 So, good morning everybody. So, I will be taking up the topic of skin flaps and crinotomies in skull based approaches. And I must say this is one of the very basic aspects of neurosurgery and for the residents in training. But I must say that this is one thing which actually makes the sense and your surgical outcomes depends upon many times your surgical positioning as well as the way you function the crinotomy. The basic principles of any crinotomy it should provide the adequate surgical exposure and there should be the minimum brain retraction, minimum damage to the surrounding neurovascular structures. And the most important thing is the base of the flap should be wider so that to preserve its vascularity and the preservation of the neurovascular bundles of the scalp so that the nerve splice there they should not be any anesthesia or that the minimum anesthesia should be there in the scalp following the crinotomies made. So, you must know the basic landmarks of the skull because this is important to function a particular crinotomy in the patient. So, these are the nasions then there are the bregma then there is the lambda here that is the lambda suture meeting in the midline and then there is the ion and then there is the asterion this is the union of parietal temporal and the occipital bones and it is the junction of transosinus and the sigmoid sinus and then there is the tereon tereon there is a four bones here and you know that frontal and this is reaching the this is greater wing of the spinoid and the temporal. So, the Taylor-Horton line this is very important thing this is my personal feeling that you all must draw the Taylor-Horton line once you are making the making the any supratentorial crinotomy. So, the how it is done that so mark the anion this is the nasion and this is the anion and this is the hemi circle that is the from nasion to anion and divide into the four parts the first 25 percent then 50 percent then 75 percent and then this is 100 percent. So, these are four things you have to make. So, now the another point is that the lateral aspect of the orbit supra-lateral part of the orbit another point then the midpoint of the zygoma zygomatic arch. So, these are the points you should always mark in these patients. So, now the thing is that connect the supra-lateral part of the orbit to the 75 percent of the line joining the nasion to the anion another point from the midpoint of the zygomatic arch to the round 2 inches behind the coronal suture or that 2 centimeter behind the 50 percent mark of this line joining the nasion to anion. So, now this is the line drawn and this is the line drawn. So, now it bisects at this point. So, from this that is the supra-lateral aspect of the orbit till where it is joined the vertical line this is the silvian fissure in the normal person. And then if we extend this line joining the this vertical line joining from this horizontal line from here till here this is the central sulcus. So, this is the important. So, now you know that anything anterior to that is frontal lobe then pridal lobe below this line this is a temporal lobe. So, for example, what happens is that you have a very small tumor in the temporal lobe for example. So, once you draw the temporal these Taylor-Horton lines. So, you know that your temporal lobe is likely to be below this line. So, your crinotomy is not like likely to be the fashion to a very big way. So, that it is a small crinotomy Taylor to that particular tumor only. Another thing is that you can make out then the imaging especially in MRI in the sagittal view that what is the location of the tumor in relation to the coronal suture and to the motor step you can always try to make it out. And then you replicate those things on the patient's skull. For example, the tumor lies in the parietal lobe. So, you draw these tumors on the patient's skull first draw the lines then draw the tumor there and so that then you function your that crinotomy accordingly. So, that it is smaller Taylor to that particular lesion and it is to the point. So, that it is direct. So, if you are not sometimes doing is you are either too far away from that particular lesion or the lesion is at one of the edge or you are may be totally missing the lesion sometimes. So, this is important. So, neurovascular spire of the scalp is you know that there is the supratochlear nerve then the suprorbital nerve, zygomatic temporal nerve, oregulotemporal nerve, lesser occipital nerve then the greater occipital nerve. Similarly, the vessels are the supratochlear artery then the suprorbital artery, zygomatic temporal artery, then superficial temporal artery, posterior oregulatory and the occipital artery. So, there is a lot of anastomosis among these vessels the scalp is highly anastomosed and the highly vascular structure. So, the avascular necrosis of scalp is practically a very rarely we see, but I must say that if we are not careful by fashioning the flaps. So, avascular necrosis can happen sometimes. So, be careful and second thing is always keep in view these nerves fly of the scalp and try to minimally incise these vessels. So, that the post-operative anesthesia of the scalp should not be there and many of the patients they are debilitated due to their anesthesia. They