 Before we go on to understand these patterns, what are the findings in chronic sinusitis? We're all aware of those, but for a quick revision, we could have secretions within the sinuses, which could be hyperdense, as we see here. We could have adjacent bony thickening, adjacent bony sclerosis, which is a marker of chronicity. We could have certain calcifications, which would be peripheral and scattered. Remember, hyperdensity is a sign of benign disease. It basically excludes tumor for us, the other cause of hyperdensity being fungal infection and hemorrhage. There are various patterns, type 1 to type 5, which have been described based on the distribution of disease, based on these dino nasal drainage pathways, and which helps the surgeon in turn to decide on his choice of surgical technique. Pattern 1 is the infundibular pattern. We have seen the infundibulum draining the maxillary sinus and the ethmoid sinuses. So, when the infundibulum is obstructed, the sinuses that are involved are the xylateral maxillary sinus and the anti-ethmoidal group of sinuses. Pattern 2, the osteo-metal unit pattern, which will obstruct all the anti-a group of sinuses. So, we have disease in the anti-a group of cells, including the frontal, the anti-ethmoidals, and the maxillary sinuses. A sub-pattern here would be the frontal-resus pattern, which just obstructs the frontal sinus drainage pathway, and hence disease will be localized to the yylateral frontal sinus. Sphenoethmoidal-resus pattern, which is the type 3 pattern involving the posterior group of sinuses, and now disease will be localized to the sphenoid sinus plus minus posterior-ethmoidal air cells. As we go from type 1 to type 3 pattern, the chances of recurrence after surgery would increase. Also, the surgery becomes more and more complex. It helps us prognosticate in a way. Type 4 is synonasal polyposis, which is diffuse involvement of the sinuses. Usually treated medically, surgery reserved only for refractory cases, very difficult to operate upon. Type 5 is the sporadic pattern, which is a random involvement of often single sinuses. So, this is the infundibular pattern of the disease, where disease involves the maxillary infundibulum, and it is mucosal thickening in the maxillary sinus, the normal infundibulum on the right side. OMU pattern, which involves the entire OMU as a 3D space, and hence obstructs the frontal anti-ethmoidals and the maxillary sinus. The frontal-resus pattern involving the frontal-resus on the left side, right side being normal, and hence disease limited to the left frontal sinus. The spheno-ethmoidal-resus pattern, which involves the posterior group of sinuses, where we see this mucosal thickening involving the sphenoid sinus, blockage of this osteum and recess, seen well on the sagittal, as well as the axial images, sagittal being a little better, easier to evaluate, SCR pattern. And there is this mucoperiosteal thickening, leading to this sclerosis of the bony walls, and hyperdensity within the ipsilateral sphenoid sinus. Sino-nasal polypossess, which is the type 4 pattern, which is, we all, we have seen this very commonly, polyps leading to expansion of the nasal cavity, expansion of the infundibular with some hyperdensity within, and this hyperdensity could also represent allergic fungal sinusitis, very commonly seen in these cases, despite extending superiorly, despite eroding these bones, despite remodeling these structures around it, the polypoidal shape is still maintained in a case of sino-nasal polypossess. Truncation of the middle turbinate, the bulbous portion of the middle turbinate is a clue to the presence of polypossess in a case of chronic rhinocinositis.