0:00

What I'd like to do is separate the pathology of the

0:03

inner ear into these four categories: congenital

0:06

lesions, inflammatory lesions,

0:08

and then we'll look at the neoplasms,

0:10

the benign and malignant, understanding that this

0:13

represents a relatively small portion

0:15

of the pathology of the inner ear.

0:17

Most of the inner ear pathology is congenital

0:19

and inflammatory. Frankly,

0:21

there are some people who have devoted their entire

0:23

career to understanding the congenital

0:25

lesions of the inner ear.

0:27

What I would do is give you an overview with just a

0:29

little bit of a taste of the difficulty of some of

0:33

the eponyms associated with inner ear anomalies, as

0:36

well as some of the embryology associated with it.

0:39

I have to admit that currently there's a big

0:42

emphasis on the genetic abnormalities that are

0:46

associated with the congenital inner ear anomalies.

0:49

And that's something that I'm not as strong in.

0:51

But let's proceed ahead.

0:54

So inner ear pathology generally leads to sensorineural

0:59

hearing loss. Remember, we have two types of hearing loss

1:02

that we typically refer to: conductive and sensorineural.

1:06

The conductive lesions are often our inflammatory

1:09

lesions of the external auditory canal and middle ear,

1:12

most common being otitis media.

1:14

But when we're talking about sensorineural hearing loss,

1:17

We're usually talking about inner ear pathology

1:19

that may or may not affect the cranial nerves,

1:22

The cochlear nerve in particular.

1:25

Within these,

1:26

You have a lot of genetic abnormalities,

1:28

as I mentioned, and a lot of different syndromes.

1:31

And I will provide to you a sort of chart of some of

1:36

these genetic syndromes and the anomalies

1:39

of the inner ear associated with them.

1:41

But they keep expanding and expanding as we

1:44

understand the genetics of how the inner

1:46

ear is constructed in embryology.

1:49

So let's start with how we have our abnormal

1:53

development of the inner ear structures.

1:57

So initially, we have our otic pit and otic placide,

2:02

and we have our auditory plate, and these usually develop

2:06

at about 21 days, 22 days gestation.

2:10

And these are influenced by fibroblast growth

2:14

factors and all the genes that are associated

2:16

with fibroblast growth factors.

2:20

When we have absolutely no development

2:22

of these structures,

2:23

we often refer to it as Michel's deformity or

2:27

complete labyrinthine aplasia in which you have no

2:30

cochlea, no vestibule, no cochlear promontory,

2:33

and the 8th nerve is missing in these individuals.

2:35

So these are part of these complete aplasias,

2:38

if you will, of the inner ear structures.

2:41

And again, this is at 21 days gestation.

2:43

And frankly,

2:45

this is possibly occurring at a time when the mother

2:50

may not be aware that she is pregnant.

2:53

Then after that, we have the influence of

2:56

fibroblastic growth factor number three, which

3:00

takes it from the otic placode to the next step,

3:03

the otic pit. And then we have the otic vesicle,

3:06

and then finally, we have the otocyst.

3:09

And these structures are developing the separation

3:13

and the creation of the cochlea from the vestibule.

3:17

In fact,

3:18

the cochlea and the vestibule separate at around

3:21

three and a half to five weeks gestation.

3:23

So again, you're just a month,

3:25

a little bit more than a month into the pregnancy

3:27

when these things are happening,

3:28

critical things for the patient's, for the child's

3:31

development of hearing as well as balance.

3:34

At the same time,

3:35

you have enlargement and development

3:37

of the endolymphatic sac.

3:39

And what we're going to be seeing as the vestibular

3:41

aqueduct on the CT scan and what we refer to

3:44

as the endolymphatic sac on the MRI scan.

3:47

If these do not separate,

3:49

you have a common cavity between the

3:51

cochlea and the vestibule.

3:54

And this is sometimes referred to as cock's deformity

3:57

for the people who like eponyms.

4:01

Here is an example of a FIESTA or CISS image in

4:06

which we are seeing on the left-hand side

4:09

the normal basal turn of the cochlea.

4:11

And we're seeing a portion of the

4:13

semicircular canal system.

4:15

So what's pointed out by the arrow

4:17

is the basal turn of the cochlea.

4:21

And here we have posterior semicircular

4:23

canal. On the contralateral side,

4:26

the arrow is pointing to the absence

4:28

of development of the cochlea.

4:30

We don't have a basal turn of the cochlea.

4:32

You've got just this tiny little nubbin

4:34

right here of cochlear development.

4:38

And we do have the vestibule and the lateral

4:41

semicircular canal developing. So in this case,

4:44

we have selective deficiency of the cochlea on

4:48

the right-hand side. So cochlear aplasia.

4:52

When you have cochlear aplasia,

4:54

it's typical that you would not

4:57

have a cochlear nerve that

5:00

goes to the absent cochlea.

5:02

And so,

5:03

as opposed to the inner ear structures

5:06

that you've seen previously,

5:08

here we have these nondescript, ill-defined cochlea

5:14

and vestibules. So let me circle those for you.

5:17

So this is going to be your

5:21

what should be your cochlea and your vestibule.

5:23

You can see that this is a bilateral process.

5:26

We have the internal auditory canal on

5:27

the left-hand side of this image.

5:29

We're not quite there on the right-hand side.

5:32

Here we have the internal auditory canal,

5:34

but we don't have any well-developed cochlea.

5:38

And in this case,

5:41

this is the superior portion of the IAC where we are

5:45

seeing 7th cranial nerve and the

5:49

superior vestibular nerve.

5:51

But when you go down to the inferior portion

5:53

of the internal auditory canal, no cochlear nerve.

5:56

And this is also demonstrated on

5:58

the coronal reconstruction here,

6:00

that we see a single nerve going into the internal

6:03

auditory canal, we're not seeing the cochlear nerve.

6:07

And we have this really poorly developed cochlea

6:12

system and really poorly developed

6:15

vestibular system.

6:16

So this is one of these situations where you may

6:19

have a common cavity between the cochlea and the

6:23

vestibule in this nondescript cystic structure.