 All right, we'll go ahead and get started. It is now 1201. Just want to say hello and welcome to the sixth of many live stream noon conferences hosted by MRI online. In response to the changes happening around the world right now and the shutting down of in-person events, we have decided to provide free daily noon conferences to all radiologists worldwide. Today we are joined by Dr. Jeanette Collins. She is a thoracic radiologist, an editor of seminars in a rent genealogy and MRI online. She is a prior program director, prior dean of graduate medical education and prior radiology chair. She is the author of Essentials in Test Radiology and over 225 papers. She is a past president of Society of Thoracic Radiology, Association of University Radiologist, Association of Program Directors in Radiology, Alliance of Clinician Educators in Radiology, Radiological Society of North America, the recipient of the RSNA Outstanding Educator Award, the AUR Gold Medal. Just a reminder that there will be time at the end of this hour for a Q&A session. Please use the Q&A feature and we will get to as many of those as we can before our time is up. That being said, thank you so much for joining us, Dr. Collins. I will let you take it from here. Thank you, Ashley. I'm honored to be a part of MRI online's initiative to provide free live streaming and on-demand education to trainees and practicing radiologists worldwide. Thank you all for attending. I also want to thank all of you who are making personal and professional sacrifices during the COVID-19 pandemic. The topic today is CT Patterns of Lung Disease. I have the following disclosures. I get paid by Walters-Clure Publishing. I get paid by Elsevier as Editor of Seminars in Rancology. And I get paid by MRI online as the Director of Medical Content. None of these entities influence the content of this presentation. These are three objectives for you. So this is what I want you to be able to do at the end of this presentation. To describe seven patterns of disease seen on CT. To recognize each of those seven patterns when you see them on CT. And lastly, to give a differential diagnosis for each of those patterns. This is a list of the seven patterns I will discuss. But I want you to look at the thumbnail images on the right because I think you can appreciate that the appearance of each is very different from all the rest. And that's why it's important to recognize patterns because doing so can help you narrow the differential diagnosis. And in some cases, suggest a specific diagnosis. I'll start with the honeycomb pattern. This is cystic air spaces that have thick, clearly defined walls. Typically layered along the pleural surface. Honeycombing represents pulmonary fibrosis. The most common cause of pulmonary fibrosis is idiopathic pulmonary fibrosis or IPF. This is the imaging equivalent of the pathologic diagnosis of usual interstitial pneumonia. Other causes of pulmonary fibrosis are collagen vascular diseases, asbestosis. And if you see a predominantly upper lung distribution of honeycombing, you want to think about end stage sarcoidosis and chronic hypersensitivity pneumonitis. This is a macroscopic specimen of a lung of a patient with pulmonary fibrosis. You can appreciate multiple holes in the lung representing the honeycomb pattern. This is a case of a 62 year old woman with chauvin disease. I'm showing you four images of the lungs spanning the upper lungs to the lower lungs so that you can appreciate that in most cases of pulmonary fibrosis with honeycombing, the disease is worse in the basis than it is in the upper lungs. If you look closely, you can see the cysts with clearly defined walls layered along the pleural surface. And if you get really close, you may even hear the bees buzzing in this honeycombing. There are two other features of pulmonary fibrosis that are also featured on this image. One is traction bronchiectasis. We can see that in the posterior right lung where we see dilated airways that are being pulled toward this area of fibrotic lung. And in the more anterior right lung, we can see a pulmonary vessel with a very arcuate contour because it too is being pulled toward this area of fibrosis. This is architectural distortion. So three main features of pulmonary fibrosis are honeycombing, traction bronchiectasis and architectural distortion. The next pattern is a cystic pattern which is thin walled circumscribed air filled structures in the lung. There are unlimited number of diagnoses to consider when you see this pattern. The two most common are Langerhans cell histiocytosis and lymph angioliomyomatosis. That's kind of a tongue twister, so we often call it LAM. Other diagnoses to consider are lymphocytic interstitial pneumonitis which commonly occurs with chogren syndrome, collagen vascular diseases and pneumocystis pneumonia. Now there's another item on this list, emphysema. I put that item here even though emphysema is not a true cystic lung disease, but it can look like cystic lung disease. This is what central lobular emphysema looks like typically. You can see numerous loosened areas throughout the lungs. Some people have called this the Swiss cheese appearance. As with any smoking related disease and central lobular emphysema is a smoking related disease, the findings are more prominent in the upper lungs. So how can you differentiate central lobular emphysema from true cystic lung disease? There are two ways. One, if you look at these loosencies throughout the lung, you can see