 Anterior trans-Petrus approach in the central skull base is a very important area. The best thing about the central skull base is that 90% of tumors are benign. Right from meningiomers, pituitary adenomas, to cranioferringiomers, to schwannomas, 90% of them are benign. Practically all of them are very risky here. So they can have an interior which you need anterior-clionoid process with orbital feature and orbital apex. You can have the cavernous sinus and you can have the posterior-clionoid process in the Petrus. This is the area where the Petrus apex process will be used. The lateral part of the central skull base can be more easily taken off by a micro-surgical approach. The anterior ones by the orbital zygomatic anterior-clionoidectomy, the middle ones the trans-cavernous approaches and posterior ones by anterior-petrus approach. But the central ones cannot be done from the middle approach. They can be but it becomes the caudumers and all, they can be done but only the lateral extension. These are best used by the endonasal endoscopic approach. That is the key thing you must remember. This is the area which is very important here. That is the Petrus apex. If you see the Petrus bone, the apical part of it behind the foramenilacinum, this is the area which I am talking about, the Petrus apex and if you see, if you feel the Petrus ridge, that is the Petrus ridge and the anterior surface of it, if you feel an eminence there, that is the Arqueate eminence. That Arqueate eminence is this. This groove which you see, that is the groove for the GSPN. If you see the Meckels cave, that depression there, that is this area. All bone between this is actually a very dead bone. This is a bone, I would not say dead, it is devoid of any cranial nerves or any vessels. It is a bone that if you can remove, you can actually take off a spectrum of lesions very safely with minimum morbidity and mortality. So this is the where I am actually talking about. This is the V3, medial to GSPN, lateral to the Petrus sinus. So this is the modification in which we do some cavernous sinus splitting. So what are the steps? The steps are first, that is the foramenovallae, that is the foramenovallae and that is the foramenovsinus. This is the foramenovsinus. So how do you must identify the middlemen angel artery? So extradurally, you define the durat down, look at the middlemen angel artery, dilate this foramenovsinus, cut the middlemen angel artery. Define this, bring this down, expose the V3 and the V2 as well. That is the usual kawasis triangle that we have. But if you do some lateral wall of the cavernous sinus, if you feel over the V3 and the gasoline ganglion, you actually have a bigger exposure. So what are the steps? Steps is a simple temporal incision, simple temporal incision, but this has to go down the zygoma, typical small question mark incision, even linear incision can do. Next is you have to preserve the facial nerve. So given incision in the fascia, in the line joining, the key burhole and the root of the zygoma. So where this area is, that is the one which you should not peel your skin down. There you actually, just in size your fascia there, let this fascia go along with your skin flap and this actually remains. This can be a part of the osteoplastic flap or you can actually keel a cuff of the muscle to stitch back and take a temporalis fascia. So that is the standard temporal exposure. This temporal exposure can be there, this can be temporal or terional, depending whether you want to tackle a tumor which is more anterior or which is more posterior. More anterior tumor, when I say anterior posterior, it is with the risk to the cavernous sinus. That means it is with relation to the cellar. So with, it is anterior to the one, towards, more towards the anterior clioenote process you are actually doing an obitus diagrammatic osteotomy and whether you are doing, this is an obitus diagrammatic and even if the thing is posterior, the key, this is the side of the key burhole, the temporal or a terional. You can do a standard temporal craniotomy like you always do or a terional craniotomy. Drill this bone down. You can or maybe even leave this region of bone, but better if you do an obitus diagrammatic or a small diagrammatic osteotomy. So then this is something which is nice. When you are doing a diagrammatic osteotomy or an obitus diagrammatic, there is always nature has given us a nice diagrammatic pad of fat. So you do not have to harvest fat from thigh or abdomen. You can actually just dissect the temporalis muscle and you will see that nice pad of fat which is enough to plug your clinoid defect or your anterior peteris defect. The rest of your muscle or your fascia can help. Even you do a sub temporal exposure, drill off all these. No need to drill the temporal base and expose the temporalis muscle because if you drill all this temporal base, there will be a lot of oozing from this muscle. So the inner shell has to remain, go down, take off the lateral of the orbit and that is the superior orbital fissure, frontal duora, temporal duora. Now the anterior clinoid rectum, you may not do in this case, you may just go here. This is the root of the zygoma. Follow the root of the