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Classifications of Supratentorial Malformations of Cortical Development, Dr. Asim F. Choudhri (7/21/22)

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

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

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radiology community through free live educational conferences that are accessible

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

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

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and share ideas to help the community learn and grow.

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

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

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

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on supratentorial malformations of cortical development. Dr. Choudhri is

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

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

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

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

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

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

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

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

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

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

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

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

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

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The malformed brain can also seem very intimidating.

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

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

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

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

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

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

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

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

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

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

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where the cells form a mature six layer cortex.

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And this is now sometimes called post migrational organization,

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acknowledging that the process of migration involves some organization as

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

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

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

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

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

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don't organize into a mature six layer cortex.

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

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

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

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So abnormal proliferation results in malformations of cortical development.

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

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

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for instance. And you can have abnormal cells.

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

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

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the germinal zone cortex, you have six waves

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

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

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

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

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

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

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

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

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even after birth, up to two years of age.

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Some of this post migrational organization takes place and matures.

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So that creates the normal cortical architecture. And

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you have abnormal gyro formation and organization that

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

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

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development or abnormality, you can get schizencephaly. So,

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

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

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development between proliferation, migration, and post migrational organization.

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

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

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

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

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

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

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

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So, if we see here on this brain,

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

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

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

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

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

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

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

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there may be a...

Report

Faculty

Asim F Choudhri, MD

Chief, Pediatric Neuroradiology

Le Bonheur Children's Hospital

Tags

Neuroradiology

Neuro

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