that they don't all have circumferential walls. So I'm showing you one of these loosen areas in the left lung where you can see the posterior margin is not walled off. It does not have a true circumferential wall like true cystic lung disease will have. A second feature of central lobular emphysema is seeing an opaque dot or linear opacity or arcuate opacity within the center of the loosency. This represents the central lobular artery. You will not see this in true cystic lung disease. So let's look at some cases of true cystic lung disease starting with this case of a 50 year old woman with progressive shortness of breath and a history of spontaneous pneumothorax. This is a case of lymph angiomyomatosis. This is a pretty typical appearance of lamb where there are multiple round circumscribed nice looking cysts throughout the lung with absolutely normal intervening lung parenchyma. Lamb is a disease where the cysts occur throughout the lungs upper, mid and lower. You can suggest the diagnosis of lamb if it's a female pre menopausal patient. Lamb occurs in females. I actually did read a report of a male blue nose dolphin who had lamb, but I think it's safe to say that if it's a male patient unless he has tuberous sclerosis complex which is along the same spectrum of diseases lamb that it's going to be a female that has lamb not male. Now there are other features of lamb that can help distinguish it from other cystic lung diseases. One is that they often have pleural effusions, specifically chylous pleural effusions. And another feature associated with lamb are renal angiomyopomas. Here's another case of lamb where you can see multiple cysts in both lungs and this patient developed a common complication of lamb and that is spontaneous pneumothorax. There is a large pneumothorax on the left with partial collapse of the left lung. The pneumothorax is smaller on the right seen at the right apex and at the right base. Here's a third case of lamb. This is a very severe case. This patient had end stage lung disease secondary to lamb. Developed a spontaneous pneumothorax as shown by the letter P on the right. And when the case of lamb is so severe as it is here it can be sometimes hard to appreciate the cystic pattern because it almost looks just like diffuse honeycomb lung. This next case is of a 40 year old man with a history of cigarette smoking and an abnormal chest radiograph. He had no respiratory symptoms. This is a case of lamb's cell histiocytosis. This is another smoking related lung disease and therefore you would expect the findings to be most prominent in the upper lungs. So I'm showing you four images of the lungs from top to bottom so that you can see that the bases of the lungs are normal except for minimal ground glass opacity in the posterior lungs, which represents dependent adolectasis. But the findings of lamb's cell histiocytosis are in the upper lungs. And what are those findings? Cysts and nodules. Now, lamb's cell histiocytosis starts out as nodules which become cysts. So you may only see nodules or you may see both nodules and cysts or you may only see cysts. Typically the cysts of lamb's cell histiocytosis tend to be a little more thick wall than those seen with lamb and more irregular or more nasty looking. Not like the nice happy cysts that I showed you in the case of lamb. Lamb's cell histiocytosis is seen in the upper lungs. Lamb is seen, the cysts of lamb are seen throughout the lungs. Here's another case of longer Han's cell histiocytosis where you can see nodules and cysts. If you see nodules and cysts in the upper lungs of a cigarette smoker, you can make the diagnosis of longer Han's cell histiocytosis with about 99% degree of confidence. This is a case of lymphocytic interstitial pneumonitis, a patient with chauvin syndrome. Now this is a cystic lung disease that tends to occur predominantly in the lower lungs. You can see nice round cysts with circumferential walls. And there is a feature of LIP that can help distinguish it from other causes of cystic lung disease. And that is that patients with LIP have a greater incidence of maltomas and other types of lymphoma, as did this patient, which we can see by the presence of this nodule in the periphery of the left lung. This is a case of pneumocystis pneumonia, the most common feature on CT of pneumocystis pneumonia is ground glass opacity, which I will be discussing in just a minute. This patient does have a lot of ground glass opacity in both lungs, but another feature is this cyst. In this case, this is an irregular cyst. And in fact, in pneumocystis pneumonia, the cysts are actually expanding pneumata seals. That's what the P stands for. You can see cysts with pneumocystis pneumonia that are very small and very thin wall, or you can see cysts that are quite large and have thick walls. You may see one or two cysts or there may be multiple cysts. Here's a different case of pneumocystis pneumonia, presenting predominantly with ground glass opacity, especially in the left lung, but also this multi-loculated cystic structure. And that's been a defining feature of pneumocystis pneumonia, is cysts that are multi-loculated. If you see this pattern of ground glass opacity and multi-loculated cysts in a patient with AIDS or who is otherwise immunocompromised, you must suggest the diagnosis of pneumocystis pneumonia. I'm going to talk next about four nodular patterns. One is the perilimphatic pattern. Another, when there is no discrete pattern, I call random. Third is a