0:00

There is an 80% rule, like

0:03

with most head and neck areas.

0:06

We have 80% rules. In the sinus malignancy,

0:10

the 80% rule is that 80% of sinus

0:13

malignancies arise in the maxillary antrum,

0:16

although they may grow into the sinus and nasal

0:18

nasal cavity and the ethmoid sinus.

0:21

80% are squamous cell carcinomas.

0:23

80% show bone erosion at presentation.

0:27

And interestingly, 80% have a prior

0:30

history of chronic sinusitis or polyps.

0:33

This is particularly true with inverted papilloma cases.

0:36

Now, how do we make any type of histologic

0:40

discrimination when we're dealing with sinonasal cancers?

0:44

Well, one of the ones that's easier

0:46

to make a distinction for is melanoma.

0:51

Melanin has high signal intensity on T1

0:55

and darker signal on T2-weighted scanning

0:57

because of its paramagnetic effects.

1:00

So, were we to see a malignancy that was

1:03

intrinsically bright on a T1-weighted scan,

1:06

we would suggest that it may be a melanoma.

1:10

Unfortunately, most cancers are

1:12

going to be dark on T2-weighted scanning.

1:15

However, if you see a bright signal

1:18

intensity cancer on T2-weighted imaging,

1:21

you may want to favor adenoid cystic carcinoma.

1:25

And we can think, ah, this is the mnemonic—

1:27

cystic is going to be bright on T2-weighted scan.

1:31

Not all adenoid cystic carcinomas are bright

1:34

on T2-weighted scan, but if I see a malignancy,

1:37

something that has perineural spread and is bright

1:40

on T2, I'm going to think maybe it's an adenoid

1:43

cystic carcinoma, a minor salivary gland tumor.

1:46

Those lesions that have homogeneous

1:48

intensity would be unusual for those that

1:51

have a particular matrix associated to it.

1:55

So, for example,

1:56

chondrosarcomas are not going to be homogeneous because

2:00

they have that chondroid, popcorn-like matrix to it.

2:04

Similarly, an osteosarcoma would be unusual.

2:09

The inverted papilloma, because it

2:11

generally has calcification, usually

2:14

does not have homogeneous intensity.

2:16

Contrast that with something like a lymphoma.

2:20

Lymphomas are usually bland and relatively

2:23

homogeneous in their signal intensity

2:26

on sinonasal imaging, and therefore,

2:30

you may suggest lymphoma.

2:32

Lymphoma also will have very low ADC values,

2:36

and therefore, you may suggest that if you

2:38

see something that is very bright on the DWI

2:42

and low in signal intensity on the ADC maps.

2:46

So, this again gets to the internal

2:48

architecture of the cancer.

2:51

If you have something that's highly vascular,

2:54

well, then you may be suggesting something like

2:57

a juvenile nasopharyngeal angiofibroma,

3:00

or JNA, which can grow into the sinonasal cavity.

3:05

You may also think about meningiomas that

3:08

can grow downward into the sinonasal cavity.

3:11

There is one other entity, and that is

3:14

the sinonasal adenomatoid craniopharyngioma, which

3:20

is a tumor type that may have calcifications

3:25

and cysts associated with it, that you may be

3:28

able to make that distinction histologically.

3:31

Finally, as I mentioned previously, olfactory

3:34

neuroblastomas, also known as esthesioneuroblastomas,

3:37

are a tumor that may be associated

3:40

with intracranial cysts at the margins of the tumor.

3:45

That may suggest that specific diagnosis.

3:49

However, most of the time, the role of MR is not

3:52

to make the histologic diagnosis, since it's

3:54

relatively easy for the endoscopist to get a

3:58

piece of the tissue of the tumor through the

4:01

endoscope with little morbidity and mortality.

4:05

What we're really trying to do with MR is to

4:07

define what's secretion, what's tumor, and that's

4:10

usually very helpful with T2-weighted and post-

4:12

gadolinium scanning. Is there intracranial extension?

4:15

To what extent is that intracranial?

4:17

Is it into the parenchyma?

4:19

Is it into the dura?

4:20

Is it into the PF (posterior fossa),

4:21

for example, is there orbital involvement?

4:24

Is there perineural spread along the cranial nerves?

4:26

Most commonly, the maxillary nerve, and is

4:29

there deep spread into the masticator space?

4:33

The pterygoid musculature,

4:35

the masseter muscle, or the

4:36

adjacent parapharyngeal space.

4:39

Let's now look at some more of the sinonasal

4:42

malignancies, and we're going to start with melanoma.

4:45

As you see in the graphic, melanoma is probably

4:50

the second most common of the malignancies

4:53

after the squamous cell carcinoma, red here,

4:57

and then the large group known as the others,

5:00

and we'll talk about that in a moment.

5:03

So, as I mentioned, melanomas are going to

5:05

be very bright on a T1-weighted image.

5:08

Here we have a lesion, which is in the

5:11

nasal cavity, growing into the maxillary

5:14

antrum with secondary obstructive secretions

5:17

associated with it in the maxillary antrum.

5:20

This bright signal intensity on pre-contrast

5:23

T1-weighted imaging is characteristic

5:25

of a melanoma that has melanin within it.

5:29

There are

5:30

amelanotic melanomas.

5:32

When we have melanomas that don't have

5:34

melanin within it, they're gonna look

5:35

the same as squamous cell carcinomas.

5:38

Here's another sinonasal melanoma given to me by Azita

5:42

Khorsandi, and you notice that on the T1-weighted scan

5:45

you have some element of bright signal intensity

5:49

on the sequences. On the T2-weighted scan,

5:53

a dark lesion that is infiltrating the maxillary

5:57

sinus, growing outside the maxillary sinus,

5:59

into the pterygopalatine fossa and extra-sinus

6:03

soft tissues, as well as in the nasopharynx.

6:06

You see the heterogeneous enhancement of the

6:09

lesion, and it does show reduction on the ADC

6:13

map, dark signal intensity, which on a DWI

6:16

image would be seen as bright signal intensity.

6:20

How do we know this is a melanoma?

6:21

We don't, but the presence of the bright signal

6:24

intensity in an aggressive, infiltrative mass with

6:29

low ADC is going to be

6:31

suggestive of a sinonasal melanoma.