That's great. Thank you very much, Debbie. Really, really nice intro to all the different imaging modalities you can use in the head.
It's amazing how much I suppose CT and MRI has potentially changed a lot of things. Do you think that We know enough about what's normal versus abnormal? Do you think there's a lot and kind of a bit of a way to go regarding how we can actually interpret these images?
I think, yeah, I think there's always a learning curve whenever you're starting to use something to try and diagnose a particular group of diseases, and there's always more that we we learn. I think, there's some fairly nice work on what's normal, and, you know, those sort of, those, that, that textbook that I mentioned is, is really nice. It's got, very nicely in the sort of the normal horse, so you can work out what's going on.
And, and obviously, it's, enabled us, to know that some little compartments like the nasal bully, you know. I actually appreciate that actually in clinical cases, those structures are really important, whereas before we might have thought they were just an interesting little finding on, on, you know, anatomical dissection and cross sectioning of a horse's head. But yeah, I think over the next few years we'll, we'll see an increasing amount of, yeah, sort of information coming out as, as different centres, you know, and, and thinking outside the box, you know, there's always slightly different ways you can do.
So I think over the next, next 5 years, I think we'll, we'll see a big increase in that. Yeah, well, and then I suppose it costs, got a little question regarding cost as well coming up, but, do you think as, as more centres, you know, actually have more CT scanners, do you think costs will come down? Because we've got a question that does the extra cost of the CT, for example, does it actually justify its use.
So, you know, I in general practise, you know, so with insured cases, you're, you know, you're often thinking, well, let's just do it, they're insured, they can afford it. But when it actually comes to somebody that Maybe it's not insured, but considering more expensive imaging modalities, does, does the benefit of the extra information that we're getting from these images actually justify its cost, or does it really, I suppose it does benefit from case to case, but. Yeah, I think that's a really good question and that's where again your clinical examination.
You know, does sort of, you have to start thinking, well, you know, sort of cost benefit, you know, with a quick endoscopic examination of the horse's larynx, for example, show us that little pony's got a tumour, likely tumour that's going on in its larynx, that doesn't need a CT scan to diagnose that. But I think perhaps more telling, is that we rarely take, radiographs, the standard views of the head in the hospital anymore. And investigating horses with sinus and dental disease, where we think, you know, there might be something like a perioical infection involved, or even just the sinusitis cases, we would tend to jump straight into CT, partly because by the time you've added in the costs of, you're taking your, your, your images, and certainly within the hospital environment, it's actually as cost effective to get a CT scan as it is to run through all those.
Other modalities. So I think it depends what your costs are, what you can do in the field, but certainly if you think there's something more complex going on in the head or you think there's something going on with a tooth that, you know, isn't really straightforward and obvious, you know, I think the, the benefits of the CT are absolutely huge, and it's something that's Alison's talk will show it's very easy to, to perform. Yeah.
And do you think then with the advancements of these imaging modalities, we're gonna be developing new treatment techniques or or better techniques. So I suppose dental, it's kind of beyond the scope of this talk, but regarding dental disorders, rather than just reporting teeth and do you think endodontics and stuff, do you think that's gonna be a benefit as well overall? Yeah, and I think I think it it is already, and I know Justine will go through, through that, just in, trying to work out, you know, particularly if you've got teeth that have erupted abnormally and you've got something a little bit more bizarre going on there, it can give you a real heads up as to whether, you know, orally extracting a tooth is going to be a little bit more tricky.
The, you know, the nature of, how the tooth is, formed, so yeah, absolutely, and, and I know Justine's going to run through that in a bit more detail. Brilliant. That's great.
Well, thanks again, Debbie, really, really good talk, really nice, introduction. So now, we'll move on to our next speaker, who is, Alison Talbot. So Alison graduated from the University of Edinburgh in 1999 and worked in equine practise where she, gained her our CVS certificate in equine practise.
She then completed a residency in equine imaging at Bristol University where she obtained her, our CVS certificate in equine orthopaedics. She then worked back in equine practise, but then she was appointed as a clinical teacher in equine orthopaedics at the equine Hospital in Liverpool in 2009 and subsequently as senior lecturer. A diplomat of the American College of Veterinary Sports Medicine and rehabilitation and has clinical interests in all aspects of equine sports medicine and imaging, and she's currently the academic lead for the for the CT service at the university's equine Hospital, which has the only medical grade moving gantry CT system in the UK, which I'm assuming she'll explain what that means, in her talk.
So over to you, Alison. Good morning. Thank you very much, Sophia.
Thank you for that and, and good morning to everyone who's joined us, this early on, on a Sunday morning. So thank you, Debbie for that great tour overview of imaging of the equine head and that moves us on to a more depth view of computer tomography of the equine head. And I'm gonna talk for the next hour regarding.
Disorders that are not related directly to the dental structures. The dental structures are, are gonna be covered in much more detail in, in the following our lecture. So, I think it's safe to say that computed tomography has really revolutionised the workup of head disorders in, in the horse in, in recent years and it's really quite exciting for, for those.
Of us using the technology to be able to visualise this, these disorders in much more detail and to really understand both the anatomy and the pathophysiology that that goes hand in hand with our clinical findings. Computed tomography is a cross-sectional imaging and therefore it allows much more detailed anatomical reconstructions of the patient that you could ever see with radiography, which only provides you with 2D images of a 3D structure. And the digital advances in in both hardware and software of equipment have really allowed this technology to, to take off in, in recent years.