central lobular pattern. And then fourth, bronchovascular. I'll start with the perilimphatic pattern. Note that my differential diagnosis includes only one thing because the most common cause of the perilimphatic pattern is sarcoidosis. To understand what I mean by perilimphatic, it's helpful to look at an illustration of the lymphatic distribution in the lung. The lymph starts in the subplural lymphatics and courses more centrally along the bronchovascular bundles to drain into the higher lymph nodes. So now hopefully you can see how a perilimphatic distribution will be subplural and bronchovascular. A perilimphatic distribution is subplural and bronchovascular. The classic appearance of parenchymal sarcoidosis is nodules in a perilimphatic distribution. Note the nodules in a subplural location. Remember that the fissures are also plural line. So expect to see nodules along the fissures as well. The bronchovascular bundle on the left shows that it is very beaded in appearance, very irregular. You can see how it differs from the bronchovascular bundle in the right lung. So this is peribronchovascular nodules. These are subplural nodules. This represents a perilimphatic distribution of nodules. The classic parenchymal findings of sarcoidosis. Here's another case of sarcoidosis with subplural nodules and nodules along the bronchovascular bundle. Note that some of these nodules are a little bit larger than the nodules I showed you in the last case. The nodules in sarcoidosis tend to be one to five millimeters in size but can sometimes be a sonometer or even larger. And yet another case of sarcoidosis with perilimphatic distribution of nodules, subplural and bronchovascular. Now, when there is no dominant pattern, we can think of it as a random pattern. And the diagnoses to consider in this case would be silicosis and co-workers pneumoconiosis, tuberculosis and fungal infection. And by the way, whenever I say tuberculosis, fungal rolls right off my tongue because all of the features of tuberculosis can also be present with fungal disease. And metastases also will have a random pattern of nodules. In this case, we can see multiple small one to three millimeter nodules profusely throughout both lungs. Now, you may be seeing that there are some nodules in a subplural location, but the dominant pattern is not subplural. The dominant pattern is random. This is a typical appearance of simple silicosis. And with this appearance, with this profusion of nodules, these patients are often asymptomatic. But over time, these nodules coalesce, they become mass like, progressive massive fibrosis is the term we use for that. And those patients are symptomatic. This is a case of biliary tuberculosis. Looks very much like silicosis. And this is a case of colon cancer metastases. There are a couple typical features of metastases to the lung, whether it's from a primary bronchogenic carcinoma or an extra pulmonary tumor. And that is that the nodules tend to be well circumscribed and they tend to be varying in size with some very small and some very large. The next nodular pattern I'll talk about is the central lobular pattern. And to understand this, I'm showing you an illustration on the left of the secondary pulmonary lobular architecture. The secondary pulmonary lobules are the smallest unit of lung that may be seen on CT. They are seen best in the periphery of the lung. The hexagonal shape of the secondary pulmonary lobule is formed by the inter lobular septae. And in the middle of the secondary pulmonary lobule is the core pulmonary artery and bronchiol. Now, if you take away the septae and just leave the core structures behind, as I'm showing you on the right, you can see that the central pulmonary arteries or whatever may be affecting the central lobular structures are fairly equidistant apart. So a central lobular pattern of nodules will be nodules that appear fairly equidistant from each other. And here are two diagnoses to consider when you see this pattern. Subacute hypersensitivity pneumonitis, also called extrinsic allergic alveolitis and respiratory bronchiolitis. Now, respiratory bronchiolitis is a disease of exclusion. It occurs in the upper lungs of cigarette smokers. Remember that all smoking related lung disease tends to occur predominantly in the upper lungs. This is a pretty typical appearance of hypersensitivity pneumonitis. Note when the main features of the central lobular pattern, at least how I define it, is that the nodules are not dense like they are in the cases I showed you of silicosis or miliary tuberculosis. These nodules are hazy ground glass opacities. And I think you can imagine that they're fairly equidistant apart because they're so hazy, they're a little bit hard to recognize as discrete nodules. But that's part of the typical appearance of hypersensitivity pneumonitis. This CT scan is of a patient who had multiple symptoms, cough, dyspnea, shortness of breath, et cetera. And she went to the hospital, she was admitted, she was treated with antibiotics and got better. And then she went home and all of her symptoms reappeared until it was discovered that she was allergic to her parrot. This is a typical scenario of people with hypersensitivity pneumonitis. They'll get better in the hospital, not because of the antibiotic treatment, but because they're away from the offending substance that they're allergic to. Here's another case of hypersensitivity pneumonitis, numerous hazy ground glass nodules. Perhaps you can imagine that