0:01

So here's another example of a lesion

0:04

involving the posterior fossa.

0:06

But what I'm going to do is going to take you through

0:08

my thought process when I see something like this.

0:11

So here is an example of a mass involving

0:14

the posterior fossa with contrast.

0:16

And we can see that there's an enhancing lesion.

0:19

So what are the questions that I ask myself?

0:22

The first question I ask myself is, is there a dural tail?

0:25

To specifically look for the dural tail,

0:27

I look at the relationship of the enhancing component

0:30

of this mass with the adjacent bone.

0:33

And what I see here is an acute angle instead

0:36

of the obtuse angle on the opposite side.

0:39

Same thing, a very acute angle.

0:41

So there's no dural tail.

0:42

The second question I ask myself is,

0:45

is there involvement of the internal auditory canal?

0:48

So here's a normal internal auditory canal on the

0:51

patient's right side, and on the patient's left side,

0:54

we can see that this enhancing mass is

0:56

extending through this opening here,

0:58

which is the porus Acousticus, and extending laterally

1:01

to involve the internal auditory canal.

1:04

So I have that CP angle mass,

1:06

no dural tail extending into the internal auditory

1:09

canal. Why do the patients present?

1:11

Because they present either with

1:13

hearing loss or dizziness.

1:15

So why do they present with those clinical symptoms?

1:17

What is the anatomic and clinical correlation?

1:21

The heavily T2-weighted images.

1:23

We can see the CSF signal in the internal

1:26

auditory canal. In this particular case,

1:29

we see one nerve here extending into the base

1:32

of the cochlear, through the cochlear canal.

1:34

That's the cochlear nerve.

1:35

And if we're at the level of the cochlear nerve,

1:38

this nerve extending into the vestibule

1:41

is the inferior vestibular nerve.

1:43

When we look laterally through the porus Acousticus,

1:46

all we see is CSF.

1:48

And then we run into the middle cerebellar peduncle.

1:52

In this particular case,

1:53

we can see the mass right here involving the CP angle.

1:56

But when we take a very close look at the bottom right

1:59

images and we look at the internal auditory canal,

2:02

here's our cochlear nerve.

2:04

And as it's running laterally,

2:06

it runs right into that mass.

2:09

And this involvement of the cochlear nerve,

2:11

which we learned earlier,

2:13

is the way hearing gets transferred from our external

2:17

auditory canal to the middle ear to the cochlea,

2:22

through that hydroelectric plant that

2:24

we call the organ of Corti,

2:26

which then transmits fluid into electrical energy that's

2:29

transferred along the nerve into the brain.

2:32

It's this discontinuity that's caused by the

2:35

cerebellopontine angle tumor that results

2:38

in the patient's hearing loss.