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Facial Nerve Schwannoma

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So now what we're going to do is take the information

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that we learned in the prior sections and apply it

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to a little bit more complex disease entities.

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So when we look at this specific image,

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this is a heavily weighted T2-weighted image,

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and we see this little mass right here that's involving

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the distal aspect of the internal auditory canal.

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Now, on first glance, we look at this and we say,

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my gosh, this could be another vestibular schwannoma.

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Because remember,

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vestibular schwannomas can arise in the distal aspect of

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the internal auditory canal near the fundus

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of the internal auditory canal.

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So this is what we see on the heavily T2-weighted

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images. So point number one is that we see this,

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but we always want to remember to give contrast when

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we're looking at the internal auditory canal because

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if we didn't give contrast and we just saw this,

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we could say, aha, this is a vestibular schwannoma.

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But when we do the contrast-enhanced study, remember

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a lot of these vestibular schwannomas start to occur in

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the internal auditory canal and then grow laterally

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through the porus acusticus into the

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cerebellopontine angle. But instead,

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what's happening here is notice what this mass

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is actually doing, is it's growing distally.

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It has a little bit of a semicircular appearance to it,

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and then it curves back on itself.

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This is the normal course of the facial nerve.

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And what this is is actually a schwannoma not involving

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the cochlear nerve or the superior vestibular nerve.

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Rather, this is a schwannoma involving the facial nerve.

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So the normal course of the facial nerve is that it

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extends distally into the fundus of the internal

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auditory canal. It has a labyrinthine segment.

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It then runs into this ganglion,

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which is referred to as the geniculate ganglion.

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It does a 180-degree curve at this level,

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which is referred to as the anterior genu,

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and then extends

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posteriorly along the tympanic segment.

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So this is actually a schwannoma,

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not involving the cochlear nerve or

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the superior vestibular nerve,

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but this is the classical appearance of a facial nerve

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schwannoma. And it highlights a couple of things.

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Number one,

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remember the complementary nature of your sequences.

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So on the heavily weighted T2-weighted images,

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it looks exactly like a schwannoma.

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Number two,

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always remember to give contrast so these

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things can enhance. And number three,

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look at these important spread patterns,

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because if this lesion is extending distally towards the

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fundus of the internal auditory canal and then extends

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along the expected course of the facial nerve,

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then we can make a very sophisticated diagnosis of a

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facial nerve schwannoma, but the key is the anatomy,

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and combine that with high-quality imaging.

Report

Faculty

Suresh K Mukherji, MD, FACR, MBA

Clinical Professor, University of Illinois & Rutgers University. Faculty, Michigan State University. Director Head & Neck Radiology, ProScan Imaging

Tags

Temporal bone

Skull Base

Non-infectious Inflammatory

Neuroradiology

Neuro

MRI

Idiopathic

Head and Neck

Brain

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