keep on coming and complaining that they have got anesthesia of the scalp and they cannot feel anything. As I told that the location of the lesion you must plan before the incision is made taking into consideration the Taylor-Horton lines. Position of the important structures like so these are the important structures this is the sagittal sinus, this is the transverse sinus, this is the sigmoid sinuses. So, again try to mark these structures because many of these complication arises if we are not careful. If we are crossing the midline and if we are doing the retromastoid suboccipital craniotomy. So, if we are not careful we are likely to damage then the consequences are very serious. And another thing is that many times you may need to extend your craniotomy or the extend the flap. So, that the contingency plan for the extension of these flaps must be there. If you are expecting that because pre-operative you may know that this is a lesion that you may have to extend this craniotomy or the flap and this particularly happens especially in head injury patients. So, that you may need to extend your craniotomy. So, the minimum brain retraction should be there for any situation any tumor any vascular structure which you are going to operate. So, the brain retraction should be at the minimum. So, these are the basic thing which you have to keep in mind. Another thing is that the surgical positioning. So, this is also very important aspect of making a craniotomy. So, what is the importance of that? It should provide the direct access to the surgical target. Another thing is that you should minimally retract the brain and the retraction should be facilitated by the gravity. So, make sure that you are positioned the head in such a way that it is the retraction is gravity assisted. Another thing is that ensure that venous return is good and there should not be any pressure on the neck. There should not be undue rotation of the neck which can compress the jugular veins and consequently raised ICP and the interoperative lot of venous oozing and the bleeding may be there. So, make sure the after final positioning always question yourself that is there any a problem with the venous return put hand on the patient's neck see that where the chin is there is it compressing the neck and if your question is coming in the positive then reposition. So, another thing is that always check the airway potency because the airway potency because already the patient is anesthetized and intubated the how to check it always check the airway pressure. Ask the anesthetist is the airway pressure is okay. So, if the airway pressure is a little on higher side again reposition the patient's head. So, that again this problem is going to create the interoperative is reflected interoperatively with the brain swelling and the surgical ergonomics but what is that the positioning should be said that the surgeon is at comfortable position. He should not get tired off during the surgery his hands are rested properly. So, that his heads are dexterity of the hands is maintained the movements are very good. So, that the final position especially in vascular surgeries or the smaller micro vascular situations the hand tremor should be at the minimum. So, this is important to where the hand should be where the hand should be rested and I would give the another particular position of cross approach where the patient is sitting and you are operating in this position. So, again position the patient in such a way position yourself in such a way that you are at a comfortable position and the hand tremors are at the minimum. Surgical positioning may be supine for lot of anterior cranial fossa surgeries or the supracellar surgeries. So, even the middle fossa surgeries we always operate through the supine position. Then it was prone position then sitting position then concord position for the pineal region tumors or the lesions and the park bench position lateral position. So, these all are the positions which we usually undertake during the neuropsychical procedures. So, scalp lab the general principle I have already told you. So, another thing which I would like to add here is the cosmetic effect. So, what is that? So, try not to extend your incisions, bur holes, posters at the end of the surgery where we put the mini plates or the screws on the scalp they should not be over the visible part of the head. So, many times if the bur hole is there on the exposed area of forehead. So, it is gives a very bad cosmetic result because ultimately it is going to sink back or sometime there will be this dural pulsation may be visible through that and the it gives a bad cosmetic results. Your incision should not come to the forehead it again gives a bad cosmetic result right. And another thing is that your craniotomy is especially from the terenol craniotomy or the question mark craniotomy for the temporal region. So, the inferior limb should not come quite down in front of the triggers again it is visible area and it gives a bad cosmetic result. Another thing is that if the flap is a random pattern for example, not particular name flap is there the length of the flap should not be 1.5 times the breadth because if the length is more. So, it is again going to the ischemia of