 So, we come to the posterior part from the middle skull base, the interior petrus approach. This is the area which I will be focusing on. What do you see the red dots there? Can you see the anterior clientoids? Just behind that the posterior clientoid and then there is a petrus bone. Just put your finger on the petrus bone and follow it from anterior to posterior and then first posterior to anterior. You always feel an ineminence at the junction of the anterior two-third and the posterior one-third, that one. That is the aqua-teminence. Then under and lateral to the aqua-teminence would be all semi-circular canals, cochlea, labyrinth and everything. This bone constitutes the posterior or medial and the posterior lateral triangles. This is then divided by a line that is a groove. You can see the form in lacerum, the form in ovale and then the form in spinosum. Just behind the form in spinosum is a groove which goes towards the aqua-teminence. That is the form in ovale. And then the form in spinosum, can you see that? And then the form in lacerum. Beautiful. Can I see? Then the form in spinosum is just that there is a groove going towards the aqua-teminence and that groove is the groove of the GSPN. That is the GSPN. So now you have two bones, two parts, the posterior medial and the posterior lateral. Lateral to the GSPN and medial to the GSPN. Lateral to the GSPN is the glascox triangle. This is form in ovale. This is form in spinosum. And if you trace this form in spinosum back, you will feel a groove there. You can see that groove going towards the aqua-teminence in this one. That is the groove. It is going towards the aqua-teminence. This is the aqua-teminence. This is the important part of the bone that we will be dealing with today. Something in front of the form in lacerum is important and I think behind this aqua-teminence is something we cannot drill into. This is the bone that we can drill into. But only the one which is medial to the, we cannot drill it here. We cannot drill here. This is ICA form in lacerum V1, V2, V3 and that is the GSPN. Under this, this is the glascox triangle. Under this will be the ICA, the petrus part and the eustachian tube. No drilling here. This is one part of the bone that you can drill. That is known as the kawasis triangle on the rhomboid. Then this is the thing that is the V1 going into form in spear orbital fissure, form in rotundum, form in ovale and this is what we will be focusing on. These are my teachers, these microscopic teachers. He is my endoscopic teacher and this is the area of interest. The triangle, the kawasis triangle which is bounded by the V3 here, by the petrus ridge, by the aquitaminins and the GSPN. You can see them all here. This ridge is the petrus ridge. That is the aquitaminins. That is formin spinosum, tracing it back is the GSPN and the line joining the formin ovale till the meccal scape. This, the projection over the lacerum, you can put your finger there, there is a depression there is the meccal scape. Just behind the formin lacerum. The line joining the formin ovale to this meccal scape is the V3 and the gasoline ganglion. This is the V3 and the gasoline ganglion. Like my probe is sitting there. So whatever bone is there between this area is the petrus apex. That bone can be drilled and that is known as kawasis triangle. There is some modification which we have done along with my cover is mobilization, done some cadaver dissections and done some volumetric analysis, then conventional and then kawasis and then modified kawasis. We have seen that a modified rhomboid is a better exposure than the classical triangle that is given. So I will just come to the steps, I will just briefly state the steps here. The first step is sectioning of the middle menangeal artery. So you have to expose the formin spinosum, see the middle menangeal artery, section the middle menangeal artery there, peel the lateral wall of the cavernous sinus down, peeling it down, dissect your dura over the GSPN. The GSPN is always enveloped into a dural fold. That has to be dissected, bring it back. Then opening the temporal dura, we will revise the steps. You can also do an anterior clienterectomy if it is required so that if your legion is petrocliocavernous legion or a joint trajamel schwannoma along with the superior orbital fissure involvement, then the part of the medialization of the V3 and opening of the posterior fossa. Now I will go very step by step, the basics. You have done a standard, the incision is usually a small Falkner's incision, a small question mark incision over a superior temporal crest which you are all familiar with. You can do auto-menaciation for this approach. After that is made, this is a free bone flap. You can also make an osteoplastic. Leave a cuff over the temporal crest, cuff of musculocotinus. Take the myocotinus and the muscle and the temporal fissure in one flap. Before that, preservation of the facial nerve is important. How to preserve the facial nerve? The line joining the keybar hole, that is the root of the frontal process of the zygomatic bone and the zygomatic process. The imaginary line joining, that is where you should cut your temporal fissure and go subfascial or below the fat, it will be somewhere here. The line joining this area of the keybar hole and this area, you take the, go into the, it can be subfascial or into the fat and that has to go along with the skin. The