 We will start with the far lateral approach, have a look at the ferraman magnum. The ferraman magnum is an oval structure, the occipital condyles are located in the anterior two thirds of the ferraman magnum. The posterior part of the ferraman magnum you see does not have the occipital condyles. The occipital condyles is an oval structure, it is about 21 millimeters long but if you look at the articular surface, the articular surface is facing outwards and downwards. So, it is not a flat articular surface, it is a sloping articular surface which phases downwards and outwards. So, behind the condyle you see there is a fossa that is called as the condyla fossa. This always I will have an emissary vein which enters the sigmoid sinus. So, when you are operating in this region you will get severe venous bleeding in this area because of the condyle of vein. So, you will have to apply bone wax there to stop this bleeding. Now, you look at the hypoglossal canal, you look inside the hypoglossal canal is located in the upper third above the condyle, are you seeing the tip of my pen? This one, this is the hypoglossal ferraman but if you see this is the condyle, so it is above the condyle in the upper third of the condyle. If you measure this distance, this distance is about 7 millimeters. So, if you take the posterior third of the condyle, middle third of the condyle, anterior third of the condyle, divide the long axis of the condyle into three parts. So, you get the hypoglossal canal in the middle third of the condyle. This is the extrachranial end, this is the intracranial end. So, if you look at the angulation of the probe, it is angulating anteriorly, laterally and forwards, is not it? So, the long axis of the hypoglossal canal is anteriorly, forward and laterally. That means, you can drill the posterior third of the condyle without entering the hypoglossal canal. And if you restrict your drilling of the occipital condyle to posterior one third, you do not need to do a fusion procedure. If you drill more than that, you risk the re-stabilization of the craniovertebral junction. Can you see the upper surface of the articular surface of C1? So, this is also sloping, it is sloping medially to meet the occipital condyle. The other part is you look at the transverse process of C1 and the foreman transfer cerium through which the vertebral artery comes out. The peculiarity is that is projecting more laterally than the transverse foreman of the lowest cervical vertebra. So, the vertebral artery which comes out of the C2 foreman has to travel laterally to reach the transverse foreman of C1. After it comes out, you look at the posterior aspect of the condyle, C1 condyle, there is a groove. That groove is for the vertebral artery. And you see a flattening of the C1 arch, here it is thick posteriorly. As it extends more laterally, it flattens. So, that is the sulcus for vertebral artery. So, when you are working on the C1 on either side, as it starts sloping downwards, that is the point where you have to do subperiostial dissection. If you do subperiostial dissection with a periostial elevator, you elevate the vertebral artery without damaging it. So, you should not do cottery dissection there. Once you do the C1 arch exposure, cut the periosteum, do subperiosteum and you can sweep the muscles off and the periosteum without damaging the vertebral artery. Now, to the next point, so, you see the internal end of the hypoglossal canal. Follow it 5 millimeters anteriorly, you see a prominence. Look at the internal end of the hypoglossal canal, follow it anteriorly. What is that prominence? So, that is the jugular tubercle. If you look at the hypoglossal foramine, there are two ways in which this drilling can be extended anteriorly. One is above the hypoglossal foramine. You can start drilling after resecting the posterior third. When you are drilling inside the condyle, you will have cancellous bone. That means it is porous and red. Once you reach the hypoglossal canal, it becomes white. That means you reach cortical bone. So, once you reach cortical bone when you are drilling the condyle, that means you have reached the hypoglossal canal. So, if you drill above it, where do you reach? You reach the jugular tubercle. If you drill below it, where do you reach? You reach the lower end of the clivus. So, supra-hypoglossal drilling will take you to the jugular tubercle. When do you do that? When you want to reach anterior to the brainstem. Infra-hypoglossal drilling is for clival tumors, extradural. So, this is supra-hypoglossal portion. That means above the hypoglossal portion, here if you start drilling anteriorly, you reach the jugular tubercle. Below if you drill, you reach the anterior end of the, anteriorly you reach the lower end of the clivus. So, this is for theoretical understanding. You can drill supra-hypoglossal, intra-hypoglossal, which are transcondylar approaches. Now you look posteriorly, this is the condyle, right? This is the extrachranial end of the hypoglossal canal. What is lateral to that is the jugular ferraman, okay? So, if you follow the occipital condyle bone laterally, what is this portion of the bone called? It belongs to the occipital bone. So, what is this portion of the bone called? The posterior margin of the jugular ferraman. What is that called? It is called as the jugular process. So, you have the jugular tubercle and you have the jugular process. So, instead of doing extensive drilling of the condyle, you can still expose the jugular ferraman. For example, if you are doing a jugular schwannoma or paraganglioma, you can expose the jugular ferraman by drilling the jugular process instead of the condyle, okay? And when you have the upper border of the C 1 transverse process, you see the upper of the transverse process is in