0:01

So far, we've talked about the retrotympanic

0:04

red mass and the retrotympanic white mass.

0:08

I want to just briefly mention the retro

0:11

tympanic purplish-blue mass,

0:14

and this is a lesion that is centered

0:17

in the petrous bone.

0:19

So here we have a patient who had a CT

0:22

angiogram for pulsatile tinnitus.

0:25

And as we look at the CT angiogram,

0:29

we see that there is a process which is well-defined,

0:35

has relatively sharp borders,

0:38

and which appears to be eroding the medial

0:42

wall of the internal carotid artery.

0:45

So we see the carotid artery with

0:47

contrast opacification.

0:49

And here we have this mass that is growing from the

0:53

petrous apex region. It's undercutting the clivus.

0:59

And not only that,

1:00

but it does appear to be extending posterior

1:03

laterally to the middle ear cavity.

1:08

And this is just at the entrance to the Eustachian

1:12

tube. It almost looks like it's bilobed.

1:15

And you can see the wall of the carotid

1:17

artery is dehiscent from this lesion.

1:20

So what is in our differential diagnosis?

1:23

The thing that we want to make sure it's not, and the

1:25

reason why the CTA was performed, is we want to

1:28

make sure it's not a carotid artery aneurysm.

1:32

Carotid artery aneurysm, when they're longstanding,

1:35

can have pulsatile remodeling of the bone.

1:39

In this case,

1:40

we don't see any connection to

1:41

the internal carotid artery.

1:43

We don't see any vascular flow within this lesion.

1:46

Could it still be a thrombosed aneurysm?

1:48

It's possible,

1:49

but the shape of this makes it unlikely.

1:52

The fact that this was a blue-domed mass that was

1:55

seen at otoscopy also would suggest that

1:58

this is not a patent aneurysm.

2:02

Again, it could be a thrombosed aneurysm.

2:05

So this lesion at the petrous apex is classically

2:11

a cholesterol granuloma.

2:13

Cholesterol granulomas are thought to occur due to

2:17

changes in the pressure within the aerated petrous

2:21

apex leading to blood products weeping

2:23

into the petrous apex.

2:25

And then you have a foreign body reaction to these

2:29

blood products leading to the expansion

2:31

mass in this foreign body reaction.

2:34

And usually what you're seeing is these cystic

2:36

oil-type lesion with blood products within it.

2:40

Let's look at the MRI,

2:41

because the MRI has a relatively pathognomonic

2:44

finding associated with it.

2:46

So here's the MRI scan on the same patient.

2:50

So again, I'm going to show you from the MRI,

2:56

T1-weighted scan, we're seeing the

3:00

vessels as bright.

3:02

But almost immediately you see something

3:04

that does not look like a blood vessel,

3:06

and it is bright in signal intensity.

3:09

It's expanding the petrous apex.

3:11

It's eroding the clivus, as we saw before.

3:15

There is that internal carotid artery

3:17

that is being displaced by the mass.

3:20

And this mass has two lobes to it.

3:24

And in point of fact,

3:26

this patient looks like there's probably aberrancy

3:29

of this internal carotid artery.

3:31

We have to go back to the CT,

3:33

but the carotid canal seems to expand

3:35

into the medial aspect here.

3:38

So right on a pre-gadolinium T1-weighted scan.

3:42

And then when we look on our T2-weighted scan,

3:46

we see that it is blood products as well.

3:50

Dark in signal intensity on this T2-weighted

3:52

image. And with gadolinium enhancement,

3:55

there is no enhancement.

3:56

This is the same signal intensity as it

3:59

was on the pre-gad. So to prove that,

4:02

let's get this side by side.

4:05

Here we have that image, and here we have this image.

4:09

So

4:11

it is as bright on the, it actually might even be

4:15

brighter on the pre-gad than the post-gad image.

4:19

So there is no enhancement.

4:21

So this is indeed a cholesterol granuloma,

4:25

and it's bilobed, as you can see.

4:28

Bright on T1, bright on T2.

4:31

And let's just double-check and make sure that the

4:34

carotid wall was intact on the previous CT scan.

4:39

It's probably just the erosive nature of the

4:42

cholesterol granuloma that we got fooled by.

4:46

So here we are.

4:47

And we'll put this to a bone window here.

4:50

And let's watch the carotid wall.

4:54

So it's fine.

4:55

So it's not extending into the middle ear cavity.

4:59

And what we're seeing is just the cholesterol

5:03

granuloma coursing the bone and simulating

5:07

an aberrant internal carotid artery.

5:09

So blue-domed cyst, retro-tympanic,

5:13

potentially blue mass would be

5:15

a cholesterol granuloma.

5:16

They can occur de novo in the middle ear cavity.

5:19

That's pretty uncommon. But more commonly,

5:22

they occur at the petrous apex.