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I'm going to share with you some tricks for

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finding the elusive, very small 6th nerve.

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Only the fourth nerve is more challenging.

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And here we are at the level of the portio major,

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mostly of the fifth nerve.

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So if you find the fifth nerve and you go a little craniad,

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a little bit north of the fifth nerve,

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you're going to run into the 6th nerve,

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which has an anterolateral course out of the

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pontomedullary sulcus or inferior pons.

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Now, as it courses over obliquely from mesial to

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anterolateral, it's going to do something else.

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Let's look at the sagittal.

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Now, it's not easily appreciated,

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so I'm just going to draw it.

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It's coming out of the pons and it's working its way up.

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So the nerve doesn't go straight,

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it goes slightly craniad or slightly north,

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where it then follows a course into Dorello's canal

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before it reaches the cavernous sinus.

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Now, here in the coronal projection,

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its identification is brutal.

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The only way I was able to identify it

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is I cross reference this structure and that structure

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with these two structures.

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Now we'll scroll them again

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and you'll see how hard they are to pick up.

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You see them going back again,

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or forward, sorry.

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You see them going anteriorly.

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Now, you lose them.

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Now, let's go back.

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You have them again.

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There they are.

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There's one.

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There's two.

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And then, they're going to go right back into

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the ponto midbrain sulcus or the inferior pons.

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Now,

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a critical location for the abducens nerve

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is the cavernous sinus.

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Sometimes you have to infer its location,

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but one way to identify it is to go to the cavernous

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sinus and you look for a series of dots.

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And the most mesial of the dots that's closest to the

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carotid artery is going to be the abducens nerve.

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There's your carotid artery, there is your white dot,

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there is your abducens nerve.

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And that is the nerve that is most prone to compression,

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because A, it's small

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and B, its medial,

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directly adjacent to the cavernous portion

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of the carotid artery.

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So, an aneurysm there may present with a 6th nerve palsy.

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And that's a wrap.

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Dr. P out.