0:01

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

0:03

that we learned in the prior sections and apply it

0:05

to a little bit more complex disease entities.

0:09

So when we look at this specific image,

0:11

this is a heavily weighted T2-weighted image,

0:13

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

0:16

the distal aspect of the internal auditory canal.

0:19

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

0:22

my gosh, this could be another vestibular schwannoma.

0:25

Because remember,

0:25

vestibular schwannomas can arise in the distal aspect of

0:29

the internal auditory canal near the fundus

0:31

of the internal auditory canal.

0:33

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

0:36

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

0:41

but we always want to remember to give contrast when

0:44

we're looking at the internal auditory canal because

0:48

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

0:51

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

0:56

But when we do the contrast-enhanced study, remember

1:00

a lot of these vestibular schwannomas start to occur in

1:03

the internal auditory canal and then grow laterally

1:06

through the porus acusticus into the

1:08

cerebellopontine angle. But instead,

1:11

what's happening here is notice what this mass

1:13

is actually doing, is it's growing distally.

1:17

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

1:20

and then it curves back on itself.

1:23

This is the normal course of the facial nerve.

1:26

And what this is is actually a schwannoma not involving

1:31

the cochlear nerve or the superior vestibular nerve.

1:34

Rather, this is a schwannoma involving the facial nerve.

1:38

So the normal course of the facial nerve is that it

1:41

extends distally into the fundus of the internal

1:44

auditory canal. It has a labyrinthine segment.

1:47

It then runs into this ganglion,

1:50

which is referred to as the geniculate ganglion.

1:52

It does a 180-degree curve at this level,

1:55

which is referred to as the anterior genu,

1:58

and then extends

2:00

posteriorly along the tympanic segment.

2:02

So this is actually a schwannoma,

2:05

not involving the cochlear nerve or

2:08

the superior vestibular nerve,

2:09

but this is the classical appearance of a facial nerve

2:11

schwannoma. And it highlights a couple of things.

2:14

Number one,

2:15

remember the complementary nature of your sequences.

2:18

So on the heavily weighted T2-weighted images,

2:20

it looks exactly like a schwannoma.

2:23

Number two,

2:23

always remember to give contrast so these

2:26

things can enhance. And number three,

2:28

look at these important spread patterns,

2:30

because if this lesion is extending distally towards the

2:34

fundus of the internal auditory canal and then extends

2:38

along the expected course of the facial nerve,

2:40

then we can make a very sophisticated diagnosis of a

2:43

facial nerve schwannoma, but the key is the anatomy,

2:48

and combine that with high-quality imaging.