they're about equidistant apart from each other. This next case is of a 43-year-old man with shortness of breath and a history of cigarette smoking. This patient had no respiratory symptoms, but I saw all of these ground glass nodules. The arrows point to a couple larger nodules, but if you look closely, you can see that there are multiple tiny ground glass nodules all over in the lungs. Now you wanna be careful in situations like this that you don't automatically start thinking about cancers and infections and numerous other diagnoses that this could represent in a patient who's asymptomatic. If it's a cigarette smoker, at least be thinking about the diagnosis of respiratory bronchiolitis, particularly if they have this appearance and they have an upper lung predominant distribution. Now the last nodular pattern I will discuss is the bronchovascular pattern. And here are some things to consider. Lymphoproliferative disorders, lymphengetic carcinomatosis, capacy sarcoma, sarcoidosis, organizing pneumonia and infectious pneumonia. This is a patient who had undergone bone marrow transplant and developed post-transplant lymphoproliferative disease. This is a very typical appearance of post-transplant lymphoproliferative disease. Ill-defined nodules along the bronchovascular bundles. If you know this patient has had a bone marrow or solid organ transplant and you see these findings, you can be very confident in suggesting the diagnosis of post-transplant lymphoproliferative disease. Now you can't exclude infection, but the treatment for post-transplant lymphoproliferative disease is a decrease in immunosuppressive therapy, which is very different from the treatment of pneumonia, which is some kind of antibiotic. And if you don't decrease the immunosuppressive therapy, this disease can progress and become malignant lymphoma that isn't well treated. This is a case of capacy sarcoma, which is still occurring in patients with AIDS. Nodules along the bronchovascular bundles tend to be in the lower lungs. They may be small nodules, causing a beaded appearance to the bronchovascular bundle. Or the nodules may become a little bit larger, creating what people have referred to as flame-shaped nodules. Or the nodules can coalesce, as we're starting to see in the left lower lung, creating more mass-like appearance. It's hard to distinguish individual nodules when the disease progresses to this state. There are a couple other features of capacy sarcoma that help differentiate it from other causes of bronchovascular nodules. One is septal thickening. In the left anterior lung, we can see this opaque linear opacity representing thickening of the interlobular septa. This is equivalent to the curly B lines that you see on chest radiographs. This patient also has small pleural effusions. If you see these findings of bronchovascular nodules, septal thickening and pleural effusions in a patient with AIDS, you should suggest the diagnosis of capacy sarcoma. I show you again this case of sarcoidosis just to remind you that bronchovascular nodules are a subset of the perilympathic distribution. Remember the perilympathic distribution is subplural and bronchovascular nodules. The next pattern is ground glass. If you've never seen it before, well, here's an image. And what it is, is glass that you can see through. You can see the person's hand through the glass. On chest CT, ground glass is hazy opacity that does not obscure the underlying airways or vasculature. It's a very nonspecific finding and the differential diagnosis is very long. But here are some of the most common findings when you see most common causes of ground glass pattern or at least when you see ground glass, it's very typical for the particular diagnosis. Infectious pneumonia commonly presents as ground glass opacity with or without consolidated areas of lung, pulmonary hemorrhage, particularly in a patient who say a month out from bone marrow transplant. If you see diffused ground glass opacity, you want to be thinking about pulmonary hemorrhage. Organizing pneumonia, pulmonary alveolar prodenosis, and even one type of cancer, adenocarcinoma in situ. Less common causes of the ground glass pattern, but very typical for those diagnoses, is deschromative interstitial pneumonitis and nonspecific interstitial pneumonitis. I put the very last item in capital letters, emphasized with an exclamation point, so that you always will remember to think about pulmonary edema when you see ground glass opacities. Although it's very nonspecific, edema is very common. Well, here's a case of diffused ground glass opacity. Note that you can still see the pulmonary vessels and the airways. This is a case of mycoplasma pneumonia, but this could just as easily be any other infectious etiology, especially any viral disease. This could be a severe case of COVID-19 pneumonia. This could be diffused pulmonary hemorrhage. This patient does have small pleural effusion, however, which is not a typical feature of COVID-19 pneumonia. Here's a case of a patient who has scattered ground glass opacities and also small cysts in the right posterior lung and the left anterior lung, as well as a few areas of more consolidated lung. Now you might already know what the diagnosis is because I showed you a similar case earlier, a patient who had ground glass opacity and cysts. This is a case of pneumocystis pneumonia. This is a typical case of organizing pneumonia, peripheral ground glass opacities. In about 50% of cases of organizing pneumonia, you