0:00

I'd like to talk about the end stage of labyrinthitis,

0:05

and that is labyrinthitis ossificans.

0:08

This, at the end stage, is the bony

0:10

obliteration of the cochlea,

0:12

the vestibule, and the semicircular canal that can

0:15

occur at the chronic phase of a

0:18

long-standing labyrinthitis.

0:20

And this will often lead to a sensorineural hearing

0:25

loss secondary to the obliteration of the cochlea.

0:29

The MR findings, however,

0:31

suggest that before you see the bony obliteration

0:36

of these labyrinthine structures,

0:38

you may see fibrous obliteration.

0:41

So in the process of going from an acute inflammatory

0:45

process of labyrinthitis to the chronic

0:49

phase of labyrinthitis ossificans,

0:51

we pass through a fibrous phase

0:53

which is only visible on MR.

0:55

It's not seen on CT because the canals of the

0:59

endolymph and the perilymph have not been bony

1:03

obliterated, but fibrously obliterated.

1:05

Here is what we are looking for on a CT scan.

1:08

As you can see by the arrows,

1:09

you have bone that is appearing within the turns of

1:13

the cochlea on the coronal reconstruction on your

1:17

left and the axial original data on the right.

1:20

So if I just want to point this out to you,

1:25

what I would say is that this is the normal density

1:28

of the internal compartments of the cochlea.

1:31

But we have this plaque of bone that has

1:34

been laid down in the basal turn here,

1:37

which is also demonstrated as the increased density

1:41

within the basal turn of the cochlea on the axial

1:45

scans. Now, again, this is labyrinthitis ossificans.

1:50

This is not otosclerosis.

1:53

Even though this is sclerotic,

1:54

bone is a different entity than that autoimmune entity

1:59

of otospongiosis where you have demineralized bone.

2:03

Making that emphasis.

2:06

What are the causes of labyrinthitis ossificans?

2:09

Well,

2:10

this again is similar in that you may see meningitic

2:15

spread from a CNS infection that leads to obliteration

2:21

of the labyrinth bilaterally,

2:23

or as with labyrinthitis itself,

2:26

you may see a tympanic form where it's a complication

2:30

of long-standing chronic otitis media.

2:34

The hematogenous form also would be expected

2:37

to be bilateral. As far as the etiologies,

2:41

both infection, as well as trauma,

2:45

autoimmune disorders, and hemorrhage in the labyrinth

2:49

can lead to labyrinthitis ossificans.

2:52

And as I mentioned,

2:54

enhancement seen on MRI scan

2:57

in the cochlea or vestibule

3:00

is predictive of sensorineural hearing loss.

3:03

Here we have a patient who has, on the axial scans and

3:08

on the coronal reconstructions, obliteration

3:12

of the lateral semicircular canal.

3:15

We would normally expect to see the

3:17

lateral semicircular canal here.

3:19

This is the posterior semicircular canal, and this is

3:24

the lateral one. On the coronal reconstruction,

3:27

you see this superior semicircular canal.

3:29

And very faintly, you see the obliterated

3:32

lateral semicircular canal.

3:34

And what is obliterated is, you're seeing, bone

3:38

infiltration where there should be

3:40

the normal endolymph and perilymph.

3:43

So this is labyrinthitis ossificans.

3:46

Note that on the MRI scan,

3:48

although we see quite nicely the cochlea and the CSF,

3:53

or the CSF signal intensity fluid,

3:56

it's actually the perilymph and the endolymph in

3:58

the cochlea, and we see the normal vestibule.

4:02

On the left side,

4:03

we actually see the semicircular canal,

4:05

but you don't see that on the right side,

4:08

corresponding to the finding on the CT scan with

4:11

lateral semicircular canal labyrinthitis ossificans.

4:16

Here is another example on CT of different grades of

4:22

labyrinthitis ossificans. On the lowermost images,

4:26

you see just a faint area of bone obliterating

4:31

a portion of the basal turn of the cochlea.

4:35

This ingrowth of bone into that basal turn of the

4:38

cochlea is the beginnings or the early

4:40

phase of labyrinthitis ossificans.

4:44

On the upper image on the left,

4:48

you can see that the cochlea has too much bone.

4:51

This is more than one would expect for modiolus.

4:54

And this is, in fact, another example of

4:57

labyrinthitis ossificans affecting the cochlea compared

5:01

to the more normal side on the left.

5:04

And this is

5:07

the CT example of the normal side

5:10

on the left and the right side,

5:12

where there is bone ingrowth in the basal turn

5:16

of the cochlea. So here is the round window.