So what we're going to do during this lecture is briefly review the history of equine head CT. And the principles of image acquisition and reconstruction. And I think it's important to review these, these findings, not so much in that many of you will, will not be involved in actually taking these images or even reading them, but in order to understand how, just how far we've come as a as a veterinary profession and how these technologies evolved.
And then I want to present some examples of these conditions that you may find CT of the head useful for. And I appreciate that we are extremely lucky in the situation that we're in to have the equipment available to us, but understanding the use of the equipment and And the conditions that we may be able to, appreciate more clearly with CT I think is an invaluable, lesson for all of us within, any sphere of equine practise that understanding the information. Out of papers from CT is important in diagnosing these clinically and then to be able to diagnose more things clinically, potentially thinking about a referral option for, for CT is also useful.
It just as in any walk of life in our, our, our vein we work, we also need to think a bit about the limitations of CT for imaging of the equine head. So it is a great leap forward and it's a great advancement of our capabilities, but there are limitations and certainly it's not an encompass all technique, even with the equipment that we have available nowadays. So computer tomography was initially known as computed actual tomography and it was first introduced into medicine in the in the 1970s.
The methods of image reconstruction had actually been known in theory for, for many decades prior to this, but it was only with the advancement of the capabilities in computer hardware and software and the digital computer that allowed this theoretical branch of abstract mathematics to be refined and improved sufficiently to give us the images that we're accustomed to today. Early CT scanners used a single X-ray source and a single detector, which gave a single slice at a time through the patient's anatomy. In just the actual scan, hence computed actual tomography and was the name of this technique at the time.
And a single detective and made the image acquisition really lengthy, so scans of 10 to 20 minutes at a time, which was great for certain parts of the anatomy that stayed particularly still, such as the, the limb. You can get a patient to sit there with his head or its limb still, but for looking at the thorax and abdomen or anywhere that was prone to respiratory artefacts, this was still a huge problem. Over the last 20 to 30 years, and the addition of the banks of detectors that had a very rapid glow time and memory were introduced, and these were able to then measure data simultaneously from different slices within the body.
And this significantly reduced the scan time from a number of minutes down to just a few seconds in certain parts of the body. Something called the slippering technology was also then introduced, which instead of the machine having to rotate once and then go back to the start and rotate again and go back to the start. This then allowed for continuous data acquisition with the radiography and equipment, .
Sending through the X-rays to the detector on a continuous basis throughout a 360 degree rotation without having to go back to the start again without wires getting in the way. So this, this slip wing technology really did advance the actual. Hardware capability of the machine involves.
This allowed the advent of the multi slice and CT scanner, allowing us to see a number of slices and a number of sicknesses of the patient within literally a few seconds of acquisition time. So for those of you who are not used to using CT I think this diagram is particularly useful. The circular donut type shape equipment that we see houses essentially a high output X-ray X-ray tube, which then is used to create X-rays in multi slices through the patient, which are detected on the opposite side of the patient as the the gantry rotates.
And this happens extremely quickly that will get multiple revolutions per second and therefore multiple slices per second that are are taken of the patient lying within the . Within the country of the the CT equipment. For human patients, this is all particularly easy.
They lie on a table and are told to lie still until the scan has finished. But for equine patients, it has required a little bit of ingenuity in, in developing the equipment is necessary to get a diagnostic scan. So that the equine CT was really just a theoretical process until a revolutionary system was developed by Alastair Nelson at Rainbow Equine Clinic.
So CT could be performed in our equine patients, but they always required general anaesthesia to be performed for this to happen prior to Alistair's invention. And the late Alistair Nelson worked at Rainbow equine clinic as. As Debbie said in her first lecture and developed a play an air driven platform system where the horse was levitated up towards the CT machine and the head cured to a custom driven platform and then moved through the CT machine, similar to a patient, a human patient lying on a CT table being moved through the gantry, while they're lying down.
And he proved that this was safe and reliable to perform in multiple at home patients and led to a really way ahead of his time, and development of standing CT in the sedated horse and contributed vastly to the literature available within within the veterinary journals. A similar system was then installed in many UK systems for over the next 1015 years, including our own clinic, and we had a system that was very similar up until very recently and formed very adequately for, for the needs that we had of it at, at the time. More recently at our, our clinic, really due to the high throughput demand rather than anything else and the very variation in sizes of horses that we see in our patient caseloads, we've installed a sliding gantry system and that's allowed us to have a much greater flexibility in terms of the parts of the patient that we can scan.
And also in the size and temperament of patients that we can, we can scan as well. So this is a short video of our CT setup and you can see in the video, if I start it start it going. Oh.
So you can see in this video that the that the horse stands sedated on a platform. They're restrained by metal stocks area that, That are completely dismantable and the horse is lifted up or down to the required height on a hydraulic platform. The head is secured to a carbon fibre table.
Which is radiolucent. And weighted down gently with sandbags on top of the patient's neck. And the nose kept still with a foam pad.
The gantry is then advanced towards the horse gently. At different spades. And the gantry will start off in the scanning position that we want the animal to to be in.
We'll just let this video run a little bit so that you can see how quick the whole process is. So this is in pretty much real time. We've had a few little bits edited out of the whole scan, but that's really just for, for slickness more than anything else.
