Frontal Sinus Dissection (Cadaver)
Alright so, we're going to start by doing the frontal sinusotomy. Basically when you’re - when you're starting your frontal sinusotomy, you got to switch to curved instruments, and so keep that in mind. The other thing you can do is hyperextend the head of the patient, so that gives you better access to the frontal sinus. So what you want to do is go into the frontal sinus outflow tract or the frontal infundibulum, and this is bordered by - Sorry, I'm using here a 45-degree by the way. I'm in the left nostril. So just for you guys to get oriented, this is the inferior turbinate right there. This is your maxillary, and then looking up this is the middle turbinate that you see kind of sitting attaching to the - sitting on the septum. And this is the middle turbinate attachment. So the frontal infundibulum is bordered anteriorly by the back wall of the agger nasi. And then posteriorly, it's bordered by the frontal suprabullar cell. The anterior wall of the suprabullar cell. Laterally, it's bordered by the orbital roof, and medially it’s bordered by the vertical attachment of the middle turbinate.
Frontal sinusotomies are divided by Wolfgang draf and to draf I, draf IIa, draf IIb, and draf IIc. So draf I, which is the first stage of any frontal sinusotomy, is a good anterior ethmoidectomy. So if you do a good anterior ethmoidectomy - you have to do a good anterior ethmoidectomy before you do your frontal sinusotomy. And the other landmarks that you want to keep in mind besides the one we've mentioned is the uncinate process and its attachment, because it will dictate where the frontal sinus drains, and as Dr. Ramakrishnan mentioned, the anterior ethmoidal artery, which is right there, and it's usually it's one centimeter behind the frontal infundibulum - back wall of the infundibulum. So here - looking here you have the skull base right there, and then you have like - kind of like - you see how it goes down, so you have some anterior ethmoidal cells that Dr. Jiang left for us, so we can do the dissection.
You can use any instruments that you like. But basically we want to make sure that we remove all these anterior ethmoidal cells right there. So here I'm going to use the frontal curette to kind of dissect a little bit more the cells on.. This is very… So here...So here we’re dissecting the suprabullar cells and then you see again, you still have one cell here, for example, that you can dissect as well. So you want to skeletonize everything to the skull base. And here you can see better, your - the anterior ethmoidal mesentery.
Alright so and then to dissect the agger nasi. One way of doing that is basically, you put your kerrison in here and usually it, it falls down, and you can bite. And what you're biting here at the, the middle turbinate attachment is the agger nasi. And that will give you also space to work and to see what what you're doing so...What you want to keep in mind is that this is the - here you have the bulla, the suprabullar cells, and then the frontal sinus outflow rack is going to be actually medial to the suprabullar cells. So I'm suspecting that it's right there, and if I'm dissecting here I usually use two fingers. I don't go with my full force hands, because you know, you're close to the skull base.
Just going to clean up these cells. Agger nasi. This is the suprabullar, and then I suspect that my frontal sinus will be, if we go through here. Yeah, you should always study your scan, study especially - study it before doing any frontal sinus dissection. So alright, so there it is. So this is the agger nasi. This was the suprabullar cell, and you can see where your frontal sinus is going to be right there. So it's medial to it. Then you have this - this is - and now you can see it very well. Your frontal - frontal sinus is going to be here. This is the back wall of the frontal sinus, which is another landmark that you use. You got to make sure that you preserve the mucosa when you're dissecting the frontal sinus so - because the frontal sinus is very prone to scarring, so you want at least preserve that back wall mucosa and the medial one, and usually you can, you can try - you have to try and preserve - preserve it circumferentially.
But now we're going to basically crush the agger nasi anteriorly, and we have a better view of the frontal sinus, and you can see it here.
So another way of of knowing that you're in the frontal, if you don't have navigation is when you open up the frontal sinus, if you transilluminate it and you see that the transillumination is going to the medial canta - medial canti, it means that you are in the suprabullar or the agger nasi. But if it's transilluminating the forehead - here it's not because the, the cadaver has a darker skin coloration. So usually the forehead should transilluminate to know that you're in the frontal sinus. Now that we uncapped - we removed the superior edge of the agger nasi; that's our draf IIa. It's also called uncapping the egg, meaning removing the superior aspect of the agger nasi and - and that gives you this frontal sinusotomy right there. You can see it. This is the anterior wall. This is the forehead. Opps, a little bit of blood. And so your next step will be to do a draf IIb. So the draf IIa, your boundaries are the vertical attachment of the middle turbinate medially, the orbital roof laterally, the back wall of the frontal sinus posteriorly and anteriorly it's going to be the frontal beak - the nasal frontal beak. Sorry the - the vertical - the attachment of the vertical lamella.
Now if you want to do a draf IIb, then basically you're extending your frontal sinusotomy from the orbital roof towards the septum. So you got to remove the vertical lamella of the middle turbinate, and so looking here at this frontal sinusotomy, the other thing that you kind of notice is the relationship of the anterior ethmoid artery, which runs - which runs posterior anterior from lateral to medial. It's always oblique in this fashion, and you can see it's usually one centimeter, almost one centimeter behind the frontal infundibulum.
