 Looking at the frontal sinus drainage pathway as I said, sagittal plane is a very very good plane to delineate the frontal and the sphenoth model recess drainage patterns and we shall see this as we go along. This is the parasagital image showing us the level of the frontal, this is the frontal beak and nasal process of the maxilla forming the frontal beak and this is where is the level of the frontal recess. Above a frontal ostium, so above this is the frontal sinus, at the level of beak is the frontal ostium and below it is the frontal sinus drainage pathway and anterior to the frontal sinus drainage pathway is your agarnasi cell and posteriorly lie the bulla and the supra bulla cells. On the coronal scan this is our frontal sinus drainage pathway, this location on the coronal scan would be determined by what is the insinate process attachment. So the insinate has different superior attachments, this one here is going up and attaching both to the skull base and the middle wall of the orbit and the FSDP then lies medial to this insinate process. So this insinate process is a sabersheet bone, anterior attachment to the lacrimal bone posterior free margin. This is your bulla ethmoidalis and this is the hiatus semilunaris, this is the insinate on the coronal scan attaching inferiorly to the inferior turbinate going superiorly attaching to the medial wall of the orbit and the FSDP lies medial to this insinate attachment. This is type one attachment of the insinate process resulting in this formation of this blind recess called the recesses terminalis. The other types of attachments are type two and three although they have been classified differently some have classified into type six types as well but these are the main kinds and this is type two attachment to the skull base and type three attachment to the middle turbinate. In these two cases now the FSDP lies lateral to the insinate and drains into the infundibulum. There are chances of cross infection between ethmoidal cells and the frontal sinuses now increase. Here the FSDP was lying medial to it and draining directly into the middle meatus. Now here it drains into the ethmoidal infundibulum. So looking at our CT examples this is our insinate traveling up attaching to the skull base, FSDP lying lateral to it and this one here has a combination of attachment both through the skull base and the middle wall of the orbit and this one is to the middle turbinate. Frontal sinus drainage pathway is surrounded by a lot of cells called the frontal ethmoidal cells which alter the path and are very critical for the surgeon to know because as it is frontal sinus surgery is a challenging procedure because the endoscopist requires a very angulated approach to reach there. So the presence of these cells which further alter the path are critical for the surgeon to know before he goes in. So this is the agar nasi cell which is anterior to the frontal sinus drainage path frontal recess and this is the anterior most anterior model air cell. Behind it is your FSDP and behind the FSDP the frontal sinus drainage pathway let me call it FSDP from now making it simpler. So this lies the bullar and the suprabullar cells. Agar nasi also is very closely related to the nasal lacrimal duct and hence remember that infections can cross from one to another here as well. So these frontal ethmoidal cells which surround it have been classified by various authors and we are very used to following the modified cones classification till a long time back and we still continue to do that in many institutions. That's perfectly fine. What I'm going to talk about is the International Frontal Sinus Anatomy Classification which was proposed by Wormold at all in 2016 and they claim that this gives us a more precise aiming of cells. The nomenclature is more precise based on the relationship with the FSDP. They have been classified into anterior posterior and medial cells and it is proposed that they will allow easier communication between surgeons and radiologists hence a better planning of surgery. So anterior cells which lie anterior to the FSDP. So these would include the agar nasi and the supra agar cells. The supra agar cell and the supra agar frontal cell. These will push the drainage pathway medially, posteriorly or posterior medially. So let's see how they look like. Again use your 3D platform. This is the agar nasi cell. This is how we see it on all the three planes and the cursor would align it on all the three planes for us making our job much simpler. The satchel image now will show us the cell superior to it much better. So this is the agar nasi and this will now be the supra agar cell lying above the agar nasi but not extending into the frontal sinus. This is the supra agar frontal cell which is further up extending into the frontal sinus that means above the level of the frontal beak because the frontal sinus lies above the level of the frontal beak. Cells which are posterior to the FSDP are the bulla and the suprabular cells. So we have the suprabular cell, suprabular frontal cell and supra orbital cells. Since they lie posterior to the FSDP now this pathway will be pushed anteriorly by these posterior cells. So this is our bulla etymodalis on the coronal and the sagittal scan. This is a parasage image and above this is your suprabular cell. Even above this is your suprabular frontal cell. All these cells are not present in all individuals. They will have variable prevalence rates. So don't expect to see all of them together in one patient. We may have a few in one and some other cells in another patient. So this is your suprabular frontal cell which reaches the skull base