Hi, everyone. My name is Faisal Nabi. I'm a multimodality cardiac imager here at Houston Methodist, and it's a real pleasure of mine to be involved with the hybrid imaging workshop and to be able to present to you today incidental findings on CT you do not want to miss. So everything that I'm going to be talking to you about really comes from the hybrid imaging guidelines chaired by Dr. Almulla, and the citation is here below if you'd like to review this further. So there's a big push now to incorporate the use of cardiac CT in conjunction with nuclear cardiology, and the reason is along with the functional information received with SPECT and PET, we can get anatomical imaging with the use of CT, and both of these combined can provide very powerful diagnostic and prognostication. So the way most of us will interact with CT in the nuclear cardiology department is either with the use of CT attenuation images or a coronary artery calcium score. A lot of the imaging systems now are hybrid systems, and generally these are two of the ways you'll be able to view CT images. Now in general there will be a difference in image quality between a calcium score and a CT attenuation correction scan. A lot of it depends on the type of scanner you have, and then of course kind of the acquisition technique that's employed and the patient's body weight, but in general, you know, a calcium score will have a much higher image quality than a CT attenuation correction scan. However, still very useful information can still be obtained. So in table seven of the guidelines, they really make an emphasis that of certain findings that really should not be missed on a CT scan, and the reason is of course they have important, you know, diagnostic considerations that these findings are present, but they very well likely could be the cause of the symptoms that led to the test being performed in the first place. And as my talk goes along, I will be showing you images of each of these abnormalities and hopefully showing you how you can go about recognizing and describing that. So I think the first thing before we can do that, it's important to know normal anatomy of the thorax, you know, in this with CT images as you're going from the apices of the lungs all the way down to the diaphragms at different locations in the chest, you know, there are different structures, and it's very important to know that within each region, what are the normal structures that are there? Because one of the big emphases of this document is the ability to identify abnormal. If you can identify abnormal, you can always recommend further testing or, you know, if you work closely with radiology, be able to get them involved to figure what exactly is going on. So another very important thing to know is that, you know, we're used to looking at images through, you know, working with our axial source data, but do know that there's, of course, other ways we can look at these images. You can look at them through the coronal plane or the sagittal plane, and each of these can be helpful in certain situations. Also, when we're identifying different structures in the thorax, it can be very helpful to use the correct imaging window. The most common imaging windows we use are either the mediastinal or heart window, they call it, the lung windows, the abdomen windows, the bone windows. They really help you to, you know, properly be able to identify structures within these different regions. Another important point is, although, you know, your technologist may give you a CT scan with a field of view just limited to the heart, it's important to know that, you know, you really, if you're going to be looking for extracardiac findings, it's very important to get a full field of view reconstruction, which is often obtained, because that's the only way you're going to be able to see these things. All right, so how to go about image interpretation. Now, in general, there are many different ways. I will just kind of go along with the way that was suggested in the guidelines, and I think the most important thing to say is that no matter which way you decide to do it, you just have to have a very consistent way, and you apply the same kind of philosophy for every CT scan you read, and that way you really avoid missing any abnormality. So, in general, the kind of the way to read, you know, these images is to first begin with a scout image. This can be very helpful, because, you know, oftentimes the actual images that are acquired are a smaller field of view than the scout images, so you may actually pick up some abnormalities that may be important in the patient's case that were not really in the true data set that is acquired, so I always start with that. From there, you know, my eyes will go towards the heart and the great vessels, and, you know, we'll talk a little bit about that. From there, going on to the breast and soft tissue of the mediastinum. After that, I'll look at the lung and the pleura. After that, I'll look at the upper abdomen, and lastly, finally, look at the bony structures, and so how I've kind of went ahead and structured this for the rest of the talk, you know, I'll just describe, you know, kind of in each location, kind of the structures that we're interested in looking at, and then show you, you know, findings that you definitely don't want to miss. So when it comes to evaluating the heart and great vessels, you know, it's very important to, you know, to, you know, we will be using the heart or mediastinal windows, and it's very important to play with the