0:01

So, the next topic that we'll cover when we talk

0:03

about imaging techniques of the cerebellopontine angle

0:05

is the technique.

0:08

And one thing that I want to emphasize:

0:10

the way that I look at the cerebellopontine angle,

0:14

my approach to this is that the whole purpose of

0:17

the technique is to visualize the anatomy.

0:20

And you have to understand the anatomy.

0:22

And remember,

0:22

the whole goal of imaging is to identify

0:25

and define this detailed anatomy.

0:27

So we always have to remember that there are

0:29

four nerves in the internal auditory canal.

0:32

So this nerve is the facial nerve,

0:34

the one below it is the cochlear nerve.

0:37

This is the superior vestibular nerve,

0:39

and this is the inferior vestibular nerve.

0:41

This is anterior, and this is posterior.

0:45

So if you've ever heard the term "seven up,"

0:47

"coke down," that means the 7th nerve is superiorly,

0:51

and the cochlear nerve, or the "coke," is inferiorly.

0:54

And the superior vestibular nerve is

0:56

at the level of the facial nerve,

0:57

and the inferior vestibular nerve is at the level

1:00

of the cochlear nerve. So remember,

1:02

the end goal of the technique is to visualize

1:04

These specific pieces of anatomy.

1:06

So when we start looking at our technique because

1:10

these structures are so thin, remember,

1:13

we can only see thin anatomy with thin section

1:16

imaging. So, as a general rule,

1:18

when we're looking at the cerebellopontine angle,

1:21

our slice thickness should never exceed 3 mm.

1:25

We should always perform pre-contrast

1:28

Axial and Coronal T1-weighted images.

1:31

And then we always want to perform post-contrast

1:33

Axial and coronal T1-weighted images.

1:37

Now, I mentioned here 3 mm,

1:39

But if you're at a higher field strength,

1:41

like at three tesla, we can bump this down to 2 mm.

1:44

But we always have to remember the trade-off

1:46

between signal to noise.

1:49

So if you have a higher field magnet,

1:50

you have a little bit more currency,

1:52

and then you can perform your imaging

1:54

at thinner sections.

1:56

We always want to perform axial T2-weighted imaging.

1:58

Because remember,

2:00

as we'll see later,

2:01

some people with demyelinating diseases or strokes

2:04

can sometimes have areas of demyelination involving

2:07

the region of the cochlear nerve.

2:09

And finally,

2:10

We always want to add the heavily

2:12

T2-weighted image. Now,

2:14

each vendor has its own flavor of the

2:17

heavily T2-weighted images.

2:19

These images here on your right-hand side are

2:22

from the heavily T2-weighted images.

2:24

But these should be routinely performed

2:26

on all of your CPA sequences.

2:30

The other thing we always have to remember,

2:31

and again, I come from this,

2:32

from a head and neck radiologist's approach,

2:34

is that sometimes I get tunnel vision.

2:36

And occasionally, we have to worry about that

2:38

accessory organ that I refer to as the brain.

2:41

So just remember that lesions that involve the brain

2:45

can also cause the symptoms of

2:47

hearing loss and dizziness.

2:48

So we always want to perform T1 pre- and post-contrast.

2:51

We want to perform some type of FLAIR sequences and

2:53

we also want to perform the diffusion-weighted sequence.

2:56

As we'll see later,

2:58

to look for things such as infarcts.

3:00

But as we'll see later,

3:01

diffusion-weighted imaging can also be used to help

3:04

differentiate between arachnoid cysts and

3:05

epidermoids of the posterior fossa.

3:08

So these are some examples of the elegance

3:10

epidermis of the posterior fossa.

3:13

So these are some examples of the elegance

3:16

of these heavily T2-weighted images.

3:18

On the left-hand side is an axial image

3:21

through the internal auditory canal,

3:22

we can very nicely see the modiolus.

3:25

We can see the cochlear nerve extending

3:27

through the cochlear canal.

3:28

We can see the inner scalar septum and with the leap

3:31

of faith, we can actually see the Basilar membrane.

3:34

Now,

3:34

these are normal anatomic structures that you should

3:37

be able to visualize on your routine sequences.

3:41

And when you perform your reconstructions,

3:43

if you will,

3:44

you can actually see very nicely the two

3:47

and a half turns of the cochlea.

3:48

We can see the superior semicircular canal and

3:51

the lateral semicircular canal and the CSF that is

3:55

a combination of the utricle and the saccule.

3:58

So when we start looking.

4:00

Looking at the detailed anatomy of

4:02

the cerebellopontine angle,

4:04

this is the classical example that we have

4:07

here of a vestibular schwannoma.

4:08

We'll talk about this in detail,

4:10

but very briefly for the anatomy.

4:12

We can see the porus acusticus here.

4:14

The distal aspect of the internal auditory

4:17

canal ends at this region right here.

4:19

That's referred to as the fundus.

4:21

When we start talking about more of the pathology,

4:23

we'll talk about the various appearances of this

4:26

pathology which is a vestibular schwannoma.

4:28

This is the classic ice cream cone

4:30

of a vestibular schwannoma.

4:32

And on your right-hand side demonstrates the power

4:34

of really performing high-quality imaging and the

4:38

importance of the T2-weighted sequences.

4:40

So on the top right corner here,

4:42

we can see thin-section imaging performed through

4:45

the internal auditory canal. And look,

4:47

with the leap of faith, there's a little focal area

4:50

here of enhancement that I would argue can be

4:52

missed on a bad day.

4:54

But on the other hand,

4:55

when we do the heavily T2-weighted images, we

4:57

can see this little pebble right here, which

5:00

demonstrates a small little vestibular schwannoma

5:02

located in the fundus of the internal auditory

5:05

canal. So all of these sequences are important.

5:08

But remember,

5:09

the importance of imaging technique is to see

5:13

the anatomy. And if you can see the anatomy,

5:15

that unlocks the power of head-neck imaging.

5:19

We have to remember that when we look

5:21

at the cerebellopontine angle,

5:23

eventually all of this information gets transferred

5:27

through the 7th and 8th nerves into the brain.

5:30

And as I mentioned before, yes,

5:32

we want to perform the very,

5:33

very thin-section imaging to evaluate the

5:36

cochlea and to evaluate the nerve.

5:39

But always remember to look at the brain.

5:41

And when you look at the brain,

5:42

we want to look at the FLAIR sequences.

5:44

Because infectious processes can cause hearing loss.

5:48

Congenital malformation in this ase pachy,

5:50

gyre and lissencephaly can cause hearing loss.

5:53

Multiple sclerosis can cause hearing loss with the

5:56

various demyelinating plaques. And as we get older,

6:00

remember,

6:00

always remember that ischemia

6:02

can result in infarcts.

6:04

And this can result in hearing loss as well.

6:07

So not only look at the cerebellopontine angle,

6:10

but always remember to look at the brain.