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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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...
Asim F Choudhri, MD
Chief, Pediatric Neuroradiology
Le Bonheur Children's Hospital
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