This, this really is how long it takes us to, to take a scan. But the CT machine is being moved into the horse's head. Horses just being studied at the front end by Cathy McGowan, our hospital .
Hospital director. And then all of the personnel leaves the room during the actual scan period. Or stands behind a reinforced sledge shield, and there we go, there's the machine, moving, it's scanning away from the horse.
The horse is just reacting very slightly with its ears, but not unduly. And that's the scan finished. So in just those few seconds, it's about 90 seconds long, the head protocol.
We've acquired all of the data and necessary to fully evaluate the head and skull region of this whole. With very little fuss and intervention. I think it's Debbie mentioned in in her lecture, we very rarely actually take raid graphs of the horse's head now because getting the whole scan is quicker than than taking one raid graph in in a lot of cases.
So the control room in the background from the machine, we can see the, the equine CT sat behind this leaded screen. The nurses and the technicians will obtain the scans and direct it from the console behind the the lead screen and we can scan either in towards the horse or away from the horse. For practical purposes, we like to scan away from the horse because it gives us it allows for the horse and to move a little bit without hitting itself on the machine if it wants to, and then all you have to do is to to retake that, that scam if there is, is the movement.
So you can see the raw data. Be acquired again in real time. And this is this that reconstructs on the image software to allow us to view the head in any plane that we'd we'd like to see it in.
So this is Justine, who's giving the next lecture, and she's reconstructing the data according to the bit of anatomy that she'd like to look at in, in this case, one of the, the teeth. So the image once it's, once it's acquired all of the data, then uses a very complex mathematical algorithm called filtered back projection to create an image of the anatomical structure that it's just seen. So in a very simized Overview.
This involves adding up all of the anatomical structures that the that the X-ray beam has acquired in a single plane and then placing them at a point in time on on a mathematical grid and filtering those projections so that then you get an average of the of the anatomical structures. The actual measurement that the machine is using is the average linear coefficients of the of the material within its within the X-ray beam path, and then it's projecting those into. The Voxxel grid giving us the average linear attenuation coefficient for each ray of for each X-ray and the anatomical tissues that that X-ray has come, come in contact with.
So this means it's not completely true, accurate depiction and there are various artefacts that can occur along the way if you have an area of very high density or very low density that can average out the, the anatomy, a little bit, inaccurately. But on the whole, it is, it is a very useful way of representing the anatomy, within, within the patient. So the CT image is then displayed on a matrix of voxels, which is usually a 512 by 512 matrix, and the value of that number that's stored in each of the voxel, and a voxel is just a volumetric pixel.
So if you think about a pixelated camera image, a voxel is a volumetric measurement of, of a pixel. And this represents the average linear attenuation coefficient to the tissues, so the density of those tissues, as we, as we radiate the patient. The number that's generated, which is the average linear attenuation coefficient of these tissues, is known as the CT number and this is the same thing as the Hounsfield unit after Sir Jeffrey Hounsfield, who first described a clinical CT machine.
Due to the way that linear attenuation coefficients are worked out, which you, you don't need to know by any stretch of the imagination. But what you do need to know is that air and water are used for the calibration of this CT number scale. And by definition of the equations that are used, water has a CT number of 0 and air has a CT number of minus 1000.
The CT number therefore, of the various body tissues that we encounter varies because these tissues are heterogeneous and they're not completely air or completely water or completely soft tissue. But this does allow us to be really quite specific in determining which tissues we're looking at using an objective measurement rather than just eyeballing the grey scale. So we can look at the grey scale and we can say, OK, well, black equals there.
And grey or soft tissue. There's a whole range of shades of grey in between white and black, but actually are represented by the CT numbers. And if we measure objectively those CT numbers, we can get an idea of which tissues are involved.
From a clinical point of view, this is really important and it's one of the major advantages of CT grayscale over and above radiology. It gives you a much wider range of grey scales and it allows us to Distinguish between fluid and soft tissue, whereas on a radiograph looking at sinuses, for example, that are full of pus, and you don't know whether you're looking at a soft tissue mass that might be a sinus cyst or fluid apart from the shape of that that density that's that's appearing within the sinuses. So by looking at the range of the CT numbers, we can see that fluid is going to have a lower CT number than a purely soft tissue structure.
And there are various different CT numbers published for for the human field looking at looking at the, the head and the, the thorax and, and the abdomen. There's still quite a lot of work to do within the equine field looking at CT numbers. But for example, if we measure the CT number on a melanoma, we can distinguish a melanoma compared to another soft tissue structure simply from the CT structure CT number that's And that's given in that location.
So it really is a useful objective as well as subjective measure of the of the density and linear attenuation and coefficients of the tissues involved on on the image. And that's important from a clinical point of view. So CT numbers can range from -1000, which is pure air, to around 3000, which would be dense cortical bone.
It gets a little bit more complicated still and that the human eye can really only appreciate around 50 shades of grey, and I don't know whether that's where the popular Look in film, 50 Shades of Grey originates from, but I quite like to think that it is that actually there are a lot more depths of grey that are, are there, but we can only perceive and see around 50 shades of grey. It's certainly a very useful way of remembering that particular number in, in any case. But what we can do, because we can only physically appreciate 50 Shades of grey, what we can do is to window a particular image post acquisition to allow us to see these different contrasts of grey, depending on which structures we're interested in.
