So this presentation will be the second part of the principles or an introduction to intercranial surgery. And in this particular talk, we will cover some of the basic surgical approaches as well as some of the post operative management that's required in in these patients. So the craniectomy, various procedures have been described, there's modified transfrontal or also there there's a transfrontal approach that's used to access the .

Forebrain and the particularly the prefrontal and frontal lobes, there's a rostratorial craniectomy, which gives us access to the majority of the cerebral hemispheres. And then there's the suboccipital approach that allows us to approach the brain stem and cerebellum. Eventual approach to the caudal brain stem has been described, but this is very rarely used and so this won't be covered.

So again, the three basic approaches that we are going to discuss are the trans funnel approach, the rostro tentorial approach, and the cao tentorial approach or suboccipital, and again, giving us access to various portions of the brain. These approaches and in many instances are combined in order to maximise the exposure that we need to . Reach the pathology that that is of interest.

So the trans frontal approach was described the original. Type of transronal approach by Doctor Glass and this consisted of a diamond shaped incision or removal of, of bone. Over the cribiform plate and the prefrontal and frontal lobes, used to access meningiomas in the prefrontal and frontal lobes fairly frequently as these are common locations for.

Tumours. The transfrontal approach is again very useful as it is relatively straightforward and provides pretty good access to the prefrontal and frontal lobes. A dorsal incision is made basically between the eyes, the media canhi, the eyes to the level of the ragma and sharp dissections used to expose the bone as you can see in this picture.

And the the subcutaneous tissues in the frontalis muscles are removed. And then a dry sponge is actually pretty helpful to remove some of the additional tissue and at that point. A sagittal saw or an oscillating saw is used to perform cuts of the bone.

Generally this is done at about a 30 degree angle and again notice that the gelpie retractors are used to . Provide adequate exposure. And then the finished craniectomy, trans frontal would show this is the inside of the frontal sinus and the curviform plate would be present below.

So again that this diagram demonstrates you know what it would look like as far as the standard prefrontal approach and and different types of incisions that we can use to access this area. Doctor Sturges recently described a modified transal approach that can be very beneficial in some dogs depending on the size of the or the shape of their skull. And so as you can see from this particular image, this actually is a, provides a much larger exposure of the prefrontal and frontal lobes and allows for, better access to to those lesions.

So again, the modified trans frontal approach is, is particularly useful in large breed dogs with prefrontal and frontal lesions, it gives you both increased visibility in those areas, and it also allows for a very cosmetic closure. It involves removing additional bone over the frontal sinus, as well as elevating some of the rostral portion of the temporal muscles. With the modified transfrontal approach, one of the important landmarks of the lateral osteotomy is the orbital ligament, which again is demonstrated here, in this, in this diagram.

We're looking for the point of the fusion of the inner and outer tables of the frontal bone, in order to identify, you know, where our cuts are made and I'll show a diagram of that. And then another important point of this particular procedure is that we need to remove that mid sagittal bony septum in order to preserve the the flap of bone. Otherwise, the bone will split and it's much more difficult to replace.

So as you can see this is this dog had a modified transronal approach and we can see this is the curb of form plate here. And you can see the frontal sinus in this region and then the nasal bones turbinates. And then this is the same dog really immediately after surgery and notice that it's very cosmetic as far as replacement of that bone flap.

Remember though that it case selection is really important unfortunately for the brachycephalic breeds, it's very difficult to perform this procedure because of the angle required to remove the bone and so in these particular patients, you're probably gonna need to use more of the the. Traditional transronal approach in order to avoid any type of damage to the to the brain perkima. So this is an example of a midline incision to orient you the patient's eyes would be here and here, occipital occipital protuberance would be here, and we've made a fairly liberal incision.

And the diagram that I, I use, generally the rough guideline for removal of the or I should say drilling the bone flap is what you notice here in this slide. First, we begin by removing the, the temporal muscles. So this, this is the temporal muscle on the dog's right side and then the same on the, the left side, and we've exposed all of this bone.

We'll go down to the level of the orbital ligament again which is right here. And it's just an a guideline as to how lateral to make this. And then an oscillating saw is used to make our actual cuts.

I find it particularly useful to draw those lines prior to making those cuts and then I also will use a burr to make burr holes and then connect those burr holes. I find that that's probably the easiest way to make sure that we're actually in the sinus and not. In an area where we would cause a problem such as the orbit.

So again notice that this oscillating saw is is placed at a 30 degree angle, which would help to facilitate replacement of that bone. So again, that lateral osteotomy is, is extended past the attachment of the orbital ligament. Again, if you feel like it's necessary to get exposure, that ligament attaching to the zygomatic process, the frontal bone, and again it's said that there's a point of fusion that that you can see in some patients of the inner and the outer tables of the frontal bone.