5:21

Here's the basal turn of the cochlea.

5:22

And this is the normal side.

5:25

On the right side, we have the round window,

5:28

but we also have this little area of bony ingrowth

5:33

and that is labyrinthitis ossificans.

5:35

Where this is most important is that if you have this

5:38

and the patient is being considered for

5:40

a right-sided cochlear implant,

5:42

which again is inserted through the round window,

5:45

they wouldn't be able to insert the cochlear implant

5:47

because they'd be pushing up against bone.

5:50

The bottom image on CT shows two cases of labyrinthitis

5:55

ossificans affecting the lateral semicircular

5:57

canal. On the left side,

6:01

relatively minor involvement. On the right side,

6:05

you've lost about 60 degrees of the lateral

6:10

semicircular canal to labyrinthitis ossificans.

6:13

And the MR findings are similar in that you have

6:18

absence of the turn of the lateral semicircular canal

6:22

on the bottom image and a little less involvement,

6:26

but still involved on the left-hand side

6:30

compared to the right-hand side.

6:32

So these are the same patient showing the CT findings

6:35

and the MR findings of labyrinthitis ossificans

6:39

affecting the lateral semicircular canal

6:41

and the cochlea. Another example,

6:44

labyrinthitis ossificans affecting the basal

6:46

turn of the cochlea. And on the MRI scan,

6:49

one can see the obliteration of the normal high signal

6:53

intensity on the T2-weighted scan of the internal

6:57

architecture of the cochlea on the right

6:59

side compared with the left side.

7:01

So,

7:01

as you can see by the diagram or the chart below,

7:06

acutely, the CT scan is normal and the MRI might show

7:09

some faint enhancement. And then in the chronic phase,

7:13

you start to lose the signal on T2

7:15

and in the ossific phase,

7:17

both the CT is abnormal, as well

7:19

as the MRI is abnormal.

7:22

Here is the initial CT on your left-hand side

7:24

and the final CT on your right-hand side,

7:27

as the internal architecture of the cochlea is being

7:31

replaced by labyrinthitis ossificans. On the MR below,

7:35

we see a normal appearance to the vestibule

7:41

and semicircular canals.

7:43

Vestibule, lateral semicircular canal.

7:46

Vestibule, lateral semicircular canal.

7:48

And over the course of time, as you can see,

7:51

there was loss of the normal architecture of these

7:54

semicircular canals, secondary to bony obliteration

7:58

with labyrinthitis ossificans.

8:00

Another example of a patient who had a basal turn of

8:04

the cochlea that was negative on CT. Looks pretty good.

8:09

Internal scala tympani,

8:10

middle and apical turn, all look good.

8:13

However, on the MRI scan,

8:15

this is not just partial volume effect.

8:17

You see the early fibrous obliteration of the basal

8:20

turn of the cochlea when compared to the normal side,

8:23

where we see

8:25

the scala in between the endolymph and the perilymph,

8:31

but normal bright signal intensity that

8:34

is obliterated on the right side,

8:36

at least at the proximal-most portion

8:39

here.

8:40

Here is labyrinthitis ossificans affecting

8:43

the superior semicircular canal.

8:46

And it's seen both on the MRI, as well as the

8:50

CT scan with the red arrows.

8:53

Once again,

8:53

one of the complications of labyrinthitis ossificans

8:57

is the inability to insert

9:00

a cochlear implant.

9:01

And although this is a relatively old slide,

9:03

it's useful in demonstrating that only one of the

9:07

beads of this person's cochlear implant was able to be

9:13

inserted because of the obstruction that was

9:15

present secondary to labyrinthitis ossificans.

9:18

So this is a potential complication or a

9:22

contraindication for inserting cochlear implantation.

9:27

This is a patient who had a sensorineural hearing loss

9:30

after an airplane trip. And as you can see,

9:34

there is high signal intensity in the vestibule

9:37

and lateral semicircular canal.

9:39

The key to this case is asking yourself,

9:42

has this patient received gadolinium or not?

9:45

In this case,

9:46

since you do not see enhancement in the nasal

9:51

turbinates nor of the mucosa of the maxillary sinus,

9:55

we are actually looking at a non-contrast study.

9:58

And that high signal intensity represents

10:02

methemoglobin or blood products in the vestibule and

10:06

semicircular canals from

10:08

barotrauma after an airplane trip.

10:10

This is a potential source of future labyrinthitis

10:15

ossificans.