data set to be able to go all the way from the top all the way to the bottom, and if you do this a couple of times, you want to generally look at the cardiac anatomy. Is it normal? Do you see coronary calcium? Where do you see it? What's the extent of it? Look at the pericardium. Is there any thickening or calcifications or effusions? Is there any masses present that you can see? From there, I'll often then go ahead and look at the vessels, you know, and here you want to, the great vessels here, you want to make sure what are the sizes of the ascending, descending, the main pulmonary artery, you know, do you have a right or left-sided arch? Do you see any abnormalities with the pulmonary veins? These are, you know, kind of the general ways you want to do this. Now, important findings when you're looking at the heart and great vessels that you don't want to miss, of course, are pericardial effusions. These are generally, you know, quite frequent and have a variety of causes. In a supine patient, they're usually going to first appear posteriorly, and similar to how we describe it with echo, you know, a small effusion is less than 10 millimeters, a moderate effusion is 10 to 20 millimeters, and then a large effusion is greater than 20. And one of the things that we can do further is actually measure a ounce per unit of the pericardial effusion that you're seeing, and, you know, if it's close to water consistency, less than 10 ounce per unit, that's consistent with a transudate, whereas 10 to 60 would be an exudative, where the more than 60 would be hemorrhaging. I think the most important thing is that if you were to see an effusion of at least moderate caliber, you know, that may be a reason to put in the report that you recommend at least an echo to look for, you know, its hemodynamic significance. Another finding you don't want to miss in this space is pericardial calcification. The pericardium is a very thin, less than two millimeter curvilinear structure circumambulating the heart. When you see calcium in the pericardium, this is really the end result of an inflammatory process. And the biggest risk, of course, is this, that this could be a sign of constrictive pericarditis, especially if the patient is presenting with heart failure symptoms. So, you know, in a non-contrast scan, it's very easy to see calcium, so it's an important finding to see, and then if it is seen, to recommend, again, an echo to look for constrictive physiology. Another finding that can be very helpful is to look for evidence of an old myocardial infarction, oftentimes in nuclear imaging. You know, you may have a perfusion defect and you're tossing between whether this is a true fixed defect or whether this may be simply an artifact. And if on the CT scan, you see evidence of an old myocardial infarction, that includes things like pulmonous metaplasia, or in this particular case, what you see in this image, myocardial calcification. These are signs that the patient has had a myocardial infarction. Other signs that you can also see, of course, are if the walls look very thin or aneurysmal. Again, those are signs of MI. Other findings, such as perfusion abnormalities or thrombi, obviously, you know, you will not see without the administration of contrast. When it comes to the great vessels, of course, we frequently see dilation of the mid-ascending aorta. You know, anything greater than four is generally considered dilated. And if I see anything that's at least moderately dilated, which I consider 4.5 centimeters or more, I'm going to recommend a contrast scan to evaluate the remainder of the aorta as well and to serve as a reference for future surveillance studies. Now, an important point here is that you really want to make your measurement perpendicular to the axis of blood flow and try to do it at reproducible landmarks. So, for example, for the ascending aorta, I like to do it at the P8 bifurcation. Similarly, if you look at the coronal views, if you have a little bit of fat around the aortic root, you can really make out the borders very nicely and you can make a measurement of the aortic root. So, after we've examined, you know, we looked at our scout images, looked at our heart and great vessels, the next thing that I look at, because the window leveling is actually very similar to the heart, is to look at the breast tissue and the soft tissue of the mediastinum. And here, really, you're going to be looking for nodules or masses within the breast, calcifications, whether you see gynecomastia. In the mediastinum, you know, there can be often lymphadenopathy or evidence of pyrogranulomatous disease. You may actually see anterior mediastinal masses. So, it's very important to pay attention to this area as well. So, important findings that you don't want to miss in this area is, of course, breast masses. These will just generally be nodular, you know, densities within the breast tissue. And in general, you know, we try to describe its size and kind of give an idea, is it circumscribed? Is it very irregular appearing? Is it speculated? And we may even look for other signs that could suggest that the mass you're seeing is a malignant process. And those would include things like nipple retraction or invasion, skin retraction or thickening, invasion of the underlying skin and muscle, associated adenopathy. So, you know, these are just two examples here on the screen of breast masses, which, you know, if we see, we're quick to recommend further mammography for evaluation. In the mediastinum, you know, we don't want to miss