zygoma, just 2 centimeter under it would be the foramen spinalsome. There is no way your foramen spinalsome is, especially in surgery. Just feel the root of the zygoma, 2 centimeter under it will be the foramen spinalsome. Dilate it, coagulate and divide the middle meningeal artery and just anterior to it will be the foramen ovale, anterior to it with the V3. That is the division. Why you must dilate the foramen spinalsome? Because you cannot completely coagulate it, it can actually retract. So then the foramen rotundum. You have V2, V3, this is a very good approach and for a fifth noshonoma which is just a middle fossa tumor, this is a very simple approach that you can straight forwardly do within by an extradural approach. You do not have to open the duora, you just have to do this and actually a fifth noshonoma comes right away. You do not have to even peel off the nerve. Then you find a junction between the meningeal layer and the membranous layer of the lateral wall of the cavernous sinus. Always it will be located the moment the nerve is going into the foramen. You will never locate it here. You will always locate it where you have actually dilated this foramen. Then just strip these, this that is complete cavernous. You do not need that. You need till here for an anterior transpetrus approach. For the sake of dissection, this is the Parkinson's triangle between the fourth and the V1. This is V1, V2, V3 Parkinson's triangle, third, fourth and this is the area of if you are taking out a cavernous hemangioma or taking a giant pituitary adenoma going to the paracellar or even a fungal granuloma, this is a safe approach but you do not need in this. So that is anterior. That is the cavernous ICA, that is the sixth nerve. That is important for a cavernous hemangioma of the cavernous. Now the next step is behind the fifth nerve, you must look for a groove for the GSPN. We will now have found a groove. We will find a dura being stuck there. So never try to peel the dura off. Just give an incision, leave that dura there and actually incise the dura, it is a pretty thick dura. Some part of the dura will be left behind with the nerve and the rest will come back to you. If you try to pull it, you will pull the geniculate diagonal and create a seventh nerve damage. So that is a nice quadrangle of bone which is exposed that you can just drill it away and by this the middle fossa communicates directly with the posterior fossa. This bone is absolutely avascular, especially if you have defined the Michael's cave and the casein ganglia and you are never close to the ICA. I have never drilled, there were initially when I started, I used to drill the glass, this is the glass cox triangle where the Petrus ICA is there, you never have to drill that. Give a derotomy in the middle fossa like you normally do a subtemporal approach. Then open the posterior fossa dura. Between that, there will always be a middle fossa, posterior fossa, that is a superior petrosil sinus which is made. So superior petrosil sinus can be divided 1 centimeter behind the Petrus apex. You will have enough collateral to take care of that but has to be divided immediately just behind the fourth nerve like you saw. Just to revise you have, we stripped it down and exposed the middle meningel artery divided, exposed the kavasis triangle here, make it into a rhomboid, drill this off. This is middle fossa, behind this is the posterior fossa. Take this away and you have the two compartments opened. That is a usual small incision, temporal incision. You can do a zygomatic osteotomy which can be free or even osteoplastic. So now it depends on the resident, he is more happy with osteoplastic, so we will leave it to him. That is a petroclival meningioma in the middle clivus, upper and middle clivus. That is the middle meningel artery being coagulated, peeling over the, that is the fifth nerve. You have to incise at the junction. The simplest where you can peel the cavernous sinus, one is a supereorbital fissure, two is the v3, v2 most difficult. So v3, this is all v3, just keep on stripping, stripping, it is very similar, just comes on its own. We just with some blunt and very intermediately sharp dissection, keep on and that is it, you drill, find the caversus triangle, drill it, drill it. By drilling this in meningioma, you actually de-vascularize the tumor also there. So that is the posterior fossa dura, the middle fossa dura. Tumor is here. That is the sinus, the ICA would be down below. So simple, some temporal deorotomy, that is the temporal base. Make another T there. These actually make the closure slightly difficult but it gives a smaller deorotomy with, it actually creates a big square and then the supereorbital sinus. This is the fourth nerve, divide the supereorbital sinus, so that the tent is here, your posterior fossa dura is here, you are actually dividing the tent, that is the fifth nerve. The moment this opens, right from the third nerve, third, fourth, fifth, sixth, seventh, eighth, all these nerves along with the basilar can be in your vision. De-compress that. Till here, this approach is helpful. After that, it is in pitroclival meningiomas, it is not the approach that guides you. It is the inherent property