moment that goes, the facial nerve is preserved. Then you lift the muscles and the facial flap. You can do a zygomatic or an obit or zygomatic osteotomy. In these cases, a zygomatic osteotomy is good enough. Zygomatic osteotomy is simple. You make one cut here and you make another cut like this. So, two straight cuts and your bone is out and that you can fix it later. So, this is obit or zygomatic. Then a standard temporal craniotomy, lesion is big, you can do a trionnal craniotomy. For a trionnal craniotomy of obit or zygomatic, just a temporal craniotomy. How do you decide? If your lesion is a pitrot-level meningioma, temporal craniotomy. If your lesion is a pheano-cavernous meningioma, then both a trionnal craniotomy. Then obit is zygomatic or a zygomatic osteotomy. If a zygomatic osteotomy is simple, now we have a cartoon again. One barhol is here, simple. Another one, this is your extent of flap, a small temporal craniotomy. You can make it smaller because this is just for depiction. This much is also enough. You can drill this bone down. This really helps. The moment you take this part of down, you are actually under the temporal dural. You see the difference, you are actually under the difference. So, you have to track, you are actually going down. This is something which we found that once you do a zygomatic osteotomy, there is always some zygomatic pad of fat. And you just dissect your muscle back and you will find, you can actually deliver with your list, a good chunk of fat that you can place it there to provide an CSF leak. So, you do not need any thigh or umbilicus opening. Then you reduce the sphenoid wing there, bring it down. Then the V2 exposure, this is V2, V1, this is the recliner process. Take off the dura back. This is what we are doing here. Look at the middle meningiol artery and the formant spinosome. Always dilate the formant spinosome. Never try to divide the middle meningiol artery without dilating the formant spinosome. Otherwise, the MMA will retract and you will have a lot of bleeding. If you have a big extradural hematoma in your head injury patient with a swirl sign and the bleeding does not stop, just take your base down and you will coagulate it at the formant spinosome. Then the formant rotundum, find the V2. Then the formant ovale, V3. So, we are at the moment here. Then strip the dura, the membranous layer from the meningiol layer, which some blunt and a lot of sharp dissection as V3, the simplest over the V3, toughest over the V2, then V1. This is fourth nerve and that is the third nerve. This lateral water is the cavernous sinus. This is the Parkinson's triangle. That is the spirovital fissure. That is the anterior, that is the cavernous exposure. Yeah. I think this is important. Then we are over the GSPN with some sharp dissection. You must leave the GSPN back over the bone, take the dura up. That blue is of the ICA, nothing glass coax triangle, that is the ICA and here you see the difference. That is the Petrus apex and that is the gasoline ganglion. This bone has to be drilled, arcoitaminase, GSPN, Petrus ridge and that is the gasoline ganglion. Then after some dural opening, before that you can mobilize this mandibular nerve and gasoline ganglion. You can go down and reach to the apex here. See, you actually get rhombus. Here I have just exposed the ICA. Then a simple temporal dural opening and a posterior fissure dural opening and that is the Petrus ridge. That is the superepetrusal sinus, which you divide or coagulate. It is actually a sub-temporal approach with the extra dural modification where you are opening the petrusal dural also. That is the fourth nerve. Dural must be cut behind the fourth nerve. There is a normal tentorial opening that you do, the PCA and you see the whole thing is opened up. Just to revise once again, reduction of the sphenoid ridge, lateral wall of the cavernous sinus and middle meningel artery is being divided. This is the usual kawasis triangle. If you do not do a major cavernous mobilization, this is the GSPN. That is the aquiteminence and that is the Meckles cave with some dural reflection over V3 and V2. But if you mobilize all this and take off your gasoline ganglion back, you actually, this was difficult because the exposure was conical and you are very close to the ICA and the semi-circuit clowns and the cochlea and the internal artery canal. But you see the difference. The moment you mobilize this, you actually convert this triangle into actually a squarish quadrilateral. Simple supine with head turned to 60 degrees small. You can reduce your incision to as small as this. Temporal craniotomy and as agomatic osteotomy which can be, we use always osteoplastic. That's good for healing of our patients. Pitruclavul meningioma. In this, the lateral limitation is the internal artery canal. If your tumor is going beyond that, you have to combine an extended temporal along with the retrosigmoid approach and only a retrosigmoid would be difficult if you are taking care of this part of the lesion. That is actually a tentorial meningioma. Firmins spinosum is dilated, middle meningiol artery is cut, then the V3. Then the section over the V3, that part has already been done. That's the GSPN. As you proceed over more videos, we will see the dissection meta. Then the kawase triangle is, the rhombus is being drilled. One, this thing is done, then temporal ura is opened, the tentorium is