the peripheral part of the flap. So, that make sure your the base is always broader right and integrity of the major blood vessel is maintained wherever you are making a flap make sure the question yourself is the blood supply is maintained and to which particular named blood vessel this flap is actually made because there are 5, 6 major blood vessels spying the scalp. So, always position your flap on these vessels vessels only and what are the fundamentals of the bone flaps again initially I told you the direct access to the target then the for cerebral convexity lesions for example, there is a meningioma or there is a glioma or the cavernoma or there is a AVM. So, that it is directly centered over the lesion. So, for that the Taylor-Horton lines definitely play a major role for the skull base lesion flap made to be at the cranial base. So, that you are directly at the base and you need not to retract the brain too much. The number of bur holes in young patients as fewer bur holes it gives a better cosmetic results and the single bur hole many times in the younger patient is enough. For the elderly patient where you expect that there is going to be the adhesions to the under surface of skull. So, multiple bur holes need to be made. So, that I will individually pick up the different craniotomy is the tyrannol approach. I think this is the one of the most commonly used approach in neurosurgical practice for all the anterior fossa then the supracellar lesions and incision is starting from the midline just behind the hairline and ending just at the level of the zygomatic arch. So, you need not to go to behind. So, I have seen that many of the residents or the patient operated elsewhere the incision starts from the opposite sides go till the coronal suture then comes down. So, this is not enough because if you are operating into the supracellar region there is a small for example anterior communicating artery aneurysm middle cerebral artery aneurysm or most of the lesions in the supracellar you need not to bring your skin flap till behind the coronal suture. So, this hairline and season is enough because now you should understand we are going to the area of a minimally access surgery where we are giving the keyhole approach there the eyebrow incision. So, the bigger scalp flap is not required ultimately if you realize that after giving such a big skin incision making a big craniotomy, but you are utilizing only this part of the retraction. So, then this everything is superfluous right. So, that judicially give incisions and make sure that they are not big enough because large incision more blood loss then the time consuming by opening and closure is more and these are the problems. So, I would like to say that because most of the pictures I have taken from internet they are quite old book pictures, but I will try to modify these things. So, this is the terional craniotomy after making the scalp flap. So, instead of this burhole this is a key burhole is actually made here right. So, this is a terion and have to make the burhole here actually the importance of that this opens up into the interior fossa as well as the middle fossa and at the same point if you point your burr anteriorly and inferiorly you enter into the orbit also. So, from this point you can open the three compartments right. So, one burhole here and then in a younger patient just put your craniotomy then make a craniotomy completely okay. So, you only come here at this level the spheroid ridge usually obstructs you here and that you can easily break up with your osteotome or whatever right. So, this is the craniotomy and then you see that there is usually a spheroid ridge which you can either nibble it off or you can drill it off just like here and then you can give you a redirection here right. So, this is important the frontal craniotomy. So, frontal craniotomy is done for example if you are going to the midline supracellar regions okay then the frontal lobe tumors like frontal glioma maybe a small avium or whatever. So, there are a lot of regions which can rise into the frontal lobe. So, the frontal craniotomy is fashioned now this is a patient's head position is fine and it is not related to the either side and around 10 to 15 degree extension is required if you are going to the basal situation and the neutral if you are going in to operate on to the parenchyma of the brain right. So, the thing is that how to make the incision again the incision is always behind the hairline okay. So, because you need to go to the midline. So, you may need to cross the midline a little bit to the just at the edge of the hairline then bring your incision behind and go till the level of the coronal suture and at the level of you can say that at the level of sylvan feature you can stop you need not to go to the base of the temporal lobe to open if that because you only have to expose the frontal lobe okay. So, then again this one burhole is enough at the level of the terion okay because these four burholes are not required and this burhole under all circumstances ideally should be avoided because this gives a very bad cosmetic risk right then you can combine and the only exception I would say that elderly people where you expect that the dura is likely to be very