lymph nodes. Again, lymph nodes usually occur as a result of a wide range of pathologies. There's actually quite a few different locations where these lymph nodes can be. There's 14 stations in seven different zones. But in general, the most common are, you know, what we're going to be seeing are the mediastinum or the hyla. And we're kind of describe whether these lymph nodes are calcified or non-calcified. And you really want to raise the alarm for further dedicated imaging, be it another CT or maybe even PET CT, if you see lymph nodes that are more than one centimeter large. In this image, you can see a very large calcified lymph node which usually goes along with prior granulomatous disease. So after the scout images, after looking at the heart grid vessels and looking at the breast and soft tissue, the mediastinum, now we'll adjust our window leveling so we can see the lung tissue better. And here, what we're going to be looking for is consolidated lungs. We're going to look for abnormalities in the lung parenchyma, such as fibrosis, emphysema. We're going to look for nodules and masses. And we're also going to evaluate the pleura for whether there's any effusions, thickening, or even maybe even a pneumothorax. So, you know, the hybrid imaging document, you know, recommends that, you know, pleural effusions be reported out if they are seen. These are, in a supine patient, again, these appear as sickle-shaped opacities, usually in the posterior costrophenic sulci, you know, which is the dependent part of the thorax. And sometimes, depending, you know, on what else is seen in the lung fields, you may identify an underlying intrathoracic cause. Now, one way it's a little bit different than the pericardial effusions is with pleural effusions, you know, simply checking a H-hounsfield unit will not tell you whether it's a transudate or exudate. Rather, if you're concerned about an exudate, you have to look for other features, such as loculation, pleural thickness, or pleural nodules, which are more common with exudates. So these are just some images of some rather large pleural effusions in these patients. Another finding, you know, along this is what we call, another finding is this, what we call a pleural pseudotumor. This is a pleural effusion that is kind of loculated within the major or minor fissure. And this is frequently mistaken for a mass, but, you know, just to bring this up, that this is something that you can easily check a H-hounsfield unit if it's close to water, you know, it's fluid, and it's this very characteristic appearance of this very rounded oval structure. And then most specifically, look for, you know, where the major or minor fissure is. And if it's within that, you know this is an effusion and not a mass. Pneumothorax, you know, hopefully you will rarely see this. Yeah, you know, this is obviously if you, a pneumothorax can have, can be a life-threatening entity if there's compression of the mediastinal structures. But what the definition is really that you have air in the pleural space. And so what you'll see is usually, you know, a lung that has collapsed, a very sharp lung marking and no lung markings beyond this, where the lung ends. This is just where, you know, now there's air. And so it's important, you know, to recognize this. And, you know, if you see any compression of right-sided chambers to raise the alarm that, you know, this may be an urgent, this patient may require an urgent intervention. Lung consolidations are another important finding that will be seen. This is really defined as an alveolar filling process where you replace air with either fluid, pus, blood, or cells. And the best way to recognize this is to see not a consolidated lung, but to see air bronchograms within that consolidation. And generally, one of the most common, you know, cause of this is a pulmonary infection. So you'll see air-filled bronchi visible or within the consolidated lung. When it comes to evaluating the lung fields, of course, you know, along with the air spaces, you have the interstitium of the lung. And if the interstitium is thick, this is considered pulmonary fibrosis. This is just an example of very thickened interstitium. Obviously, we've all seen cases where this can be very dramatic, where you can actually have honeycombing of the lungs. If the interstitium is spared, but rather you have destruction of the alveolar wall and enlargement of the air spaces, this is an example of emphysema. Emphysema is, you know, there's a couple of different types, but again, it is the enlargement of the air spaces and destruction of the actual alveoli without obvious interstitial fibrosis. Very frequently, you will find lung nodules, and this can be of quite, you know, it's important to know what to do when you encounter these. You know, we like to describe its size. We like to describe, you know, its morphology, whether it's calcified or not calcified, if it's partly solid, if it's a ground glass in appearance. And, you know, the Fleisch Society has come up with a whole group of recommendations of what further testing should be done on patients who have lymph nodes. So it's important to take a look at, or at least have in your lab, those criteria readily available. So should you see nodules, especially the benign looking ones, you can make recommendations of what their follow-up should be. But if something does not look right, you know, do not hesitate in recommending further testing. You know, there are some, you know, appearances of more malignant processes, and these generally will