0:00

Hello and welcome to Noon Conference hosted by MRI Online. Noon Conference

0:06

was created when the pandemic hit as a way to connect the global

0:08

radiology community through free live educational conferences that are accessible

0:13

for all. It has become an amazing weekly opportunity to learn alongside

0:16

radiologists from all around the world, and we encourage you to ask questions

0:20

and share ideas to help the community learn and grow.

0:23

You can access the recording of today's and previous Noon Conferences by

0:26

creating a free MRI Online account. The link will be provided in the

0:29

chat box. Today, we're honored to welcome Dr. Asim Choudhri for a lecture

0:34

on supratentorial malformations of cortical development. Dr. Choudhri is

0:39

the chief pediatric neuroradiology at Le Bonheur Children's Hospital. He

0:43

is also a professor and associate chair of research affairs in the Department

0:46

of Radiology at the University of Tennessee Health Science Center. We truly

0:49

appreciate Dr. Choudhri for joining us today and for being a part of

0:52

our MRI online faculty. A reminder that there will be a live Q&A session

0:56

at the end of the lecture for any questions you may have.

0:59

Please use the Q&A feature to submit your question and we will get to as

1:02

many as we can before our time is up. But that being said,

1:05

we welcome you. Dr. Choudhri, please take it from here.

1:08

Today I'd like to talk to you about malformations of cortical development

1:11

in the supratentorial compartment. So the background, the brain is complex,

1:21

we know that. The developing brain is very complex and can be intimidating,

1:27

and it differs in structure and appearances at different stages of development.

1:32

The malformed brain can also seem very intimidating.

1:37

But we can understand the malformed brain, at least the basics,

1:40

without having to get a deep knowledge of embryology. And that's what one

1:45

of our goals today is. So how does the cortex form?

1:50

Well, there's several stages, there's neuronal proliferation, neuronal migration,

1:55

and cortical organization. In neuronal proliferation, cells are born in

2:02

the germinal matrix, and we see on this coronal image,

2:06

in this location along the superolateral margin of the body of the lateral

2:09

ventricles, that's where we see germinal matrix hemorrhages on neonatal

2:13

ultrasounds. Then there's neuronal migration, cells move out to where they're

2:18

going to live, out to the periphery. And then there's organization,

2:23

where the cells form a mature six layer cortex.

2:27

And this is now sometimes called post migrational organization,

2:31

acknowledging that the process of migration involves some organization as

2:35

well. So for those, cortical malformation, well you can have

2:43

abnormalities, neuronal proliferation, where there's too many cells, too

2:47

few cells, or abnormal cells. You can have abnormalities of neuronal migration,

2:52

where there's aberrant migration, basically the cells go to the wrong location.

2:56

And you can have abnormalities of cortical organization, where they just

3:00

don't organize into a mature six layer cortex.

3:06

So, for neuronal proliferation, that happens primarily in two to four months

3:13

of gestational age. And cells that will become cortex form from the neuroblasts

3:19

in the ventricular and subventricular zones, or the germinal matrix.

3:24

So abnormal proliferation results in malformations of cortical development.

3:31

As I mentioned, you can have too few cells, which results in microlissencephaly

3:35

spectrum disorders. You can have too many cells, which results in hemimegalencephaly,

3:41

for instance. And you can have abnormal cells.

3:45

And that's the prototype for that is focal cortical dysplasia.

3:57

So, next comes neuronal migration. From three to five months gestation,

4:04

the germinal zone cortex, you have six waves

4:09

guided by these radial glial fibers. Those radial glial fibers are sort

4:12

of the roadmap for the cells to get to their eventual location.

4:17

The first wave is the deepest. The last is the peripheral cortex.

4:23

And abnormal neuronal migration leads to heterotopia in particular if there's

4:29

an abnormality of those radial glial fibers. So, you can have heterotopia

4:34

that's subependymal, band type heterotopia, or subcortical heterotopia that

4:40

we'll discuss. And then cortical organizations happens towards the later

4:46

part of gestation, the five months of gestational age. And it actually happens

4:51

even after birth, up to two years of age.

4:55

Some of this post migrational organization takes place and matures.

5:02

So that creates the normal cortical architecture. And

5:06

you have abnormal gyro formation and organization that

5:10

can happen during that time. In particular, if there's a superficial injury,

5:15

you can get polymicrogyria. And if there's a full thickness injury during

5:20

development or abnormality, you can get schizencephaly. So,

5:27

speaking of schizencephaly, it's very important to note that for a lot of

5:31

these abnormalities, you can get abnormalities in more than one aspect of

5:35

development between proliferation, migration, and post migrational organization.

5:39

So, it is not all just one. And I gave the time frames

5:44

for those stages of development. But at a given time point,

5:47

more than one process is going on at once. Some neurons are migrating

5:51

while others are being born. Some are already maybe starting to organize.

5:54

So, not everything is as compartmentalized, as I said. But that compartmentalization

6:02

is a very easy way to start to understand the differences.

6:07

So, lissencephaly, what does that mean? That is a smooth brain.

6:12

So, if we see here on this brain,

6:14

we see this smooth, featureless brain surface. At most, we see a very

6:20

rudimentary sylvian fissure. We may see a very rudimentary attempt at the

6:26

cingulate gyrus anteriorly. But we're not really seeing much sulcation.

6:35

Agyria, which I would consider this to be, is the most severe form.

6:40

There's a thick cortex, or it's actually not even a true mature cortex.

6:48

It's a cortical plate with only two to four cell layers.

6:51

As mentioned before, a mature cortex has six cell layers. Subjacent to that,

6:59

there may be a...