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This is a three-month-old child with some varied

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skin manifestations sent by a dermatologist

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for imaging of their brain and total spine.

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In particular, there were these

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melanotic nevi seen on the skin.

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So, an MRI of the brain and total

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spine was performed, and at first

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glance, everything looks very normal.

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But then, if we look a little closer, we

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can see this asymmetric area of T1 hyper

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intense signal in the right hemisphere.

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And if we look, this is the hippocampus.

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Here is the temporal horn of the right lateral

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ventricle, in particular, the choroidal

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fissure that extends between the temporal

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horn and the perimesencephalic cisterns.

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And anterior and superior to that is

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this area of hyperintense signal.

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Now, if we look at the contralateral

0:58

side, we see a normal appearance.

1:01

Here's the hippocampal head, body, tail.

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This hypointense rim is the choroidal fissure.

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and anterior and superior to the

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anterior portion of this is the amygdala.

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This looks like a normal appearance of the

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amygdala that has a gray matter-like signal.

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On the right side, the amygdala is

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hyperintense on T1-weighted imaging.

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Then here we see it on coronal imaging.

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That then gets us to the question, what

1:31

is bright on T1-weighted imaging and why?

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Well, I see here the posterior limb

1:35

of the internal capsule is bright.

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Why is that?

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Well, two things that are bright on T1

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weighted imaging are fat, And protein.

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Well, myelin is a proteolipid, and the posterior

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limb of the internal capsule is one of the

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earliest areas that's starting to myelinate.

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To a lesser extent, we see hyperintense signal

1:54

along the developing optic radiations,

1:57

potentially the splenium of the corpus callosum

2:00

and the forceps major in the brainstem.

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We're seeing several different findings.

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We're seeing the descending

2:07

fibers of the corticospinal tract.

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matter and middle cerebellar peduncles.

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But why would we have asymmetric myelination?

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Well, that's not what's going on.

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What else is bright on T1-weighted imaging?

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Fat.

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We know that fat is bright

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in T1-weighted imaging.

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This is a T1 fat-suppressed image.

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This is a T1-weighted image

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without fat suppression.

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We see the subcutaneous fat as hyperintense.

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We see the intraclonal and extraclonal

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fat of both orbits as hyperintense.

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And on the T1 fat-suppressed imaging, there's

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suppression of that hyperintense signal.

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This hyperintense signal

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in the amygdala persists.

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So this is not fat.

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So what else is hyperintense?

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Well, methemoglobin.

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Methemoglobin is a stage

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of hemoglobin degradation.

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There's intracellular and extracellular

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methemoglobin, but methemoglobin is

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hyperintense on T1-weighted imaging.

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I don't have any reason to expect there to be.

3:09

methemoglobin here.

3:11

It does not look like a hematoma.

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It does not look like there's any edema.

3:17

It does not look like there's any reason

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that there'd be blood products there.

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So it's not that.

3:25

Well, gadolinium is bright

3:27

on T1-weighted imaging.

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In particular, it's because of

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the unpaired balanced electrons.

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in gadolinium, it actually results

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in T1 shortening or T1 hyperintense

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signal in things adjacent to it.

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gadolinium itself, but the gadolinium's

3:47

effect on the surrounding parenchyma.

3:49

Well, this image was not performed

3:52

after gadolinium administration.

3:54

There are some minerals that end up being

3:58

hyperintense in T1-weighted imaging, some

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calcium, some, uh, manganese, things like

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that, that can be seen in different conditions.

4:05

We can see deep gray nuclei deposition

4:08

in manganese and in chronic TPN.

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We can see T1 hyperintense forms of

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calcium in cortical laminar necrosis,

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but none of that applies here either.

4:19

And why would it be unilateral?

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There's one additional substance that

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is bright on T1-weighted imaging that we

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don't often think about, but it's important

4:28

to be aware of, and that's melanin.

4:31

So, if anything, people discuss the melanin

4:35

T1 hyperintense signal when discussing

4:37

melanoma metastatic deposits, but in this

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case, it's important to note that This is

4:44

related to a melanin deposit in the amygdala.

4:47

Melanin deposits in the amygdala are

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a noted finding in neurocutaneous

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melanosis that can result in seizures.

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This patient at this time didn't have

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seizures, but being able to find this

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abnormality allowed this patient to get

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an EEG to see an epilepsy neurologist.

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They got routine EEGs and Several years

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later, when they started to develop seizures,

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they were well known to the neurologists

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and the seizures were able to be controlled.

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So, places to look for the melanin deposits,

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in particular the amygdala, which both is

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a place where it can commonly occur, but a

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place where it can end up being symptomatic.

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It can also be seen along the margins of

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the cerebellum and along the spine, but in

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particular, the amygdala is a place to look

5:39

when you're suspecting neurocutaneous melanosis.