Hi, my name is Satish Govindaraj and I'm Director of Rhinology at the Mount Sinai health system in New York. Welcome to our course, Acute and Chronic Rhinosinusitis: A Comprehensive Review. Now we're gonna be starting off with module one, where we will discuss Normal Sinus Anatomy and Function. Many times, we take for granted what the sinuses, and the nose do on a normal, every day fashion. And, in all honesty, before we can talk about the pathological processes in these areas, it's important to walk away with an understanding of how the sinuses normally function as well as the normal sinus anatomy. So many times when I'm in the office one of the most common questions I'll receive is you know doctor what do the sinuses do what is their function? And the honest answer is we to this day still do not know what the true function of the sinuses are. But one thing we do feel is that the sinuses serve the purpose of humidifying and filtering the air that we breathe everyday. And one of the other functions they presumable do is to act as almost a shock absorber to the head in the setting of trauma. And what I mean by that is if you look at the forehead area, there's frontal sinus that lives there. You can imagine if there was no sinus and that was solid bone. A forest to the forehead would be directly delivered posteriorly to the brain. But with the sinus intervening, it almost acts like a shock absorber and absorbing all that pressure to the brain and underlying structures are not hurt in that setting. So the sinus although we do not know what the true function is. Our presumed functions actually serve a great deal of purpose and are likely spot on. Now let's look at this schematic coronal view that we have. If you look, in this view there's three sinuses that we can see in the coronal section. The first is the forehead sinus or frontal sinus. That lives at the area behind the forehead, starts to be produced and developed right around the teenage years and then finishes shortly after puberty. The function of that sinus we don't know as we talked about, but if it is infected or has a pathologic process patients may complain of frontal tenderness, frontal pain. And if that issue is severe, they may notice actually swelling and redness overlying the skin of that area. And that's a suggestion of an underlying process called, Pott's Puffy Tumor, which is in reality, a chronic Osteomyelitis or even an acute Osteomyelitis of the frontal bone. Knowing where the sinuses are and seeing what disease process is occurring over them gives us an idea what's going on with the patient. The second sinus you see in this coronal view is the Ethmoid sinus. The Ethmoid sinuses are essentially a honeycomb of air cells that live right next to the eyes. So if you have an infection or a process that occurs in that sinus, it can easily spread into the eye, causing a patient to have infections such as orbital cellulitus or an orbital abscess which is a collection of pus around the orbit. That's a surgical condition, it has to be drained. The third sinus that you see is the Maxillary sinus. Now, that's the largest sinus and it's also the first sinus that's present at birth. The significance of that sinus is it has a very intimate relationship to the underlying upper teeth. And we're taught right away in residency that if someone has a unilateral maxillary sinusitis, you have to rule out an odontogenic process, number one. Number two is a tumor, and then you go into the rest. So, the sinuses in this view, the frontal, ethmoid, and maxillary, each hold different degrees of importance. Now if you rotate that head into a sagittal view, you see in another dimension the relationship between the frontal, Ethmoid and Maxillary sinuses. The reason this view is brought in is because it tells us about the fourth sinus, which is the Sphenoid sinus. The sphenoid sinus as you can see is located in the back of the head, so patients, if they have disease their, will complain of occipital headaches or pain behind the eye, retroorbial headaches. And very rarely, a sphenoid sinusitis, although located in the back of the head can present with frontal headaches. So the location of a patient’s pain can dictate and help you find out where the underlying disease may live. The other value of the sphenoid sinus is that it serves as a gateway. If you look here, the arrow takes us from the nose, all the way to the Sphenoid, to this area here, called the sella turcica. And the pituitary gland lives in that area many times, otolaryngologist along with neurosurgeons will perform approaches to that area and remove tumors for that region. So the Sphenoid sinus is also a nice gateway to the skull base for us endoscopically. Now, if we move from the schematic to the CAT scan, you'll see here on the left, the coronal CAT scan, and here is the eyes. And here again you see that maxillary sinus that very large sinus has an intimate relationship to the upper teeth but one thing you can see this very large sinus but it has a very narrow outflow that you can see here. So even the smallest amount of edema or congestion can result in obstruction of that outflow developing into an acute sinus process. If you look at the scan on the right, that's a coronal scan looking at the sphenoid sinus and you can see here this black is essentially air. So we know the sinus is well aerated and if we look at the star, that indicates the location of the optic nerve. The optic nerve is dehiscent 6% of the time on CAT scans. And that's important because if someone has an acute sphenoid sinusitis, that infection can spread to the optic nerve, causing blindness, if there's no bone in that location. The arrow is pointing to another important structure, surrounding the lateral wall on the sphenoid sinus, the carotid artery. 