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Dr. Laser, this is a 28

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year-old man. He's got a known brain tumor.

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He's had an operation.

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There's some packing in the left

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oto mastoid air cell region.

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Let's do a little bit of scrolling

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on the left. We have an extraxial mass flare

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in the center, we have an axial T2,

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there's the mass,

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there's the compression of the brain stem

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and the mass appears riding along the dural edge

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portions of the tentorium cerebelli involved.

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There's the cochlea.

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It's a little hard to see the 7th and

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8th nerve complexes,

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but a big differential here is

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is this a cerebellopontine angle meningioma?

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Or is it a vestibular schwannoma?

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Now in my experience, uh,

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many schwannomas in this area are cystic.

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In fact, they can even look like epidermoids,

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and while you can get cystic meningiomas,

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this is really uncommon.

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Uh, you'll also see

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little microcystic meningiomas like you have here,

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but uh, dominant cysts or the whole thing being

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cystic with some nodular enhancement

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much more typical of a schwannoma,

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and that's true. By the way, in MRI,

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schwannomas tend to be pretty cystic

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in the peripheral aspect of the body.

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This patient has a dural tail

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and what's the other name for that dural tail sign?

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Dovetail sign

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be another name for

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dovetail sign or dovetail enhancement,

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and how often have you seen that? With a schwannoma

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very rarely, very rarely, maybe a plexiform one

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it could happen,

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but I can't remember the last time I saw it.

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you know, is there a hyperostotic reaction

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and that can be a little challenging on an MRI,

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but I will say this

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everything is just a little bit thicker and blacker

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on the left side than it is on the right side

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so you should be,

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you know, perhaps a little bit suspicious

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that there are some bone changes

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and these bone changes can be

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osteolytic, but they're more commonly sclerotic.

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The fact let's bring down an SWI

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or susceptibility-weighted image

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to see if there's a little more

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prominent hypointensity in the bone area

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and admittedly that's hard to tell.

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Perhaps right here maybe there's a little hyperostosis,

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but within the lesion, there's a lot of low signal,

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and while those signals could represent hemosiderin and blood

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uh, in this case, calcification,

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especially this sort of chunky shape or irregular shape

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seems most likely, so calcification

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it occurs in Schwannoma, but

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between Schwannoma and Meningioma,

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what do you like better for calcifications,

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Meningioma? It's pretty rare in a Schwannoma.

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Yeah, it is it is rare. In fact,

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typically none.

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Meningioma is what about 20%

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yeah, that's about right

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and um as far as the enhancement goes,

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let's bring back down our

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axial C plus. Image

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tell me a little bit

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about the internal character of the enhancement

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and Meningioma versus Schwannoma is that helpful at all.

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Uh, it can be,

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uh and the Meningioma typically has uniform enhancement.

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The Schwannoma can have heterogeneous enhancement, um

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about 10% of the time, but it's uh,

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Meningiomas will avidly enhance quickly

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and uh or are light bulb bright

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so more intense,

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frequently more homogeneous

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more early.

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Uh, this one's enhancing a little more heterogeneously,

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but it does have that nice

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little dural tail or dovetail sign

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which helps you a lot.

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Now another aspect of this lesion that

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helps you favor Meningioma is it's growing

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along the surface of the cerebellum,

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but not into the IAC.

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It's not growing directly

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into the internal auditory canal,

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it's behind it.

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and typically

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Schwannomas will

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arise from and involve the internal auditory canal

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or porus acousticus.

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This lesion does not.

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We didn't do spectroscopy in this case,

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but Meningiomas have an elevated alanine

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on SPECT and Schwannomas have elevated tyrosine and GABA,

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and then finally, if you've got a CT,

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Schwannomas are not typically hyperdense,

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um and Meningiomas are often hyperdense.

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Do you have any other comments on this one?

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We do have an ADC map, which shows that it

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doesn't diffusion restrict very much,

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even though this is a hard firm lesion.

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There's no real dark areas right here on the ADC map

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as you would expect

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for something that restricts diffusion.

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Other comments before we move off this case.

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Only

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other comment I would mention is the Mass Effect.

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This would be a call to the clinician

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just due to the mass effect upon the brainstem,

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so I think that would probably be the most important

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clinical aspect of this case.

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Yeah, although the mass effect has probably

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been there for some time,

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it's chronic correct.

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It's very important although the patient is in no

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imminent danger.

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And I will say mass effect in distinguishing

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between Meningioma and Schwannoma.

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Not so helpful because

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they both can produce a fair amount of mass effect.

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So that concludes our comparison

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in the posterior fossa of Meningioma versus Schwannoma.