So if we're interested in the soft tissue structures, which have an average CT number of around 30 to 40, we can level the window, which is the figure WL on your screen, at around 35 to 40, so that gives us the average centre of that that grey scale. And then we can give it a width of another 350 C. Units, which is an equal number either way from from the level that we're viewing.
And that would give us a soft tissue window in that there's lots of contrast between the different soft tissues. But most of the bone structures would show up as completely white and, and be, be indistinguishable, in different contrast levels from each other at the top end of the, the scale. And about a soft tissue window, Algorithm is shown on the bottom left hand image.
And then we've got the same area of anatomy, the same slice in what we would call a bone window level instead, and this is simply pressing a mouse on your your console. You don't need to do anything else but just simply level where you'd like, like to look at those shades of grey depending on which stretches you want to evaluate. And the bone window we level this much higher.
About 350 CT units or Hounsfield units. Remember they're the same thing. And then we give it a much wider window width because bone can really have quite a wide variation of CT numbers, depending on whether it's very thin, and wispy bone or or conky if you're talking about the nasal passages, or whether it's very dense bone and cortical bone on the margins of the stretches.
So we have a window level of about 300. 50 and a window width of 2700 to 3000. You can see there's a huge difference between those two images, even though they are, they are reconstructed from exactly the same data.
We've not taken the scan again. We have simply displayed the image post acquisition in a different shade of grey and from one to the other. The other handy thing about CT imaging is that we can do multiply our reformatting MPR and this allows us to take the same set of data and to reconstruct it in any plane that we fancy.
We can look at it in the sagittal, the actual or the dorsal or coronal just as as as the standard views, but we can move those bars and you can see super proposed over the three different images in front of you into any plane and rotate that image in 360 degrees so that we can really slice through any particular structure and a value. It more clearly, depending on which area where we're interested in clinically. And for me from my anatomy point of view and understanding clinical, clinical disease, multiplaar reformatting has really increased my depth of anatomy that I never actually thought was possible as an undergraduate, or postgraduate, veterinary surgeon.
Three dimensional surface rendering again from the same set of data, you don't retake it again, that 90 seconds that you've taken the images is all you need to do. This is simply asking the computer to do all the hard work for you and it puts everything together again, depending on which bit you'd like to look at, whether you'd like to look at the soft tissues or the bone, and gives you a three dimensional, surface image of that structure. This is particularly handy for looking at fractures, as Debbie alluded to, and particularly if you want to demonstrate to clients, the anatomy and importantly for surgical planning.
So the image in front of us shows a little fracture of the. The nasal bone on this particular horse, which would be difficult to appreciate fully radiographically due to superimposition of the other stretches in that region of the soft tissues and the very thin area of bone that you've got in in that area. Other fairly fancy image processing and display techniques, again, all from the same data set, which I find incredible and certainly my my mind doesn't completely understand all of the mathematics involved.
But virtual endoscopy is another variation on the 3D surface rendering technique, and this is used to, instead of display the outer wall. It displays the inner walls of the body stretches and can give you a really detailed fly through projection of the nasal cavities, the larynx, the tracheal bronchial tree and basically perform endoscopy without actually being invasive to the patient. It's not as accurate as doing.
And live endoscopy, as you would imagine, but it certainly allows you to see a number of structures that wouldn't be possible without it and potentially in horses that are not amenable to to scoping and for whatever reason, but will allow you to perform the standing sedated CT or even a GACT. And it's another option. Maximum and minimum intensity projections also allow us to look at a particular volume of interest.
So instead of looking at area of interest, we're looking at a volume of interest. And this is particularly useful for things like CT and geography or for looking at Airfield, tracheo bronchial region, and we can ask it to subtract or add on the minimum or maximum CT number depending on the actual tissue type that we're interested in, which is an an amazing advance in in imaging technology. We also use contrast agents quite a lot in, in CT imaging.
These are the same contra contrast agents that are used in radiographic imaging and the the usefulness relies on the fact that they have a very high linear attenuation coefficient due to the mass number, and they are pretty much all iodine-based contrast agents. These can be ionic or non-ionic, but if we are looking at stretches within a side of your cavity or within the . The CSF, they have to be non-ionic solutions, otherwise we will get various severe adverse reactions.
So the vast majority of the solutions that we tend to use are non-ionic and for every contrast study, even though you can use ionic intravenously or Intraarterially or in cavities that are not synovial or are not going to give you as much adverse reaction, we tend to in reality, just use the non-ionic low osmolar agents for all of our procedures just so that they, they don't get mixed up. The disadvantage of this is cost, but certainly the the chance of having an adverse reaction is, is definitely decreased for non-ionic osmolar solutions in, in any body cavity, as I say, it's absolutely essential for things like myography and for synovial structures. So there's a variety of products available and intro as we said intravenous or intraarterial administration has been safely reported in in the horse and the the advantage of using intraarterial over intravenous is that you need a much lower volume compared to intravenous, which makes the, the procedure a lot cheaper, if not a bit more fiddly.
So let's go on to some of these clinical conditions of the equine heads that have been both reported in the literature and that we have seen as a case load here at the Lee Hurst equine Hospital, and over the number of years that we've been performing CT evaluation. And this is the thing that really gets me very excited is the range of clinical conditions that we can see now, compared to when I first started in practise 20 years ago. So, starting off the literature, available, within, within the veterinary literature, and there is a plethora of CT papers coming out now, which is, which is great, but hard to keep up with, with all of them.
