0:02

This was a patient who had a known parotid mass by palpation.

0:10

The protocol that was used for this case was our high-resolution

0:16

skull-based protocol to evaluate the parotid mass.

0:20

So that means that there is not

0:25

wide field of view or lengthy cavernous science down to the

0:32

thoracic inlet sequence being performed for the known mass.

0:39

Instead, we are doing our high-resolution MR sequences.

0:43

So I will start with the T1-weighted sequence.

0:47

So this is 0.9 millimeters.

0:49

So again, sub-millimeter thick slices to allow us

0:51

to have multiplanar reconstructions

0:55

for the evaluation of a parotid mass

0:58

or parotid pathology of any type.

1:01

T1-weighted scans are the best at identifying the pathology,

1:07

seeing it amidst the brighter signal intensity parotid tissue.

1:12

So I always go with the T1-weighted sequence

1:14

first and then I characterize it,

1:17

the lesion with the T2-weighted and

1:20

the diffusion and the post-gad.

1:22

So my go-to sequence for identifying whether or not there's

1:26

a pathology is going to be a T1-weighted sequence.

1:30

So in this case,

1:32

it's pretty easy to compare the right side from the left side.

1:36

On the left side, we have our normal anatomy with the vein,

1:40

the retromandibular vein, and we have the parotid tissue.

1:45

And we would apply the stylomandibular tunnel to identify

1:50

the deep lobe of the parotid gland versus the superficial lobe.

1:54

This is probably the styloid process right here, actually.

1:58

So deep versus superficial.

2:00

I don't normally see the facial nerve.

2:02

The thing that we usually look at that may show linearity within

2:07

the gland that you might suggest might be the facial

2:10

nerve is most kind, in most cases, just ductal.

2:16

So, for example,

2:17

this kind of courses the way the facial nerve would course.

2:21

But this is just ductal anatomy rather

2:26

than facial nerve anatomy.

2:27

It doesn't go all the way into the stylomastoid frame in here.

2:32

So this is the normal side, and we have the bright superficial

2:36

fat, we have the masseter muscle, we have the mandible.

2:40

So we're comfortable with this anatomy.

2:43

Here we have pathology.

2:46

So the parotid gland brighter tissue is seen here, and within

2:51

it, we have a mass which is kind of multilobulated.

2:58

Here is our styloid process.

3:00

Here is the mandible. If we draw our line of the quote,

3:03

unquote styromandibular tunnel.

3:05

So I should say that the stylomandibular tunnel is not an actual

3:08

structure. It's just the plane that we're referring to.

3:11

We would say that there's a portion of it which

3:13

goes to the deep portion of the parotid gland.

3:16

Here's more of the deep tissue of the parotid gland.

3:18

Okay, so this is the mastoid tip.

3:21

This is the styloid process.

3:24

And even here,

3:25

you can see a piece of the tissue of the tumor

3:29

in the deep portion of the parotid gland.

3:31

Why is that important? Well, for the most part,

3:34

if it's a superficial lesion,

3:37

the dissection of the facial nerve still will occur,

3:41

but the lesion is removed quite easily and readily

3:44

with a superficial parotidectomy.

3:46

Once you have portions that are going into the deep portion of

3:49

the parotid gland, first off, the facial nerve may be involved,

3:52

but also it's usually more of a cervical incision,

3:59

and you're more likely to have to sacrifice the facial nerve.

4:06

Okay, so here is our mass,

4:09

and it's predominantly in the superficial

4:12

portion of the parotid gland.

4:13

A little bit of it comes over top of the masseter muscle.

4:16

So I identify the lesion on the T1-weighted scan.

4:21

I next look at the lesion on the T2-weighted scan.

4:24

Here is our T2-weighted scan.

4:26

As you can see,

4:27

we're starting sort of in the mid portion of the brain,

4:29

and we end down here at the tail of the parotid gland.

4:33

And then we include

4:38

the lower portion of the neck.

4:40

These are not high-resolution imaging.

4:42

As you can see, this is four-millimeter thick slices.

4:44

So this is our STIR sequence, our T2-weighted STIR sequence.

4:48

You note that we have pretty good fat suppression throughout.

4:53

And with this sequence,

4:54

we're seeing lymph nodes on the left side,

4:58

but on the right side, we are seeing this mass,

5:02

which has somewhat heterogeneous signal intensity to it.

5:07

Now, if I'm just looking at this bright area here

5:13

that is typical of a pleomorphic adenoma,

5:16

it kind of lights up very brightly

5:18

on the T2-weighted sequence.

