0:00

For each of the cases that I'm going to

0:03

show in this temporal bone series,

0:05

I'd like to spend a little bit of time at the beginning

0:07

reviewing the anatomy because

0:09

the more you go through it,

0:10

the better off you are in learning the anatomy

0:13

and recognizing the various structures.

0:15

So we'll start with this first case,

0:17

which was a patient who actually had

0:19

hearing loss on the right side.

0:20

But we're going to look at the left temporal

0:22

bone in the axial plane.

0:24

Now, the scanning plane for the external auditory canal is important.

0:29

It shouldn't be done straight transaxial.

0:32

Some of the cases that we do at Johns Hopkins are

0:35

scanned straight transaxial with zero point six to

0:39

zero point seventy-five millimeter thick slices.

0:42

So that way we can reconstruct

0:44

it in any plane we wish to.

0:45

But we're just going to go with the anatomy

0:48

as it was scanned originally.

0:50

So here we are looking at the external auditory canal

0:53

and what we see are the structures of the

0:56

external ear and the helix of the ear.

0:59

This is the external ear.

1:01

When we have a small external ear on a congenital basis,

1:06

the term that we usually use is microtia.

1:09

And that may or may not be associated with

1:12

external auditory canal atresia.

1:14

But this looks like a normal cartilaginous

1:17

and soft tissue of the external ear

1:21

going in in this direction.

1:23

We come to the external auditory canal and as we

1:25

described in the original anatomy PowerPoint,

1:29

we have two parts of the external auditory canal.

1:31

We usually refer to the cartilaginous part and then

1:34

the bony part of the external auditory canal.

1:37

And we'll be seeing this obliquely on the axial scans.

1:41

At the level that we're looking at

1:43

the external auditory canal,

1:45

we identify the mandible and we're going to be

1:47

seeing the temporomandibular joint shortly.

1:49

And we have some of the mastoid air cells.

1:51

We have a little bit of the jugular fossa.

1:53

And over here, let's continue to scroll.

1:57

And as we scroll,

1:58

we see a greater portion of the bony portion of the

2:02

external auditory canal. Here you see the bone,

2:06

the anterior wall and the posterior wall

2:08

of the external auditory canal.

2:10

We are no longer seeing the cartilaginous portion,

2:13

we are just seeing the bony portion.

2:15

Where does the external auditory canal end?

2:17

It ends on this structure,

2:19

which is our tympanic membrane.

2:21

So depending upon how you window the case,

2:24

you will see the tympanic membrane a little

2:27

bit better or worse. And as you can see,

2:30

I can sort of make the tympanic membrane go away

2:32

completely versus highlight it as you move more towards

2:36

an air window, a lung window, if you will.

2:40

So part of reviewing of the external canal and temporal

2:44

bone anatomy is scrolling back and forth as well as

2:48

changing the window and level of the CT scan.

2:51

So the tympanic membrane is identified as the

2:57

medial most portion of the external auditory canal.

2:59

Now.

3:00

So the pathology is going to be in the cartilaginous

3:03

and bony portion and the adjacent soft tissues.

3:06

Now that said,

3:06

there is often a lot of pathology that will extend from

3:10

the external auditory canal potentially through the

3:13

tympanic membrane and into the middle ear.

3:16

So here we find the middle ear ossicles.

3:19

And I'm just going to move this a little bit more

3:22

centered. Here we go. And let's identify the anatomy.

3:27

The most anterior of the middle

3:31

ear ossicles is the malleus.

3:34

And the one that is usually seen at the same

3:38

level as the malleus is the incus.

3:41

And we usually identify the anatomy in terms

3:45

of the ice cream and the ice cream cone,

3:49

with this being the head of the malleus and

3:52

this being the short process of the incus.

3:56

So you're seeing a little bit of the ice cream and a

3:59

little bit of the ice cream cone in this anatomy of the

4:02

middle ear ossicles. This is the middle ear cavity.

4:07

And when you have this little waist here that

4:10

expands into the mastoid air cells,

4:14

this area of the waist is called the atticrum.

4:19

And I'm not sure how many Ds there are in aditus,

4:24

but close enough, aditus ad antrum is the connection

4:28

from the middle ear cavity into the mastoid

4:32

air cells and the mastoid antrum.

4:35

So the aditus is referring to the middle ear cavity,

4:38

the antrum referring to the mastoid air cells

4:41

and the connection between the two.

4:44

Many people have referred to this as kind of the

4:47

womb, not the best example of a woman's body,

4:50

but the womb-like space

4:53

of the aditus ad antrum.

4:55

In addition,

4:56

you're seeing a small soft tissue structure which

4:59

is heading towards the head of the malleus.

5:02

And that soft tissue structure

5:03

is the tensor tympani muscle.

5:06

So there are two main muscles in the middle ear cavity.

5:10

The largest one is the tensor tympani muscle

5:13

going from the cochleariform process,

5:15

which is this little bone prominence here to the

5:20

head and neck of the malleus.

5:22

And the other one is the stapedius muscle.

5:25

The stapedius muscle goes from the

5:27

pyramidal eminence to the stapes.

5:30

And that is very rarely seen even on high-resolution CT.

5:34

But we'll see how we do on this particular case.

5:38

On this same section,

5:40

we are identifying the internal auditory canal.

5:43

You have the widening of the cochlear aperture

5:48

and you're seeing portions of the cochlea.

