0:01

So we're going to continue our conversations

0:02

with CP angle masses.

0:05

And now we're going to take a look

0:07

at another disease entity.

0:08

So when you look at the axial T2-weighted images,

0:12

what we see is another cystic mass that's located

0:14

in the cerebellopontine angle. Again,

0:17

notice how the 7th-8th nerve complex

0:19

is extending laterally,

0:20

extending through the porus acusticus and is now

0:23

indistinguishable once it reaches the lateral margin

0:27

of this mass. So this is high signal on T2.

0:30

So it's a cystic lesion.

0:31

On the non-contrast T1-weighted image,

0:34

we can see that it's low signal, again,

0:36

indicating that it's fluid.

0:38

And this image on the bottom right-hand corner is

0:42

following contrast and we can see how there's no

0:44

enhancement. So when we look at sequence number one,

0:48

sequence number two,

0:49

and sequence number three,

0:50

this looks a lot like an Arachnoid cyst.

0:53

But the differentiating feature in this particular

0:56

case is this sequence on the top right and this

0:59

is the diffusion-weighted imaging sequence.

1:01

And when we look at the DWI sequence,

1:03

notice how it's very,

1:04

very high signal on the diffusion-weighted sequence.

1:08

When you have this combination of something that is

1:10

a cystic cerebellopontine angle mass

1:13

and it's high signal on diffusion,

1:15

this allows us to make the diagnosis of an

1:18

epidermoid. Now, when we do our DWI sequence,

1:21

we can either perform this sequence,

1:23

which is the echo planar sequence,

1:24

which is what most of us have on our magnets,

1:27

but the best way to do it is some

1:28

type of line scan diffusion,

1:30

which is not completely available on

1:32

all our magnets. But in general,

1:34

what I found out in my experience is that the

1:36

echo planar imaging sequence can be very beneficial

1:39

still for differentiating between an

1:42

Arachnoid cyst and an epidermoid.

1:45

So if you do just have the echo planar sequence,

1:47

don't hesitate to use it.