So the most important cut is the cut that we make here dorsally on the very dorsal aspect of the skull. This is the bone that attaches to the to the frontal sinus and so to orient you the eyes are here and here this particular cut needs to be a relatively . Shallow angle in order to facilitate the a proper cut.

I'll demonstrate that. And so again, notice when we remove this mid sagittal septum, that angle of the osteotome is again is a much more flat than the other angles of the the bone of the cuts that we made in the other aspects of this flap, and the reason for that is because we're removing both the. Inner table of the the bone in the frontal sinus as well as the .

Bony septum which can can really be quite thick in some of the large breed dogs. So again this angle is is very important. So here is an example of an inoperative patient.

Or case where we're using the sausage home. And you'll notice we really want to. Follow that angle.

And continue to remove that septum. If you don't remove the septum, this will tend to split. Right along the midline.

So here we removed the septum. And we've exposed the inner contents of the. Skull I should say that.

Sinus. So again another example of the angle that's used to make this cut. And again removal of that bone flap.

So the bone flap then would be kept in in a moist saline in order to replace it at the end of the surgery. So now we have the inner table of. The curbiform plate is located here, and so at this point we'll begin drilling and, removing the inner table or the curbiform plate to expose the brain tissue.

So you noticed here that we're just suctioning or removing excess blood and tissue in order to. Expose that curve before plate. And when just to give you a sense for what this is gonna look like this is an example of a post operative CT that demonstrates.

That transfrontal approach and some removal of that inner inner bone. It's helpful to drill. Remember that when we drill, the curbiform plate is really can be very uneven.

It's actually very thin. And so when, when drilling, don't place a lot of pressure and it's easy to go through the curbiform plate rather quickly. And so at that point, I tend to use Keras and run jus to continue the craniectomy.

Do your best to avoid lacerating that dura. Sometimes it's attached to the bone. But once the, your craniectomy is, is performed, then the neurotomy is done and the tumour tissue is, is identified.

So this is an example of drilling that cur reform plate. You'll notice that it's really just cortical bone for the most part. There's really no cantus bone to identify and it's, it's really quite thin.

And then I'm not gonna worry too much about making the entire craniectomy with that bu my goal is to really get into the. Through that bone and then to allow me to, to increase the size of the craniotomy with Rogers. So again notice we're drilling and sometimes there's some bleeding in those blood vessels.

And then notice now I'm using a love garrison to extend that. Cranniectomy and notice the underlying dura. Here And I'm trying to preserve that dura prior to doing the neurotomy so that I can protect the brain as much as possible during the craniotomy.

And any bleeding, particularly from the bone is best controlled with bone wax. And it's important to have as much exposure and visualisation as possible. So here we're we're removing that inner table again that that I should say the inner table has been removed in this particular dog, the tumour was on this lateral aspect.

And again we're we're just cleaning up the edges of this this before the terotomy. And as you can see that that love garrison is a really useful tool for this type of work. And then we've performed our derotomy which was unfortunately done by the love garrison and you'll notice that here we're using a lens loop.

To help remove some of the tissue. Unfortunately it's sometimes it's very difficult to visualise. I apologise for the quality of this film.

So notice those are abnormal pieces of tissues that are removed. I can't stress enough the most important piece of tissue that you take is that first piece in order for histopath because you, you don't always get a chance to remove much more tissue or it's removed via suction and you can't. You, you really need that to identify the, the lesion.

So again you'll notice that using a lens loop to probe this resection cavity. And slow general blunt dissection is used to remove that that tumour tissue. And the goal there would be then to create a what we call a resection cavity.

And so in this particular dog again I've used fluoresce stain and so you'll notice that that particular tumour is a little bit more yellow. Than it would be normally. So again taking those samples and then you'll notice in this still picture there's section cavities forming and we have tumour tissue that's that's been.

Probed And here I'm using the lens loop and I'm actually gonna go along the fox because the fox can help you with a landmark as far as knowing the extent that medial extent of the tumour and the fox will feel very smooth. As you run the the probe along it and helps you to identify again. The margins of your tumour.

So again adequate suction is is really important. And unfortunately you do have to be somewhat aggressive in order to remove this, this tumour. The nice thing about this particular part of the brain is that it's a very low morbidity when it comes to manipulation.

So you know that tissue again is removed. So following surgery, really adequate. Lavage is, is really important and you know the resection cavity is here and there's some haemorrhage, but it's not severe.

