0:00

If we think about our mnemonic for pathology in the

0:04

central nervous system or head-neck region, we remember

0:08

the mnemonic of vitamin C and D: vascular, infectious,

0:11

traumatic, acquired, metabolic, idiopathic, neoplastic,

0:15

congenital, and drugs.

0:16

We're now at the I for infection, and external

0:20

ear infections are pretty common.

0:22

They usually do not require imaging

0:25

evaluation.

0:26

Patients will present with a painful ear,

0:30

sometimes with a discharge coming out of the external

0:33

auditory canal, and this is what

0:35

we would call external otitis.

0:37

There is a higher rate of infections that occur in

0:40

individuals who are swimmers, and this is because of

0:43

the pathogens that may occur in the swimming pool.

0:46

And of these,

0:47

Pseudomonas and Staphylococcus aureus are the most common

0:51

sources of external otitis associated with swimming.

0:56

The

0:58

infection that we are called upon to evaluate as

1:03

neuroradiologists and head-neck radiologists

1:06

is malignant otitis externa.

1:08

Malignant otitis externa is an infection that

1:10

typically occurs in elderly diabetic patients who have

1:14

an inflammatory process that's affecting

1:16

the external auditory canal; however,

1:19

spreads to the skull base. The typical history

1:22

here is a patient who presents to the family

1:27

practitioner with an external otitis, and the family

1:31

practitioner irrigates the ear under pressure.

1:35

So the problem with this harkens back to an anatomical

1:40

structure that I pointed out on the anatomical drawing,

1:44

which are the fissures of Santorini.

1:46

The fissures of Santorini are at the junction between

1:49

the cartilaginous and bony portion of the

1:51

external auditory canal, oriented inferiorly,

1:55

immediately heading towards the skull base.

1:57

What happens is that when the ear is irrigated to kind

2:01

of clean it out and hopefully resolve the infection,

2:05

instead,

2:06

what happens is that the Pseudomonas bacteria is

2:09

driven down the fissures of Santorini to the skull

2:14

base, and that leads to osteomyelitis and

2:16

cellulitis that occurs at the skull base.

2:19

So the typical history is an elderly diabetic patient

2:24

who presented with external otitis and had their ear

2:28

irrigated by the family practitioner, and then presents

2:32

with cranial nerve deficits from

2:34

this skull base infection.

2:37

So this is an example of a patient

2:40

who has external otitis.

2:42

If you look at the walls of the external auditory

2:45

canal, you see that there is thickening

2:47

of the soft tissue.

2:49

In most cases, at the level of the bony portion of the

2:53

external auditory canal, you do not see any soft

2:57

tissues. It looks like it's just a bony canal with

3:00

air on either side. In this patient example,

3:03

you see that there is soft tissue both on the anterior

3:06

and posterior walls of the external auditory

3:09

canal, and on the coronal image,

3:11

you see this both on the superior and inferior

3:15

walls of the external auditory canal.

3:17

All this tissue should not be visible.

3:19

We should just be seeing bone and air in

3:22

the normal external auditory canal.

3:24

So this is a patient who has external otitis.

3:28

This was not a patient who was an elderly diabetic.

3:30

Why do the elderly diabetic?

3:32

The diabetes leads to the potential for severe spread

3:36

of the infection in malignant otitis externa.

3:40

You notice that all of this infection is superficial

3:43

to the tympanic membrane identified here.

3:46

So there is no middle ear component

3:49

to this external otitis.

3:53

Let's review again the importance of otitis

3:56

externa or external otitis.

3:58

It's inflammation of the external auditory canal,

4:00

usually infection. As I mentioned,

4:03

Staphylococcus aureus and Pseudomonas.

4:05

Occasionally, you'll have fungal overgrowth,

4:07

if it's something like Aspergillus or mucormycosis.

4:09

It can have a deeper spread to other structures,

4:14

including the vascular structures.

4:17

So here now we have a patient who's an elderly

4:19

patient with painful hearing loss.

4:22

As we look on the coronal image on the left,

4:27

one sees that there is thickening along the superior

4:30

wall of the external auditory canal, as well

4:34

as opacification of the middle ear cavity.

4:38

So here is the superior wall of the external

4:41

auditory canal with thickening.