will see a peripheral distribution of ground glass opacities and also in some cases, consolidation. You may be familiar with this appearance of peripheral ground glass opacities if you've been seeing some of the cases of COVID-19 pneumonia that have appeared because this is a typical finding in the early stages of COVID-19 pneumonia. As well as in addition to peripheral ground glass opacities, you may also see rounded nodular areas of ground glass opacity. And after about 10 to 12 days, COVID-19 pneumonia can progress to more profuse ground glass opacity and even areas of consolidation. Now it's not surprising that COVID-19 pneumonia presents in a similar fashion to organizing pneumonia because pathologically we know that what we're seeing on the CT scan in cases of COVID-19 pneumonia is organizing pneumonia. This is a case of pulmonary alveolar proteinosis. In addition to ground glass opacity and even some areas of consolidation, we see amidst the areas of ground glass opacity, these thickened intralobular lines and intralobular septi, creating what is called crazy paving. Crazy paving is a buzzword. It was coined, the term was coined for pulmonary alveolar proteinosis. But since then, we've identified multiple other causes of crazy paving. So it's really a non-specific finding. This is another case of pulmonary alveolar proteinosis where you can see the few areas of ground glass opacity and intralobular lines and thickened intralobular septa, crazy paving. There's also an incidental finding on this coronal CT scan. Did you notice this arcuate opacity in the right apex? And do you know what that is? Well, if you said that's an accessory asagis fissure, you are correct. Now, what is this rounded opacity abutting the inferior edge of this fissure? Well, if you said that's the asagis vein, then you are correct a second time. Normally, the asagis vein is positioned at the right tracheobronchial angle, but the asagis vein is always abnormally superior in position when there is an accessory asagis fissure. As I said earlier, you can even have cancerous causes for ground glass opacity in the lung. Most typically, that will be adenocarcinoma in situ. These two images are from two separate patients with adenocarcinoma in situ, showing the typical appearance of a rather ill-defined but rounded area of ground glass opacity. You have to be vigilant to look for these areas and you can't determine that if they've been stable on a CT scan for a year that they are okay, benign, and you can forget about them because adenocarcinoma in situ can be a very indolent type of cancer. And I've seen numerous cases where these ground glass nodules do not change perceptively in a year or two years. And I have a couple cases where they did not change significantly in five years and then they can start to enlarge and become more aggressive. Here's a case of numerous areas of ground glass opacity and septal thickening. This is a case of pulmonary edema. Remember that pulmonary edema is such a common diagnosis that you need to think of it often. The next pattern is the mosaic pattern. Now mosaic just refers to heterogeneity. And I've already showed you infiltrated disease that can cause a mosaic pattern of lung attenuation such as multifocal pneumonia. So I'm gonna focus on two of the other main causes of a mosaic pattern of lung attenuation, small airways disease and pulmonary vascular disease. This is a patient who had a bone marrow transplant and developed chronic rejection which pathologically is seen as obliterative bronchiolitis. This is a disease where there is closure of the small airways in the lung. I'm showing you two images. One is taken during inspiration. The second image was after the patient was instructed to take in a big breath, blow it all out and hold it. So that's an expiratory image. If you haven't seen expiratory images before, you should become familiar with the features that define them as expiratory. One is that on expiration, the posterior membranous trachea will be bowed anteriorly. Note that on the expiratory image, the trachea is either nice and round or ovoid in shape. On expiration, the trachea is bowed and takes on an arcuate shape. The second feature of expiratory images is decreased lung volume. You would expect that because when you blow the air out of your lung, the lungs have less volume. In addition, with less air in the lung, the overall Houndsville attenuation of the lung will increase. So you expect to see more opacity in the lungs on expiration compared with inspiration. Now, this inspiratory image looks normal. If you look really closely, you may be able to see a little bit of heterogeneity in the lung attenuation, but most days I call that normal. But it's wildly abnormal on the expiratory image. These images were taken one minute apart. What's happening is the air is getting into the small airways, but it can't get out on expiration. So the air is trapped and that's what these loosen areas represent is trapped air. The more highly attenuating lung is the normal lung where the air gets out on expiration. This is a mosaic pattern of lung attenuation due to obliterative bronchiolitis. In some cases of obliterative bronchiolitis, the disease is so severe that most of the lung traps air and even on inspiratory images, you may not be able to appreciate the mosaic pattern of lung attenuation. I think you can still see it a little bit in this case where there are areas of lung that are more loosen next to areas of lung that are