of the tumor, whether it is stuck to the basilar perforators. Here you have to decide whether you want to leave 5 percent or 10 percent. I am against that thing that why not just plan it as a subtotal excision. You cannot plan. Pitroclival and meningiomas, you can never plan a subtotal excision. It always happens a subtotal excision because if you plan a subtotal excision, you will be actually leaving nearly 70 percent of it because you never know how much you have removed. Same middle meningiol artery coming down, remove the kavases triangle, fourth nerve, how do you cut the tent? Behind the fourth nerve, postrolateral, you cut it, that is the posterior fossa dura and the posterior fossa dura is opened, tentorium is opened and you coagulate and cut the suprapetrosal sinus. With this, your posterior fossa and the middle fossa are together. So, you can actually see the basilar artery here. That is the more important thing. This was distilled. The fourth nerve can be released by around 3 to 4 millimeters. It has a sheath. You can release it by 3 to 4 millimeters, not more than that. Third nerve can be released by 7 to 8 millimeters. There is always a noculomotor trigone. This is a very important step. Especially, even if you are not doing anterior peterous approaches, if you are doing a simple middle medial clientoidal meningioma or maybe a PICOM aneurysm or something or maybe a meningioma or the tentorium edge anterior and you have a third nerve and you want to dissect the tumor off, decompress it, try not to handle the third nerve too much. Find the junction of the third nerve and the tentorium. There is always an oculomotor trigone, which is around 1 centimeter in length, 7 to 8 millimeters. The moment you incise that, you can actually mobilize the third nerve by 5 to 7 millimeters. That's enough to actually dissect the tumor out without handling. The moment you handle the third nerve, third nerve is gone, partial or complete. Third nerve, I have realized is the most sensitive nerve. Every nerve is sensitive, but third nerve is most sensitive. When you damage many of them, you realize that all are sensitive. Then that is the dural sleeve and that is the basilar put the temporary clip here. That is the aneurysm. This was, we don't usually never do basilar aneurysm. This was field embolization at two centers, including our center where they actually tried twice. They didn't want to give up, then they gave up and then we clipped it. Our experience in basilar aneurysm is coming down, but still it's there. And always coagulate, broad neck aneurysms, always coagulate, find a neck, clip it. Never put clips directly because the moment you coagulate, find a neck, your perforators will automatically be separated. This is clip, so we can use this approach in several. You can have dumbbell shape, fifth nerve sonoma. You can take them out with this approach as such. You cannot do it with any single approach, middle fossa or upper stirra fossa. This was the fifth nerve sonoma, I'll just skip. This is the same thing. You can just open this and you can actually take this tumor out. You can have, we've done some Rosseid Hoffman, we've done Petro-Cliable Cordomas. This is the one we never knew endoscopy. So we did an anterior petrus, but for this small residual, we did a usual microscopic transfenoidal. Giant crinopharyngeumas, this has been, we've used this approach. It helps because we realize that these kind of crinopharyngeumas can be easily delivered from other places, where it is stuck is always at the base of the hypothalamus. So it is here that we can use this. And epidermoids, giant epidermoids going everywhere, this actually gives a bigger corridor. So what does these approaches help? I would say skull-base approaches, actually anterior clientoid activity like, and he will be talking about far lateral, all these three approaches, far lateral, anterior petrus, anterior clientoid, these are skull-base approaches. They are not extensive approaches. I would say they are minimally invasive to the brain and to the nerves. Another approach is that everyone should know. You may not be occulting giant aneurysms, but there will be a meningioma that will come across and simply removal of a segment of bone, you may not be doing a great dissection there, but an extra-dual, simple removal will give you a far better results than usually, see. The main idea is that it can vexitize a conical exposure, like you saw the cylinder of a pyramid actually became the base of a pyramid. It automatically can vexitize. Suppose that aneurysm, if you replace it by a meningioma, you actually de-vascularize the whole meningioma there. Along with that, this I feel is more important for minimally invasive brain protection and venous protection. I am very, very careful about venous protection, because I feel that in all these skull-base approaches, if you damage a major vein, your patient will have a bad time, wider angle of approach. So, for the most important thing, I think has been, so if you have to know the neural anatomy, that is most important, the pyramid, the tissue handling, you have to understand the neurovascular structures. There are two steps that specially doing in microsurgical skills.