0:01

This is a patient who has had a

0:03

canal wall down mastoidectomy.

0:06

By canal wall down, we mean that the posterior wall

0:09

of the external canal has been removed.

0:11

And you see that on the CT scan in the case above.

0:17

In the case below we have a canal

0:19

wall up mastoidectomy.

0:21

The posterior wall of the external

0:23

canal is still there.

0:25

So as we look at these two different cases we are

0:29

asked is what is seen within the postoperative

0:34

cavity granulation tissue or is it cholesteatoma?

0:39

Once again the way we make this distinction is by

0:42

looking at the diffusion-weighted scan and looking at

0:45

the post-contrast enhanced scan to distinguish the

0:50

granulation tissue versus the cholesteatoma.

0:53

So let's look at the top case.

0:55

So in the top case we have a canal wall down

0:57

mastoidectomy and yet there is soft tissue

1:00

filling the operative cavity.

1:03

On the T2-weighted scan, mixed signal intensity with

1:07

some darker and some brighter signal intensity.

1:09

On the T1-weighted scan.

1:11

Before gadolinium we see that there is some soft

1:14

tissue here which is a little bit brighter in signal

1:16

intensity and other that's darker

1:18

in signal intensity.

1:20

On post-gadolinium enhanced imaging what we're seeing

1:24

is enhancing tissue anteriorly which is the

1:27

darker tissue. On the T2-weighted scan,

1:31

the posterior tissue does not show contrast

1:34

enhancement and is likely just

1:37

hyperintense fluid on the T1-weighted scan.

1:40

And when we look on the diffusion-weighted scan we're

1:42

not seeing anything that's bright on the DWI scan.

1:46

So this is what we would typically expect of

1:49

granulation tissue showing contrast enhancement

1:53

and absence of restricted diffusion.

1:57

A word about the diffusion-weighted sequence.

1:59

We usually will do a fast bone-co diffusion-weight

2:02

sequence for looking in the temporal bone because of

2:05

the possibility of susceptibility artifact from

2:08

the air, bone, and potentially fluid interface.

2:12

In point of fact,

2:13

this tiny little area of curvilinear bright signal

2:18

on the diffusion-weighted scan is actually secondary

2:21

to an artifact from that bone-air interface

2:25

and can be generally ignored.

2:28

You see the same thing over here at the Petri's tip.

2:30

You see a little bit of that bright signal intensity

2:33

interface at the middle cranial fossa

2:36

floor on the left side.

2:38

So this area right here is an artifact from

2:43

susceptibility similar to this little bright

2:46

area over here on the right side.

2:50

But the vast majority of this tissue that is showing

2:53

contrast enhancement is not showing any restricted

2:56

diffusion. Let's compare and contrast that with the

3:00

example below.

3:01

So here we have the canal wall up mastoidectomy.

3:04

In other words,

3:05

the posterior wall of the external

3:08

canal is still intact.

3:10

We have soft tissue that is seen in that

3:13

operative bed in the inferior mastoid.

3:16

We look on the T1-weighted scan before and after

3:19

gadolinium and we see that although there are some

3:22

portions which are showing contrast enhancement

3:24

like granulation tissue,

3:26

this area where the green arrow is,

3:29

is the area in question.

3:31

And when you look on the DWI,

3:34

you see that in point of fact,

3:35

it does show bright signal on the

3:37

diffusion-weighted scan representing

3:41

a cholesteatoma.

3:43

So uppercase contrast-enhancing tissue which does

3:47

not show restricted diffusion, granulation tissue,

3:51

lowercase soft tissue which is not showing contrast

3:54

enhancement on the post-gad T1-weighted scan but

3:58

does show restricted diffusion representing

4:02

recurrent or residual cholesteatoma.

4:05

This is the second case showing the value of

4:08

diffusion-weighted imaging. So we have the T2-weighted images and then we have

4:15

our diffusion-weighted scan.

4:17

And down below we have axial scans with the CT scan,

4:20

the T2-weighted image and the diffusion-weighted

4:23

scan, and then the coronal CT scan.

4:26

So in this instance,

4:28

what one can see is that there is an area of high

4:33

signal intensity on the coronal diffusion-weighted scan

4:39

indicative of a small area where there is residual

4:43

cholesteatoma which corresponded to this area

4:46

on the T2-weighted image. In the second case,

4:49

we have an erosive process along the anterior

4:52

epitympanic space which is eroding into the middle

4:57

cranial fossa on the right

4:59

side on the T2-weighted image,

5:01

we saw this as this rounded area corresponding to

5:05

the same area on the CT scan in the

5:07

anterior epitympanic space.

5:09

As you can see pretty nicely on the diffusion-weighted

5:11

scan, it's ovoid and bright in signal intensity.

5:16

And you can see that on the CT that there

5:19

is erosion of the tegmen tympani.

5:21

So this would not be granulation tissue.

5:23

Clearly, with erosion of the tegmen tympani, we're dealing

5:27

with a cholesteatoma which is verified

5:29

on the DWI scan.