Following that, I'm gonna make sure I really place a lot of gel foam, in order to form a hematoma over that craniectomy or I'm sorry, the, the defect that we created from the tumour removal. And this is to help prevent a complication and I'll show you in just a minute. The other goal of this picture is to show replacement of the skull flap and so the skull flap is replaced with using non-absorbable sutures such as nylon and placed in in multiple locations.

And you'll notice that here we've replaced that skull flap and it's really it creates a fairly cosmetic appearance. So we've gone from This, to here where you notice the multiple sutures and that we can then tie in place and have a very secure fit. And so after surgery you'll notice that it's a, it's a very cosmetic again closure.

So in some patients where the modified trans frontal approach is not practical for anatomic reasons, I do what I call a freeform type hole in the sinus and as long as you maintain the ridges of the bone, then the the frontal bone, it's, it's still gonna be a very cosmetic closure the one difference is that there's no bone to protect the, the sinus and also there may be some movement from air. Initially, while the as the patient recovers. So as I mentioned, I really try to place gel foam over the the opening of that .

Defect that's created by removing that tumour and the reason for that is because one of the complications that can be fairly significant is the development of tension pneumocephalus and this occurs from the the recess here of the lateral ventricle and any contact with that can potentially allow air from the sinus to enter the ventricular system. And this is what an MRI of that particular type of patient would look like and so you'll notice that we have this hypo attenuating . Material which air in this particular case in the lateral ventricle and this tends to follow the ventricular system.

Now it's in the fourth ventricle and you even see some in the AO space here and with that come signs related to compression of of those particular structures. So this dog developed worsening of seizures and then vestibular signs and tetraparesis. And correction of that particular problem is basically to go back in and and pack that area again with more gel foam.

Sometimes it can be hard to find the exact opening of of that defect the air itself really doesn't need to be addressed. It will resolve in a in a few days once the area is sealed. So now we're gonna move to the rostrotentorial craniotomy, which is a fairly common procedure.

This is a CT that demonstrates, a midline mass that is in all likelihood of meningioma originating from the Fox cerebral. We see the, the postoperative resection of the mass. And then you can see a CT reconstruction that demonstrates that's a fairly large defect that in this particular case was not was not .

Covered. So various roster tentorial approaches are gonna be used depending on the location of the pathology. This is a patient who had a .

A more lateral lesion. This is a patient that had a more frontal type lesion that we didn't actually have to have access to the, the frontal sinus. Raster tentorial approach is generally gonna be a dorsal midline or or curve linear type approach again at the site of the pathology it's important to identify that superficial musculature that interscutallas muscle, well we want to excise that and then expose the underlying temporal fascia.

And so here you can see that temporal fascia, which should be fairly evident in most patients. And then once we are at that temporal fascia, you notice that we're making a sharp incision. I use a 15 blade typically and I'm preserving about 3 millimetres of the tissue medially and that allows you to suture it once you're finished with your exposure or your surgery.

So again, we've it's we've incised that temporal fascia and then we use a freer to sharply dissect the underlying temporal muscle. Both the freer or periosteal elevator work well or and then, . A dry sponge, dry gauze is also very useful to remove additional muscle tissue.

So with the roster tentorial approach again it's gonna be very dependent on location but typically as as shown in this diagram burr holes are made at the extent of . The craniectomy and then generally they're gonna be connected with a smaller type of burr hole. So again notice in this dog, this is a very similar location we're creating burr holes.

Those are typically just press cuts, so you're pressed straight down and you'll notice that as you go through that bone, the dura, you'll notice that you have a loss of bone and the dura is very tough. So as long as you're not pushing too hard, you'll, you'll stop at that, that level. Remember that the bone dorsally is a lot thicker than the bone laterally and so, you know, count for that when drilling.

So here I've created this a burr hole and then moving along in the surgery, we, what we've done is we've created that . We're beginning to create a flap, again connecting it with smaller burrs. And here you'll notice again we're we're creating those burr holes notice that's just a press cut.

And we'll probe and see if we can feel that dura. And see there I noticed that I'm through the dura so pretty much finished with that and you'll notice now we're using a smaller burrer that's about a 2 millimetre burr. And connecting those.

Burholes. And then once the burr holes are we've connected those or and and again because the undulations of the skull, you can also use kerosins in order to remove that. And now what we've done is we've, we're removing that flap of bone, it basically created a hinge there eventuallyr, and are able to remove that flap all basically in one piece and you can replace that if, if you feel it's necessary or you, you don't have to replace that.

