0:01

Well, you've seen differential diagnosis of retrotympanic

0:05

vascular mass with regard to the tumors.

0:07

And the two tumors that we consider are the

0:09

glomus jugulare and the glomus tympanicum.

0:11

And sometimes the way they fuse together

0:14

into the glomus jugulotympanicum,

0:17

as I mentioned in the introduction

0:18

to the retrotympanic,

0:20

red mass in the differential diagnosis also

0:24

is the aberrant internal carotid artery.

0:27

This is an unusual case in which there is bilateral

0:30

aberrancy of the internal carotid artery.

0:32

And what one does not see is the posterior

0:36

wall of the carotid canal.

0:38

So that bony wall that I pointed out on the CT scans

0:42

previously is missing bilaterally. And as you can see,

0:45

this lesion presents over the cochlear promontory

0:50

just like a glomus tympanicum would.

0:52

And so that surgeon looking through the otoscope and

0:56

seeing a retrotympanic vascular mass doesn't know

0:59

whether this is a glomus tympanicum or

1:02

an aberrant internal carotid artery.

1:04

And this little tiny area of narrowing here is

1:08

the so-called inferior tympanic canaliculus.

1:13

And that gets expanded in the example

1:17

of aberrant internal carotid artery.

1:19

Here is a bone window showing again,

1:23

bilateral internal carotid arteries going

1:26

too far laterally, too far posteriorly.

1:28

And without a posterior carotid canal.

1:32

On the raw data from an MRA.

1:35

You're nicely demonstrating that portion

1:37

of the internal carotid artery,

1:39

then the inferior tympanic canaliculus,

1:41

that little narrowed area where the internal carotid

1:45

artery protrudes through and expands and then has a

1:49

portion of its anatomy in the middle ear cavity

1:54

overlying the cochlear promontory,

1:56

where it may simulate a glomus tympanicum or glomus

1:59

jugulotympanicum. So that's on the arterial side,

2:04

here is what it looks like on the jugular side.

2:07

So, there are several anatomic variants

2:11

associated with a jugular vein.

2:14

We call it a high-riding jugular

2:19

vein or jugular bulb.

2:22

When it rises above either the internal

2:25

auditory canal lower margin,

2:26

or some people will use the external auditory canal.

2:30

So usually,

2:31

because we're looking at the temporal bone medially

2:36

and looking at the internal auditory canal,

2:38

if you see the jugular bulb at the level

2:40

of the internal auditory canal,

2:42

we would call it high-riding.

2:43

And that occurs in about 15.2% of patients.

2:48

Here is a dehiscent jugular bulb.

2:53

You no longer see the bone overriding

2:57

the jugular bulb.

3:00

So if you're looking through the otoscope,

3:04

you look posteriorly and you see a retro

3:07

tympanic vascular protrusion. Again,

3:11

is this a glomus tympanicum?

3:13

Is it aberrant internal carotid artery which

3:16

you see the canal just along here?

3:18

Or could this be a dehiscent high-riding jugular bulb?

3:24

High-riding jugular bulbs occur in

3:27

2% of asymptomatic patients. Finally,

3:31

you can get a little bulbous extrusion from the

3:35

jugular bulb that protrudes through the dehiscence.

3:38

And this would be what we would

3:39

call a jugular diverticulum.

3:42

So a jugular diverticulum occurs in less than 1% of cases,

3:45

but again presents as a retro tympanic vascular

3:49

mass. So here we are on the venous side.

3:53

Another vascular abnormality or normal variant that

3:57

can occur is what's called the

3:58

persistent stapedial artery.

4:01

So the persistent stapedial artery is a branch of the

4:05

internal carotid artery which can override the cochlear

4:09

promontory and present just at the facial canal,

4:14

which you're seeing in these arrows on

4:16

this article in radiology from 2004.

4:20

So the persistence stapedial artery presents also

4:24

as a retrotympanic red vascular mass in close

4:28

association with the facial nerve and overriding

4:31

along the cochlear promontory.

4:33

Usually with persistent stapedial arteries,

4:37

you do not see the middle meningeal artery or the

4:40

foramen spinosum ipsilateral to

4:43

the persistent stapedial artery.

4:46

This vascular abnormality can course along the

4:52

tympanic cavity to the region

4:55

of the crura of the stapes,

4:58

the oval window framing of the stapes, and be a

5:03

vascular mass that is present at the framing

5:07

at the oval window on coronal image.

5:12

I think sometimes it's better seen.

5:14

And that is that you have the little star here,

5:16

which is the internal carotid artery.

5:18

And then you have that little vascular abnormality

5:21

which extends from the internal carotid artery and

5:23

then rises from the internal carotid artery over the

5:26

cochlear promontory as a retrotympanic vascular mass.

5:30

And from there, it can present at the oval window

5:34

at the oval window framing of the stapes.