line with which bone with the jugular process. So, if you see the transverse process of C 1, when it is articulating with the condyle, the transverse process is in line with the jugular process. So, the muscle stretches from the upper border of the transverse process to the jugular process. So, if you look from behind that muscle covers the internal jugular vein. So, that is a very important landmark for the internal jugular vein when you are operating through a posterior lateral approach. What is that muscle? Rectus capitis lateralis. So, that is the muscle which serves as a marker, it is not a suboccipital triangle. Suboccipital triangle is if you look at it from behind, it is more medial from the tip of the transverse process to the tip of the C2 spinous process are the muscles supereoblique and infereoblique. So, they are lateral to rectus capitis lateralis. So, the medial margin is rectus capitis posterior major that is the suboccipital triangle, I will show you there. So, these are landmarks which I want to show. So, one of the muscle you have to remember is rectus capitis lateralis. Then I will take out the C1 process, this is the jugular foramen. What is lateral to the jugular foramen? So, lateral to the jugular foramen is the styloid process and behind it is the stylo mastoid foramen. So, the seventh cranial now comes there, this is the stylo mastoid foramen. You will see the exit of the seventh cranial now. Another way to locate the seventh cranial now is this is the mastoid process. At the base of the mastoid process you see a groove. What is this groove? Digastic groove. So, you follow the digastic muscle in the dissection you will reach the seventh now. That is one more way of locating the seventh now. There are several ways of locating the seventh now when you approach this through trans mastoid surgery. One of the ways is follow the digastic groove anteriorly, okay. So, this is the anatomy which I wanted you to see and one more anatomy is the distance between the hypoglossal internal end and the jugular tubercle is about 5 to 7 millimeters. And this from the hypoglossal to the jugular foramen is around 1 to 1.5 centimeters, okay. Then the other landmark which you must be aware of this is the lambdoid suture, this is the parietomastoid suture, this is the occipitomastoid suture, okay, occipitomastoid suture. What is this point called as asterion? What does it localize? The inferior border of the junction between the transverse and sigmoid sinus. Another way of locating is draw a line along the zygomatic process posteriorly it leads to the asterion. So, in the basic far lateral approach we have the dissection up to the occipital condyle. We do not dissect and drill the occipital condyle per se. So, you go up to the occipital condyle, it is similar to a tyrannal approach. The more bone you remove up till the occipital condyle you will have a more lateral view towards the brainstem. So, here when you dissect the muscles you get an exposure of the C1 transverse process and the suboccipital triangle. Once you identify the posterior arch of C1 including the sulcus for vertebral artery it is easy to do an identification of the vertebral artery. So, you will never damage the vertebral artery if you follow these basic steps of identifying the C1 arch the thicker portion towards the midline as you go laterally it starts thinning that is where you have to be careful and do subpareostal dissection. And between the transverse process of C1 and C2 you have muscles which attach to the transverse process. So, that muscle is a marker again which goes and attaches in a oblique direction to the tips of the transverse process is a marker again for identification of the vertebral artery between C1, C2, C2, C3, C3, C4. So, when you are in that third deepest layer of the neck musculature the muscles which go oblique to attach to the tip of the transverse process is the marker for vertebral artery. In a far lateral approach you also have a suboccipital craniotomy or craniectomy and posterior half of the C1 arch is also excised. In a clinical case you do not have to recognize all the muscle layers step by step they can be reflected along with the skin flap. But the third layer is the most important layer where you have to recognize the muscles of the suboccipital triangle and the rectus capitis lateralis if your surgery is going to be in that region. Important considerations are relationship of the occipital condyle to foramand magnum which we saw it is in the anterior third it is oblique anterior posteriorly relation of the hypoglossal canal to the condyle relationship to the jugular tubercle the jugular process of the occipital bone the mastoid and the facial canal. I hope all of you are now aware of the anatomical factors in this osteology of far lateral approach. So just for recapitulation 21 millimeters long this is an inferior view and the hypoglossal canal is roughly around 8 millimeters that means roughly a centimeter from the posterior end of the condyle. So one centimeter of the occipital condyle can be safely resected and we dealt with all these points jugular foramand stylo mastoid foramand again these are the things which we dealt with. One more thing if you observe you follow the occipital mastoid suture anteriorly where does it lead? Stylo mastoid foramand you look at it it ends at the stylo mastoid foramand this is the occipital mastoid foramand if you trace it forward it ends at the stylo mastoid foramand. So you have two bony landmarks posteriorly for the facial nerve. One is the digastric groove second one is the occipital mastoid suture. So we have talked about these points internally again if you see the sigmoid sulcus there is a peculiarity what is this? What is the peculiarity? If you follow the sigmoid sinus it has a