hello everybody and welcome back to another radiology tutorial today we're going to be discussing the anatomy of the paranasal sinuses we're going to look at how they relate to the nasal cavity in space as well as how they communicate with the nasal cavity itself we're also going to look at a couple of important structures that surround these paranasal sinuses that we need to be aware of and may need to warn our friendly surgeons about before they go poking around within these paranasal sinuses so let's start by identifying them and naming them on a scan here we have a coronal plane ct we've bone windowed it we want to come to the most anterior portion of the scan the first thing we notice is we can see our frontal sinuses within the frontal bone here as we head more posteriorly we'll see our maxillary sinuses starting to form as well as our ethmoid sinus here so we can see our left and our right maxillary sinus our ethmoid air cells of the ethmoid sinus heading all the way back and then we should see the sphenoid sinus then come into view here is our sphenoid sinus so we have our frontal maxillary ethmoidal and sphenoid sinuses those are the four paranasal sinuses so here we can see our sphenoid sinus we're at the level of the anterior clinic processes as we head more posteriorly we should see that dip into the cell tursica as we can see here dips down and then we should come up to the dorsum cell here with our posterior clinoid processes as we had even more posteriorly we'll see our clive is forming here that's where our basilar artery will be coming on the other side of that clivis okay so let's head forward we're going to go and just describe the nasal cavity now the anatomy of the nasal cavity is really important when we're describing the communications between the paranasal sinuses and the nasal cavity itself so let's start by having a look at the boundaries of the nasal cavity the bony boundaries the floor of the nasal cavity is made up by the hard palate our lateral walls are made up by the medial walls of our maxillary sinus we can then look at the roof of our nasal cavity let's go slightly more anteriorly we can see just a little bit of a crista galli coming up here and then we have an our ethmoid bone coming all the way and attaching to our frontal bone that makes up the roof of the orbit there's three segments to this ethmoid bone that we can describe there's a horizontal lamella coming away from the crystal galley now the crystal garlic is separating our two olfactory bulbs which lie on top of this horizontal lamella it then cups round the olfactory bulb and we get a vertical lamella coming up and then we get the roof of the ethmoid sinus itself and that's what's called the fovea ethmoidalis that bone coming across here we've got our laminar paparasia making up the medial wall of our orbit here or the lateral wall of our ethmoid sinus now we can see we've cut the nasal passages in the coronal plane we can see that the three turbinates that make up each side of the nasal cavity we have our superior turbinate this soft tissue coming down here our middle turbinate and our inferior turbinate you can see this aerated space lateral to those turbinates that's what's known as a meatus our superior meatus our middle meatus and our inferior meatus now the sinuses drain into specific meitain meatuses whichever way it is the frontal sinus and the maxillary sinus as well as the anterior portion of our ethmoidal sinuses are going to drain into our middle meatus our sphenoid sinus is going to drain into our superior meatus as well as our posterior ethmoidal cells they are going to drain into our superior meatus that's how we differentiate anterior and posterior ethmoidal sinuses it's where they drain into the anterior drains into the middle posterior ethmoidal drains into the superior sinus so let's look at these drainage pathways and these are what you're going to have to look at within a scan when you're assessing the paranasal sinuses and this used to be done on plain films but now ct has become the gold standard for looking at these paranasal sinuses and you can imagine these sinuses are lined with mucus producing cells they've got cilia pushing that mucus in towards the nasal cavities and if that were to become blocked for whatever reason if there was a mass or if you've got an infection that's causing swelling of those exit points we obviously can have buildup of fluid within these sinuses and that's rife for infection as well as if we have any fractures in these points that can also prevent mucus from coming out of these sinuses so let's start at the frontal sinus now we already know that that drains into the middle meatus the pathway in which the frontal sinus drains into the middle meatus is what's known as the frontal recess and i'm going to show you how you can find that frontal recess on the scan so let's have a look at this right frontal sinus we can work our way down now the anterior ethmoidal cells can share this pathway can share this frontal recess and on this coronal pain can be a little bit difficult to see but let's head our way down we can see as you follow my mouse cursor here i'm staying within the frontal sinus as i come down i can then see this pathway here going to the middle meatus this is what's known as the frontal recess just like that quite easy to identify here the frontal recess is what what drains the frontal sinus into the middle meatus let's have a look at the maxillary sinus and how that drains we can see a drainage point here this is what's known as the osteomeatal complex it's made up of the maxillary ostium the opening into this tube the tube itself is called the