badly stuck you may fashion a burhole here, but make sure that it is properly repaired at then you can take the burhole covers. So, lot of burhole covers are available in the market and try to cover it up right. So, then you can fashion your frontal craniotomy. So, bifrontal craniotomy is done for the many of the large anterior skull-based lesions okay. So, the bicarbonate season is required and again these two burholes on one on the right side of the terion and the other in the left side the key burholes are made and the two burholes at the either side of the superior sagittal sinus behind the hairline okay just interior to the coronal suture. So, the thing is that what I prefer is that first thing is that make the two burholes here two burholes at this level then you strip off the superior sagittal sinus of the bone here right. So, then make a cut here cut here and then cut here. So, stop here then you make a cut here then stop here here the crystal gala is going to stop you okay and another thing is the point of importance is that this basal cut should be flush with the floor of the anterior cranial fossa okay. Make sure that the foot plate of your craniotomy is touching the base okay. If you are higher up then you may need to retract the frontal lobe quite badly because you need to go to the base. So, make sure that this is at the basal level. So, at last you have to make a cut here then you start lifting up the and this flap and then keep on separating under vision especially the superior sagittal sinus okay and there is likely to be the little venous bleeding here do not get panicky and do not try to coagulate these small beaters from the superior sagittal sinus. So, just put some sericell flow seal and then try to press it for a while and these this venous bleeding is likely to be stopped. If you try to chase with this bleeding with the coagulation and sometimes you can land up injuring the actually the sinus right. So, this is a truss basal craniotomy. So, this is actually done in a single way okay this is a one flap you can make it in the two piece flaps this is the frontal flap then this is the orbital flap okay orbital rims. So, you can make into the in a one way. So, two burr holes on either sides you need not to go to the key burr holes on the anterior one. So, thing is that after separating the superior sagittal sinus make a cut here make a cut here and just lateral to the supra orbital foramina just end your craniotomy at that level and there then with the help of your oscillating saw or with the help of your C1 drill bit of your Midux racks then make a cut into this orbital rim here orbital rim here now the thing is that you need to make the basal cuts. So, now you have to strip off all the pericranium off the bone till the nasion right. So, then you may need to make the cut with the help of your C1 though by making the cut actually you are ultimately entering into the anterior earth model sinuses don't worry there is nothing down here just the anterior air sinuses are there make a deep cut here. Now, you have to strip off the periorbita of the orbital roof then with the help of your retractors just retract this contents of the orbit this orbital this fat down and thus make a smaller cuts with the help of your C1 to the roof of the orbit. So, it is not visible here but the roof of the orbit you have to make a little cuts here. So, this is free except at the few places of the superior orbital this roof of the orbits then you lift it up and you just have to break because once you are lifting it up. So, Christa Gali and the orbital roof they are very weak points then you can easily break up okay. So, now this is the reversed flap this is the one piece flap in the reverse way you see that the one cut was given here with the help of the C1 it is completely that the only thing is that this is part of the Christa Gali may not be cut properly but you can easily break it off. Then here you have already given a cut here you have already given a cut this cut was given from here with the help of the C1 and this is a very very weak point of the orbit and the once you just rotate it it easily gets broken okay. So, now you see that this is the very wide exposure. So, this is the not a big chronotomy but it gives a very wide exposure. So, these these are the packed interior ethyl model cells you are directly at the base of the interior trillion fossa okay. If you want more extension to the going toward the for example planum all that you can exentrate these etymal sinuses and go deeper also okay. So, this is the two piece chronotomy again this frontal orbital chronotomy the one piece was this okay then second piece now you see that after doing that this is such a wide exposure. This is a case of actually the multiple times repaired anterior trillion fossa defect and patient was presenting with the CSF recon recurrent episode the meningitis. So, at multiple points that this patient was repaired endoscopically transcranially but it never settled down. So, then what we did that that exentrated everything and this is the sphenoid sinuses a sphenoid sinus here and there were defects at the planum till the level of the tuberculums early there were the defects. So, that we all repaired after doing this complete