So again notice here we've what we've done is we've created a a hinge so I haven't drilled all the way through this bone here, just enough to allow the bone to move and then you can use a lever for your elevator works well and again we've removed the flap to expose the dura. So I also in some patients will not create a specific square or a flap in some patients it's actually easier to just use a round juror both lampards and Harrison ranjus in order to expose, you know, the underlying pathology. This is a cat meningioma and, and again, this particular case it was easier to just use onjus to remove that tissue.

So once we have the area of interest exposed, it's important to again have an idea of what. Problems you may encounter and again the middle meningeal artery is the biggest one when going after a lateralized lesion such as this mass in the puriform lobe. And again you may need to cauterise that especially if you're going ventrally.

So The other part of of this type of surgery to to keep in mind is that you'll notice here we've, we've created this flap and you notice that we really don't see any evidence of a mass and that's because both intra. Or I should say extradural masses and intramedullary or intrapranal masses are on the inside of the dura. So you're really not gonna find your lesion until you've done a neurotomy in the vast majority of your patients.

So once that, that craniectomy has been finished, that's the time to incise the dura. So this is an example of a feline meningioma and a fairly common type of tumour that we might approach. I noticed on this particular CT we have the characteristic changes that you'd see with a feline meningioma.

We have some hyperostosis or thickening of the bone. We have some mineralization of the mass itself. And then at the time of the surgery, this is the typical meningioma appearance of the meningioma in a cat.

So the last area last type of approach that we make is the infratentorial approach, and this gives you access to the cerebellum, the caudal aspect of the medulla, and the caudal aspect of the 4th ventricle. So here you'll notice that . We have a mass in the 4th ventricle that we can access through a suboccipital approach.

It also should be noted you can reach or you can approach the cranial dorsal aspect of the cervical cord at this level as well. So again this is an example of a mass that would be very accessible through a suboccipital approach. I'll be the most common reason for this approach at this point in time would be the frame and magnum decompression for caudal occipital malformations.

So again, just some examples of where an in tutorial approach may be helpful. This is a dog with a meningioma impacting the cerebellum. And this is an interoperative photo of or video I should say of removal of a mass from within the 4th ventricle and here we're actually retracting the the cerebellum.

Dorsally and this. This probe is actually located within the 4th venture. That allows very nice access to that region.

So patient positioning with this particular surgery is really important. It is gonna be somewhat dependent on the location of the lesion, but it's important to understand that in most cases, fairly significant flexion of the neck is necessary. And so for that reason, we need to consider that when they're placing our endotracheal tube.

So here you'll notice this patient is, is flexed and this really opens that, that caudal or the, you know, the caudal aspect of the skull. It makes the surgery much more accessible. So this is a patient that had some dynamic images for another problem, but you'll notice that this is in a neutral position.

You notice how little space there is. And then when we flex the patient, how much room is created and how much space it gives you to, to work and facilitates that, that surgery. So again, a guarded tube is essential.

We don't want something like this as you noticed that would include the airway and cause a lot of other problems related to surgery. So again, the guarded tube is essential in this particular case. And to discuss a little bit more the frame and magnum decompression, this is a procedure again that's that's fairly common based on the popularity of certain breeds, .

Probably the Cavalier King Charles the spaniel is gonna be the most common dog, but there are certainly other breeds that we treat. I think prior to any type of surgery, it's important to discuss prognosis and expectations with the owner. These are patients I really try to manage medically, but if, if that fails, I, I do offer surgery.

It's really important to note that the eccentric syrinx, as seen in this particular slide is one that's gonna have probably a more guarded prognosis with regard to scratching. And that that patient there on the right is a patient who had an eccentric syrinx and, and continued to scratch post surgery even though pain was, was controlled, . After surgery.

So the approach to this particular region is really the dorsal midline incision in most cases and the dog's head in this case may be a neutral or or ventroflex, . And the goal is to remove the. Occipital bone in this particular region there on the midline to expose the vermis and then we remove 60 or 70% of the dorsal arch of C1 depending on the the pathology.

It is important though to bear in mind that some of these patients don't have complete ossification of their skull. And so why this is important is because you have to be really careful when probing that area, you may not actually have bone under and that's not something you would see with an MRI. So, yeah, particularly in the Maltese and the Chihuahua, those are patients that you may want to consider a CT prior to surgery.

And the approach is made. I, I like to identify both the occiput as kind of the midline marker and then the, the spinus process of C2 and I try to find the arch of C1, with a freer and then bluntly dissect from there. And so in this particular image, the bones of the skull and the C1 have been exposed.