There's, there's that much information being produced. This was a particularly nice original article published in equine Veterinary Education in 2015. And this was a retrospective study of 59 horses that were over the age of 8 years of age, undergoing a CT of the head for a variety of reasons.
And this simply gave an overview of the different types of diseases, and the different types of pathology that we may expect to see in CT of the head. Unsurprisingly, the vast majority of the horses within this study, 42%, sorry, 2 horses were were horses that were undergoing, undergoing, . CT because they had dental or cyno nasal problems.
You'll see the, then the, the next category of horses that were, were most common were osseous or articular diseases, but only 11 of the 59 horses. And then 6 out of the 59 horses were categorised as having primarily soft tissue diseases. Pa was quite interesting in that they found multiple pathologies in a number of horses, even though their primary region reason for going to CT was categorised as either dental or cyanosal osseous or articular or or soft tissue disease.
And, Justine's going to go over the dental conditions in, in the next lecture. If we think about the about the head in various different regions, we can start off by thinking about the nasal bone and the nasal passages. Of course, when we radiograph a horse, we can, we can see parts of the nasal bone but it it is quite thin and superimposed on various other structures depending on which view is taken radiographically.
And the nasal passages can be evaluated beautifully by endoscopy within the actual ventral and middle and dorsal meatus, but we can't see the conky that make up the interior walls of the meatus very clearly and we can't visualise those bully within the within the meatuses, either. And these have become recognised as quite significant sites of ongoing disease within the nasal passages of the horse. So the structure in front of us is a 3D surface rendered image of a reconstruction of a fractured nasal bone, and we can see very nicely the portion of bone that has been damaged on the 3D reconstruction.
And then on the multiplanar reformatted view, we can see that the area of, of bone fragments and fracture, and we can Also see that the conky and the nasal mucosa around this region has become thickened and has narrowed the nasal passages towards the front of the nose. And so it allows us to really visualise this in in much more detail. Painatal sinuses have a number of primary conditions as well as dental related conditions.
So primary sinusitis is recognised in a number of our patients, which seems to be remote from a dental pathology or unrelated to it. The most likely reason that these horses would would get it ongoing sinusitis is having had a primary respiratory infection that then thickens the nasal mucosa, allows pus to accumulate, maybe it includes the drainage angle, and then a secondary bacteria. Infection building up within in those sinuses.
Once the nasal mucosa has become sickened and the drainage angle is secluded, and the pus really doesn't have anywhere to go and can accumulate in these the the vast paranasal sinuses of the horse and and cause significant ongoing problem for that animal. So the image in front of us is a bone window. It's taken on a 5 millimetre slice, but we can also reconstruct that data into much thinner slices of of 1 millimetre or a half millimetre depending on the the parameters put into the programme.
And we can see that the area within the right rostral maxillary sinus has an area of quite marked soft tissue attenuation. So we've got a much lighter area of grey compared to the air filled sinuses. And in comparison to the left rostral maxillary sinus.
So the right max maxillary sinus has soft tissue hyper attenuating fluid within it, and, and handsfield units on this were about 20 to 30 when they were measured. And surrounding the orbital canal and also filling the ventral concourse sinus on the right hand side. The left rot maxillary silence on the other hand is nice and airfield, so that that shows up as black and the ventral concoursitis is also clear.
The this is the same horse, just a few slices further forward, and we can see that the more towards the the rostral aspect of this horse, and we can see this is at the level of the 8s, whereas the first images at the level of the 9s around the orbital canal, and we can see that the dorsal conco scroll has been squashed medially, but By an area of soft tissue or fluid attenuation, which when the hands filled units were applied to this area, it's, it's kind of a mixed CT number between fluids and soft tissue. So this is most likely to be ins insipated pus, which is pushing towards dorsal conky and squashing that bullet and sitting within the, the dorsal concoscroll. So really nice images of the, paranasal sinuses and the areas of the nasal passages, it's just not possible to get to via a, normal endoscopy.
Even going in and visualising the sinuses with sinus cystoscopy, it can. Difficult to get around all of the different angles of the drainage angle clearly and to visualise everything that we need. So being able to plan the approach meticulously prior to going in with endoscopy or surgical evaluation is absolutely invaluable in these cases of of long standing and sinusitis cases.
Sinus cysts, so another reason for, for having ongoing sinus discharge and, and, destruction of the nasal cavity would be the sinus cysts. We can see in this particular example, this is a very extensive. Sample of a sinus cyst, which is filled both the rostru axillary and the cold maxillary sinus and extended in towards the frontal maxillary sinus and really is obliterating the right hand side of this, the perinatal sinuses on the right hand side of this skull.
Often it's very difficult to work out exactly where the primary disease has started and where this structure actually originates from, but we can certainly see from the CT examination that a number of the sinus cavities are now in and that there is deformation of the nasal septum on the midline, pushing the nasal septum over towards the left hand side and squashing the nasal passages because of the mass effect of that fluid filled sinus. By applying the CT units and the objective measurement to this to this structure, we can tell that this was much more of a fluid structure rather than a solid mass. Very important for prognosis for this animal because if we can say with confidence to the owner well this is a sinus cyst, it looks clinically like a sinus cyst and importantly, the CT number tells us that this is fluid filled rather than solid tissue.
