Fetal CNS Pt. 3 Flashcards
(37 cards)
What is the spectrum of congenital anomalies affecting the fetal central nervous system (CNS)?
Enormous
Major congenital anomalies include neural tube defects, spina bifida, anencephaly, and others.
What can axial images through the fetal brain reliably detect?
Serious abnormalities that warn a poor prognosis for the fetus
These images are obtained during routine measurements of biparietal diameter and head circumference.
What is Filly’s Rule in relation to fetal CNS anomalies?
Most life-threatening abnormalities can be detected before 20 weeks gestation
What can polyhydramnios and discordant biometric measurements indicate?
A more focused look at the fetal CNS
Define neural tube defects.
Spectrum of fetal anatomic abnormalities resulting from failure of closure of the neural tube
When does the rostral (head-end) closure of the neural tube occur?
Day 25 (conceptual)
When does the caudal (tail-end) closure of the neural tube occur?
Day 27 (conceptual)
List some types of neural tube defects.
- Spina bifida
- Anencephaly
- Exencephaly (acrania)
- Encephalocele
- Iniencephaly
What is spina bifida?
A defect in the spinal column resulting from failure of neural tube closure
What characterizes spina bifida occulta (hidden)
- Mildest form
- Defect in the posterior bony arch
- Skin and tissue remain intact
- Often causes no symptoms
What characterizes spina bifida aperta?
- Visible opening along the spine
- Allows herniation of neural tissueTypes include:
* Myelocele: Herniation of meninges only
* Myelomeningocele: Herniation of meninges and neural tissue
* Rachischisis: Complete opening of the spinal canal (most severe form)
Associated condition: Tethered cord (spinal cord abnormally attached)
- Allows herniation of neural tissueTypes include:
Differentiate between myelocele and myelomeningocele.
- Myelocele: herniation of meninges alone
- Myelomeningocele: herniation of meninges and neural tissue
What is rachischisis?
- Also known as complete spina bifida
- Severe form of spina bifida with a cleft through the entire spine
- Involves the entire neural tube, from cervical spine to sacrum
Commonly associated with cranial neural tube defects such as: - Anencephaly
- Acrania
- Iniencephaly
- Almost always fatal
What are common signs of spina bifida occulta?
- Tuft of hair on the lower back
- Dimple on the lower back
What is a tethered cord?
A spinal cord that can’t move freely inside the spinal canal
What is the conus level in a normal spinal cord?
Approximately at the L2-L3 disc space or higher
What are the sonographic findings for spina bifida?
- Transverse Spine: splaying of posterior ossification centers
- Sagittal Spine: discontinuity of parallel lateral ossification centers
- Intracranial: lemon sign and banana sign
What is the Chiari II malformation?
Condition in which brain tissue extends into the spinal canal, present at birth
What is anencephaly?
- Absence of the cranial vault and cerebral hemispheres
- Most common neural tube defect
- Portions of the midbrain and brainstem may be present
Associated facial features:
Microphthalmia: Small eyes
Macroglossia: Large tongue
Severely shortened neck
What are the epidemiological and clinical characteristics of anencephaly?
- Most common neural tube defect
- Incidence: ~1 in 1,000 pregnancies in the U.S.
More common in:
Females (4:1)
Caucasians vs. African-Americans (6:1)
Caused by: Failure of cranial end of neural tube to close
Recurrence risk: 2–3% if prior pregnancy had an open NTD
Prognosis:
Up to 50% end in fetal demise
Most of the remainder die at birth or shortly after
Diagnosis: Often made prenatally via ultrasound, especially after elevated maternal serum AFP levels
What is the role of folate during pregnancy?
- Folate is essential for DNA, RNA, and amino acid synthesis. During pregnancy, higher folate levels are needed due to rapid cell and tissue growth.
- Inadequate folate can impair DNA synthesis and fetal development.
What does an alpha-fetoprotein (AFP) test measure?
- AFP is a protein made by the fetal liver
- Small amounts cross into the mother’s blood and can be measured in the second trimester
Name some conditions indicated by abnormal AFP levels.
- Neural tube defects (e.g., spina bifida, anecephaly)
- Down syndrome
- Twins or multiples (icreased AFP)
- Miscalculation of due date estimation
- In open neural tube defects, AFP leaks into the amniotic sac, causing elevated levels in both maternal blood and amniotic fluid
What are the characterizes of exencephaly and associated aomalies?
Sonographic findings:
* Absent cranial vault
* Presence of cerebral hemispheres
* Thin membrane covering exposed brain tissue
Associated anomalies:
* Clubfoot (talipes)
* Cleft lip and palate
