0:00

I'd like to move from our discussion of congenital

0:03

lesions of the inner ear to the inflammatory

0:05

lesions of the inner ear.

0:07

And these are generally called labyrinthitis.

0:09

There are different potential sources

0:12

of inflammation in the inner ear.

0:15

These include labyrinthitis that is typically viral in

0:19

etiology, although bacterial labyrinthitis can occur.

0:22

We have one of the end points of labyrinthine

0:26

inflammation as labyrinthine ossification

0:28

or labyrinthitis ossificans,

0:31

sometimes also referred to as labyrinthitis obliterans

0:35

to describe. We have otosclerosis

0:38

which is that autoimmune phenomenon of

0:41

demineralization of the bone in the fenestral

0:44

and cochlear forms. We have Bell's palsy

0:47

which is inner ear inflammation of the 7th cranial

0:49

nerve coursing through the internal auditory

0:52

canal and its labyrinthine portion.

0:54

And then we have petrous apicitis

0:56

which is inflammation of the petrous apex portion of

0:59

the temporal bone. I want to just start, however,

1:02

with Bell's palsy.

1:03

This is not typically what we think about

1:05

with labyrinthine inflammation,

1:07

but it is one of the more common causes

1:09

of a facial nerve paralysis.

1:11

Bell's palsy is typically found on imaging as an area

1:16

of enlargement and/or enhancement of the labyrinthine

1:21

portion of the 7th cranial nerve or the

1:24

intracanalicular portion of the 7th cranial nerve.

1:27

This arrow is pointing to the preganglionic,

1:31

the labyrinthine portion of the 7th cranial

1:33

nerve before the geniculate ganglion.

1:36

And you see that there is abnormal

1:38

contrast enhancement. Remember,

1:40

as I said in the middle ear talk, that enhancement of

1:44

the tympanic horizontal portion of the facial nerve or

1:48

descending intramastoid portion of the facial nerve is

1:51

entirely normal, and it may even be asymmetric

1:54

from right to left. However,

1:56

enhancement of the 7th cranial nerve in the internal

1:58

auditory canal or in its labyrinthine portion

2:01

before the geniculate ganglion is abnormal.

2:04

And it is the most common finding on imaging of Bell's

2:08

palsy. Thought that at the aperture here from the

2:12

internal auditory canal to the labyrinthine

2:14

portion is the narrowest portion of

2:17

the canal of the 7th cranial nerve.

2:20

And when that nerve is inflamed by typically

2:23

viruses in Bell's palsy,

2:26

it will lead to enhancement of that portion of the

2:30

nerve. Here's a patient who has Ramsay Hunt syndrome

2:34

which again is a herpetic infection that

2:37

typically is seen in the ear region

2:41

which extends and inflames the 7th cranial nerve.

2:45

So, in this case that was provided to me by Bill Dylan,

2:48

one sees that within the internal auditory canal, you

2:52

have enlargement of the 7th cranial nerve and no CSF

2:56

space between the 7th cranial nerve and

2:58

the superior vestibular nerve as

3:00

opposed to the contralateral side. When

3:02

one gives contrast enhancement,

3:05

you can see that there is enhancement of this 7th

3:10

cranial nerve in the internal auditory canal,

3:13

as well as its labyrinthine portion,

3:15

both of which are going to be abnormal. Enhancement

3:17

of the geniculate ganglion and

3:20

the tympanic portion of the 7th cranial nerve,

3:22

however, may be a normal finding.

3:25

And this patient had relapsing polychondritis

3:27

which you see as inflammation of the cartilage of

3:31

the external ear that led to a predisposition

3:37

to herpetic infection,

3:39

so-called Ramsay Hunt syndrome of

3:41

the 7th cranial nerve. However,

3:43

when we typically think about

3:44

labyrinthine enhancement,

3:46

we are usually thinking enhancement of the

3:49

cochlea, the vestibule, and the semicircular canals,

3:52

and rarely the endolymphatic sac.

3:54

As I mentioned,

3:55

the most common infectious etiologies will be viral,

3:59

followed by bacterial.

4:00

Sometimes you may have syphilitic or

4:02

luetic inflammation of the labyrinth.

4:06

There are autoimmune disorders that

4:09

can lead to labyrinthine enhancement,

4:11

including an entity called Cogan's syndrome.

4:14

Labyrinthine enhancement may also

4:16

occur secondary to fistula,

4:19

either from barotrauma or from things like

4:23

middle ear infection and cholesteatoma.

4:26

It may also be caused by post-traumatic hemorrhage

4:31

in the labyrinth, which then leads to inflammation

4:34

and subsequent enhancement.

4:36

The thing that is least likelier is a schwannoma

4:40

of the labyrinthine structures.

4:41

Schwannomas are very common in the internal auditory

4:43

canal and the cerebellopontine angle cistern.

4:46

But to see a schwannoma in the vestibule or in

4:49

the cochlea is actually quite uncommon.

4:52

Here are a few examples of patients

4:54

who had labyrinthitis. So,

4:57

on this

4:59

axial MRI scan with gadolinium that

5:01

you see on the left-hand side,

5:03

we see abnormal enhancement of the

5:05

cochlea on the right side,

5:06

abnormal enhancement of the vestibule

5:08

on the right side.

5:09

And we have on the left side abnormal enhancement

5:12

not just of the vestibule,

5:14

but of the lateral semicircular canal and probably

5:17

a limb of the posterior semicircular canal.

5:20

This bilateral involvement is something that we would

5:25

consider either an infectious etiology or,

5:28

as in this case,

5:29

an autoimmune phenomenon known as autoimmune

5:32

labyrinthitis. And as I mentioned,

5:34

one of the syndromes that is associated

5:36

with this is Cogan's syndrome.

5:37

This patient on the right-hand side of the screen,

5:41

you see a little bit of enhancement in

5:43

the posterior semicircular canal,

5:45

a tiny area of enhancement in the

5:47

basal turn of the cochlea.

5:48

This was another patient who had

5:50

unilateral labyrinthitis.

5:52

Unilateral labyrinthitis is more commonly secondary to

5:56

infection from middle ear disease that

5:59

spreads to the inner ear structures,

6:01

whereas those patients who have bilateral involvement

6:04

are more likely to have a systemic infection like

6:07

a viral infection or bacterial infection or the

6:11

autoimmune phenomenon that I mentioned previously.