0:00

So in continuation with Dr. Guzman's

0:02

discussion of perineural spread,

0:04

the masticator space lends itself,

0:06

you know, really nicely for the next case.

0:08

So I'm showing you a representative image of

0:11

someone who is 25 years old and has a

0:15

lesion situated in the masticator space.

0:18

I just want you to think about what

0:19

your differential diagnosis is.

0:20

It's always, you know, hard with these lesions

0:22

specifically to come up with a specific

0:24

diagnosis, but what is, uh, what is

0:26

your differential to start thinking of?

0:28

And then, uh, the obvious question is which of

0:31

the following is not a masticator space muscle?

0:34

The temporalis muscle, medial pterygoid,

0:37

the masseter, or the buccinator muscle.

0:41

Okay.

0:41

So masticator space anatomy is, to me, one of

0:44

the more fascinating spaces of the

0:46

suprahyoid neck for a couple of reasons.

0:48

One, it's typically ignored because the

0:52

pathology isn't as common as other spaces.

0:55

Number two, there are so

0:57

many confusing phrases.

1:00

And so many diversions between surgeons

1:03

and radiologists in terms of how we define it.

1:05

So I want to spend a little bit of time discussing

1:07

the anatomy, the boundaries, and the subspaces

1:09

before turning our attention to the case.

1:11

So starting first by talking about

1:13

the contents of the masticator space.

1:15

So predominantly, the contents are,

1:17

you know, muscles of mastication.

1:19

which include the lateral, uh, pterygoid

1:21

muscle, uh, the medial pterygoid muscle,

1:23

the masseter muscle, and the temporalis muscle.

1:26

Uh, and then there is a small component

1:29

of the mandibular, uh, bone,

1:30

which includes the posterior body and the ramus.

1:33

And we also have, uh, V3 nerves.

1:36

So, in, in keeping with

1:38

Dr. Guzman's discussion branches of V3, including

1:41

for, uh, you know, the, uh, V3 branches

1:44

going toward the inferior alveolar canal.

1:46

And lastly, we have a few vessels,

1:50

also depending on the variation of the anatomy,

1:53

that are branches of the inferior alveolar

1:54

artery vein and pterygoid venous plexus.

1:57

In terms of, you know, terminology, and then

2:01

you, and how we divide it, for radiology

2:03

standpoint historically, we've divided the

2:05

space with respect to the, uh, to the, uh,

2:11

uh, zygomatic arch into suprazygomatic space

2:14

and, uh, you know, infrazygomatic space.

2:16

And the suprazygomatic essentially

2:18

predominantly contains the temporalis

2:20

muscle, which is equivalent to what the

2:22

surgeons typically call the temporal fossa.

2:25

And to the surgeons, the temporal

2:27

fossa is essentially that superior

2:28

extension of the masticator space or

2:30

the suprazygomatic masticator space.

2:32

And it's further divided surgically into

2:35

potential spaces of superficial temporal fossa

2:38

between the fascia and the muscle, and the

2:40

deep between the muscle and the temporal bone.

2:43

In terms of the infrazygomatic space,

2:47

it's, you know, further divided into spaces

2:49

or subspaces in the literature

2:51

historically as one of the, is the

2:54

masseteric or submasseteric space

2:57

between the masseter muscle and the mandible.

2:59

And then we have the pterygomandibular

3:03

space between the medial pterygoid and the

3:06

mandibular bone, and that

3:09

essentially corresponds to,

3:13

you know, the surgeons basically calling

3:15

it the infratemporal or the pharyngeal

3:18

component of the masticator space.

3:21

Lastly, and not to add to the confusion,

3:24

you hear people sometimes using the phrase

3:25

the infratemporal fossa or space, which

3:28

is the part of the masticator space that

3:30

is immediately inferior to the skull base.

3:33

And then it extends from the

3:35

pharyngeal wall toward the muscle.

3:37

So those are, and then it's posterior to

3:39

the posterior wall of the

3:41

posterior lateral wall of the maxillary sinus.

