0:00

I'd like to show another example of a mucocele,

0:03

which is in a more characteristic

0:05

location and having both CT and MR correlation.

0:10

So here we have a patient who has a lesion

0:12

in the left frontal ethmoidal region, and

0:15

you notice that there is expansion here into

0:19

the periorbital region on the left side.

0:24

In this case, it has a little

0:25

bit of irregular margins on the—

0:28

CT scan, which you will see on the MR, is

0:32

not present actually and is well defined.

0:36

And this lesion is a mucocele, which is

0:39

basically a backup of secretions in a patient

0:43

who has had an obstructed outflow tract of the sinus.

0:48

So in this case, a frontoethmoidal

0:50

mucocele. One way we would expect

0:52

the frontal recess to be obstructed.

0:54

And as you can see, like a subperiosteal abscess,

0:59

this lesion does have mass effect on the globe

1:03

and the medial rectus muscle.

1:05

But in this case, it's a well-defined abnormality.

1:09

On T1-weighted scan, you notice that it's

1:12

bright, so increased signal intensity on T1-

1:15

weighted scan because of the high protein content.

1:18

This is post-gadolinium, but

1:19

this is really not enhancing.

1:21

This is bright on the pre-gad.

1:24

So this is just basically T1 shine through, if

1:27

you will, from the pre-gad, and it doesn't have

1:30

that wall of enhancement that you would expect

1:32

with a subperiosteal abscess, and it has no low

1:36

density on the CT or high signal intensity on T2

1:40

weighted scan to suggest that this is an abscess,

1:45

which usually is more fluid-centered.

1:48

The dark signal intensity here is related

1:51

to the increased protein in the secretion,

1:54

so hyperproteinaceous secretions.

1:56

You remember that graph I showed you with

1:58

the T1 and the T2 signal intensity.

2:01

And as the protein content increases, you will

2:05

have a period where it's bright on T1.

2:09

Here's our bright on T1 and dark on T2,

2:13

where it's around 30 to 40% protein content.

2:16

So this is a mucocele, typical in the

2:20

frontal ethmoidal region, with impact on the

2:22

orbit causing proptosis, as well as lateral

2:25

deviation of the orbit and expansion of the

2:28

sinus secondary to obstruction at the fronto-

2:31

ethmoidal recess.

2:33

So once again, just to review, the mucoceles

2:36

are most common in the frontal and ethmoid

2:38

region, or what we sometimes will just say frontal

2:41

ethmoidal region, more than the maxillary sinus.

2:43

And you did see a case of a sphenoid sinus

2:46

mucus seal, which I mentioned was unusual.

2:48

On the MRI study, this is secondary to an obstructed

2:52

osteo leading to expansion of the perinasal science.

2:55

And that expansion may have impact on the

2:58

orbit with proptosis or deviation, or it may

3:01

expand intracranial and actually push brain

3:04

tissue away, does not infiltrate the orbit.

3:07

Does not infiltrate.

3:08

The brain is not usually associated

3:11

with meningitis or with encephalitis.

3:14

Remember that the signal

3:15

intensity may be quite variable.

3:17

It depends on the protein content of the mucus seal,

3:21

so it may be bright on T one, it may be dark on T one,

3:24

it may be bright on T two, it may be dark on T two.

3:27

Depending upon the protein content, it

3:30

usually will either not enhance or have

3:33

a very thin rim of enhancement, which is.

3:37

Unlike the enhancement that we

3:38

typically see with an abscess.

3:40

Here's another example.

3:42

In this case, an ethmoid mucus seal, where similar

3:46

findings, the bone may be thinned out, but it is

3:50

usually confined by the periosteum of the bone.

3:53

As you see anteriorly here,

3:55

there is a mass effect expansion.

3:57

There is potential dehiscence here at the

4:01

posterior ethmoid and cribriform plate.

4:05

T two weighted scan.

4:06

T one wayed scan, in this case

4:08

bright on T one, bright on T two.

4:12

So if I had to draw my graft again,

4:15

signal intensity of the secretions.

4:17

Here's T one weighted, here's T two weighted.

4:20

Here we have a, and here's our ISO intense

4:23

line here we have an example where it's bright

4:26

on T one as well as bright on T two, and.

4:32

Probably around 20% protein content,

4:35

bright on T one, bright on T two.