This makes A much better prognosis and following surgical outcome than if this was a solid tumour, for example. So really important application of the of the CT numbers in in this situation. This is the same cyst in the sagittal view and we can see the rostral and cordal extent, the cordial extent of the cyst pressing on the ethmoid region and really filling all of the air filled perinatal sinuses on that particular side of the head.
The Concord bully, as, Debbie alluded to, are, have recently been described in their anatomical features, and they're basically air filled cavities within the, the dorsal and the ventral concourse scrolls, which form little bully, rostal to the main sinus cavities. They have been largely ignored, up until recent years or not thought to be all that clinically relevant and also fairly confusingly for those of us that that graduated a few years ago now. The ventral, the, the Concord bulla used to refer to the septum between the rostral and the caudal maxillary sinuses.
That no longer is the case. The ventral conker bullet is not the septum between the rostral and the corral maxillary sinuses. It is actually the airfield space, rostral to the ventral con sinus encased within the ventral con scroll, and the dorsal concorbula is slightly rust and .
Rostral to the dorsal concosinis, and again, it's an air filled buller, which should be separate to the sinus cavity, that can often be involved in an extension of disease from those sinuses, and the thin wall of that conco below can be completely destroyed by in to pus and ongoing and chronic sinusitis, both primary sinusitis or secondary sinusitis due to dental disease and these conical bully can then wall off and end up with with areas of insipated pus in them. And I think again justine's going to go over to into this in greater detail. But the advent of CT have really allowed us to look at the anatomical morphology of these structures in, in, in huge detail.
And this was a really nice paper from the Edinburgh group several years ago in equine. Veterinary journal and this described in detail the anatomical features of those conical bullies both dorsal and the ventral conle bully, which are both associated with the the maxillary arcade. And we can see that the rotral limit of both of these conquerbuly varies significantly, but the dorsal conquer bully, the rostral limit is usually in in the vast majority of horses parallel with the maxillary a sevens, but can come as far.
As the 0606s or be as far back as the 08. And the cordal limit can stretch, usually to about the tens, but can go as far back as the 11th or only stretch as far back as the 8s, depending on the horse. Fed cocker bullet is slightly smaller in size than the, dorsal cocker bullet.
And the ros to limit is most likely to be parallel with the 07, but can go as far forward as the 6s, and be, or be start as far back as the 08. And the coral limit, is usually around the 9s, but, but can be, no further back than the 08s or as far back as the tens. So, this is not where the sinuses are, this is where the bullae are, but it can confound our interpretation of both radiographs and from a clinical point of view, trying to deal with those infections.
So radiographically. If we have a soft tissue opacity that appears to go without the outside the sinus margins, we need to be thinking about these concor bully and the dorsal concor bully or the ventral conor bully as being potential sites of further infection. Unsurprisingly, these bully had greater volume in older horses simply because the teeth roots in younger horses press in on the bully and prevent them having their, having a greater volume due to the reserve, reserve route that's, in that, that horse.
So this is a diagram of the, the conquer bully and taken at the sagittal and taken a transfer section of the 08s and we can see that we've got the dorsal conkerbuli with the white arrow and the ventral conkerbuly outlined with the blue arrow. The, dorsal section is at the level of the dorsal conca bullet, so really quite, dorsal within, within the skull. And we, this is a, a middle aged horse.
So the ventral cocker bulla has a really volume in in this particular animal. If there was still an awful lot of this tooth to erupt, then the volume available for the ventral concabulo would be much smaller and they can really be very, very, small structures in in younger horses. Fungal sinusitis is not a condition that we see commonly in our patients, but if we do see it, it has a different CT appearance compared to a bacterial sinusitis.
And, this case is a nice case example of that where we've got a very mixed, CT appearance within, the, within the maxim. We sinuses, and we can see complete obliteration of the normal structures of the roster maxillary sinus and extensions they call the maxillary sinus and a little bit into the frontal sinus as well. And we, we can't make out the infras can now clearly at all on the right hand side of this transfer section, whereas we can see the in for all.
To now really clearly on the left hand side. This mixed ecogenicity mixed hyper attenuation and patchy type appearance, which is almost stuck on to the side of the sinuses, as well as filling filling parts of the cavity of it is a typical appearance of a fungal infection, not common in our patients, but, but just sometimes occur. The temporary mandibular joint is another area of clinical concern in, in some horses and has received a little bit of attention within the veterinary literature recently.
The temporal mandibular joint on the left hand side is has nice smooth margins. It has a nice clear joint space and even subchondral bone and, and cortical thickness. Whereas the TMJ on the right hand.
Side of the screen has a much more irregular articular margin and narrowed joint space where the meniscus sit and luncies within the bone and hypo attenuation areas suggestive of a subchondral bone lesion. In a nice retrospective multicenter review of the appearance of the temporal mandibular joint in 1018 horses by Carmel and colleagues. They evaluated the appearance of the sea of the temporary mandibular joint and for horses.
That had undergone CT for reasons that were deemed to be other than suspected TMJ pathologies. These were horses that they thought clinically were normal within the TMJ or nobody had noticed any problems anyway. But there was a wide variation, in appearance of the TMJ.