exentration. So, you can see that the exposure which you can attain after these chronotomies right. So, then the temporal chronotomy the temporal chronotomy is done for most the middle fossa lesions and the temporal lobe lesions. So, thing is that this is the superior temporal line okay the muscles are attached here. So, these are reverse question mark chronotomy is done and just at the level of anterior to the triggers this should stop okay it should not go down otherwise it will be visible and the risk to the facial nerve is always this if you are too down okay. So, then you have to make the flap in the question mark now the thing is that is the osteoplastic or the free brown flap it is the individual choice but you can make this good exposure by this incision. Now, when to do the reverse question mark the reverse question mark is also important for example your lesion is somewhat here posteriorly. So, if your lesion is for example the lesion is here at this level. So, if you are going to make this question mark you are likely to extend your question mark back and bringing it down now you understand that the length of the flap is more than the base understand. So, you are directly cutting the lesser occipital posterior auricular and the lesser occipital artery here. So, if you are extending the flap back so this area is ischemic okay. So, you have started here gone back here. So, this is only getting supply from the middle superficial temporal artery. So, many times what we have seen that in the many of the resident what they have done the mistake especially in head injuries. So, this is the area which becomes black margins okay. So, never do that for that if the lesion is back or you need to make a bigger cranotomy either you can make a u flap large u flap or the reverse question mark. So, this flap is based on now based on the blood supply from the superficial temporal posterior auricular and the lesser occipital they all spying this flap. So, it is little you just have to stop here you start here in season from there and you just bring it down. So, you are maintaining the integrity of the blood vessels another way of freshening the temporal cranotomy the u flap you can make. So, another point I would like to emphasize here especially for temporal lesion this is the position and this is the lateral flexion of the head okay. So, the head is bent down so that your line of vision towards the temporal base is like that. So, if you are laterally extending your head then your line of vision becomes that this. So, it is easy to go to the base then at this level if it is position like this then it becomes extremely difficult to go to the base. So, for temporal cranotomies make sure because many of the youngsters they make mistake by positioning especially for the temporal lesion okay. They just keep the head at this position fashion the cranotomy then it becomes very difficult to see what is going on okay. It at least spoils your day and the surgical organomics are very bad here. Then the orbitofrontal cranotomies orbitofrontal cranotomies again you can do the it can be fashioned with the help of the t-reonal in season just like that. So, you can start at the just behind the hairline cross behind the hairline and end at the level of just above the zygomatic arch okay. So, then one burhole at the level of this is a t-reon then you can make this burhole in such a way that it opens into the interior clean fossa and then position your perforator in this way that it enters into the orbit also okay. So, you are opening the orbit as well as the interior fossa simultaneously at from the single burhole. So, now with the help of your oscillating saw or with the C1 that you have to make a cut here one single cut then you can bring your crinotomy from here and just to the medial aspect of the superior orbital margin. So, your crinotomy starts from here it goes like this and ends here. Now, you have already made your cut to the orbital rim here your crinotomy is stopped here now with the help of the C1 you need to deepen this cut down till the roof of the orbital roof of the orbit retract the orbital contents down and with the help of the C1 then you make to cut to the roof of the orbit then again you have to break it off okay. So, the only situation here there that you are likely to open up the frontal sinus then you have to deal with the frontal sinus accordingly if you have opened up orbit of zygomatic crinotomy I would say that it is a little complex and complicated things it cannot be taught just like that but I would like to mention the few points. So, the thing is that a crinotomy is this made in the frontal temporal region then the single piece crinotomy of the orbital rim as well as the zygomatic arch till that temporal region okay. So, thing is that first we have to make the temporal crinotomy in the two-piece crinotomy this can be made in the one piece crinotomy can be made but that usually the two-piece is easy you have to make the frontal temporal free bone crinotomy or the even the osteoblatic crinotomy you can make now you have to expose the whole of the rim of the frontal bone okay or front orbital rim then you strip off the soft tissue till this zygoma this is zygoma okay and the zygomatic arch you have to