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This is an MRI of the brain

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in a two-year-old child being performed for seizure.

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Fortunately,

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the brain was normal and didn't show any

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abnormalities that would commonly be

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associated with causation of seizures.

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However,

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one area that was puzzling was the appearance

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of the posterior cranial fossa.

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At an outside institution,

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this was referred to as

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a Dandy-Walker malformation.

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Well, the first thing we do in evaluating this

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is look at the cerebellar vermis.

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We have a normal superior medullary velum,

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normal vestigial angle,

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and a normal inferior medullary velum.

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That is a normal fourth ventricle.

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A normal cerebellar vermis.

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If you have a normal cerebellar vermis,

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you do not have a Dandy-Walker spectrum malformation.

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So, now, we just have a little bit more likely

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CSF in the posterior cranial fossa.

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So, let's evaluate it.

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If we look on the T2-weighted image,

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it's hyperintense.

1:00

It's along the left aspect of

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the falx cerebelli here.

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The content suppressant FLAIR imaging.

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So, we know that it's not going

1:14

to be protonaceous fluid.

1:17

We do not see any susceptibility

1:20

abnormality within.

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So we know that it is likely not

1:23

going to be hemorrhagic.

1:25

We see facilitated diffusion.

1:27

There's no diffusion restriction,

1:28

so this does not represent an epidermal cyst.

1:32

So, what does that leave us?

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We have an arachnoid cyst that's inferior

1:39

to the cerebellar vermis.

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An infravermian arachnoid cyst.

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An infravermian cyst is a normal variant.

1:47

Now,

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this is in a location and an appearance that

1:52

people sometimes will refer to

1:53

as a mega cisterna magna.

1:57

But the cisterna magna,

1:59

the CSF space here,

2:00

doesn't just get big on its own.

2:01

It's usually distended because of a cyst.

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But this arachnoid cyst is a normal variant

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In the absence of symptoms,

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in the absence of mass effect on other structures,

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n infravermian arachnoid cyst is a normal

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variant that does not require follow up,

2:17

does not require surgery,

2:19

does not require any cause for consternation.

2:23

So this is an infravermian arachnoid cyst,

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which is a normal variant.

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Otherwise, the brain is normal.