Neuroembryology B&B Flashcards

1
Q

what CNS structures develop from the:
a. surface ectoderm (3)
b. neural tube (4)
c. neural crest (3)

A

a. surface ectoderm: anterior pituitary, lens, cornea

b. neural tube: brain, spinal cord, posterior pituitary, retina

c. neural crest: autonomic system, sensory nerves, skull

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2
Q

describe the steps of neural tube development (4)

A
  1. notochord secretes SHH
  2. this induces overlaying ectoderm to become neuroectoderm
  3. neuroectoderm becomes neural plate
  4. neural plate becomes neural tube + neural crest cells

notochord in adults = nucleus pulposus (IV discs)

all occurs days 17-21 in embryo

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3
Q

what do the 5 secondary brain vesicles become?

A

prosencephalon —>
telencephalon: cerebrum [it takes thinking to TELE someone on the phone!]
diencephalon: eye cup, thalamus, hypothalamus, epithalamus [these structures keep you from DIEing]

mesencephalon: midbrain [MESE = MID]

rhombencephalon —>
metencephalon: pons, cerebellum [you’d get ataxic if you MET your celebrity crush!]
myelencephalon: medulla [closest to the spinal cord, where fibers are MYELINated]

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4
Q

during what weeks of embryological development are the 3 primary vs 5 secondary brain vesicles present?

A

3-4 weeks: primary (prosencephalon, mesencephalon, rhombencephalon)

5 weeks: secondary brain vesicles (telencephalon, diencephalon, mesencephalon, metencephalon, myelencephalon)

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5
Q

failure of caudal vs rostral neuropore closure =

when is the neuropore supposed to close?

A

neuropores fuse in the 4th week

rostral (head) failure = anencephaly

caudal (tail) failure = spina bifida

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6
Q

what are 4 major risks for neural tube defects?

A
  1. low folic acid intake
  2. Type I diabetes
  3. obesity
  4. valproate and carbamazepine (anticonvulsants)
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7
Q

both spinal cord and meninges bulging out from spine =

A

myelomeningocele - almost always associated with Chiari malformation

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8
Q

how is anencephaly detected in utero? (3)

A
  1. open calvaria (skull that is open) on ultrasound
  2. frog-like appearance of fetus on ultrasound
  3. maternal polyhydramnios (fetus can’t swallow)
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9
Q

what occurs with encephalocele, and where does it most commonly occur?

A

brain or meninges herniate through skull, least common NTD

most common site is occipital bone

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10
Q

what are the 2 follow-up tests done if alpha fetal protein (AFP) is high at 16-18 weeks?

A

high AFP may indicate NTD, but interpretation is difficult, follow-up with:

  1. amniotic fluid AFP (requires amniocentesis)
  2. amniotic fluid acetylcholinesterase (AChE)

if both elevated, strongly suggests NTD

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11
Q

what is the “triple screen” of prenatal screening?

A
  1. AFP
  2. estradiol
  3. HCG
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12
Q

holoprosencephaly occurs during weeks ____ and is failure of ____ signaling

A

holoprosencephaly occurs during weeks 5-6 and is failure of SHH signaling

—> failure of prosencephalon cleavage, L/F hemispheres fail to separate

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13
Q

what are the key findings (2) and associations (3) with holoprosencephaly?

A

key findings: cleft lip/ palate and cyclopia

associations: trisomy 13 (Patau syndrome), trisomy 18 (Edward syndrome), fetal alcohol syndrome

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14
Q

what is associated with Chiari I vs Chiari II malformations?

A

Chiari I: cerebellar tonsils displaced below foramen magnum; associated with syringomyelia

Chiari II: cerebellar vermis + tonsils displaced downward; associated (almost always!) with myelomeningocele

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15
Q

when/how does Chiari I malformation present?

A

cerebellar tonsils displaced below foramen magnum; associated with syringomyelia

usually no symptoms until adolescence/adulthood (~18yrs) —> headaches due to meningeal irritation that are worse with cough (“cough headache”)

may also have ataxia (cerebellar dysfunction) + CN dysfunction (brainstem compression)

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16
Q

“beaked midbrain” on neuroimaging + spinal myelomeningocele =

A

Chiari II: cerebellar vermis + tonsils displaced downward; associated (almost always!) with myelomeningocele

17
Q

how does Chiari II malformation present? (3)

A

Chiari II: cerebellar vermis + tonsils displaced downward; associated with myelomeningocele —> detected in utero

  1. blockage of aqueduct —> hydrocephalus (large head circumference, distended anterior fontanelle)
  2. myelomeningocele —> paralysis below defect
  3. “cracked pot” abnormal percussion of skull (Macewen’s sign)
18
Q

child born with hydrocephalus + delayed development + motor dysfunction (crawling, walking) should make you think of…

A

Dandy Walker Malformation: cysts of 4th ventricle cause hydrocephalus, which causes hypoplasia or agenesis of cerebellar vermis