22% of the time, that bone overlying the carotid artery can be missing, and not a big deal here where you see all this air in the sinus. But you can imagine if that sinus filled with polyps and the bone overlying the carotid is dehiscent, well that creates a great deal of concern if you have to go in there to do any type of surgery to remove polyps. So very important to appreciate the integrity of the bone, overlying the optic nerve and the carotid artery when performing any surgery or reviewing scans of this area. So let's move on to the Sinus Epithelium. Say we take this sagittal view and we take a cut through the maxillary sinus, and then take that sinus Epithelium and take a look at it under the microscope. What are we gonna see? What we're gonna see is basal cells, goblet cells. We'll see here columnar cells with overlying cilia. And then you see some mucus glands that help produce the mucus that overlies this ciliary layer. And the importance of this ciliary layer is something called mucociliary clearance. And why it's important is that it's a host defense mechanism. It helps protect the sinus cavity and the nasal cavity from foreign bodies, particles, allergens, bacterial agents. And by working together the cilia and mucus help move pathogens in a anterior to posterior direction in a motion called metachrony, as you see here. You see how the cilia are very synchronized. In this overlying mucus layer here you see the mucus is moving and flowing at an anterior to post your direction as directed by that arrow. But what happens if there is an abnormality to the cilia, an infection that causes paralysis of the Cilia? Or an inherited condition such as cartilaginous syndrome where theres an abnormality to the structure of the cilia. What can happen is that there's dismotility of the cilia and ineffective movement called dyskinesia. And now you see as you watch the video, stagnation of allergens, bacterial pathogens, particles, debris and this is a setup for chronic sinusitis. Because that ciliary defense mechanism is no longer functioning cuz mucose ciliary clearance is ineffective. Now what you have to understand is that mucose ciliary clearance is not just taking place in the nose, it takes place in each sinus. For example if you look at the left Maxillary Sinus shown here, even though we have a nice opening up at the top. The sinus extends all the way down to the nasal floor, and sometimes even lower in the adult. So the sinus still has to move mucus from that floor up to that natural opening. ANd that's the cilia who are responsible for that function. The way we used to do surgeries would make sense. Okay, if the sinus is blocked, why not make an opening down here? We'll make it much easier for the sinus to drain. The problem is the sinus does not care where that accessory opening is. It still wants to drain up at the natural opening and we see that best here in this right side of the patient who has here a normal left maxillary sinus opening. And then that accessory opening that we saw in the previous slide. And what happens is mucus leaves that normal sinus opening and recirculates back into that accessory opening. This is a process referred to as mucus recirculation. And this is a set up for recurrent maxillary sinusitis, chronic maxillary sinusitis or that feeling of thick post nasal drip. What the patient is experiencing is this thick mucus being dislodged and going posteriorly. And that's what they feel is sticking to the back of their throat. So a very treatable condition just by taking down this bridge and making that opening one common entity. Now what about the frontal sinus? This is a little bit different, and the reason why is when you look at mucocilliary clearance in the frontal sinus, it goes up the medial wall, flows along the roof and mucus exits down the lateral wall of the sinus. We find that in certain cases and in most cases, that frontal sinus recirculates mucus ten percent normally. So there's a normal amount of mucus recirculation that's occurring in the frontal sinus. If we have any obstruction, as you see here in the yellow, what happens is that recirculation phenomenon is increased. And now you have ineffective drainage and that mucus continues to recirculate within the sinus. So our understanding of normal mucus early clearance in the frontal has helped dictate some of our extended frontal sinus procedures. So we can do is if someone has an obstruction to both outflows, we could remove this central segment, it's a procedure called the Draf III, or modified Lothrop procedure. And by doing that we can remove it safely, and even though we've done an extended opening, we can still preserve normal mucus ciliary clearance down that lateral wall. So although we sometimes take for granted what the sinuses do, Our understanding of how they function helps dictate and allows us to perform extended procedures, while at the same time, protecting normal sinus function. So let's finish off with discussing sinus drainage pathways. You can see here in the red we have anterior drainage pathway. And in the blue a posterior drainage pathway. The anterior pathway in red drains the frontal, anterior ethmoid and maxillary sinuses. Whereas the blue arrows drain the posterior ethmoid and St Sphenoid sinuses. Just by performing nasal endoscopy and seeing where drainage is with respect to this structure, called the eustachian tube orifice, we can in some ways figure out Where is the disease without getting a CAT scan. And the way you can do that is if you see mucus draining above the Eustachian tube orifice here, then that process has to be originating from the posterior ethmoid or the sphenoid sinus. However, if we see mucus draining below the Eustachian tube orifice, in red here, that is disease process originating from the frontal Max their anterior ethmoid. So knowing the sign as drainage pathways is very important, especially when performing that physical exam or nasal endoscopy in the office. So let's summarize what we learned in module one. One is that we have four paired sinuses. The frontal, ethmoid, maxillary,and sphenoid sinus. Each one has its own mucociliary clearance which is a key host defense mechanism both for the nasal cavity as well as for the paranasal sinuses. The frontal sinus normally has a certain amount of mucus recirculation that occurs, and that percentage is increased if any detection of blockage occurs in the outflow. So important to appreciate that. And lastly, of anterior and posterior drainage pathways that help us determine where the area of pathology may be with respect to drainage around the Eustachian tube orifice. I wanna thank you all for joining us with module one, we hope you enjoyed our overview of normal paranasal sinus anatomy and function. And hopefully you'll join us in modules two, three, and four, where we'll move things further and discuss the pathological conditions that occur in the paranasal sinuses. Thank you.