expose another cut is made just anterior to the on the posterior most aspect of the zygomatic arch then another cut is made at the zygoma level okay. So, this is the line of incisions okay. So, this is the orbital rim cut it is in the roof and this is a superior orbital fissure this is an inferior orbital fissure you need not to go so down but this cut is important and this cut can be made by the help of the B1 foot plate of the midas rest just put the B1 plate here and go there and it just stops at this level then you can cut with the help of C1 also. So, another cut on the posterior aspect of the arch at this level okay so these are the cut now it is very flimsically attached to the very roof of the orbit here you can easily break it up okay supraorbital keyhole crinotomy I will be dealing with the salient points it starts from the just start the lateral aspect of the supraorbital foramina so that you are not damaging the this is the supraorbital nerve okay that is important so just remain inside the eyebrow go down to the lateral aspect you can extend this region around a centimeter lateral also and this is enough then you once you have gone gone to the bone deep so thing is that then you have to expose this keyhole here and rest of the crinotomy is just like anything you can make a single crinotomy including the rim of the orbit as a one piece just I have told for the frontal orbital crinotomy and just have to follow that and after that you are exposed orbital contents as well as the frontal dura so that is enough for you so one burhole here if this burhole is not required after that you go to this level make osteotomy here this burhole actually enters into the it should is wrongly marked here it should be here in the frontal anterior glenosa as well as into the orbit make a cut here to cut into orbital rims and the roof this is the crinotomy then break it up you have opened up the orbit as well as the anterior fossa so that is all now another thing is that crinotomy across the sedetal sinus and this is important especially for the tumors of fox okay so for example felsine meningiomas or if you are entering through the inter hemispheric transclosal approaches to the lateral or the third ventricle for that region you may have to fashion your crinotomy across the midline then what needs to be done so then two burholes on either side right one burhole on the either side of the sedetal sinus and then these two burholes are not required just have to make crinotomy here then join these burholes then separate under direct vision from the superior sedetal sinus on both sides and then you complete your cuts and then you can make the crinotomy so again point of thing is that venous bleeding from superior sedetal sinus is always there but do not panic try to control with the gel form and flow seal and it is not difficult to control here so now you see that we have gone across the midline this is the superior sedetal sinus so it gives a very wide exposure okay you are actually going into the exactly in the midline so that exposure becomes wider you can even put your retractors sometimes if required on the this medial fulsine structures also if need arises okay and you can directly access to the ipsilateral ventricle or to the opposite ventricle so what happens that if you are fashioning the crinotomy to the ipsilateral side okay then this bone is actually hanging here so sometime going to the midline may be a problem sometimes so that is a issue so that it gives a wider exposure so retromastoid is suboccipital approach the position I initially I told you that how to position the thing is park bench lateral so these are the position for the patient so thing is that first you have to mark the transit sinus and the sigmoid sinus junction this is the most important thing here so how to mark first you have to mark the inion so put a point there then you need to see where is the zygomatic arch so one finger at the zygomatic arch another to the inion droil line okay droil line here in fact it is not according to the patient's dimension so droil line here and then line joining to inion to the zygomatic arch is actually running along the transit sinus one finger breath behind the master tip is the in fact the sigmoid sinus right now the thing is that how to give an in season so whatever the in season you are giving whether is the lazy ass or situation whether it is more horizontal or little vertical but another thing is that the inferior margin of this limb should be matching to the angle of the mandible it should not be down if you are bringing it to down it is not going to serve purpose okay so this is enough okay and one third above the transit sinus and two third below that okay that is enough so midline suboccipital craniotomy is again the patient is positioned on the three pin mayfield and another thing is that once you position here initially I told you that I always try to put two fingers beneath the chin of the patient so that you know that there is any adequate space there ask the anesthetics if their airway pressure is adequate because you have flex the neck too much so these are the important okay and then the midline in season is given just above the inion to the C2 level that is the lower most aspect then you can