Neuroembryology B&B Flashcards
what CNS structures develop from the:
a. surface ectoderm (3)
b. neural tube (4)
c. neural crest (3)
a. surface ectoderm: anterior pituitary, lens, cornea
b. neural tube: brain, spinal cord, posterior pituitary, retina
c. neural crest: autonomic system, sensory nerves, skull
describe the steps of neural tube development (4)
- notochord secretes SHH
- this induces overlaying ectoderm to become neuroectoderm
- neuroectoderm becomes neural plate
- neural plate becomes neural tube + neural crest cells
notochord in adults = nucleus pulposus (IV discs)
all occurs days 17-21 in embryo
what do the 5 secondary brain vesicles become?
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]
during what weeks of embryological development are the 3 primary vs 5 secondary brain vesicles present?
3-4 weeks: primary (prosencephalon, mesencephalon, rhombencephalon)
5 weeks: secondary brain vesicles (telencephalon, diencephalon, mesencephalon, metencephalon, myelencephalon)
failure of caudal vs rostral neuropore closure =
when is the neuropore supposed to close?
neuropores fuse in the 4th week
rostral (head) failure = anencephaly
caudal (tail) failure = spina bifida
what are 4 major risks for neural tube defects?
- low folic acid intake
- Type I diabetes
- obesity
- valproate and carbamazepine (anticonvulsants)
both spinal cord and meninges bulging out from spine =
myelomeningocele - almost always associated with Chiari malformation
how is anencephaly detected in utero? (3)
- open calvaria (skull that is open) on ultrasound
- frog-like appearance of fetus on ultrasound
- maternal polyhydramnios (fetus can’t swallow)
what occurs with encephalocele, and where does it most commonly occur?
brain or meninges herniate through skull, least common NTD
most common site is occipital bone
what are the 2 follow-up tests done if alpha fetal protein (AFP) is high at 16-18 weeks?
high AFP may indicate NTD, but interpretation is difficult, follow-up with:
- amniotic fluid AFP (requires amniocentesis)
- amniotic fluid acetylcholinesterase (AChE)
if both elevated, strongly suggests NTD
what is the “triple screen” of prenatal screening?
- AFP
- estradiol
- HCG
holoprosencephaly occurs during weeks ____ and is failure of ____ signaling
holoprosencephaly occurs during weeks 5-6 and is failure of SHH signaling
—> failure of prosencephalon cleavage, L/F hemispheres fail to separate
what are the key findings (2) and associations (3) with holoprosencephaly?
key findings: cleft lip/ palate and cyclopia
associations: trisomy 13 (Patau syndrome), trisomy 18 (Edward syndrome), fetal alcohol syndrome
what is associated with Chiari I vs Chiari II malformations?
Chiari I: cerebellar tonsils displaced below foramen magnum; associated with syringomyelia
Chiari II: cerebellar vermis + tonsils displaced downward; associated (almost always!) with myelomeningocele
when/how does Chiari I malformation present?
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)