hook you can see the hook it hooks forward anteriorly and laterally to enter the jugular foramand and the jugular tubercle you saw the jugular tubercle what is the importance of the jugular tubercle which now hooks around it it acts as a trochlea for one nerve. So the nerve which hooks around it is the nerve which arises into the head from the neck the accessory nerve. So the spinal accessory now hooks around the jugular tubercle as a trochlea and then enters the jugular foramand. So these pictures are again from Roton you can palpate below the mastoid tip you can palpate the transverse process of C1. So it is the most easy landmark to feel the transverse process of C1. Transverse process of C1 again serves as a landmark for the accessory nerve. The accessory nerve as it descends behind the jugular vein hooks around the C1 transverse process to supply the what are the muscles supplied by the accessory nerve trapezius. So this C1 transverse process can be felt about 1.5 centimeters below the mastoid tip. So there are three stages in a far lateral approach. One is the muscle stage second one is the extra dural stage where you do the bony drilling expose the vertebral artery do a craniotomy and cervical amyretomy third one is the interdural stage. So you come to the first layer of muscles you have the sternocleidomastoid and the trapezius they form what triangle of the neck posterior triangle of the neck the floor of the posterior triangle of the neck has the second layer of muscles. One is the spleenius capitis muscle and second one is the semi-spinalis capitis muscle. So the floor of the posterior triangle has two muscles superficial layer has two muscles the second layer has two muscles. What is the importance of spleenius capitis it is a marker for the occipital artery. So when bypass is done from the occipital artery to posterior circulation artery the way to isolate the occipital artery is first find the spleenius capitis muscle and then trace the occipital artery to free it. So we talked already about the asterion and it is important spleenius capitis trapezius muscle occipital artery. When you remove the spleenius capitis you start reaching the third layer of muscles. The superficial part of the third layer of muscle is the longissimus capitis muscle. So the occipital artery usually travels between the spleenius capitis and the longissimus capitis. When it arises from the external cavity the artery it ascends up and then turns around the C1 transverse process to reach the scalp posterior scalp. So it is under the deep cervical fascia it may be superficial to the longissimus capitis sometimes it can be found underneath the longissimus capitis. Otherwise when you do not intend to preserve the artery this is a source of bleeding in a retro mastoid approach when you cut the muscle you get cut the artery and they will be bleeding. When you remove the deep cervical fascia you start seeing the third layer of muscles. You see the part of the sub occipital triangle you are seeing the supereoblique muscle. So the third layer is beneath the deep investing cervical fascia. So the longissimus capitis has been removed the superficial layer of third layer is longissimus capitis when you remove it you see the third layer. These arise from the tip of the C1 transverse process. One is the supereoblique muscle second one is the inferior oblique muscle. So you will have the vertebral artery in the depth of the sub occipital triangle. The third one which extends from the C2 spinous process tip to the skull is the rectus capitis posterior major. So you get the sub occipital triangle here with the vertebral venous plexus surrounding the artery and you have muscular branches which come from the vertebral artery which supply these muscles. Again around inferior oblique you have the C2 dorsal ramus which comes and crosses the muscle. So the oblique muscle is the levator scapulae it has several attachments to the cervical transverse processes and this muscle is the mark of a vertebral artery. So if you cut the muscle here between C1 and C2 transverse process you will find the vertebral artery there. Now the supereoblique has been reflected you see the vertebral artery with the venous plexus this is the C2 ramus going posteriorly to the scalp. This is the sulcus arteriosis of the posterior arch vertebral artery surrounded by its venous plexus. When you do a sub periostal dissection here there is no bleeding. So you see further dissection the C2 dorsal ramus ventral ramus vertebral artery the levator scapulae has been removed all the sub occipital muscles have been removed and then you see the rectus capitis lateralis. So the jugular vein lies just in front of it. So in a jugular process trans jugular process approach to the jugular foramen you need to erase this muscle. So you see the C1 laminectomy has been done C1 dorsal ramus C2 dorsal ramus C2 ganglion. So in the C1 C2 joint you have the C2 nerve root which covers it when the occipital condyle is drilled you see this is the cancellous bone and this is the cortical bone. So when you get this cortical bone that shows when you have drilled about 1 centimeter of the occipital condyle you start getting the cortical bone of the hypoglossal canal. So now you can choose to do a suprahypoglossal or an intrahypoglossal approach. So this again the vertebral artery exposure the C1 dorsal ramus when you are doing a C1 C2 fusion the C2 nerve root the ventral ramus is an important landmark and sometimes you may have to section that. So again you see when you open the cortical bone of the hypoglossal canal again you get a venous plexus which is a perivenous hypoglossal plexus this connects the basilar venous plexus to the marginal sinus. So this is after the dura has been opened it enters the dura at that point it is