which is one of the boundary of the cell and projecting anteriorly into the frontal sinus. A little more posteriorly than the level of the bulla supra orbital etymoidal cells which lie at the level of the anterior etymoidal artery which is seen as a tiny notch in the medial wall of the orbit. So it is at this level that you try and localize and look for your supra orbital etymoidal cells which form the posterior boundary of the frontal sinus. Medial cells include the frontal septal cell and this will push the drainage pathway laterally. So it is in the midline here frontal septal cell. It can compress the FSDP laterally. What else can obstruct a frontal sinus drainage pathway? We could have this. What is this? Aherated crystal galli which can also obstruct the osteum if very large. So we have talked about the anterior etymoidal artery. A couple of words more on this vessel. This is a vessel which is a branch of the ophthalmic artery coming from the orbit, runs through this canal, the anterior etymoidal artery canal, seen as a notch in the medial wall of the orbit, goes all the way across and pierces this lateral lamilla of the cribriform plate to enter the olfactory fossa. So this is your crystal galli and this is the cribriform plate, the medial lamilla up till the vertical attachment of the middle terminate and the lateral lamilla here which is the vertical part beyond the attachment of the middle terminate. So that's how this artery runs and sometimes it may be hanging in a misentry. It may hang further down, especially in the presence of supra orbital etymoidal cells and this can catch the surgeon unawares and if injured can lead to profuse hemorrhage. So it will be good for the surgeon to know whether the anterior etymoidal artery is low lying or hanging in a misentry. The posterior sinus group includes the posterior etymoidal cells and the sphenoid sinus. What delineates the anterior etymoidal cells from the posterior etymoidal cells is the basal lamilla. Now what is basal lamilla? This is the middle terminate. It has 3 attachments from anterior to posterior. So anteriorly it goes up and attaches vertically to the cribriform plate. Slightly more posteriorly it has an oblique attachment to the middle wall of the orbit and this is what is called the basal lamilla and this is the posterior horizontal attachment to the palatine process of the maxilla. So this basal lamilla is what delineates the posterior cells from the posterior cells. Again 3D platform and we can trace this basal lamilla on all the 3 planes. This is the basal lamilla. This is the middle terminate going up attaching here and anteriorly are the anterior cells. Posteriorly are the posterior cells. Posterior cells are by far fewer in number and larger in size. This is showing the same thing again. This is your basal lamilla and these are the ethmoidal cells and the sphenoid sinus. What are onodic cells? Now posterior ethmoidal sinus is pneumatized before the pneumatization of the sphenoid sinus occurs. So they have a tendency to go into the sphenoid bone and lie above the level of the sphenoid sinus above and lateral to the sphenoid sinus. So these cells are then called onodic cells. On the coronal image what gives us a clue to the presence of these onodic cells is this horizontal septation. So horizontal septation points out that yes there could be onodic cells here. Why so? Because now I am cutting through here like this and this septum will form this margin onodic cell lying above this. A cruciform septation points towards bilateral onodic cells. Sphenoid sinus drains via the sphenoid sphenoid ostium through the sphenoid model recess and then into the superior meiasis and so is the case with the austere model cells which drain separately into the superior meiasis. Sphenoid has a few critical relationships that we must all be aware of. Superior allies the optic nerve canal. Laterally here lies the internal carotid artery. Infero laterally lies the foramenrotundum and infero media realize the bideon canal. Now all these foramina carry critical neurovascular structures and these could be deheysant into the sinus which we need to really point out in our reports. Here is an example of a septum which is going and attaching to this optic nerve canal. So again traction here could injure this. So remember to mention this in your report when you see especially if the patient is to be taken up for sphenoid sinus surgery. Sometimes this bone could be very very thin making it at risk. Pneumatization of the anterior clenoid process as we see here on the left side results in the formation of what is called the carotid recess. So between the optic nerve canal and the carotid we have this narrow tunnel which is the optic carotid recess. So this surgeon has to remove disease from here. These structures would be at greater risk of injury and remember to mention that. A rarer defect is the lateral cranioferential wall which is a defect in the lateral wall of the sphenoid sinus. It is a bony defect between the basis sphenoid and the greater wing of the sphenoid resulting in this defect which is medial to the forearm and rotundum. This was a case of spontaneous CSF rhinorrhea and this defect is known to have an association with spontaneous CSF rhinorrhea. So here we could see some soft tissue here and the corresponding MR images show us beautifully well the N-cafelloseal through this defect which is called the lateral cranioferential wall. So since we have gone through this anatomy and we are all very familiar with the axial and coronal images let us I will here show you a video of the sagittal sequences and try and identify all our structures.