being cut. One of the earlier cases, this was a very vascular meningioma. So the supine-petrosil sinus is opened, this is the posterior fossa already being opened. Initially I used to put these ligar clips, now its coagulation is better. The rest is the same. The tumor is already vascularized after this exposure and you can actually dissect it. The good thing about this exposure is, the sixth nerve cannot be seen by a standard sub-temporal approach and the problem is the metal scave entry of the fifth nerve in a retrosigmoid approach. These tumors can be removed and these nerves can be seen under vision. The most important for immobility and mortality of these patients, contributory factor is the basilar perforators, which you cannot see from a standard retrosigmoid approach, there where the patient actually does not wake up. Here these are much more visible, that is the fifth nerve. That is another pituitary clavus meningioma, standard upper clavus extension. So middle meningiol artery for a mincepinosum, peeling of the dura. So how do you open the dura? You open on the base, the temporal derotomy, a T-shape incision right till the petrus ridge, that is the, so normally how you open a temporal derotomy. This is the tentorium, then the superior petrosis sinus, cut the tentorium behind the fourth nerve, the tentorium is cut, the posterior fursadura is cut, coagulate the superior petrosis sinus, that is the fifth nerve. A lot of tumor is already de-vascularized, decompress and dissect, that is the brainstem. These are the perforators, this is, it is very important and this approach helps you to actually dissect them off, but here you have to be really, pay respect to these perforators. If you cannot remove them and they are adherent, please do not try to coagulate them because that is the cause of your patient not waking up. I usually do not do basilar analysis, this was, unless they are field embolizations, so this was one of them, and with this approach may be another four of them, not more than that. They are good for low basilar, complex low basilar analysis, so same formants, pinosum, V2, V3, kavasesh triangle is drilled, that is the posterior fursadura, that is the temporal derotomy, that is the superior petrosis sinus. So you have opened the two, that is the tentorium, that is the fourth nerve, cut in a posterior lateral manner, so we had this, that is the posterior fursadura, that is the middle fursadura, that is the tentorium. So this is the superior petrosis sinus, that is coagulated and divided. The aneurysm would be somewhere here, this approach will help us to get the proximal control over the basilar, that is the fourth nerve, fourth nerve you can immobilize for nearly 2 millimeters, not more than that under the tentorium, that is the third nerve. This is something nice that there is an oculomotor trigon which is nearly 8 millimeters in size, this is a cisternal cavern over the third nerve, that if you divide you can mobilize your third nerve even in your interdural approaches by at least 5 to 8 millimeters and then the two leaves of the tentorium can mobilize, that is the basilar. So a temporary clip on the basilar artery and this is a complex basilar aneurysm incorporating the two PCA's, here you want proximal control plus you have to see the two PCA's in case there is a rupture. We hardly do posterior circulation now, maybe once in a year coagulate and reconstruct, see the opposite PCA, that is the temporary clip and the opposite third nerve. An endovascular basilar doing good job of posterior circulation, even if they do not damage the patient we cannot say anything to them, the literature supports them, well. We have done this approach with lot of other like prosaid of men, histiocytosis, petroclival, chondrosarcomas, well this was more lateral. This was the time and I did not have any endoscopic knowledge of skull base so this was removed through the anterior petrious approach but this portion was left which we did by my microscopic transfenoidal later. Then we have these huge clenifaryngeumas going through the posterior fossa that we do, another one going into the, to form a magnum. Then giant epidermoids, this approach helps in, because such epidermoids cannot be removed by single approach, this can help by the single approach. So what is the main aim of these skull base approaches which we will be listening is to just convexitize the deep lesion, to make it closer to you, devascularize a meningeal based lesion. It's an extra plus an intradural approach, our main aim is minimally is invasiveness to the brain and I believe that all these approaches there's a lot of venous protection that you have to be taking care of, especially in the extended temporal and this area. Extradural approach is very good if you are talking about the vein of labia protection, wider angle of approach and proximal control of basilar artery especially in some cases. This approach actually helps you to access the meckles cave, more visualization of the sixth nerve. The advantage is that there is no injury to cochlea or semi-circle kernels or the ICA, that was the major drawback was why people didn't want to go for kavases approach, but and the GSPN should be dissected, should not be cut. The only thing is that you need some practice, a lot of cadaver based practice over the cavernous sinus lateral wall. So you can take care of a spectrum of lesions, thank you.