Hello! Welcome to
A quick overview of embryogenesis so
that you have a firm understanding
as to where these pathologies
are arising from.
The brain tissue begins to
differentiate from the ectoderm
at approximately three weeks.
Weeks three to four, we have
something called neurulation
in which we have formation and
closure of the actual neural tube.
The anterior or the
rostral neural tube,
the closure is within 24 days,
approximately one month.
The failure of which may result
in anencephaly or encephalocele,
wherein the rostral portion of
the spine or the neural tube.
If you get into the posterior portion,
we call this the caudal portion.
This requires approximately 27 days.
So this would be a little bit
longer than the anterior
and, of course, failure
of closure here,
then puts you into the
category of spina bifidas,
either the occulta, the meningocele,
or the myelomeningocele,
which then represents both the
spinal cord and the meninges,
which are then protruding
out and by doing so,
the spinal cord being
pulled out may then cause
decreased ability to
control one’s bladder.
Let’s go into weeks
five and six.
We have vesicle formation.
By vesicle formation, prosencephalon,
telenecephalon and diencephalon.
Mesencephalon remains undivided
at five to six weeks.
The rhombencephalon, metencephalon, the
myelecephalon is what it divides into.
And then we have holoprosencephaly,
which means failure of the prosencephalon
to then divide or to cleave.
Now, when you say holoprosencephaly,
you should be thinking about
conditions such as trisomy 13,
which is your Patau or maybe
fetal alcohol syndrome
where you do not divide your prosencephalon
into telenecephalon and diencephalon,
weeks five and six.
These are clinically important.
When you get into weeks
eight and thirty-two,
this is cellular
proliferation and migration.
This is when the sulci, which means what?
The actual, the crevice or
the cavity between the gyri.
They gyri means the
tissue will be forming.
You have a condition
Lissencephaly means smooth cortical
surface due to poor migration.
Once again, remember, I want you to think
about the outer aspect of the brain,
you should have the inner crevices or the
sulci, and then you have the gyri, right?
But what if you don’t have the crevices
and you don’t have the
partitions between the gyri,
and we call this a smooth cortical
surface, which – that’s the pathology.
And we call the lissencephaly.
Weeks eight and thirty-two is where we are.
We have something called
pachygyria, which is a large gyri.
Microgyria, smaller gyri.
And then we have schizencephaly,
which is cracked brain,
cleft due to defective
Stroke is often responsible for this.
So think of this as being, well,
you know what schizophrenia is,
which is broken mentality
or cracked mentality,
think of this as being
literally a cracked brain.
Fascinating, isn’t it?