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This patient was being evaluated for facial nerve palsy,

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and the study was performed with

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temporal bone CT technique.

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We want to look at the internal auditory canal,

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make sure it's not enlarged

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on the temporal bone study.

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We want to look at the labyrinthine

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portion of the facial nerve.

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We're going to look on the right side here.

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We're going to look at the geniculate ganglion region,

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and then we see the first genu where

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it becomes the tympanic portion.

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And then we follow that down into the mastoid portion of

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the facial nerve going downward until it leaves

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here at the stylomastoid foramen.

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So this is the egress of the facial

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nerve at the stylomastoid foramen,

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and from there, it goes into the parotid gland.

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So always on these temporal bone studies,

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you want to quickly look at the soft tissues and make

0:57

sure there's not a parotid mass that may account for

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the facial nerve palsy. On the abnormal side,

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if we compare the size of the labyrinthine portion of

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the facial nerve on the left side versus the right side,

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I think we can all agree that this is markedly enlarged.

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At the geniculate ganglion, we got this big honker here,

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a big mass which compared to the contralateral side,

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which looks just like a little triangle,

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this looks like a big lump of tissue.

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And

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even the proximal portion of the tympanic portion of the

1:37

facial nerve is much wider than it is on the left side.

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And this is an example of a facial nerve schwannoma that

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was affecting labyrinthine, as well as geniculate

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ganglion, as well as tympanic portions.

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We don't see any of that reticulation or bony matrix

1:59

to suggest that this is a facial nerve hemangioma.

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We would look at the descending portion and follow this,

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again, to the stylomastoid foramen and look for a parotid

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mass, because in the differential diagnosis also is

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perineural spread up the facial nerve with thickening of

2:18

the facial nerve from a parotid mass or skull

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base mass, we do not see that. In this case,

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we would recommend getting an MRI scan because we wanted

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to see whether this is a contrast-enhancing lesion.

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Presumably, if it was not enhancing,

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we would shift our differential diagnosis from a facial

2:36

nerve schwannoma to other causes

2:38

of facial nerve enlargement,

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which may be congenital and not

2:41

show contrast enhancement.

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This is the MRI on the patient who had the enlarged

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facial nerve in its geniculate portion as well as the

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proximal tympanic portion and labyrinthine portion.

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So this would be something that would not be

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visible in our standard MRI sequences,

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but only found on thin-section images

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pre and post gadolinium.

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So here is the post-gadolinium-enhanced scan.

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And remember,

3:09

we want to see whether this lesion enhances because

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most schwannomas do enhance. So, as we come up,

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we'll just magnify a little bit

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and focus on the left side.

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And we do see enhancement of the geniculate ganglion as

3:25

well as the proximal portion of

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the tympanic facial nerve.

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And here's a little portion of the labyrinthine portion.

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So you might say, well,

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you just told us that the facial nerve may show

3:37

asymmetric contrast enhancement, and therefore,

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could this be normal? Yes,

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the tympanic portion and the geniculate portion of the

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facial nerve may show contrast enhancement.

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However, the labyrinthine portion should not.

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And this portion right here,

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which is proximal to the geniculate ganglion,

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is the portion that is abnormally enhancing.

3:59

And the size of the geniculate ganglion enhancement,

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when we compare it from right to left, is abnormal as well.

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So both the size as well as the labyrinthine portion

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suggest that this is indeed a schwannoma

4:13

of the facial nerve on the left side.