be nodules that are much larger in size. They're gonna be very irregular or speculated. They may have pseudo-cavitation within them, or air bronchograms. They may have very thick, irregular walls, very diffused calcium within them. And, you know, if you have prior imaging, they may show fast growth, or if these are PET studies, then, you know, they may demonstrate FDG uptake. So those are more worrisome findings that'll require, you know, earlier, need to be addressed earlier. And this is just an example of, you know, multiple lung nodules throughout the lung fields. And this is an example of, you know, a metastatic disease to both lungs, but with the tumor arriving to the lungs either by blood or lymphatics. So this is just one of those kind of views that once you see, you readily recognize next time you see it. So after that, once we've done the lung fields, again, the next part is frequently our images will acquire some portion of the upper abdomen. Here, you know, there's the liver, there's a spleen, stomach contents, some portions of the kidney, and we're gonna be looking for, you know, gallbladder stones, kidney stones, ascites within the abdomen, and such pathology. It's important, again, to be able to play with your images, to, you know, to look at all aspects. If your data set to identify these findings, because oftentimes the findings can be quite small. So one of the findings that's recommended not to be missed is a hiatal hernia. These are two examples of large hiatal hernias where really you have got, you know, the herniation of abdominal contents through the esophageal hiatus of the diaphragm into the thoracic cavity. They are two types. The most common type you'll encounter are the sliding hiatal hernias. And again, these are just manifestations of very large hernias. Ascites, you may notice, if there's a significant amount of fluid in the belly, this is considered abnormal and is considered ascites. You can, again, measure the Hounsville unit of ascites to determine whether it's transidative, exudative, or whether it's blood. And so, you know, this is just an example of a patient, liver disease patient with a small liver, large spleen, and a lot of ascites in the belly. With our obesity epidemic, it's not infrequent to find a lot of fatty livers. And as you know, this is an important finding to recognize because, and to report, because if this process goes unchecked, this will eventually lead to fibrosis of the liver and the development of cirrhosis. The way to identify this is the liver will have a very dark appearance, similar to the surrounding fat in the soft tissue. And an easy way is simply just to measure a Hounsville, you know, may create a large region of interest over the liver, and a Hounsville unit less than 40 is consistent with a fatty liver. Also note that you make this diagnosis, it should be done on a non-contrast CT scan. Gallstones, you know, there's several different types of gallstones. The gallstone that you're going to see are the calcified stones. Calcium is very easily seen on non-contrast CT scans. What we usually do is identify the size of the gallstone and where exactly it is that we're seeing it. Similarly, you know, there can be kidney stones. Most of the kidney stones are made of calcium, so they're very easy to identify. Again, on non-contrast CT scans, we will generally depict the size of it and the location of the stone. All right, so after looking at scout images, after looking at the heart and great vessels, after looking at the soft, looking at the breast and the soft tissue of the mediastinum, followed by looking at the lung and the pleura and the upper abdomen, finally, we are down to the bones. And here, you know, there's several bony structures in the thorax, including the sternum, the ribs, and of course, the vertebrae. And we're looking for fractures, looking for sternotomy, we're looking for possible osteolytic or blastic lesions within the vertebra, and we're looking for any sternal abnormalities such as pectus excavatum. So lesions that are not to be missed include lytic lesions of, you know, that may be seen in the ribs. Here, you can see a markedly enlarged ribs in comparison to the other ribs. And if you look closely, you'll see that the center appears hyperdense than the adjacent trabecular bone. So these would be considered lytic lesions in the bone. This requires further evaluation with additional imaging as it could be a sign of malignancy. Compression fracture, when looking at the spine, it's very important to look for compression fractures. These of course have a variety of causes, but what they will generally look like is a wedge-shaped defect. The exact definition is to lose height in the anterior, middle, or posterior dimension of the vertebral body that exceeds at least 20%. So you can see here, these look very rectangular, and this has compression both anteriorly and posteriorly. And this goes along. This is a vertebral compression fracture. So in summary, I hope I've been able to show you that, you know, hybrid imaging is here. We're gonna be interacting with CT images more and more. It can really, the addition of CT can provide a lot of diagnostic information about our patients. And it's very important to know normal anatomy on CT, so therefore you can identify abnormal pathologies and recommend further testing if necessary. I appreciate your attention, and thank you for the opportunity to speak to you today.

cardiac CT

nuclear cardiology

incidental findings

thorax anatomy

image interpretation

diagnostic imaging