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Dr. P here back with the facial or 7th nerve.

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We've got a beat on the 7th nerve on our axial high

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resolution T1-weighted image,

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and our sagittal orthogonal image.

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Now, the nerve typically travels from the pons,

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from a nucleus, which we've defined in prior vignettes,

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the loops around the abducens,

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and then comes out the side,

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just at or above the bulbar pontine sulcus.

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Now,

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when it exits,

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it's going to make this funny little loop right here.

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So if I were to draw the course of the 7th nerve,

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it would look something like this.

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Come out,

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then probably have a small little opening there on CT,

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if you could see it, the fallopian canal.

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And then it would loop around where you've

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got the geniculate ganglion.

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Then it would kind of come back

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and in a horizontal fashion.

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And then it would dive straight down into the screen

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and have its deep descent, like this,

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exiting right there at the stylomastoid foramen,

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which will be somewhere around here.

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And we're going to show that to you in a moment.

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So, that's the general course of the 7th nerve.

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Remember, it's seven up, coke down,

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so it's above the cochlear nerve.

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Don't get confused there.

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And it can be a little hard to distinguish the two in the

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axial projection unless you have uber-thin sections.

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Now,

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the 7th nerve travels in close proximity

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with the 8th nerve, as we've said.

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But the 8th nerve is a rather complex structure.

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It consists of superior and inferior vestibular nerve,

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as well as cochlear nerve.

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And we've defined these before,

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but the facial nerve supplies also preganglionic

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sympathetic fibers to the head and neck ganglion.

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The facial and intermediate nerves are collectively

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referred to as the nervus intermedius facialis,

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if you really want to get technical about it.

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Now, I want to talk about the six segments of the facial nerve,

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now that I've drawn for you its basic course.

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The first is the intracranial cisternal segment,

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and that would be the segment

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in the cerebellopontine angle cistern.

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Let's put it up right here.

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So that would be the cisternal segment, right there.

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Right as it comes out.

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So, that's essentially the apparent origin.

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Then we get into...

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let's use a different color here, just to emphasize.

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We get into what's called the meatal segment,

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also known as the canalicular segment

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within the 7th and 8th nerve canal.

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Then we get into the labyrinthine segment,

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which is the internal auditory canal segment

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all the way up to the geniculate ganglion.

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I'm going to use a different color for emphasis.

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I'll try something a little light blue right here.

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So we're working our way towards the geniculate ganglion,

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which is going to be this little condensation,

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a little ball right there.

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And then we move on to the tympanic segment,

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which is from the geniculate ganglion to the pyramidal eminence.

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So, let's use a different color for that.

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Oh, let's try something like green.

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So, we're working our way back towards the pyramidal

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eminence, and then we keep moving to the mastoid segment,

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which is from the pyramidal eminence

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to the stylomastoid foramen.

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And we have that right here,

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it's going to be right there.

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I'm going to cross-reference it for you in a minute.

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But we have it in the sagittal projection.

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This sagittal view is going right through this

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spot right here and showing you the descent.

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We should use a different color to be consistent.

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Let's go with something purple.

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We're working our way down.

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Maybe it doesn't show up as well as I would like,

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but I think you get the point.

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And it exits the brain at the level of the stylomastoid foramen.

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And then, finally, the extratemporal segment,

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which kind of goes off the screen right here.

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And we got to pick another color.

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Let's go with pink.

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One of my favorites.

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Goes from the stylomastoid foramen

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to the parotid branches.

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So that would be here and then going off the screen.

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So, we have 1, 2, 3, 4, 5 and 6 segments

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of the facial nerve.

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Now, I promised you we would cross reference,

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so let's cross-reference so we can see the stylomastoid

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foramen and the vertical portion of the facial nerve.

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There it is, right there.

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That's it.

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Now, the reason that's important is sometimes you want

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to pay very close attention to that area.

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You follow it up, you follow it...

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sorry.

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You follow it down. You follow it up.

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Here it is, becoming extratemporal right there,

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headed towards the parotid gland.

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Now we're following it up.

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And when a patient has, say,

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Lyme disease or some type of facial nerve palsy,

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like Bell's palsy,

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you want to see if that vertical segment is enhancing.

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And compare the two sides.

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Six segments, facial nerve, nerve number seven.

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Let's move on.