0:00

So here's another example of an epidermoid.

0:04

But in this particular case, we're going to focus on

0:06

the addition of a specific sequence, and that's the

0:08

heavily T2-weighted sequence, but also explain the

0:12

importance of looking at all the sequences to avoid

0:17

the potential pitfall of calling something a

0:20

negative study when there's actually pathology.

0:23

So on the top left sequence,

0:25

this is a T2-weighted image, and when you draw a

0:28

line down the middle and you compare

0:30

one side to the other side,

0:31

what I want you to do is focus on the cerebellopontine

0:34

angle. Now, if we look at this,

0:36

these really look pretty symmetric, and maybe with

0:39

the leap of faith, there may be a little bit more

0:41

impression on the flocculus, but I think

0:43

that's a tough call to make.

0:45

On the right-hand side is a contrast-enhanced T1

0:49

weighted image with fat suppression. And on the T1

0:52

weighted image with contrast with fat suppression,

0:55

we can see that there's no enhancement

0:57

in either cerebellopontine angle.

0:59

So if we didn't look at all the sequences,

1:01

in fact, if we didn't even include the sequences,

1:04

we could call this study negative

1:07

in a patient that presents with dizziness,

1:09

the next thing that we have to do is take a

1:11

look at our diffusion-weighted imaging.

1:13

And when we look at our diffusion-weighted

1:15

imaging located at the bottom left here,

1:17

we can see the high diffusion signal which we

1:21

learned in the last vignette was indicative of

1:24

an epidermoid. So in general, we could say,

1:27

aha, there is likely an epidermoid here. But really, in

1:31

order to perform state-of-the-art imaging at your center,

1:35

you really need to perform the heavily

1:38

T2-weighted images.

1:39

Because when you perform the heavily

1:41

T2-weighted images,

1:42

what you now see is this area of increased signal

1:48

that's located in the cerebellopontine angle.

1:52

And in fact,

1:52

with a leap of faith, you can see that this mass is

1:55

actually impinging on this external portion of the

1:59

fifth nerve, and compare this to the normal

2:01

appearance of the fifth nerve on the opposite side.

2:05

So when we take a look a little bit more inferiorly,

2:08

again, we can see this subtle area of increased

2:12

diffusion signal. And again,

2:14

I want to call your attention to the relatively

2:16

normal appearance on our standard sequence.

2:18

But remember,

2:19

this patient presented with dizziness, and when we

2:22

look at this heavily T2-weighted image, we can now

2:26

explain the reason that this patient presented with

2:28

dizziness. Why? Look at the patient's right side.

2:32

We can see the internal auditory canal,

2:34

we can see these two nerves which are

2:37

extending from medial to lateral.

2:39

And when we look at the porus acusticus at the

2:41

cerebellopontine angle, we just see fluid.

2:44

But when we look at the patient's left side,

2:47

we can see that these two nerves,

2:49

especially the inferior vestibular nerve,

2:52

is extending into this frond-like mass which is

2:57

the infrastructure of the epidermoid.

3:00

So it's this mass effect on the epidermoid directly

3:04

abutting the superior and the inferior vestibular

3:06

nerve that is causing the patient's dizziness.

3:09

And the only way we'll be able to confirm this

3:12

diagnosis is with these heavily

3:14

T2-weighted sequences.