So what you want basically is to enlarge this further. We can enlarge this further. But the other thing that you want is again, extend your frontal sinusotomy from the orbit to the septum, so you want to cut down the vertical or the anterior third of the vertical lamella of the middle turbinate. And so you want that middle turbinate level - be at the same level of as the back wall of the frontal sinus. So you got to remove all this. And one way of doing it is basically - Is there a lesser turn? Cutting - cutting through the vertical attachment of the middle turbinate. So what you can do is use what I was using, the lesser of curved one, and then you make your vertical cut all the way to the back wall of the frontal sinus. And then you make a cut here, and then you have the vertical lamella, and you can take out the small piece of mucosa from it and use it as a graft for your frontal sinusotomy, or you can just bite through the vertical lamella.
So we’re biting through that vertical attachment, the anterior third of it. You want it to go all the way back. All the way back to the back wall - to the posterior wall of the frontal sinus.Then you can clean it up. So it looks like you have an intersinus cell here. Sort of. So you can connect that with the rest of the frontal sinusotomy.
I love the frontal sinus punch for… So see how the opening is being extended anteriorly and medially, right? Because it’s starting to - you’ve got to start going towards the septum. That’s right. But the thing is that the skull base is rounded, so you have to come somewhat anteriorly. If you just go directly medially, you’ll get into the skull base. So you’re trying to make that - the half of that horseshoe shape you typically see after IIb. That’s right. So like, for example, you can see the back wall of the frontal sinus, which corresponds to the skull base and then, and so it's a horseshoe shape meaning that as Dr Jiang said, meaning that it bulges anteriorly and then goes goes back posteriorly. Here you have a supraorbital extension of ethmoid cell. Usually this is associated with the dehiscence of the ethmoid artery. So the other mistake that you can do is when you have a supraorbital extension is that you think you're in the frontal, and then you start crossing over to the other side to kind of widen your frontal sinusotomy, and then you will hit the cribriform plate because you're all the way posteriorly, and I've seen that happen.
We're almost done with our draf IIb here. You guys should have the angled - the curve punches and the kerrison. So it’s good to use that, when you can. Sometimes you have to drill, but if you don’t need to then don’t. Because drilling destroys a lot of the mucosa. It does, and it heats it up, and it stimulates osteoblast and osteoneogenesis. So I mean, you look at this frontal sinusotomy and it's wide and big and then you see them back in clinic like a month and it's a pinhole. Alright so we'll keep doing it with cold dissection.
So you want to preserve as much as you can mucosa. If the mucosa is floppy don't micronebriate it, just let it sit back here. Again, we see our anterior ethmoidal artery. Alright so, so now I connected this frontal sinus with the supraorbital ethmoid, and basically what we're going to do is clean up.
And then our next step would be to do the draf III or endoscopic modified lothrop procedure and connecting the two frontal sinuses together. And so your landmarks for this will be the middle turbinate of - the vertical lamella of the middle turbinate. Again the back wall of the frontal sinus, the septum, and the nasal frontal beak anteriorly. And basically - you can - there's three ways of doing this. You can go transseptal into the frontal sinus. If you don't have any landmarks sometimes you don't have any landmarks, you go transseptal. There's also what we call supraturbinal, meaning going through this, the attachment of the vertical - of the middle turbinate. And it's also called outside-in, meaning you start going from outside into the frontal sinus. Or the most popular form is you identify the frontal infundibulum, and on the side where you can identify it and then you go from known to unknown. So you start going from this side, and you cross over through the septum to the contralateral frontal sinus. And we usually do this draf III when you really have either very bad polyps centers, revision revision or you know like, for -or for skull base procedures, skull base resections.
Alright so, here we started drilling our draf III, and so what you want to do is saucerize basically, just like a mastoid. You want to drill all these bony septations that kind of occlude your vision. And your goal is going to be to create a frontal sinusotomy from orbit to orbit and from cribriform to the skin basically. You can - you can go all the way up to the skin, and so it's a horseshoe-shaped cavity as we said before. This is the cribriform. You can see the cribriform kind of peaks a little bit anteriorly from the back wall of the frontal sinus. Some people use the olfactory fiber as a landmark for their posterior dissection and so the olfactory - the first olfactory fiber is going to be somewhere around here. And the safest way of drilling in a frontal is - or basically kind of widening it is anteriorly because - towards the skin.
One of the other things that you want to do when you're doing a draf III is your superior anterior septectomy. So your septectomy - your superior septectomy has to go all the way back to the frontal - to the back wall of the frontal sinusotomy. And so one easy way of doing this is just take this light frontal sinus probe, and you put it all the way up at the level of the back wall, and you know that you have to take all this as a frontal. Wait how far anterior do you move?
So you can go all the way anteriorly - all the way anteriorly. It’s just - it’s like mostly you have to remove, you have to do an anterior superior septectomy, and it has to go all the way posteriorly to the back wall of the frontal sinus or the cribriform basically or the - So what you’re - the septectomy or basically what you're resecting here is the perpendicular plate of the ethmoid.
You have to resect it all the way to the back wall of the frontal sinus and then you don't have to go all the way down. You know, don't do a complete septectomy, just do a window kind of. So you can use your probe and that you put the probe at that at the level of the cribriform plate or the back wall of the frontal sinus here, and that kind of gives you an estimate on where you have to go. So it kind of delineates it like that. And there are multiple ways of doing your septectomy. It’s a destructive procedure. You can also save the mucosa and use it for grafting, if you can.