3:42

So those are different terminologies

3:45

of the space that you might hear

3:46

people speak of all the time.

3:48

With that, you know, I wanted to switch the

3:50

order a little bit here because I, when I go

3:52

to discuss the image, I wanted to

3:56

to have that abide as we're looking at this.

3:58

So what I'm seeing here is I'm seeing a T2 hyper

4:00

intense lesion that is extending essentially,

4:04

from the masseter muscle to the temporalis

4:08

muscle, or in other words, extending from

4:10

the infrazygomatic masticator

4:15

space to the suprazygomatic masticator

4:18

space that is demonstrating enhancement.

4:21

And then when I'm starting to think about

4:23

this from a differential standpoint, I,

4:25

you know, my first feeling is that this is a lesion

4:28

that is situated in the masticator space.

4:31

Predominantly, it's not extending from outside.

4:33

Then I start to work my differential

4:35

based on the contents of the location.

4:38

And for me, the overall appearance

4:40

makes me want to lean toward, you know,

4:42

a primary sarcoma, this lesion here.

4:44

Now, again, telling the subtypes of sarcoma

4:46

might be challenging because they tend

4:49

to overlap in imaging, with the exception

4:50

of a few of them, obviously, the osseous or

4:52

the fat-containing sarcomas.

4:56

So, that would be the reason why I would think,

4:58

you know, I would lean towards the sarcoma here.

5:00

Certainly, metastasis, if known,

5:02

malignancy would be there, and then nerve

5:05

sheath tumor would be a less likely consideration

5:07

also on board when I see a case like this.

5:10

So, further discussion, this

5:12

ends up being a synovial sarcoma.

5:14

Now, head and neck sarcomas are in

5:16

general rare and they represent 0.1 percent

5:18

of the head and

5:20

neck tumors overall.

5:23

And they are only 3 to 10 percent of the

5:25

sarcomas in general.

5:28

And then sarcomas overall are

5:31

in general rare and they constitute 1

5:33

percent of all of the solid malignancies.

5:35

Now, synovial sarcomas do overlap

5:37

with other sarcomas, but they

5:38

are a little bit less aggressive.

5:40

Historically and classically, they are

5:42

located predominantly in the extremities.

5:44

The word synovial is a misnomer, right?

5:46

Because it's not associated with the synovium

5:48

of a joint, and they are most likely or most

5:51

commonly affect, you know, males in their third

5:53

to fifth decade within the lower extremities.

5:56

But again, as I said, they can

5:58

occur in the head and neck, exceedingly rare, 1

6:00

percent.

6:01

If they are in the head and neck, they

6:03

typically, you know, the most common location

6:06

is the parapharyngeal space and the hypopharynx,

6:08

followed by the masticator space, and they

6:10

tend to be well circumscribed, T2 hyperintense

6:13

and avidly enhancing, as in this case.

6:15

Now, when do I consider sarcomas when I'm looking

6:18

at head and neck lesions versus carcinoma?

6:21

Now, the predominant malignancies

6:22

obviously are going to be carcinomas,

6:24

but location helps with the diagnosis.

6:27

So in general, carcinomas are

6:30

either going to be cutaneous, right?

6:31

Or they're going to be related, and those should

6:33

be relatively straightforward to diagnose.

6:35

Thank you.

6:36

And differentiate from sarcomas

6:38

with the exception of angiosarcomas.

6:40

Now, or they're going

6:42

to be along the mucosal surface.

6:44

So they tend to be deeper or more

6:46

central versus sarcomas in general.

6:49

The other thing is risk factors.

6:52

So obviously, with carcinomas, we

6:54

know HPV association or potentially

6:57

smoking, which, most of the time is

7:00

not typically associated with most sarcomas, and age.

7:02

A lot of the sarcomas are

7:03

in younger adults.

7:05

Not taking into account HPV,

7:07

obviously, and then lymph nodes.

7:09

So another big thing is if it's a

7:11

lymphoma or carcinoma, they're more likely

7:13

to go to lymph nodes versus sarcoma.

