0:01

So now we have another patient that presents with

0:03

right-sided hearing loss and also some dizziness.

0:06

So how do we analyze this case?

0:09

So, when we look at the right cerebellopontine angle,

0:12

we can see this cystic area that's involving the

0:16

right cerebellopontine angle that's located

0:19

just medial to the right porus acusticus.

0:22

Also, we can see a little bit of mass effect of the

0:25

adjacent right middle cerebellar peduncle

0:27

and compare this side with this side.

0:29

So there certainly is some mass effect.

0:31

So now,

0:32

once we see that there's a cystic lesion there,

0:34

what's our next step in our analysis?

0:36

Well, the next step is we want to look at the diffusion

0:39

imaging. And as we learned earlier,

0:41

if there is no increased signal

0:45

on the diffusion sequence,

0:46

then we think that this area is probably cystic.

0:49

But if there is high signal,

0:51

as we learned earlier in an earlier vignette,

0:53

then we start thinking about an epidermoid.

0:56

So in this particular case,

0:57

we can see there's no signal.

0:58

This gives us the confidence that we're dealing with

1:00

a cystic component just medial to the right porus

1:03

acusticus. As we look at the next area,

1:06

we now see that there's a mass involving

1:09

the right half of the dorsal midbrain,

1:12

the right cerebral peduncle.

1:14

And we can see there's an expansile mass that's

1:17

low signal on the T1-weighted images.

1:19

And when we give contrast,

1:20

we can see there's homogeneous enhancement to this.

1:23

So now we have a mass that's involving

1:26

the right cerebellopontine angle.

1:28

But unlike the other lesions that were all extra

1:32

axial, this enhancing component is intra-axial.

1:36

So instead of an extraaxial mass,

1:39

which can arise from the meninges,

1:41

it can arise from the nerves,

1:44

it can arise from some type of ectodermal origin,

1:49

this is now an intra-axial lesion.

1:52

And when you see a mass that's an intra-axial lesion,

1:56

now we have to start thinking about a tumor that

2:00

has glial origin. So in this particular case,

2:04

this is a juvenile pilocytic astrocytoma that's

2:08

arising from the right cerebral peduncle

2:12

that isn't associated with a cyst.

2:15

Now, sometimes when we think of juvenile pilocytic

2:18

astrocytomas, which is what this is,

2:21

we think of a cystic lesion with a mural nodule.

2:24

This just happens to be a large intra-axial enhancing

2:29

lesion, associated with that cyst.

2:30

So it's not technically a mural nodule,

2:33

but it is a densely enhancing intra-axial

2:35

mass with an eccentric cystic component.