more opaque, but it's not as dramatic as I showed you on the last image. This patient has more severe small airways disease and also has other features of small airways disease. If you look at this bronchovascular bundle on the left lung, this is in the lingula, what you see is the airway is dilated and thick wall. The pulmonary artery next to it is of smaller diameter than the adjacent airway. Normally they are the same diameter, but this airway is abnormally dilated. This is referred to as the signet ring sign. Now those were cases of mosaic lung attenuation secondary to small airways disease, but vascular disease can also cause mosaic lung attenuation. We often refer to that as mosaic perfusion. This is a case of sickle cell disease. Now what happens in sickle cell disease is that the red blood cells take on a sickle shape which clogs the pulmonary vessels. That leads to decreased perfusion to the subtended lung. And since the lung is not being normally perfused, it is more lucent appearing. The normally perfused lung will be of higher attenuation than the lung that is not being normally perfused. Another clue that can sometimes help to determine a mosaic pattern of perfusion is that the vascular structures in the abnormally perfused lung are diminutive compared with the vascular structures in the adjacent normally perfused lung. Another vascular disease that can result in mosaic perfusion is chronic thromboembolic disease. Here's another case of mosaic perfusion on coronal CT. You can appreciate the heterogeneous appearance in lung attenuation. The next pattern I'll talk about is the tree and bud pattern. This is centralobular dots and linear branching opacities seen best in the periphery of the lung. Remember the secondary pulmonary lobules I showed you? The centralobular arteries and airways run in the center of the secondary pulmonary lobules. When those small airways become impacted by mucus, or other type of debris, they are seen as these dots or linear branching opacities on CT dependent upon whether they're seen in profile or cross-section. What they are is dilatation and impaction of the small bronchioles. You may be seeing this outside your window today. I took this image outside my office window. It's a tree in bud. A tree is analogous to the airways of the lung because they both branch and taper as they go from the center to the periphery. But what's happening here is that at the very end of the limbs, it's not tapered. There are multiple rounded Y-shaped densities that represent the budding. Well, on a CT scan of a patient who has infection or something that is filling the small airways and dilating them, you will see these small irregular opacities. This is the differential diagnosis from a tree in bud pattern that I'm gonna start with because if you don't remember anything else from this presentation, I hope you'll remember that the most common cause of the tree in bud pattern is infection. The most common cause of the tree in bud pattern is infection, any type of infection. This is a case of bacterial bronchiolitis. And what we see is predominantly in the periphery of the lungs where the small airways are located. You see these linear and branching opacities. In some cases, you see dots as in the posterior right lung here, another dot here, another dot here. When you see the dot, you're seeing the impacted small airway that's not in profile. It's seen in cross-section. And when you see the linear opacities, you're seeing the impacted airways in profile. This is a case of mycobacterium avium complex showing the same tree in bud pattern. And this is a case of methicillin resistant staphylococcus aureus pneumonia showing you the tree in bud pattern. Now, this patient's pneumonia also caused occlusion of the left lower lobe airways leading to left lower lobe collapse. And that's why you see this straight edge representing the posteriorly displaced left major fissure. Well, there are other ideologies of the tree in bud pattern including allergic bronchopulmonary aspergillosis, cystic fibrosis, aspiration and diffuse pan bronchiolitis. I won't be talking about this latter entity. We don't see it often in North America, but some of you listening to me now may be from Asia, where there is a greater prevalence of this disease and it can have the same appearance as the other diagnoses that I'm going to be discussing. Allergic bronchopulmonary aspergillosis is a type of aspergillus lung disease that is not infectious. It is an immunologic response to the aspergillus hypha that accumulate in the airways caused damage to the airway walls leading to bronchiectasis. The seniquanon of allergic bronchopulmonary aspergillosis is central bronchiectasis as we see here in the right upper low, a very dilated airway. Now sometimes the airways are patent in ABPA and sometimes they are impacted with aspergillus hyphae, mucus, and other debris. When they are impacted, they will appear opaque on chest radiographs and on CT scans and they may take on the appearance of a finger in glove or a Mickey Mouse ears or other such descriptions. But ABPA not only can involve the central airways, but the aspergillus hyphae and other debris can extend into the small airways creating the tree and bud pattern that we can see in the right lower low posteriorly. ABPA is not treated with antibiotics. It's usually treated with corticosteroids because it's an immunologic process. Cystic fibrosis is a disease where patients make too much mucus that collects in the airways