make two bar hole just lateral to the midline below the superior local line okay so these are two bar hole then you can connect these two bar hole in the midline and then make a craniotomy ending at the level of the foramen of magnum okay so then your craniotomy is fashioned and you can go ahead with surgical procedures so this is the one of the very I have been technically demanding approach and you should be aware that how to make it this is the sitting position for the patient of the cross approach the patient is completely sitting up okay it creates lot of hemodynamic changes in the patient patient gets hypertension patient is sitting up the all of the blood pooling is there into the patient's lower limb the chances of dbt is also very high in these patients so these are all things you have to keep in position now what are the other problems in these patient apart from the hemodynamic changes and the venous blood pooling in the lower limb another thing is that air embolism is very high in these patient because the patient is sitting up and for then what needs to be done for to prevent that or to detect the air embolism at a early time so one thing is that your central venous line or the subclavian line should be put it should be into the right atrium okay so that is one thing it should be positioned in the right atrium second thing is that this is the flexo metallic tube endotracheal tube so that it does not collapse one means we flex the neck too much in these patients so that is another thing and this tube if you can appreciate this gray color tube is actually the trans esophageal ecocardiography tube okay that is a trans esophageal ecocardiogram this tube is put to the patient's mouth down to the esophagus and the probe and is actually directly positioned behind the heart which is actually monitoring the right atrium and the right ventricle okay so any small bubble of air entering into the right atrium and the right ventricle is actually detected by this ecocardiogram immediately okay so this is the earliest way to detect that the moment it happens you detect it and you have to make appropriate mirrors so initially before the advent of these things what used to happen is that one the patient started developing the hemodynamic changes only then we come to know that something wrong has actually happened so before something wrong goes on we need to detect and take the appropriate actions so if air embolism has happened what to do is that you can aspirate that this air from this CVP line so these are the things then end tidal carbon dioxide monitoring by the anesthetist is again monitoring the following etCO2 indicates that the patient is developing air embolism indirect evidence so these few tools anesthesia management is very important these patients now another thing comes how to position the patient so Mayfield or in this particular case the Sugita head clamp has been used so thing is that this is the Inion and this is the marking of the Tentorium okay Tentorium is always is angled ask the person to stand up just like that the Tentorium is always angled up okay from the Inion you mark the Tentorium before the patient is anesthetized or even the anesthetized patient try to mark the Tentorium seeing the sagittal section of the MRI what is the actual angle of the Tentorium in the sagittal view on that particular patient keep the sagittal picture of the MRI with you then mark point at the level of the Inion then mark the Tentorium in that particular patient and then what you have to do is that bring that line parallel to the ground okay sir that line should be parallel because the surgeon is going to stand back so this line of vision should be directly in relation to the Tentorium if your Tentorium is up so you can understand your line of vision is from below upward and it becomes very poor surgical ergonomic it's very difficult to operate in these patients you will get tired up you may have to retract the patient little bit your microscope is going to obstruct you so everything is not in your favor so make sure your position is very important in these things okay so occipital trans-Tentorial approach that is a Popman's approach for the again the Pineal region tumors so this is the particular this positioning is important here okay so thing is that we are going to approach this legion from the left side okay and the left side is actually now down the patient is in the prone position and head is rotated towards the opposite side and the surgical side is dependent so what is the importance of that this is the midline okay now we are going to make the craniotomy just let you do the sagittal sinus posterior sagittal sinus and this is the craniotomy side and once you open up the Dura what you see that now open up the inter hemispherical fissure your occipital and the parietal lobe is going to fall with the gravity towards you so that you do not need to retract the brain this is the importance of taking the help of gravity so that you have to make sure then you have reached the inter hemispherical fissure go down you will directly encounter the Tentorium just lateral to the Tentorium you need to ensize the Tentorium lateral to the state sinus to reach the superior this quadigerminal system that is all thank you