I will make burr holes in both the occiput and occipital bone and then the archer C1. Remember that the bone of, of the occipital portion of the skull can be pretty thin and so don't, you don't want to press too hard or or be too aggressive with burning. And then I tend to connect the two openings with Keri and Roger.

And so you try to remove as much bone as possible prior to actually accessing the the dura we excise the lao occipital ligament with a number 12 blade in this particular instance, and this is a nerve root retractor that's used to lift that up. You can also use a number 11 blade as well. And this is an example of using a gross hook and spoon to lift the actual fibrous tissue that Atlanta occipital ligament which is really pretty tough in these dogs and you'll notice that vermi.

The tip of the vermmi is here. And we have that 4th ventricle evident right in this location. So again, once that's been excised, I will try to remove the peel tissue and make sure that all of that tissue has been exposed and that we've tried to, to restore normal flow of fluid through that region.

And so once it's finished, you should see something like this where the tissue is pulsating and you'll notice also that in these dogs, many of these have very significant amounts of cerebellar herniation and result in compression of that, that caudal aspect of the cerebellum. So cranioplasty, why, why would someone consider cranioplasty or placing a . A protection, protective cover over this defect, and, and I think that, what I have seen is that some of these dogs will develop so much fibrosis and it's generally from the overlying muscle that they actually recreate that compression or sometimes it's worse.

So this is a preoperative image. In a dog that that did quite well with the frame and magnum decompression for 3 months and then at 3 months we imaged it and it after it started having more signs and you'll notice that that same problem was recreated by this fibrous tissue. And so the goal of cranioplasty, which has been described by Doctor Dewey is To, limit that fibrosis that occurs with the muscle overlying the, the cerebellum.

And so either using a titanium mesh and, and acrylic or just acrylic, you can basically recreate the back of the skull but with a larger amount of space. And here is an example of of using 1.5 millimetre or I'm sorry 2 millimetre screws using titanium allows you to then image in the future.

And. This is then incorporated into the, the methacrylate. So here we have the frame and magnum decompression you'll notice the tip of the vermic here.

This is SIS or bioactive dressing that is intended to try to reduce fibrosis and here we've placed screws in the. The latter aspects of the skull and their dorsally. And then.

We'll place methacrylate over that. So again this is a diagram from Doctor Dewey's article that that shows kind of the outline for those screw placement. And generally there's gonna be about a 220 screw.

In order to protect the cerebellum and and to create a barrier once the SIS is placed, then I place a few layers of gel foam, or an absorbable gelatin type sponge, and that creates both space and does provide some protection from the the potential thermal injury as the methacrylate cures. And so finally once the gel foam is placed, you'll notice that we are placing the methacrylate. And allowing it shaping it so that it's covering that that defect.

It's important that the methacrylate, so we see here in the skull reconstruction, from the CT that the methacrylate is not placed too low. We don't want that methacrylate to come in contact with the arch of C1 where that can lead to pain. And so again you'll notice that here is an example of a.

Of a reconstruction done a postoperative CT. Another method as again that I mentioned is the use of a titanium mesh which certainly is is a viable method for. Recreating that, that region of bone, the main reason I don't use it is cost.

That titanium mesh tends to be expensive and it's not an area where we're as worried about the integrity of the bone and we're really just trying to keep that area from developing scar tissue. So after surgery, so we've removed our tumour and we have our section cavity and we closed the defect, . Management, just a few words about management.

Generally these patients are gonna respond very well to, you know, a balanced anaesthesia and recover quietly. There are times so when you, depending on the part of the brain that you work with where they'll have some dysphoria and, and we need to talk about that. Some of the drugs that we can use for that postoperative dysphoria would include, a very low dose of aromazine, fentanyl, or, dexomator, sometimes a combination of the.

Of the drugs. The most important complication. Well, they're, they're all important complications, but the one of the more common complications is development of aspiration pneumonia.

And so for that reason, we want to be very aware of the patient's position, when we feed the patient relative to it's level of arousal and it's, body position. Brain herniation can occur from continued swelling, and we wanna be able to recognise that. Anaemia can be a problem from excessive bleeding that would require transfusions.

And then intractable seizures are, are a possible complication that you should be aware of how, what options you have for treatment of that problem. So in summary, we've discussed all of the indications for surgery. We've also discussed the diagnostic considerations and ways we manage these patients with anaesthesia.

And then how we prep these patients. The instruments that we use and then the, the basic approaches we use for these patients, as well as a little bit of aftercare, considerations. This talk really isn't meant to be all inclusive of all of these procedures, but an overview of some of the more important points that that I consider when, when doing these types of surgery.

Thank you for your attention.