Interactive Transcript
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Let's take a look at the pars marginalis
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in the axial projection.
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Now, if I were to localize the pars marginalis,
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in the sagittal projection,
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the continuation of the cingulate sulcus,
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following it on up to the pars marginalis or marginal sulcus,
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that corresponds to these two foci that look a
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little bit like kind of a droopy mustache, if you will,
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perhaps Salvador Dali's mustache.
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Now, if we were to look at how we would acquire CT cuts,
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so we would acquire them obliquely like this,
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that would mean that the marginal sulcus or the pars
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marginalis kind of has the same position as we go from
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caudad to craniad in the axial projection.
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On the other hand, if we are acquiring MR images,
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they're going to be in the orthogonal projection.
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So let's, once again, draw the pars marginalis.
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This time we have orthogonal cuts.
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Let's just change color to make it really clear.
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If we're going this way,
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look at what happens to the pars marginalis.
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As we go up,
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it goes more posterior or sits more posteriorly.
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Now, let's look in the axial projection.
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Here we are down low in the pars marginalis,
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which is this ascending sulcal structure.
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Right here.
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We have our droopy mustache.
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And then as we go up,
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the mustache is a little bit straighter.
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It's also found at the widest biparietal
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diameter at the 9 o'clock, 3 o'clock position,
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typically is where you're going to see
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the pars marginalis.
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And there it is.
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Our mustache is getting a little bit straighter.
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Let's keep going more craniad.
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And now our mustache is kind of flipping up a little bit
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like Salvador Dali's mustache that's no longer drooping.
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And why is this important?
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It's important because just anterior to the
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pars marginalis is the central sulcus.
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And this little notch right here in the precentral gyrus
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is the hand motor area of the left cerebral hemisphere,
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similarly on the right side.
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The central sulcus of Rolando
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sits anterior to this little basket right here,
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so it kind of pokes its way just in
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front of the pars marginalis,
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while directly behind it is the postcentral sulcus.
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You all know from prior vignettes,
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if you've watched them,
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that the postcentral sulcus is the upswing
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of the arcuate-shaped intraparietal sulcus.
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So we've got postcentral sulcus,
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precentral sulcus, precentral gyrus, postcentral gyrus,
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hand motor area,
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pars marginalis.
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And the pars marginalis looks a little bit different
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on MR than CT for reasons previously discussed.
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Pomeranz out.
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