Joined in this, these horses, with the young horses having a much more varied alteration intensity and shape of the convales of, both the mandibular condyle and the mandibular fossa on the temporal bone, and also assists like lesions being much more common in the condyles of older horses. So they reported that 41% of horses actually over one year had some evidence of this mineralization as well within the joint space, either unilaterally or bilaterally, but they were marked it was never seen in horses under one year of age, but there was a marked frequency of disciplinarization in horses over 10 years of age. The images on the screen are of a horse that was seen and here at the Lewin Hospital.
We can see in the left temporal mandibular joint that there is one of the subchondral bone cystic like lesions where there's a hypo attenuation. Of the subchondral bone, which appears to communicate with the articular surface. And then the blue arrow on the dorsal image shows us the area of hyper attenuation within the meniscal tissue, which is which is mineralization within that that meniscu.
Interestingly, the subchondral cystic lesions and the mineralization didn't correlate. So if you saw one, you didn't necessarily see the other, but both were much more common in the older horses, particularly in horses over 10 years of age. So temporomandibular joint pathology, still probably quite a lot to learn on these, that there is a wide variation of normal and there's a wide variation of probably.
What we would class as pathological change, which probably horses can tolerate just fine and would would actually be determined as a normal ageing finding. So we do have to be a bit careful when we interpret these, but great to be able to identify these, these changes and subtleties within the joint. Dentitous cysts, these are usually a fairly straightforward diagnosis on radiographs, so you don't necessarily need to have CT to be able to diagnose them.
We have a very marked hyper attenuating dental type structure at the base of the ear on this particular CT image, whether the CT scanning really comes into its own for these particular cases. Is that we can identify the anatomy much more clearly on a radiograph these very mineralized structures would be superimposed over the density of the bone and being able to fully appreciate the the relationship of the denigous cyst with the calvarium would be very difficult. We can see quite scarringly on this particular case that the digous cyst is very very closely associated with the, with the outer margin of the calvarium and therefore very close to the, brain structures underneath that thin, bone of the calvarium.
This horse did have the dentist cyst removed successfully under the general anaesthesia. It's causing quite significant problems with both attack and with a discharging sinus, but having the CT, both the multiplanar reconstruction and the 3D image reconstruction allowed surgical planning to be, be performed accurately. So, just showing the 3D image of this particular cyst, and the surgical appearance of the cyst once it was exteriorized.
So we don't need this CT particularly for diagnosis, but certainly from a point of view of treatment and trying to give a prognosis for resection and resolution of the problem, then the CT evaluation was particularly invaluable. Moving on to structures of the orbit, and the orbit can be viewed both from the point of view of the soft tissues and also from the bone. This particular CT image is of a horse that sustained a trauma within the field, and we can see that the right orbit has areas of bone discontinuity and subtle areas of fracture compared to the intact left orbit.
The soft tissue window also revealed a detached retina in this horse which could equally be diagnosed by ultrasonography, but just using the CT alone allowed us to diagnose both conditions. So this horse had some common fracture of the orbital rim, and a slightly depressed depressed fracture of the, the area as well, which was corrected surgically. The horse lost its sight in this eye, that made a fairly uneventful recovery from the point of view of function and use and remained fairly pain free after the initial episode.
Moving on to the calvarium, the calvarium as we saw, we can look at associated masses and areas of Of pathology in that region. We can also assess some of the the intra-axial structures. CT is not particularly good for, for definition of the structures and actually because they will have a very similar CT number.
So MRI remains the gold standard for looking at the intraactual structures and in particular and subtleties of the cranial nerves and the different. And parts of, of the brain. However, what we can do is we can look at at large mass effects, and at the size of the ventricles and also for areas of mineralization or even subdural hematoma has been evident on CT due to the difference in CT number that that shows up from hematoma, fresh hematoma compared to soft tissue structures.
The particular image in front of us is from a hunt mare that was showing head pressing signs and intermittent seizure, and this mare has a large space occupied lesion within the ventricular system within the brain with areas of focal hyper attenuating mineralization. This is, this is actually cholesterol granuloma, a fairly common condition in older horses, doesn't always quite often doesn't result in. Clinical signs it would be a a common abattoir finding within, within cases, which has not caused any notable clinical signs.
However, this particular class to granuloma had grown so big that there was ventricular obstruction of the CSF outflow, and resultant brain edoema and swelling, which was causing the intermittent, seizures. So allowed a, pre-mortem. Diagnosis of mineralized cholesterol granuloma in this horse.
The, moving on to some, a quick example of a contrast study, contrast really does give us a whole new level of conditions that we can diagnose. This particular animal had a very unusual, shunned between the rotted and the jugular, systems, so a rotted jugular arteriovenous fistula, and by injecting contrast material into the left sided intravenous catheter, we could See much more clearly where this shouldn't was going and allow the surgeons to try and plan a surgery for this case. I was very glad I was the person taking the images and not performing the surgery in this case, which was actually poor Debbie, who gave the the first lecture.
We can see from the reconstruction that the contrast material is showing up as orange on this 3D reconstruction, and this allowed the surgeons to try and come up with a formulation to, to block off this this abnormal shunt. The the shouldn't. Actually causing cardiac signs in this horse as well as interfering with with breathing and with the tack region and by cluding the correct vessel, the horse has made a fairly spectacular improvement over the last few months.
