Neurology- Embriology, anatomy and physiology

Question 1

Neural tube defects

• Phatophysiology
• Association
• Tests

Answer 1

Neuropores fail to fuse (4th week) Ž persistent connection between amniotic cavity and spinal
canal.

Associated with maternal diabetes as well as low folic acid intake before conception and during pregnancy.

α-fetoprotein (AFP) in amniotic fluid and maternal serum (except spina bifida occulta = normal AFP). acetylcholinesterase (AChE) in amniotic fluid is a helpful
confirmatory test.

Question 2

Neural development

• Notochord
• Neural plate

Answer 2

induces overlying ectoderm to differentiate into neuroectoderm and form neural plate.

Gives rise to neural tube and neural crest cells

*Notochord becomes nucleus pulposus of intervertebral disc in adults.

Question 3

nervous systems origins
- Neuroepithelia in neural tube.
Neural crest
Mesoderm

Answer 3

CNS neurons, ependymal cells (inner lining of ventricles, make CSF), oligodendrocytes, astrocytes

PNS neurons, Schwann cells.

Microglia (like Macrophages).

Question 4

Spina bifida occulta

Answer 4

Failure of caudal neuropore to close, but no herniation. Usually seen at lower vertebral levels. Dura is intact. Associated with tuft of hair or skin dimple at level of bony defect.

Question 5

Meningocele

Answer 5

Meninges (but no neural tissue) herniate through bony defect. Associated with spina bifida cystica.

Question 6

Meningomyelocele

Answer 6

Meninges and neural tissue (eg, cauda equina) herniate through bony defect.

Question 7

Myeloschisis

Answer 7

Also known as rachischisis. Exposed unfused neural tissue without skin/meningeal covering.

Question 8

Anencephaly

Answer 8

Failure of rostral neuropore to close Ž no forebrain, open calvarium. Clinical findings: polyhydramnios (no swallowing center in brain).

Question 9

Holoprosencephaly

Answer 9

Failure of left and right hemispheres to separate; usually occurs during weeks 5–6.

May be related to mutations in sonic hedgehog signaling pathway.

Moderate form has cleft lip/palate, most severe form results in cyclopia. Seen in trisomy 13 and fetal alcohol syndrome.

Question 10

Posterior fossa malformations

- Chiari I malformation

Answer 10

Ectopia of cerebellar tonsils (1 structure). Congenital, usually asymptomatic in childhood, manifests in adulthood with headaches and cerebellar symptoms.

Associated with spinal cavitations (eg, syringomyelia)

Question 11

Posterior fossa malformations

- Chiari II malformation

Answer 11

Herniation of low-lying cerebellar vermis and tonsils (2 structures) through foramen magnum with aqueductal stenosis Ž hydrocephalus.

Usually associated with lumbosacral meningomyelocele

Question 12

Dandy-Walker

syndrome

Answer 12

Agenesis of cerebellar vermis leads to cystic enlargement of 4th ventricle that fills the enlarged posterior fossa.

Associated with noncommunicating hydrocephalus, spina bifida.