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This is an MRI of the brain in a six-year-old

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female that was performed for abnormal gait.

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And superintendentially,

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we can see the lateral ventricles are

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slightly larger than usually seen.

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The third ventricle

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is also upper normal in caliber.

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But the rest of the brain,

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parenchyma looks fairly normal.

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But if we go to the posterior fossa,

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there's an abnormality that,

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at first, can be difficult to identify,

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because anytime you have either a bilateral

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symmetric abnormality or an abnormality in the

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midline, it can be very challenging to identify.

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And I think it's actually easier to see this

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sometimes on a coronal view,

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where we see there's midline continuity

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between the cerebellar hemispheres.

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There normally should be an intervening

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cerebellar vermis.

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Now, if we look closely at this axial T2 image,

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we do see a small rudimentary

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cerebellar vermis,

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so it's not completely absent.

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But for the most part,

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we have midline continuity between

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the two cerebellar hemispheres,

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likely midline continuity or at least close

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in the deep cerebellar gray matter.

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So, this is an entity called

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rhombencephalosynapsis.

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During development,

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the rhombencephalon is the hindbrain,

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and if we think synapse is...

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like, comes together.

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So, rhombencephalosynapsis means

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the rhombencephalon has come together,

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or in this case, actually, it never cleaved.

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It stayed together.

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So,

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if we look on this sagittal view,

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we see the cerebellar vermis,

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or what should be the vermis,

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doesn't have a normal foliation pattern for vermis.

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This actually looks like a cerebellar foliation

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pattern with the branching points

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and secondary branching points here.

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e're not seeing the normal primary and

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secondary fissures of the cerebellum.

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We're seeing something that looks more like a

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cerebellar hemisphere than a cerebellar vermis.

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Now, anteriorly and inferiorly,

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we do see this,

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which is the rudimentary cerebellar vermis.

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So, it's a little bit trickier to identify

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on this sagittal image.

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But on the coronal image,

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we can see midline continuity of the folia

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across both cerebellar hemispheres.

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And additionally,

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we see that in the axial T2-weighted image,

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where we have both the gray matter,

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white matter,

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and deep gray structures that come together.

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So, this is a case of rhombencephalosynapsis.