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So, I've got a T1 contrast

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1.2 millimeter image on your left,

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a T2 spin echo,

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slightly lower resolution,

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5 mm of slice thickness on the right.

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Now, my purpose in showing you the

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T2-weighted axial image

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is to simply draw the real origin of the

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abducens nucleus.

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So, let's do that.

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We've got our facial colliculus bump right here.

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And just deep to that bump, a little more dorsally,

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we're going to have the abducens nerve nucleus.

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And since I love blue, I'm going to draw it in blue.

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Whoops.

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Since I love blue,

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I'm going to draw it in blue, if I can.

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And now I can.

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And then the abducens nerve nucleus is going to take a

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pretty mesial course

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before it then sweeps out laterally

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with its apparent exit from the brainstem

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at the ponto medullary sulcus.

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Remember, it's going to come out lateral to the pyramid.

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It's got a pretty long course through the brainstem.

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Now, what about the facial nerve nucleus?

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Because this is called the facial colliculus bump.

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Let's draw that in orange.

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Here's my orange.

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And it's going to sit a little more anterior and slightly

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lateral to the abducens nerve nucleus.

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But then the nerve comes out more obliquely,

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as you would expect,

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because that's where the facial nerve goes

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into the 7th and 8th nerve canal.

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So that's a pretty important distinction.

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And either of these nerves can get hit

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with pathology in this region,

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including involvement of the medial longitudinal

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fasciculus and periaqueductal gray,

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as in multiple sclerosis with plaques

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affecting these nuclei.

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Now, let's direct your attention over to the left side.

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We've got an axial very thin section, T1 C+ image.

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And there's a reason why I put the C+ image up,

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because that looks like the 6th nerve coming out

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of the ponto medullary sulcus, but it enhances.

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So, is it a neuritic 6th nerve?

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No, the 6th nerve was normal.

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It's not neuritic. It's a small perforator.

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And how do we know that?

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Let's look on this side, lateral to the pyramid,

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there is a bland gray structure with an oblique course

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not going to the 7th and 8th nerve canal,

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but let's see where it goes.

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Let's take away our color

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and let's follow it.

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Back to its apparent exit.

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Now, let's keep going.

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It falls right into this little groove right here.

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On the other hand,

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our enhancing structure makes a curl and goes backwards.

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It does not go into Dorello's canal,

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whereas the true abducens nerve goes into

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Dorello's canal.

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Then, it continues on.

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We can't see it very well.

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It's right there.

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It goes on into the cavernous sinus,

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and I'll show that to you better in the coronal projection

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and then continues on into the orbit through the superior

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orbital fissure to innervate the lateral rectus muscle.

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That is the apparent and real origin

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of the abducens nerve and abducens nerve nucleus.

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Let's move on, shall we?

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Pomeranz out.