5:20

This portion I'm a little bit more concerned about

5:22

because it's intermediate in signal intensity.

5:24

And we'll talk about that in just a moment.

5:26

But this appearance is typical of a pleomorphic adenoma.

5:36

So my thought process is this is most likely a pleomorphic

5:40

adenoma, but I'm concerned about this darker tissue.

5:42

Why am I concerned about the darker tissue?

5:45

Well, if you remember the 80% rule,

5:48

it was that 80% of pleomorphic adenomas remain benign.

5:52

20% of pleomorphic adenomas over the course of long-term

5:57

follow-up show malignant degeneration in some.

6:00

Thing that's called carcinoma ex pleomorphic adenoma.

6:04

So it's malignant degeneration of a pleomorphic adenoma.

6:08

And anytime you see something that's dark or intermediate

6:11

in signal intensity in the parotid gland,

6:13

you better think about the possibility of malignancy.

6:19

So let's move to the next sequence.

6:21

The next sequence I would look at is the diffusion-weighted

6:24

imaging. The diffusion-weighted imaging, as I mentioned,

6:28

helps us to analyze whether or not a tumor

6:33

is likely to be benign or malignant.

6:37

In this case, the signal intensity is bright, intermediate.

6:45

It's not dark.

6:47

It's not as dark as, for example, the cerebellum.

6:50

Let's look at the ADC map.

6:53

This is the ADC map.

6:56

And we notice that there's a difference between that deeper

7:00

portion of the mass from the component that had darker

7:06

signal intensity on T2-weighted imaging.

7:09

This, again,

7:10

would be something that would lead us to be concerned about the

7:15

possibility of malignant degeneration

7:18

of the pleomorphic adenoma.

7:21

Finally, we'll look at the CIS image.

7:25

So the CIS image, as I mentioned, 0.7 millimeter thick slices,

7:29

so submillimeter thick slices.

7:31

This is predominantly utilized for the anatomy and for

7:36

identifying small lesions. But it can also, in the right hands,

7:40

be used to try to identify the facial nerve and the

7:46

relationship of the tumor to the facial nerve.

7:49

In this case, you see that CIS imaging,

7:51

although it's T2 weighting,

7:53

it has a different spectrum,

7:59

grayscale than the traditional STIR imaging.

8:05

All tumors, whether they're benign or malignant,

8:08

tend to be this intermediate dark on the CIS imaging.

8:13

So you really need the STIR to characterize it on T2-weighted

8:17

imaging because CIS is not exactly T2 weighting.

8:21

But we can see the lobularity of the lesion.

8:24

We can look for the facial nerve in this case

8:29

if we continue superficially and try to identify.

8:33

Here is the stylomastoid frame.

8:35

And I'm really not identifying the facial nerve on this case.

8:40

Here, again, can't really identify the facial nerve from

8:45

these 0.7 millimeter thick slices.

8:48

We could do very nice multiplanar reconstructions.

8:51

Let's look at the post-gad.

8:52

Now, the post-gad, we know that pleomorphic adenomas, by and large,

8:57

enhance, and usually they enhance relatively avidly.

9:00

In this case,

9:00

we have the very avid portion of the pleomorphic adenoma and we

9:05

have this portion that is not enhancing in the traditional way

9:10

corresponding to that darker area on T2 and the area of lower

9:15

ADC raising the possibility of malignant degeneration.

9:20

On this sequence,

9:23

we are still not able to identify the facial nerve.

9:28

I want to point out that that little slab

9:31

of tissue that we were worried about

9:34

going into the deep portion of the parotid gland is not enhancing

9:39

or is identified on the Vibe or the CIS imaging.

9:45

There's a small component right here

9:48

that would be in that deep portion on the CIS.

9:53

Let me just try to see where that is here.

9:58

Not as well identified, maybe this little enhancing portion.

10:02

And then we will often do the post-gad CIS imaging again to

10:08

better characterize the anatomy as well as to characterize

10:14

the tumor.

10:16

But as you can see,

10:17

the vast majority of this tumor is in the superficial portion.

10:20

So, in summary,

10:22

the analysis of this case would be that although there are

10:27

components that are typical of a pleomorphic adenoma being well

10:31

defined and bright on T2 and showing

10:35

consistent contrast enhancement,

10:38

there is a portion which is intermediate in signal intensity

10:42

both on the T2-weighted sequence as well as the

10:46

post-gad sequences that shows reduced ADC,

10:51

which is worrisome for malignant degeneration

10:54

of a pleomorphic adenoma.