0:00

The vast majority of patients that are evaluated

0:03

for sinusitis are evaluated with CT scanning.

0:07

Why don't we use MR instead of CT scanning

0:11

and spare the patient the radiation exposure to the lens

0:15

of the eye, which we know is a sensitive organ

0:18

or the scatter radiation potentially to the thyroid gland.

0:22

Well, MR.

0:24

Obviously is something

0:25

that is much more expensive than CT scanning

0:29

and it's kind of a use that may not be very valuable

0:33

with respect to the very common finding of sinusitis.

0:38

That said, MR is very sensitive on T two weight scanning,

0:42

in particular for mucosal thickening.

0:45

And sometimes it is so sensitive that it will find things

0:48

that you do not see on CT scanning,

0:51

including the nasal cycle.

0:54

So that passive congestion decongestion I mentioned,

0:58

that can occur from right

0:59

to left in normal variation in normal subjects

1:03

may be demonstrated on MR scan

1:05

and be misinterpreted as active inflammation.

1:09

The other thing that is difficult with MR is

1:12

that like CT scanning, it can be difficult

1:16

to evaluate in patients who have inspissated secretions.

1:21

Hyper protein tenacious secretions on MRI scan can have

1:25

such little water content

1:27

that it can appear dark in signal intensity on both T one

1:32

and T two weighted imaging and

1:34

therefore simulate normal aeration.

1:37

When you've got a real concretion, think of it like bone

1:41

or calcified secretions.

1:43

It's gonna look black on this Mr.

1:46

T one and T two and

1:47

therefore look like it's air containing when it may in point

1:51

of fact be so inspo

1:53

that there's no water content in those sinus secretions.

1:57

So there was a very beautiful paper that was done

2:02

by Peter Som from Mount Sinai in New York,

2:06

back in again the 1980s and 1990s.

2:10

And what he did was he looked at the signal intensity

2:14

of sinus secretions

2:17

and then had his

2:20

ENT colleague do aspirations of those secretions

2:25

and measure the protein content of the secretions

2:29

and see whether it correlated in some way

2:31

to the signal intensity or an mr.

2:34

And in point of fact, it was beautifully demonstrated

2:38

that at low protein concentration,

2:41

if it's basically like water content,

2:43

it's gonna be dark on a T one wayed scan.

2:46

This is the T one wayed graph

2:49

and it's gonna be bright on T two weighted imaging.

2:52

However, as you get higher

2:53

and higher protein content within the sinus

2:57

secretions, and this

2:58

Is as the secretions kind of get more inspissated,

3:03

more dry, you see that the signal intensity on T one way

3:07

and imaging actually rises.

3:10

So there is a point, this is our ISO intense line.

3:13

There is a point where the sinus secretions are bright on T

3:16

one and bright on T two.

3:19

This is at a protein concentration, let's say of about 20%.

3:24

As you get less and less water

3:25

and the protein content increases, you notice

3:28

that there is a point where the T two way scan actually

3:31

falls below ISO intense

3:34

and becomes dark in signal intensity.

3:37

So we have this range here where it's bright on T one

3:40

and dark on T two, pretty concentrated

3:45

secretions from chronic sinusitis.

3:49

And finally at the ultimate endpoint we have a point

3:53

where the secretions have such little water content

3:57

that once again it's dark on T one, but also dark on T two.

4:02

This is our danger zone where it looks like it's air,

4:06

but it's really just so highly concentrated protein

4:10

that you don't see any signal intensity on T one weight

4:14

and T two weight imaging.

4:16

So this was very beautiful work

4:18

that Peter did in describing the signal intensity of

4:22

secretions on MRI.

4:24

Let me just show one example.

4:26

So here we have a patient that has complete opacification

4:32

of the left maxillary antrum and the nasal cavity.

4:36

And you see on the CT scan it's hyper dense,

4:40

it's very concentrated.

4:43

Well, if we look on the T one

4:45

and T two weighted images, we see that it's very dark

4:50

on these pulse sequences, and this is dark

4:53

because of that hyper protein tenacious

4:56

material in the sinus.

4:57

This almost looks as dark

5:00

as the normally aerated, right?

5:03

Maxillary antrum.

5:05

Kind of hard to tell you see, I've windowed this in a way

5:07

to try to show that they are not actually the same.

5:11

But if you do a routine window

5:13

with without this bright T two weighted image, you would

5:16

suspect that there was normal aeration here.

5:19

That's the potential pitfall of mr.

5:22

This is post gadd T one way scan. This is the same patient.

5:26

This dark area is not air.

5:29

This dark area is hyper protein tenacious secretions on T

5:33

one way scan where it's gotten so dark that there's

5:36

so little water content that it's black

5:39

and looks like almost the normal aerated contralateral,

5:44

right maxillary antrum.

5:47

Here's another example of a patient pre gad post gad.

5:51

You notice that the secretions are bright

5:53

in signal intensity.

5:55

So these are hyper protein tenacious

5:57

Secretions in the 20 to 30% range as opposed

6:01

to the previous case where we're out in the 40 to 50% range.

6:06

So it becomes bright on the T one, this is post gad.

6:10

You just see mucosal thickening around it.