0:00

I want to mention a couple of classification

0:03

schemes that people will refer to.

0:06

I personally do not use the Keros classification.

0:09

I leave this to the endoscopic sinus

0:11

surgeon to make that distinction.

0:14

But what the Keros classification refers

0:16

to is the depth of the olfactory fossa

0:20

with respect to the crista galli.

0:22

So you can see how it's measured, and that is

0:25

this cross-section of the lateral lamella and the

0:28

cribriform plate and the depth of the olfactory

0:32

fossa: Type 1, one to three millimeters; Type 2,

0:36

this depth being four to seven millimeters; and then

0:39

Type 3 being eight to 16 millimeters in depth.

0:43

This helps the endoscopic sinus surgeon

0:46

to avoid potential intracranial

0:50

penetration when taking down the anterior

0:53

ethmoid air cells or potentially that

0:54

vertical attachment of the middle turbinate.

0:58

Here is an example where you can see the depth

1:02

of the lateral lamella to the ethmoid air

1:06

cell roof, and it's measured as Keros Type 1.

1:10

Here, a little bit larger—the four to seven

1:13

millimeters—Keros Type 2, and here even more

1:17

depth, you know, beyond eight millimeters

1:19

in superior-inferior height being

1:21

Keros classification Type 3.

1:23

In my typical dictations on paranasal sinus CT

1:28

scan, I do not do the Keros classification,

1:31

but you may see that in some of the literature

1:35

as well as the sinus surgeon's requests.

1:39

A couple of things that I do mention and I think

1:42

is critically important, is the area of dehiscence

1:46

that may occur within the paranasal sinuses,

1:49

and I generally look at four specific locations.

1:53

I look at the

1:55

cribriform plate to see whether there are any

1:58

dehiscence at the cribriform plate, that there

2:00

could potentially be inadvertent intracranial

2:03

penetration at the time of sinus surgery.

2:06

I look at the wall of the optic nerve.

2:09

We mentioned that before, which is medial to

2:12

the anterior clinoid process, to see whether

2:15

it itself is dehiscent, that could potentially be

2:18

injured at the time of sphenoethmoidal surgery.

2:21

I look at the walls of the carotid arteries,

2:25

because again, if you're operating in that

2:28

posterior ethmoid-sphenoid complex, you could

2:31

have inadvertent lateral penetration through

2:34

the wall and injure the cavernous sinus.

2:37

So here what you're seeing are the areas along

2:40

the optic nerve where you have dehiscent bone.

2:43

Here's an exposed optic nerve.

2:46

Here we have the carotid artery, and on the

2:50

right-hand side, we don't see that wall.

2:53

This is contrast enhancement in the carotid artery.

2:56

Here's our normal carotid artery with a good

2:59

lateral wall. The sphenoid sinus here,

3:00

it is dehiscent.

3:03

Here we have a normal variation where we have the

3:05

maxillary nerve exposed in the sphenoid sinus.

3:09

And the other area, as I mentioned, was the

3:12

cribriform plate to look for potential areas

3:15

where the penetration intracranially could occur.

3:19

The fourth area that I mentioned

3:21

is the lamina papyracea of the orbit.

3:25

So if there are areas of dehiscence in the

3:28

medial wall of the orbit, the lamina papyracea—

3:32

then at the time of endoscopic sinus surgery,

3:34

even doing an ethmoidal bullectomy, removing the

3:37

bulla of the ethmoid air cell, potentially there

3:40

could be exposure where you may enter the orbit

3:43

inadvertently and cause an orbital hematoma.

3:46

This, uh, black arrow showing an area of

3:49

dehiscence along the cribriform plate.

3:51

You can see that on the sagittal

3:52

reconstruction—there's an opening there.

3:54

This patient has had previous surgery.

3:56

In this case, the middle turbinate has been removed

3:59

on the right side, as well as the uncinate process.

4:03

There's been a partial ethmoidectomy, but

4:06

either preoperatively or as a consequence

4:10

of the operation, we now have an area

4:12

of dehiscence in the cribriform plate.

4:15

So lamina papyracea dehiscence here.

4:20

Cribriform plate dehiscence here.