0:01

So, this case will illustrate not only the most common

0:05

indication we image the cerebellopontine angle,

0:10

but it'll also help identify the most common pathology

0:14

that we'll see in the cerebellopontine angle,

0:17

and that is the vestibular schwannoma.

0:19

So in the next series of cases,

0:22

what we'll do is we'll help identify the imaging

0:26

characteristics of the vestibular schwannoma and also

0:30

separate it from some of the other diseases

0:34

that can involve this area.

0:36

We've already talked about arachnoid cysts and epidermoids.

0:40

Those are non-enhancing lesions that can be separated by

0:45

diffusion sequences and the heavily T2-weighted

0:48

sequences. Now we'll talk about the vestibular schwannoma.

0:52

So vestibular schwannomas typically involve the cerebello

0:56

pontine angle and they can either involve the fundus of

1:00

the internal auditory canal where they can be isolated,

1:03

they can have a bicompartmental involvement,

1:07

which is the internal auditory canal

1:09

and the cerebellopontine angle,

1:11

or they can predominantly just involve the

1:13

cerebellopontine angle. In general,

1:16

what we would like to see is a vestibular schwannoma

1:19

involving the medial aspect of the internal auditory canal

1:23

and the cerebellopontine angle, as is seen here.

1:26

So in this particular case,

1:27

this is a T2-weighted sequence and we can see this mass

1:31

that is an extra-axial mass that's medially displacing

1:36

the right middle cerebellar peduncle.

1:38

When we look at the non-contrast T1-weighted image,

1:41

we can see this mass is low signal,

1:44

but the low signal is not as low as we see in the fluid

1:50

in the fourth ventricle. So it's low signal,

1:53

but it doesn't have the signal intensity of the fluid

1:57

in the fourth ventricle. Then we give contrast.

2:00

So when we give contrast,

2:02

we can see this mass is very homogeneously enhancing.

2:06

Now, there are some areas that do not enhance.

2:09

Sometimes this may be due to calcification

2:11

or it may be due to hemorrhage,

2:12

but in general it's still a very avidly enhancing mass.

2:16

But two features that you should look for on the

2:19

contrast-enhanced series are the following.

2:21

Is there involvement of the internal auditory canal?

2:25

And number two,

2:26

does this mass have an acute angle with

2:30

relationship to the posterior fossa?

2:32

Or is it more of a wider angle suggesting

2:36

what we will refer to as the dural tail?

2:38

So in this particular case,

2:40

we can see that there is a very sharp demarcation and a

2:43

sharp angle with respect to the adjacent

2:46

cerebellar hemisphere.

2:48

So when we have a combination of an avidly enhancing mass

2:51

that's extra-axial without evidence of a dural tail,

2:55

and then we look at the coronal image and we can see that

2:59

this mass is extending into the internal auditory canal.

3:03

This confirms the diagnosis of a vestibular schwannoma.

3:07

The other thing that we can identify based on this study

3:11

is why patients present with either hearing loss

3:14

or dizziness. Why? Because remember anatomy.

3:18

The four nerves of the internal auditory canal

3:20

are the cochlear nerve, the facial nerve,

3:23

the superior vestibular nerve,

3:25

or the inferior vestibular nerve.

3:26

The superior vestibular nerve is felt to be the

3:28

most likely origin of a vestibular schwannoma.

3:32

If it gets large enough,

3:33

it can involve the cochlear nerve.

3:35

So because this is a contained space,

3:37

as this mass grows larger and larger, as you can see here,

3:41

it's starting to involve the internal auditory canal.

3:44

It compresses these nerves.

3:46

And that's why patients can either present with hearing

3:49

loss or they can present with dizziness.