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So now we have another patient that presents with

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right-sided hearing loss and also some dizziness.

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So how do we analyze this case?

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So, when we look at the right cerebellopontine angle,

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we can see this cystic area that's involving the

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right cerebellopontine angle that's located

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just medial to the right porus acusticus.

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Also, we can see a little bit of mass effect of the

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adjacent right middle cerebellar peduncle

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and compare this side with this side.

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So there certainly is some mass effect.

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So now,

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once we see that there's a cystic lesion there,

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what's our next step in our analysis?

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Well, the next step is we want to look at the diffusion

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imaging. And as we learned earlier,

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if there is no increased signal

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on the diffusion sequence,

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then we think that this area is probably cystic.

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But if there is high signal,

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as we learned earlier in an earlier vignette,

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then we start thinking about an epidermoid.

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So in this particular case,

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we can see there's no signal.

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This gives us the confidence that we're dealing with

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a cystic component just medial to the right porus

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acusticus. As we look at the next area,

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we now see that there's a mass involving

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the right half of the dorsal midbrain,

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the right cerebral peduncle.

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And we can see there's an expansile mass that's

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low signal on the T1-weighted images.

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And when we give contrast,

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we can see there's homogeneous enhancement to this.

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So now we have a mass that's involving

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the right cerebellopontine angle.

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But unlike the other lesions that were all extra

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axial, this enhancing component is intra-axial.

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So instead of an extraaxial mass,

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which can arise from the meninges,

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it can arise from the nerves,

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it can arise from some type of ectodermal origin,

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this is now an intra-axial lesion.

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And when you see a mass that's an intra-axial lesion,

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now we have to start thinking about a tumor that

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has glial origin. So in this particular case,

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this is a juvenile pilocytic astrocytoma that's

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arising from the right cerebral peduncle

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that isn't associated with a cyst.

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Now, sometimes when we think of juvenile pilocytic

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astrocytomas, which is what this is,

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we think of a cystic lesion with a mural nodule.

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This just happens to be a large intra-axial enhancing

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lesion, associated with that cyst.

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So it's not technically a mural nodule,

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but it is a densely enhancing intra-axial

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mass with an eccentric cystic component.

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