraindications and/or dangers in use, review of any applicable manufacturer’s product information, and comparison with recommendations of other authorities.

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