intimately stuck to the vertebral artery like the distal dural ring of the carotid artery this dural ring is stuck to the vertebral artery in addition there are few more structures which are stuck to the dural ring and that includes the C1 nerve root. So the C1 nerve root is stuck to the dural ring along with the first dentate ligament. So you have to cut the first dentate ligament if you have to mobilize the lower brainstem and the upper cervical cord to see ventral to the spinal cord. The idea of doing all these approaches to see ventral to the spinal cord or follow the vertebral artery quite high up. So just above the dural cuff you have the twelfth now crossing the vertebral artery to enter the hypoglossal ferraments and then you have the ninth now this entire thing is the multiple physicals of the twelfth now about 1 to 1.5 centimeter above the dural ring of the vertebral artery. You follow the 11th cranial now it swings around the jugular tubercle and then enters the jugular ferraments and 9th and 10th are above that above the jugular tubercle. So you see the difference in approach here a transcondylar approach has been done here a far lateral approach has been done. The difference in the two is because of the drilling of the condyle you get a much more panoramic view into the area in front of the medulla and the cervical cord whereas here it is little more perpendicular and here it is oblique. So the angle of view in front of the brainstem upper cervical cord and the structures of the posterior fossa CP angle lower CP angle are exposed to much widely when you do a transcondylar approach. We are talking about the rectus capitis lateralis this is the rectus capitis lateralis muscle attached to the tip of the upper surface of the C1 transverse process and the jugular process here is the sigmoid sinus the jugular process covers the posterior margin of the jugular ferraments and the muscle is attached below it. So drilling this bone and cutting this muscle will expose the jugular ferraments and the upper jugular vein completely. So the hypoglossal canal when you drill more than one-third you expose the hypoglossal canal fully laterally you expose the jugular bulk and here inside the condyle above the hypoglossal canal you have the posterior condylar vein again all these veins you have numerous emissary veins in this area. So all of these veins create troublesome bleeding. So this is the complete exposure of the sigmoid sinus jugular bulk jugular vein the rectus capitis muscle has been cut here. So this is a further exposition of the transcondylar approach the twelfth nerve has been exposed this is the eleventh cranial nerve which ascends and goes there these are the ninth and tenth cranial nerves above that you have the seventh cranial nerve and when you do a mastoidectomy and expose the fallopian canal you see the jugular vein and the seventh nerve side by side. So you saw in this skull the stylo mastoid is the lateral neighbor of ferraments is the lateral neighbor of the jugular ferraments. So in this when you do the bone removal of the mastoid and CV junction the condyle you expose the jugular vein and the facial nerve side by side anterior to the jugular vein is the carotid artery, cervical carotid artery. In the axial section you see the internal jugular vein medial to that or the ninth, tenth, eleventh, twelfth cranial nerves which descend in the carotid sheath medial to the vein posteriorly is the rectus capitis muscle the styloid process is here. So the facial nerve and the styloid process is lateral to the vein, medial to the vein or the low cranial nerves and when the parotid gland is removed you see the stylo mastoid ferraments with the seventh cranial nerve. So this is just a case to demonstrate for lateral approach this is an entrogensist you are there when we did this. So it is compressing and distorting the brainstem this patient came with sudden after following respiratory illness sudden quadriperesis which was progressing that is because it is an entrogensist and it got inflamed with this respiratory infection. So it is situated ventral to the brainstem so that is what I was talking about subperiosteal dissection you get the vertebral artery. So you go as far laterally as possible then that gives the for lateral approach. The same thing when you do above you meet with the condylar vein which can cause very brisk bleeding venous bleeding it is not arterial bleeding. The vertebral artery does not go up it takes a turn here and enters the dura. So the bleeding you get above the vertebral artery is from the MSR evanes. So you go up to the occipital condyle the craniotomy or craniotomy goes up to the occipital condyle you can do a for lateral C1 laminatectomy when you identify the vertebral artery and then you see the 11th cranial nerve. The 11th cranial nerve is crossed by the dentate ligaments the second and third dentate ligament whereas the first dentate ligament is in front of the 11th cranial nerve. The lower dentate ligaments are behind the 11th cranial nerve. So you cut the dentate ligaments this allows you to get a ventral view then you see the entrogenous cyst and this is the intradural vertebral artery. The 12th cranial nerve crosses just above the dural ring of the vertebral artery. So the 11th cranial nerve, the 12th cranial nerve and the entrogenous cyst this is the upper cervical cord. The difficult portion is it is stuck to the brainstem ventrally and separating it from the brainstem is a little tedious process. If this is not done if you leave the cyst wall behind it is like an epidermis there will be a recurrence and this is after the cyst excision you see the vertebral artery 12th, 11th this is the brainstem and this is the ventral surface of the brainstem. This is the post of MRI and CT. Thank you.