5:53

This is probably up maybe a portion of the basal or

5:59

middle turn. And then the apical turn of the cochlea.

6:03

You're also identifying the vestibule

6:05

and some of the semicircular canals,

6:07

but they'll be more apparent on subsequent slices.

6:12

So as we go further inferiorly,

6:16

I want to point out this section.

6:18

So on this section, we see two dots.

6:21

The first dot is the neck of the malleus

6:28

and the second dot is the long process of the incus.

6:32

So we saw with the ice cream cone the short process of

6:36

the incus. This is the long process of the incus.

6:40

And you should see these two dots on every case.

6:42

If you're not seeing them,

6:44

then there's congenital absence of the

6:46

middle ear ossicles potentially

6:51

as we continue downward.

6:53

I'm going to change the window just a little bit because

6:56

what we're trying to identify is the incudostapedial joint.

7:00

And in point of fact,

7:02

you are seeing this on this slice.

7:04

On this slice, we have a little

7:08

remnant of the malleus neck.

7:10

You have a little remnant of the

7:12

long process of the incus.

7:13

And you see that there is a little joint right there

7:17

between something that looks kind of like that

7:20

and something that looks kind of like that.

7:23

And what you're seeing is the long process of

7:26

the incus and one of the crura of the stapes.

7:30

And the communication here with what is again,

7:36

I'll be challenged on my spelling here,

7:39

the capitulum of the stapes,

7:41

which is the portion that will articulate

7:44

with the long process of the incus.

7:46

So that's the anatomy that you're seeing on this scan.

7:50

We're also seeing the vestibule.

7:51

We're seeing part of the probably

7:53

posterior semicircular canal,

7:55

just a little bit of the basal turn of the cochlea.

7:58

I made this kind of bright and with lung window

8:03

just so that way we could see the portions

8:06

of the stapes a little bit better.

8:08

Again,

8:09

here you're seeing a portion of the stapes

8:13

that's only faintly seen right here.

8:18

And you're about to see the oval window,

8:21

which is the location at which the stapes'

8:24

footplate inserts to the vestibule.

8:28

So as we continue a little bit further downward,

8:32

we cross that oval window here and cross to the section

8:39

which shows the structures of the hypotympanum.

8:44

So we have the epitympanum,

8:46

which is sort of the upper portion of the middle

8:48

ear cavity. We have the mesotympanum,

8:50

which is the middle portion of the middle ear cavity.

8:52

And then we have the hypotympanum.

8:54

The hypotympanum is characterized by three structures.

8:58

They are the sinus tympani,

9:03

the little bone here,

9:05

which is the pyramidal eminence

9:09

and the facial nerve recess with the facial nerve

9:13

nearby. So that's the facial nerve recess.

9:16

Those are the three main structures here,

9:19

the sinus tympani,

9:20

the pyramidal eminence and the facial nerve recess,

9:23

with the facial nerve seen just posterior

9:26

to the facial nerve recess.

9:28

Those are the main structures of the hypotympanum.

9:34

Right here we find that area of the airspace that is

9:39

about to connect to the basal turn of the cochlea.

9:43

This airspace is the round window.

9:46

So we talked about the oval window where the stapes

9:49

inserts at the vestibule. Here is the round window,

9:53

which leads to the basal turn of the cochlea.

9:55

And you may recall I said that this is the space

9:57

through which they insert the cochlear implant.

10:00

We're seeing just a little bit of the sinus tympani.

10:03

And I mentioned before that that little bone connection

10:06

between sinus tympani to the round window

10:10

is something called the subiculum.

10:13

And there's actually a connection between the sinus

10:15

tympani and the oval window with the stapes,

10:19

and that's called the ponticulus.

10:22

So a little bit of

10:24

middle ear anatomy.

10:26

This is the cochlear promontory.

10:29

The importance of the cochlear promontory

10:31

is that's where we usually see

10:35

glomus tympanicum,

10:41

they sit right there on the cochlear promontory.

10:46

So

10:47

I think that's a nice start to the review of

10:51

the anatomy. Let's get to some pathology.

10:53

So, as we slide over to the side that had the hearing loss,

10:58

which is the right side,

10:59

you notice that there is a soft tissue mass at the

11:02

junction between the cartilaginous portion of the

11:05

external canal and the bony portion

11:07

of the external canal.

11:09

And you notice that there is a little bit

11:11

of a low density rim around this mass,

11:15

identified as this darker area here.

11:20

And usually you see that darker area

11:22

also on the anterior wall as well,

11:26

because this is really not fixed to the bony wall or

11:30

the cartilaginous wall. This is an area of serumen.

11:34

So this is ceruminous impaction,

11:36

basically earwax that we see on CT scan very frequently

11:40

through the emergency room and on some of the

11:43

evaluations for patients with hearing loss,

11:45

it may just be something as simple as earwax.

11:48

So earwax cerumen is the most common mass in the

11:52

external canal. It's entirely benign,

11:54

it can be readily removed.

11:56

And sometimes the issue is, is it connected?

11:59

Attached to the tympanic membrane.

12:02

So you do want to scroll and identify that

12:05

separate from the tympanic membrane.

12:08

So I'm going to window this a little bit more so that

12:10

way we can see the tympanic membrane nicely and

12:14

it's far away from this cerumen impaction.

12:18

So that's our first case with a little bit of a

12:20

review of the anatomy. We'll go on from here.