FA Neurology- Embryology

What is Dandy-Walker malformation?

*Agenesis of cerebellar vermis with cystic enlargement of 4th ventricle* (fills the enlarged posterior fossa). Associated with *hydrocephalus, spina bifida*.

What is Chiari type I malformation?

*Cerebellar tonsillar ectopis >3-5mm*. Congenital, usually asymptomatic in childhood, manifests with *HA and cerebellar symptoms*.

What does the mesoderm of the neural system differentiate into?

*M*icroglia (like *M*acrophages, originate from *M*esoderm)

What is anencephaly?

*Malformation of anterior neural tube* --> *no forebrain*, *open calvarium*. Clinical findings: elevated AFP, *polyhydramnios* (no swallowing center in brain). Associated with *maternal DM type 1*. Maternal folate supplementation decreases risk.

What is a meningocele?

*Meninges (but no neural tissue)* herniate through bony defect.

What are the forebrain anomalies?

1) Anencephaly/Meroencephaly 2) Holoprosencephaly

What are the posterior fossa malformations?

1) Chiari II 2) Dandy-Walker

What are the three primary vesicles of the developing brain around week 4?

1) Forebrain (prosencephalon) 2) Midbrain (mesencephalon) 3) Hindbrain (rhombencephalon)

Elevated α-fetoprotein (AFP) is a sign of what types of defects?

1) Neural tube defects 2) Anterior abdominal wall defects

What are the five secondary vesicles of the developing brain around week 5?

1) Telencephalon (developing from the forebrain/prosencephalon) 2) Diencephalon (developing from the forebrain/prosencephalon) 3) Mesencephalon (from the primary midbrain/mesencephalon) 4) Metencephalon (developing from the hindbrain/rhombencephalon) 5) Myelencephalon (developing from the hindbrain/rhombencephalon)

From which branchial arches does the tongue develop?

1st and 2nd form the anterior 2/3rds of the tongue (thus sensation is from CN V3 and taste CN VII). 3rd and 4th branchial arches form the posterior 1/3rd of the tongue (thus, sensation and taste are mainly via CN IX, and extreme posterior CN X).

What is meroencephaly?

A rare form of anencephaly characterized by malformed cranial bones and a median cranial defect, through which protrudes abnormal tissue, called the area cerebrovasculosa.

What is syringomelia?

Cystic cavity (syrinx) within spinal cord. If it's in the central canal it's a hydromyelia. *Crossing anterior commissural fibers are typically damaged first.* Results in a *"cape-like" bilateral loss of pain and temperature sensation in upper extremities*. Fine touch sensation is preserves. Assoc. with Chiari malformations, trauma and tumors. Most common at *C8-T1*

What is the alar plate?

Dorsal portion or neural tube and future site of sensory (afferent) neurons and tracts.

What do the neural crest cells differentiate into?

PNS neurons (they migrate into the peripheral body), Schwann cells

What is Chiari type II malformation?

Significant *herniation of cerebellar tonsils and vermis* through *foramen magnum with aqueductal stenosis and hydrocephalus*. Often presents with *lumbosacral meningomyelocele*, *paralysis below defect*.

What does the neural plate give rise to?

The neural plate gives rise to the neural tube and neural crest cells, in between days 19 and 21.

What does the notochord eventually become?

The nucleus pulposus of intervertebral discs in adults.

Low α-fetoprotein (AFP) is a sign of what condition?

Trisomy 21

What are the adult derivatives of the telencephalon?

Walls --> cerebral hemispheres Cavities --> lateral ventricles

What are the adult derivatives of the myelencephalon?

Walls --> medulla Cavities --> lower part of fourth ventricle

What are the adult derivatives of the mesencephalon?

Walls --> midbrain Cavities --> aqueduct

What are the adult derivatives of the metencephalon?

Walls --> pons and cerebellum Cavities --> upper part of fourth ventricle

What are the adult derivatives of the diencephalon?

Walls --> thalamus Cavities --> third ventricle

What is spina bifida occulta?

Failure of bony spinal canal to close, but no structural herniation. Usually seen at lower vertebral levels. *Dura is intact.* Associated with *tuft of hair* or *skin dimple* at level of bony defect. *Normal AFP.*

What is holoprosencephaly?

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 palate*, most severe results in *cyclopia*. Seen in *Patau syndrome* (trisomy 13) and *fetal alcohol syndrome* (FAS).

What is a meningomyelocele?

Meninges AND neural tissue herniate through bony defect.

What happens if the neuropores fail to fuse in the 4th week of development?

Neural tube defects. Persistent connection between amniotic cavity and spinal canal. Associated with low folic acid intake before conception and during pregnancy. *elevated α-fetoprotein (AFP)* in amniotic fluid and maternal serum. *Elevated acetylcholinesterase (AChE)* in amniotic fluid is a helpful confirmatory test (fetal AChE in CSF transudates across defect into amniotic fluid).

What does the ectoderm differentiate into during neural development?

Notochord induces overlying ectoderm to differentiate into neuroectoderm and form the neural plate, around day 18.

What cranial nerves are involved in tongue pain?

CN V3, IX, X 5, branch 3- trigeminal nerve, mandibular branch 9- glossopharyngeal 10- vagus

What cranial nerves are involved in taste?

CN VII, IX, X (solitary nucleus) 7- facial 9- glossopharyngeal 10- vagus (solitary nucleus

What cranial nerves are involved in tongue motor control?

CN X, XII 10- vagus n. to palatoglossus m. (elevates posterior tongue during swallowing) 12- hypoglossal n. to hyoglossus m. (retracts and depresses tongue), genioglossus m. ( protrudes tongue), and styloglossus m. (draws sides of tongue upward to create a trough for swallowing).

What does the neuroectoderm differentiate into?

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

What is the basal plate?

Gives rise to longitudinal ventral cell columns that will form ventral and lateral horns of the spinal cord; these neurons are predominantly motor (efferent) in function.