4:43

There is some irregularity here to the cartilaginous

4:47

portion of the external auditory canal as well.

4:51

And then here is our middle ear ossicles with

4:54

opacification of the middle ear cavity.

4:56

So at the very basic, this is external

4:59

otitis, as well as otitis media,

5:02

which is the term we use for middle ear infection.

5:06

However, when you look at the axial CT scan,

5:09

you're a little bit struck by the absence

5:13

of a good airway in the nasopharynx.

5:15

So normally in an elderly patient, we should not be

5:19

seeing all of this soft tissue, which is, in part, the

5:22

adenoidal tissue of the nasopharynx that usually

5:26

atrophies with age and gets smaller

5:30

in size on the CT scan.

5:31

Here we have a process which

5:36

has a low-density area centrally, and this represents

5:40

spread of this infection into the skull base.

5:44

This is the clivus.

5:46

I want to look at the bone windows of this clivus to

5:49

see whether this irregularity that you're seeing along

5:51

the superficial portion of the right side of the

5:54

clivus, and that matter the left side, represents

5:57

erosion of bone because this is the

6:00

typical pathway of spread of malignant otitis externa to

6:05

the parapharyngeal space of the nasopharynx, as well

6:09

as the clivus and skull base for osteomyelitis.

6:14

So osteomyelitis and skull base cellulitis associated

6:18

with external otitis, as well as otitis media.

6:24

So malignant otitis externa has a high mortality rate,

6:27

it's 20%.

6:29

And this is because you ultimately develop sepsis

6:32

associated with the Pseudomonas infection secondary

6:36

to the cellulitis, as well as osteomyelitis.

6:40

Complications include abscess formation,

6:42

skull base osteomyelitis, and with that involvement of

6:47

the cranial nerves that are traveling through the

6:49

skull base into the upper neck structures.

6:51

The classic history is a discharge

6:54

from the ear (otorrhea), headache,

6:56

severe otalgia, and the history of presenting with an

7:01

external otitis that may have been

7:03

irrigated on the outside.

7:06

This is a patient in which I included

7:09

just for your edification.

7:12

The age of the patient in the upper right corner.

7:15

So although I'm 60 and 73 doesn't seem that far away,

7:18

we're going to call 73 an elderly

7:20

patient for the purposes of this

7:24

example. Here we have on the left the CT,

7:27

on the right the MRI scan. On the left CT,

7:31

you see that marked thickening of

7:33

the external auditory canal.

7:34

It looks as if there is some erosion of the anterior

7:37

wall of the external auditory canal.

7:40

You have opacification of the mastoid air cells, and

7:43

the cartilaginous portion is kind of plugged

7:45

up with inflammatory disease.

7:49

This same patient gets an MRI

7:51

scan, and on the MRI scan

7:53

which is a fat-suppressed post-gadolinium

7:58

T1-weighted scan,

8:00

and on this scan, you're seeing contrast enhancement

8:04

in the wall of the external auditory canal,

8:06

both cartilaginous and bony.

8:08

You're seeing the opacification of the mastoid

8:11

air cells that I referred to on the CT scan.

8:14

But more importantly,

8:16

you're seeing enhancing tissue which is surrounding

8:20

the carotid artery flow void with extension

8:24

to the parapharyngeal space.

8:25

Notice that this is normal on the

8:27

other side without enhancement.

8:29

This is coming right to the pterygoid plate and the

8:32

pterygopalatine fossa, which is the way station for

8:35

the second division of the fifth cranial nerve.

8:38

If we look even more carefully,

8:40

we notice that the longus colli,

8:44

longus capitis muscle complex

8:46

on the left side looks normal,

8:48

but on the right side, it is showing contrast enhancement.

8:52

So we have myositis of the prevertebral musculature.

8:57

Not only that, but also on the

9:00

right side.

9:00

You see contrast enhancement of the clivus on the

9:06

right side, compared with the normal

9:08

non-enhancing clivus. And in fact,

9:12

this is probably the occipital condyle on the right

9:15

side showing enhancement versus on the

9:17

left side absence of enhancement.

9:19

So this 73-year-old diabetic patient with external

9:23

otitis has all the manifestations of malignant otitis

9:26

externa with skull base cellulitis,

9:29

probably a vasculitis, osteomyelitis,

9:33

as well as myositis.