7:14

Sarcomas can go, obviously, to lymph

7:16

nodes, but more likely they will

7:18

demonstrate hematogenous spread.

7:20

So, you know, to follow up with that

7:22

question, and you can think of is

7:24

another masticator space lesion.

7:26

And I'm looking at this as situated within,

7:28

you know, predominantly the medial pterygoid

7:30

muscle, you know, very homogeneously

7:32

enhancing, T2 hyperintense, well circumscribed.

7:35

And then this, if this is sarcoma or

7:37

carcinoma, if I'm looking at it and

7:38

having to choose between the two,

7:40

I would definitely lean towards

7:42

sarcoma given the overall appearance and location.

7:44

And this ended up being spindle cell sarcoma.

7:47

So following up and talking about those spaces

7:50

and potential spaces, then, you know, the

7:52

masticator space, one of the most common

7:56

pathologies is infection, specifically

7:58

dental infection.

8:01

This is a patient that

8:02

had a sinonasal malignancy.

8:04

As you can see, there's

8:05

extensive sinonasal surgery.

8:07

And then, post-radiation, they

8:08

had an ulceration along the mucosa.

8:12

And then, they had a superimposed infection.

8:14

And if you look closely, you will see

8:15

the submucosal or mucosal space.

8:18

And then even the pterygoid space of the

8:20

masticator space, you will see,

8:23

areas of subperiosteal abscess formation.

8:25

So again, infection is one of

8:27

the most common, particularly odontogenic

8:30

pathologies with the masticator space and

8:32

something that we see very frequently.

8:34

Another lesion that we

8:35

typically tend to see, and it's a little

8:37

bit more straightforward, is osteosarcomas,

8:38

such as this one here.

8:41

It's arising from the mandible, and

8:44

this patient previously had a lesion

8:47

that was resected, and you can see a large

8:49

recurrence. Osteosarcomas tend to

8:51

have a periosteal bone reaction,

8:53

occasionally a sunburst pattern, not here.

8:55

And then Codman's triangle with the

8:57

lifting of the periosteum,

8:59

again, not here in this case.

9:00

And then they, to a varying degree, have a soft

9:03

tissue component, such as this case here.

9:05

This was a mandibular masticator space

9:09

osteosarcoma that had occurred

9:11

and gone into adjacent spaces.

9:13

So to recap, the masticator space is a space

9:16

that is very challenging to see on physical exam.

9:19

So imaging plays a central role in diagnosis.

9:23

We as radiologists should make ourselves

9:25

familiar with it, and then it's really important

9:27

to differentiate between lesions occurring

9:30

primarily in the masticator space when it

9:32

comes to differential and lesions spreading

9:34

to the masticator space because recurrent

9:36

and primary carcinomas can frequently extend.

9:39

Remember, infection and inflammation are

9:41

exceedingly common, especially odontogenic.

9:43

Vascular malformations are a more common

9:46

presentation in pediatrics, and we went across

9:48

one of those lesions in a different space, and

9:51

then neurogenic lesions arising from the actual

9:53

V3 segments. And remember, as Dr.

9:56

Guzman showed us some examples of perineural

9:58

spread, the masticator space does have V3 branches.

10:01

And, you know, spread from primary

10:04

head and neck malignancies is not uncommon.

10:06

Lastly, the mandible is part

10:08

of the space, so pathologies of osteous

10:10

lesions of the mandible are things to consider

10:12

when you see a masticator space lesion.

10:17

With that, going back to

10:18

the question: which of the following

10:20

is not a masticator space muscle?

10:26

Yep, absolutely.

10:27

You know, and then we just talked about the

10:28

temporalis muscle, which is part of

10:31

the suprazygomatic masticator space, and then the

10:34

medial pterygoid muscle, which we discussed as

10:37

part of the masticator, the infratemporal.

10:40

And again, making yourself familiar

10:42

with all of these terminologies that vary

10:44

from person to person and in the literature

10:46

and between surgeons and radiologists.