infundibulum and the ending of that tube the opening up into the medium middle meatus is what's known as the hiatus semilunaris so we can follow that on both sides we can see it here our osteomaetal complex inferior to that infundibulum is this soft tissue protuberance coming out like that that's what's known as the incinent process there's many uncertain processes in the body we've got the internet process in the uh pancreas antenna meaning hook coming around like this and as we're breathing in air from the outside you can see how this uncertain process prevents air from going directly into the maxillary sinus and diverts it into the nasopharynx itself so as i mentioned earlier the anterior ethmoidal cells will drain into the middle meatus let's see if we can find any of those coming through now so here we have a ethmoid cell or ethmoid sinus draining down nicely into that middle measure so we know this is an anterior ethmoidal cell let's work back to the sphenoid now looking at this image here you can see there's this airfield region here and it's important to not confuse that with another sinus it's not covered it's not surrounded by bone this is in fact the nasopharynx as we're going down towards our esophagus like that so you mustn't confuse this for a sinus this is our sphenoid sinus here the bone making up the roof of the sphenoid here is called the planim sphenoidal coming up making up the roof here we can see our anterior clinic processes and we know that the sphenoid then drains into the superior meatus so if we have a look at the left side of the sphenoid sinus here we can follow this down as we come more anteriorly we're still in that sphenoid sinus still in that sphenoid sinus here we can see it draining into this superior meatus if we were to go across into the axial view it's much easier often to see this um sphenoid draining into the superior meatus we can see here we've got our sphenoid as we head down we can see our right side of the sphenoid draining into the superior meatus as well as our left side as well draining into the superior meatus on that side here we go there again our posterior ethmoidal cells can also drain into the superior measures or should drain by definition into the superior meatus we can see here if we've got an ethmoid cell we follow there's a drainage point follow it down follow it down into the superior meatus and these passages is what's known as the sphenoethymoidal recess so our frontal goes through our frontal recess posteriorly here into the superior meatus we have our sphenoethymoidal recesses okay so now we've had a look at the different sinuses let's have a look at some of the structures that surround those sinuses so let's have a look at the coronal plane here and identify some of the structures that lie in close proximity to our sinuses as i mentioned earlier our lateral borders of the ethmoidal sinus is a laminar papiracia a really thin bone here if there's any external trauma to the eye we can get a fracture of these bones here we can get communication with the orbit and the sinuses as we head back posteriorly we can see our sphenoid sinus come into view here with our anterior clinoid processes and the major things we need to know about here is one the optic nerve coming backwards and slightly lateral to the optic nerve is our carotid artery coming through here and this bone between the sphenoid sinus and the carotid canal can be extremely thin and if we're doing some type of surgery in here if you can imagine if we've got inflamed mucosa and we can't see exactly where we are it's conceivable that we can break through a thin bone there and that would lead to devastating effects if we were to rupture the carotid artery there we can have a look in our axial window where we're talking about here let's have a look at our carotid canal you can see how the carotid is in close proximity with the sphenoid sinus as we scroll further our carotid canal is going to come forward here into our cavernous sinus you can see our cella turcica here our optic nerve if we were to follow that back follow our optic nerve down here we can see into the optic canal that's coming just superior to our sphenoid sinus here our anterior clinoid process our posterior clinic process and our cellular here which has our pituitary gland in it again very little space between the pituitary gland and our sphenoid sinus so there we have it a brief run through of our paranasal sinuses we've identified the frontal maxillary ethmoidal and sphenoidal sinuses and the pathways into the nasal cavities and before you go you might be wondering okay well there's stuff draining into the superior meatus stuff draining into the middle meatus what about the inferior meatus what drain's there well it's not left out we can see here we have a lacrimal recess where our lacrimal stack sits and as we come down we can see that our let me get this in the right plane here's our lacrimal recess here alako modak sits here and our nasolacrimal duct will drain into that inferior meat as we can see here draining down into that inferior meatus there so that's why when you cry you have tears coming into the orbit as well as your nose running because there's where the tears would flow into that inferior meatus so i hope that helped this is something that's not often covered i certainly didn't cover it in medical school to in any depth but it's really important as a radiologist to know what you're looking for where you're looking for and then alerting the surgeons if there's anything in particular they need to look for intraoperatively so i hope that's helped i'll see you all in the next anatomy talk goodbye everybody