that also damages the airway walls and leads to bronchiectasis. Typically early on in cystic fibrosis, you will start to see dilatation of the central airways. And later on, as the disease progresses, it will involve the more distal small airways. Just as an ABPA, you may see the airways as patent or you may see them impacted. This patient has both central bronchiectasis as well as bronchiolectasis and tree and bud opacities from impacted small bronchioles. Uncommonly, cystic fibrosis may predominantly involve the small airways. This is unusual, but I have seen more than one case of this. I practice in a hospital where we do cystic fibrosis research and I have read numerous chest radiographs and CT scans, thousands actually, of patients with cystic fibrosis. So I have come across this where you see these tree and bud opacities representing involvement of the small airways but the central airways don't really look that bad. This is a case of a patient who aspirated which caused impaction of the small airways creating the tree and bud pattern. And you'll notice that this area of tree and bud opacity in the posterior right lung has the appearance of a jack in that ball and jacks game that you may be played when you were younger. I used to love that game myself. And that's why this is sometimes referred to as the jacks sign. Dr. Collins. Yes. I hate to cut you off here but we've got just a few minutes left and you have some excellent questions happening in the question and answer section. Thank you, Paul. So let me wind this up by saying that the last pattern is septal thickening and it can be smooth or irregular but smooth septal thickening is usually due to pulmonary edema. Look for ground glass opacities and pleural effusions to suggest that diagnosis. Look for curly lines that you typically see on a chest radiograph which you can call them that on CT. And lymphogedic carcinomatosis which tends to cause beaded septal thickening. And I wanna say this because it's important when you see beaded septal thickening and nodules throughout the lung and it involves only one lung it's almost always lymphedic carcinomatosis due to primary bronchogenic carcinoma. So let's look at some cases. Ready to see if you learned those three things that I wanted you to have as your objectives. What's the pattern? And your options are honeycomb, cysts, nodules or cysts and nodules. Let's see what you think. And 85% of you said cysts and nodules and you are correct. Excellent. This patient has numerous cysts and nodules throughout the lung but we're not done yet. So now that you have the pattern you probably have a differential diagnosis and to narrow that differential diagnosis you need to ask the question. What question do you need to ask? What is the person's occupation? Are they a cigarette smoker? Do they have fever, chills and night sweats? Or do they have a history of a college and vascular disease? Let's see what you think. Well, there's quite a spectrum of answers here. The majority of you want to know whether the patient is a cigarette smoker. And that is exactly the question that you should ask because this is a 32 year old man with a history of cigarette smoking who had nodules and cysts in the upper lungs. The typical presentation and CT appearance of Longerham's cell histiocytosis. Next case, what is the pattern? And these are your options, honeycomb, cysts, nodules and cysts and nodules. Let's see what you think. And 97% of you are correct. This is a pattern of nodules. Specifically, hazy ground glass centralogular nodules. And this is the patient's history. Worsening dyspnea on exertion, cough, fever, chills, anorexia. She is not a smoker, but she does have a pyrrhic at home. So what's the most likely diagnosis? Asbestosis, Longerham's cell histiocytosis, respiratory bronchiolitis, or hypersensitivity pneumonitis. And what did you say? 97% of you got this right, hypersensitivity pneumonitis. Now you could have thought of respiratory bronchiolitis which can appear as centralogular ground glass nodules although it's not usually as diffuse as in the case I showed you and it's a diagnosis of exclusion. Patients with respiratory bronchiolitis are typically asymptomatic. So this was a case of hypersensitivity pneumonitis. Next case. Now I want you to figure out the pattern and tell me what the most likely history is. Is this a foundry worker, a cigarette smoker, a patient with a lung transplant, or asthma? What did you think? And 82% of you said lung transplant and you were right. What we see here are numerous nodules that are predominantly in a bronchovascular distribution. In a patient with a transplant, this is very suggestive of post-transplant lymphoproliferative disease. Case four, what is the most likely diagnosis? And these are your options, asthma, aspiration, diffuse pan bronchiolitis, or obliterative bronchiolitis. Let's see what you think. And quite a smattering of answers, which I thought might be the case. But the answer here is aspiration. Now, you may be looking at this image and say, well there's tree and bud opacities and that can occur with asthma, aspiration, diffuse pan bronchiolitis, or obliterative bronchiolitis. So why is it aspiration? Well, you also had to notice another feature, an air fluid level in the esophagus, in this patient with ecolasia associated with aspiration. Ready for one more final case? What pattern is shown? Tree and bud, nodules, mosaic pattern of lung attenuation, or honeycomb? Well, what did you think? 