0:00

On the previous example, I talked about hyperdensity

0:05

on CT scan, where it's obviously bright on the

0:09

CT scan, but maybe dark on a T2-weighted scan.

0:12

And I gave that example as a potential pitfall

0:15

because of hyperproteinaceous secretions.

0:19

But this is a potential pitfall that can be

0:21

much greater than just from chronic sinusitis.

0:25

What else might be hyperdense on CT and dark on T2?

0:30

Well, it could be blood products.

0:32

So, in the setting of a patient who has had trauma,

0:35

you may see bright contents in the paranasal sinuses

0:40

from hemorrhage, which on T2-weighted imaging may

0:43

represent deoxyhemoglobin, which we know causes proton

0:48

relaxation enhancement and, therefore, T2 shortening.

0:52

I mentioned hyperproteinaceous secretions

0:55

that can occur with chronic sinusitis, but it

0:57

may also occur in the setting of mucoceles.

1:00

Mucoceles are obstructed sinuses where the

1:04

osteum has been occluded, and the contents behind

1:08

that obstructed sinus osteum get more and more

1:12

concentrated and may expand the sinus. In that setting,

1:16

you may also see

1:18

brightness on the CT scan and darkness on the T2-weighted scan.

1:22

Unfortunately, in addition to just normal

1:25

hyperproteinaceous secretions,

1:28

fungal sinusitis can also be a source of

1:33

hyperdensity on CT and darkness on a T2-weighted scan.

1:37

Well, the distinction between just chronic rhinosinusitis

1:40

versus a superimposed fungal infection is

1:45

quite important. Unfortunately, a lot of times, we're

1:47

scratching our heads, asking, "Could this be fungus?"

1:51

This is particularly true in the immune

1:53

compromised individual, where fungal sinusitis

1:56

can be a lethal infection, particularly if it's

2:00

aggressive, angioinvasive fungal sinusitis.

2:04

In addition, I want to mention some

2:06

of the benign neoplasms, which might

2:09

be bright on CT and dark on T2.

2:12

Those include osteomas.

2:14

Of course, bone osteoma is going to be bright on a CT

2:18

scan, and bone is going to be dark on a T2-weighted scan.

2:23

However, additionally, odontogenic lesions, some of

2:26

which are hyperdense—odontomas, for example—may be

2:31

dense on the CT scan and therefore dark on a T2-weighted scan.

2:36

If you have such incredibly concentrated secretions

2:40

that it actually forms a stone—what we call a

2:44

sinolith—where it's calcified or ossified within

2:47

the sinus but not coming from the sinus wall,

2:50

we would call that a sinolith, as opposed

2:52

to something coming from the sinus

2:53

wall, which we would call an osteoma.

2:56

Chondroid lesions also may be dense based on the

3:02

chondroid matrix of the lesion, so endochondromas, chondrosarcomas,

3:07

are dense on CT and may be dark on a T2-weighted scan.

3:11

The final thing that I should warn you about is

3:14

the presence of melanin. So, melanin on a CT scan

3:20

is generally slightly dense.

3:22

However, melanomas often bleed, and when they bleed,

3:26

obviously, they are going to be dense on a CT scan.

3:29

Melanin itself may have such paramagnetic properties

3:35

that it could cause darkening on T2-weighted

3:38

imaging and a bright signal on a T1-weighted scan.

3:42

So we all know that our differential

3:43

diagnosis of something that's

3:45

bright on a T1-weighted scan includes things

3:48

that are hemorrhagic, hyperproteinaceous.

3:52

It could be gadolinium enhancement, it could be

3:54

secondary to a cholesterol granuloma, for example,

3:58

but it may also be the presence of melanin.

4:01

That also is bright on T1, and susceptibility.

4:05

That paramagnetic effect can lead to

4:08

something that's dark on a T2-weighted scan.

4:10

So as you can see,

4:12

the presence of something which is dense on CT

4:15

in the sinus and correspondingly dark on T2

4:19

weighted scan has a relatively broad differential

4:22

diagnosis that you have to consider.

4:24

Quite a few entities.

4:27

These are two different 50-year-old

4:29

patients who have nasal congestion.

4:32

And I just want to point out that hyperdense mass that

4:37

you can see on CT scanning, which would correspond to

4:42

low signal on T2-weighted imaging. In this

4:45

case, the first two images show the hyperdense

4:50

osteoma that is present in the frontal sinus.

4:55

Frontal-ethmoidal location is

4:58

the most common site for an osteoma.

5:02

Contrast that case and the matrix associated

5:05

with it, with the matrix associated with

5:08

this second case, which crosses the midline

5:10

and is associated with the nasal septum.

5:14

This is the perpendicular and cartilaginous portion.

5:17

This is a patient who has more of a

5:19

popcorn-like appearance to the matrix.

5:22

This is a patient who has a chondroid lesion, in this

5:26

case, a chondrosarcoma of the paranasal sinus.

5:30

Both of these on T2-weighted scans will show

5:33

dark signal intensity, both the benign osteoma

5:36

as well as the malignant chondrosarcoma.