Interactive Transcript
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So now what we're going to do is take the information
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that we learned in the prior sections and apply it
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to a little bit more complex disease entities.
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So when we look at this specific image,
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this is a heavily weighted T2-weighted image,
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and we see this little mass right here that's involving
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the distal aspect of the internal auditory canal.
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Now, on first glance, we look at this and we say,
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my gosh, this could be another vestibular schwannoma.
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Because remember,
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vestibular schwannomas can arise in the distal aspect of
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the internal auditory canal near the fundus
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of the internal auditory canal.
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So this is what we see on the heavily T2-weighted
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images. So point number one is that we see this,
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but we always want to remember to give contrast when
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we're looking at the internal auditory canal because
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if we didn't give contrast and we just saw this,
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we could say, aha, this is a vestibular schwannoma.
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But when we do the contrast-enhanced study, remember
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a lot of these vestibular schwannomas start to occur in
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the internal auditory canal and then grow laterally
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through the porus acusticus into the
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cerebellopontine angle. But instead,
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what's happening here is notice what this mass
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is actually doing, is it's growing distally.
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It has a little bit of a semicircular appearance to it,
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and then it curves back on itself.
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This is the normal course of the facial nerve.
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And what this is is actually a schwannoma not involving
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the cochlear nerve or the superior vestibular nerve.
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Rather, this is a schwannoma involving the facial nerve.
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So the normal course of the facial nerve is that it
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extends distally into the fundus of the internal
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auditory canal. It has a labyrinthine segment.
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It then runs into this ganglion,
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which is referred to as the geniculate ganglion.
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It does a 180-degree curve at this level,
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which is referred to as the anterior genu,
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and then extends
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posteriorly along the tympanic segment.
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So this is actually a schwannoma,
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not involving the cochlear nerve or
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the superior vestibular nerve,
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but this is the classical appearance of a facial nerve
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schwannoma. And it highlights a couple of things.
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Number one,
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remember the complementary nature of your sequences.
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So on the heavily weighted T2-weighted images,
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it looks exactly like a schwannoma.
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Number two,
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always remember to give contrast so these
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things can enhance. And number three,
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look at these important spread patterns,
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because if this lesion is extending distally towards the
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fundus of the internal auditory canal and then extends
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along the expected course of the facial nerve,
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then we can make a very sophisticated diagnosis of a
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facial nerve schwannoma, but the key is the anatomy,
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and combine that with high-quality imaging.
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