The oropharynx can also be examined in much more detail. So this is an image of the guttural pouch, and we can see that we have a very large soft tissue attenuating mass within the guttural pouch. Well, just below the base of the guttural pouch wall on the right hand side, which is pressed.
Thing into the midline. This was actually her maniosarcoma and presented as an acute dyspnea and swelling in the laryngeal region of this horse, even though this was actually a chronic problem. So allows evaluation of the retrovaryngeal structures and to be assessed much more clearly.
The temporal hyoid osteo temporohyoid articulation within the guttural pouch can also be evaluated more clearly. We can scope the guttural pouches and have a look at the style of hyoid bone and the . The articulation within the guttural pouch.
But we can't assess what's going on with the temporal and pes temporal bone or the stretches outside the guttural pouch. This allows us to look at the condition of temporal hyoid osteopathy much more clearly than endoscopy alone. We can see that we've got a more normal temporal hyoid osteopathy on the left hand side of the screen and then a thickened abnormal and enlarged and sclerotic bone on the right hand side of the screen.
Temporal hyoid osteopathy can be indicated in head shaking behaviour. We can also have an acute onset vestibular or facial nerve paralysis associated with the condition due to a secondary fracture of the style of hyoid bone or the petris temple bone in the region of the cranial nerves 7 and 8. Some cases have also been documented to have a secondary meningitis following ascending infection of a fractured and petris temple bone, but that would be an unlikely scenario.
Finally, just moving on to a, a few other conditions within the er external ear canal region and multiply our reconstruction is invaluable in following the torturous ear canal, and we can identify areas of subtle infection and thickening within these tubular structures much more clearly by being able to follow those structures on any plain on, on CT. The hyoid apparatus, the the anatomy of this was a bit of a mystery to me for many years as a student and post graduation. But the CT reconstruction of the hyoid apparatus allows us to see this structure in much more detail.
We've got a normal hyoid apparatus on the left hand side and then on the right hand side, a chronic fracture of the hyoid apparatus of the style hyoid bones and the Cretto hyoid bones and the busy hyoid bone, and giving us this question actually the ventral aspect of this hyoid apparatus in between the mandibles. CT allowed us to do fancy retrictions and to really visualise this sequestrium sat on the ventral aspect of the busy hyoid bone prior to surgical intervention. Neoplasia, we can see soft tissue stretches and neoplasia much more clearly on CT as well and to understand the volumetrics of this, so this was a very nasty osteosarcoma invading the the .
The bones of the skull, and into the perinatal sinuses, on, on the case in front of us. Head shaking, just a word or two on head shaking. This is a very clinical syndrome.
We're hopeful that CT may start to shed new light on some of these cases. All too often though CT is still negative, and head shaking can be associated with temporal hyoid osteopathy, apical tooth infection, indium carries, or rhinitis. But in many Cases, it is an idiopathic condition of the trigeminal nerve and which Veronica Roberts proved quite not proved quite nicely in a recent paper that even though this is functionally abnormal, there were no his pathological changes.
So it's not surprising that in some of these cases, we still don't see any discernible image findings. So the limitations of equine head CT are that the soft tissues of the brain are still very poorly delineated and it's still not possible to evaluate the basal nuclear of the cranial nerves in depth as we would, say for example for an MRI examination. But edoema is also not evident on a CT we can only see that on an MRI.
Although within the head region, bone edoema is not such a significant pathology as it is within the limbs of our equine patients. We also do have to remember that it's quite a high radiation dose for the personnel involved with CT, so it's easy to get carried away with image acquisition process, but we do have to be mindful of the fact that CT, is a very high radiation and image acquisition process. And of course, it has high initial setup costs which are offset quite rapidly with a high caseload but initially, it is expensive to set up.
And this picture just reminds me to say that it's not just horses, we've had a pygmy goat in there as well, which gives us a really nice devil appearance to the 3D reconstructions. So I hope that was a useful rundown of the clinical conditions other than dental disorders of the head, and I'd be happy to take any questions. Great, thanks very much, Allison.
Yes, that was really, really interesting, and that's quite scary last image there. Your comment about the 50 shades of grey, do you think then there are maybe other species that can see more shades of grey that will be able to better interpret CT images in humans? I, I don't know.
I have no idea. I guess it's an interesting concept, isn't it? But, yeah, 50 Shades of Grey, it's an easy one to remember anyway.
That's definitely gonna stick in my mind. We do have, just while Justine's setting up, we just got one quick question. So regarding the virtual endoscopy, yeah, MPR in such a big subject, such as the horse head, how much risk is there of missing a lesion or unusual anatomy due to the machine filling in data gaps with normal tissue?
Or has the machine imaged the whole thing? Yeah, sure. I think that is a that is a real possibility and even in human medicine with things like virtual colonoscopy and virtual endoscopy, they do warn that there is a risk of Seeing a clinically significant lesion.
So if that lesion is quite small, and if the data set is quite large, I think we do have to be careful and certainly as far as I'm aware, it hasn't been fully validated within the veterinary literature currently. So it is, it's an interesting concept. I think it's something that we'll see more of, but, it certainly doesn't fully replace the live endoscopic examination for sure.
Great, thank you very much. OK, well, I'm afraid we don't have any time for any more questions, so thanks again, Alison for a really interesting talk.