95% of you said honeycomb. Great. Pat yourself on the back. This is a honeycomb pattern, multiple cysts layered along the pleural surface. What diagnosis should be considered? Diffuse pan bronchiolitis, bronchogenic carcinoma, lymphin genetic carcinomatosis, or silicosis. And we need the poll, Paul. Thank you. Okay, please select your option now. And what did you think? Well, I'm also not surprised that there's a smattering of answers here. A lot of people thought diffuse pan bronchiolitis or silicosis. This was a tricky one. I have to tell you that this is a honeycomb pattern, which is not a typical pattern for any of these diagnoses. So to know what the diagnosis is, you had to be able to find this bronchogenic carcinoma in the periphery of the left upper low. It's harder to appreciate nodules in patients with diffuse lung disease. So you have to be very vigilant to look for nodules that may represent cancer in patients with diffuse pulmonary fibrosis. In patients with diffuse lung disease, including pulmonary fibrosis, have a greater incidence of bronchogenic carcinoma than does the general population. So that ends my formal presentation. And I don't know if we have any time for any questions, but I can answer them if you email them to me or ask them online. Dr. Valentin, take a few minutes and answer just a couple of questions if you would like. Okay, let me go to questions and answers. How do you distinguish GGO ground glass opacity from mosaic? And that would refer to mosaic lung attenuation. Well, ground glass opacity can really be considered a component of mosaic lung attenuation because mosaic lung attenuation just means heterogeneity of the lung attenuation. Some areas appear ground glass in appearance. Some areas appear loosened. But if you want to determine whether the heterogeneity is due to an infiltrative process or due to an airway process, you should do expiratory images because the heterogeneity and lung attenuation will be accentuated when it is due to an airway process like obliterative bronchiolitis. It will not be accentuated if it's due to an infiltrative process like pneumonia. Another question is, for honeycomb, do you use specific numbers of layers to call honeycomb? Some have told me there should be three tiers to call it honeycomb. Well, to me, a layer is more than one. So if I see at least two rows of cysts, to me, that's layered. And it really doesn't matter though. I mean, sometimes in pulmonary fibrosis, you may only see one row, but it can be helpful to distinguish honeycombing from centri-logular emphysema sometimes because centri-logular emphysema won't be layered whereas honeycomb very often is. But you don't have to have layers to be able to diagnose pulmonary fibrosis. Can COVID-19 have crazy paving secondary to bacterial consolidation and pleural effusion? Yes, COVID-19 pneumonia can present with crazy paving. That's usually one of the later findings seen after 10 to 12 days, but it is one of the noted features in the cases of COVID-19 pneumonia that have been reported. And consolidation is also seen in later stages of COVID-19 pneumonia. Pleural effusion, however, has not been described as a typical feature of COVID-19 pneumonia. And if you see pleural effusion or cavatary lesions in the lung or evidence of empyema, you should be thinking of something either unrelated to COVID-19 or as a super infection in patients with COVID-19 pneumonia. And those are the patients for which CT scanning is recommended. Cystic fibrosis versus allergic bronchopulmonary aspergillosis. Well, they can look similar because they can both involve the small and the large airways. Patients with cystic fibrosis usually have a much different presentation. The diagnosis is usually made when they're young and it's a progressive disease that gets worse as they age, whereas allergic bronchopulmonary aspergillosis generally develops later in age and is not something that progresses over time the same way as does cystic fibrosis. Cystic fibrosis also affects other organs like the pancreas and the GI tract. So that can help make the differential between the two as well. On CT scanning, if you're just looking at the findings, however, of one point in time, they can look very similar. So I talked about how to differentiate paracental emphysema from honey combing. Why do you get tree and bud and anterior segment in aspiration? Well, sometimes it depends upon how the patient is positioned because aspiration is a gravity-dependent phenomena. So the aspirated material will go into the airways that are within the most gravity-dependent portion of the lung. I've seen numerous cases where patients have been prone in position while they're on the operating table and they aspirated or they may be prone for some reason while they're in the intensive care unit. And so you will see areas of tree and bud opacity in the anterior, non-dependent, what is typically the non-dependent area of lung if they have aspirated while they're in the prone position. Dr. Collins, thank you so much for your time today and thanks to all of you for participating in our noon conference. Reminder that this conference will be made available on demand within the next 24 hours on MRIonline.com. Please join us tomorrow, March 31st at 12 p.m., as Dr. Pomerance will be with us for a noon conference on critical concepts and spinal imaging. Please visit us on our website and follow us on social media to be notified of reminders and updates. Thanks so much and have a great day. Thank you.