 Okay, now we switch gears from oncological imaging and move on to imaging of the paranesial sinuses which is the bread and butter of most of our ENT practice and I shall discuss about the various synonasal drainage pathways and hence the patterns of chronic sinusitis which therefore result whenever obstruction to a particular pathway happens. So the sinuses are divided into anterior group of sinuses and the posterior group of sinuses. Anterior sinuses include the frontal sinus, the anterior model and the maxillary sinus which drain via the osteomatial unit into the middle miatus. Posterior sinuses are the posterior model and the sphenoid sinus which drain via the sphenoid model recess into the superior miatus. So let's begin with understanding of the osteomatial unit. Remember it's a three-dimensional space it is not something that is seen on just one cardinal image that we may make a mistake of kind of misinterpreting it like that. This is the representative cardinal scan which best delineates most of the components of the osteomatial unit but it actually is a three-dimensional space which is the drainage pathway of all those anterior sinuses that we have talked of. So this is the maxillary osteum which is at the anterior and the superior corner of the maxillary sinus draining via the ethmoidal infundibulum and the hiatus semilionaris into the middle miatus here. This is the unsonate process attaching inferiorly to the inferior terminate moving superiorly and this is the bulla ethmoidalis the largest usually the largest cell of the anterior group of ethmoidal cells. These are our main components of OMU that we are looking at here in this coronal picture. So let's look at these structures in a little bit of detail get into the habit of using your crosshair or cursor and using all these three planes trying to align the structure to the other two planes using this crosshair it makes life so much more simple. This is the unsonate process as we see it we are very used to seeing it on the coronal scan and look at it on the sagittal image this is the unsonate process attaching anteriorly to the lacrimal bone going posteriorly with a free margin posteriorly inferiorly we have seen it attaches to the inferior terminate and superior has a variable attachment and we shall see that later. This is the bulla ethmoidalis the larger cell here in the anterior model group this is the bulla ethmoidalis on the sagittal image learn to start looking at sagittal images when I was a resident we used to be looking at only axial and coronal scans but sagittal plane is the new kid on the block and tells us a lot about these drainage pathways so this is your bulla ethmoidalis this is the unsonate process in between lies the hiatus semilionaris this here is the hiatus semilionaris between the unsonate and the bulla. So what can encroach the maxillary in fundibulum and result in this obstructive sinusitis we can have a large bulla which can obstruct this in fundibulum we can have these cells the anti-ethmoidal cells which go into the floor of the orbit what are these called? Hala cells perfect so these when large can obstruct the infundibulum by definition these are cells which lie lateral to the lamina papyracea so lateral to this medial wall of the orbit are the Hala cells they can be various unsonate variations which can encroach onto the infundibulum for example a hooked unsonate which could just turn like this or a pneumatized unsonate here. Atelectatic unsonate, unsonate reaching very close to the middle wall of the orbit can result in obstructive sinusitis in addition this will also make orbit very prone to injury during our endoscopic procedure so it's good for a surgeon to know beforehand it is associated with silent sinus syndrome we'll also see that in a while. What else can encroach upon the ostumatal unit we can have this deviated septum with a large spur which can block it we can have these concabuloza and the lamella conca not involving the bulbous part of the turbinate usually physiologically does not have a physiological impact generally or we could have a paradoxical curvature of turbinate we are all very familiar with these variations which we deane and day out on our PNS scans certain variations that we may need to be aware of this is one of them this is accessory osteum posterior to the OMU and when present can result in recurrent sinusitis so the surgeon needs to go ahead and combine the two osteo to prevent this recurrence so we need to look at this and report this if there's maxillary sinusitis in for orbital nerve canal runs in the superior wall of the maxillary sinus or the inferior wall of the orbit and this at times can be de-heizened into the maxillary sinus maxillary sinus may have a septum within the septum may go on and be attached to this in for orbital nerve and hence traction on the septum could injure the nerve if the surgeon is trying to remove that septum so all these variations are worth reporting in our scans lamina papyracea as we see in the middle wall of the orbit here should be running in the plane of the maxillary osteum if it is more medial that means it'll be more prone to injury when the endoscorpist when the surgeon goes in and puts his endoscopy to remove the ethmoidal inflammation the lamina papyracea may then be more prone to injury lamina papyracea may also have certain defects which are normal normally seen in about 10% of the population smaller defects are very very common they could be something like this where we have fat protruding in but they become more significant as we grow more posteriorly because now the fat between the medial rectus and the middle wall of the orbit is now much lesser and hence the chances of orbital injury now increase as the defect is lying more posterior so it's not only the size of the defect but also the position of this defect so let's quickly delineate these main components again this is your maxillary osteum this one in fundibulum this is the height of semilionary this is our unsinnet process this is the bulla ethmoidalis and this is our middle mirror