 Hi, this is Mark Gosselin. We're going to now keep going with the Cardiopulmonary Imaging Master Series. This session is going to be on aspiration. And aspiration is a very common thing that we see, especially in ICU patients. The objective is to understand how common it is and that it is most likely the cause of low-grade fever in these ICU patients. And as on our previous episodes or previous sessions, atalexus is not. Atalexus is not a cause for fever. That is a myth. And if you still teach it, you need to stop. Recognize the common imaging findings of aspiration. We'll go over them and we'll briefly just kind of review again, compare and contrast the CT enhancement of atalexus versus consolidation. So this is an ICU patient, endotracheal tube, central line. And what we have here is bilateral lower-lobe areas of ill-defined opacity. We see some of the vessels of ground glass, other areas we don't, consistent with consolidation. What you notice though is that margins are a little ill-defined and the patient does have a low-grade fever. Well, rather than saying, well, it's the atalexus, no, this is more consistent with aspiration. Now another term that is commonly used and you feel free to use it is the term retained secretions. People who just can't cough up their bronchial secretions and that can sometimes have an overlapped appearance. So if it's clearly a big consolidation, call it aspiration. If you're not sure, aspiration slash retained secretions. And then again, this is most likely the cause of low-grade fevers. What does it look like? Well, it looks different than atalexus in most cases. You might see the poorly-defined three to four millimeter clustered nodules. That's really key. It spares the subplural area. So if it looks like it's touching the pleura, that's probably more of a consolidation. This is the so-called budding tree, right? Appearance, and that's what it looks like on a radiograph, three to four millimeter nodularity. There'll be airway thickening, mucus plugging. And the other thing you might notice is you'll just gestalt the radiograph and it just looks busy. And if it looks busy and you see that kind of clustered three to four millimeter nodularity, probably some aspiration slash retained secretions. It's gravity-based and that's the key thing. It just kind of goes down to the lowest point of the terminal bronchials. If you're lying on your side, that's usually part of the lung that overlies the axilla. If you're upright, it's gonna be middle low and lower lows. That's the key. It's gravitational-based. Just a quick statement about this so-called dense hyalum or B6 side. Anybody who's intubated or been extubated on a supine, the hyalum will look big and ill-defined and dense. The hyalum is not changed. That is simply adelexis or aspiration slash retained secretions in the superior segments of the lower lobes overlapping. And this is what it looks like. Look at the hyalum and the tracheal tube removed. Now look at the hyalum. The hyalum really are exactly the same. The pulmonary arteries haven't changed, but this ill-defined nodular kind of consolidated process and increased density, it's more white, represents the aspirated secretions that are in the superior segment. This is often misdiagnosed as pulmonary congestion in edema. It is not. It is a normal variant. Another patient, what do you see? Well, it's busy. You see a lot of three to four millimeter nodularity. It spares the subplural. It's in the dependent portion of both lower lobes, posterior segment of the upper lobe. This is an aspiration. You can see aspiration is airway related. And you can see the dependent portion, some of it's coalescing. This is characteristic for aspiration immunitis. If this were a trauma patient, this is aspiration, not contusion. Why? Because contusion doesn't bleed just in the airways, right? So this is aspiration, low-grade fever. Now, just to compare again with our previous session, this is adolescence. Notice it's got sharp margins and radiates from the hyalum. That's what adolescence is. It doesn't cause fever. This is different. Look at this, it's slightly busy here, right? Witness aspiration. You see these little three to four millimeter branching clustered nodules sparing the subplural, dependent portion of the lung. This is aspiration immunitis slash retained secretions. This is a few days later. This induces a low-grade chemical immunitis and is a likely cause for low-grade fever. Think about it. When a patient is aspirating, they're usually kind of on their PCA pump of morphine. They're aspirating small amounts. When you wake them up, have them use the incentive spirometer, they cough it up, clear it, and the fever goes away. That has been missed hot in our, by the many generations of physicians is saying, see, that's why adolescence causes fever. No, it was aspiration all along. Patient with a feeding tube going in the wrong direction, feeding up the esophagus and then down into the lung. Large amount of aspiration. You should be aware the endotracheal tube does not protect you from aspiration. It can still occur. In fact, does almost 24 seven. In this case, that aspiration is more than just an aspiration immunitis. That's a full-on consolidation and likely high-grade fevers, aspiration pneumonia. Another patient with high-grade fevers, remember aspiration immunitis, it'll give you low-grade fevers, atalexis gives you no fever, aspiration-based infectious pneumonia, high-grade fevers. And that can be a useful way to help differentiate the three, okay? That's a big consolidated aspiration-based pneumonia. Word-of-wise, aspiration pneumonia is almost always gram-negative bacteria. The so-called anaerobic, that was from the 50s with the skid row, bad dendition. So we don't see that as much anymore. Aspiration pneumonia should equal gram-negative bacteria like pseudomonas. Just as a review, if you have a contrast-enhanced CT scan, pneumonia or consolidation enhances less than atolectasis. Atolectasis, all the vessels are together. It fills with the contrast and is very bright. Consolidation, the vessels are separated. It does not enhance to the same degree. It should enhance the same as the perispinal muscles and it does, atolectasis enhances much more. So if you're someone who says it could be atolexus or pneumonia in a CT that's contrast-enhanced, you can favor one very strongly over another. So with that, that's review. Atolectasis is not a cluster fever. Please don't propagate that myth. It's most likely aspiration, which will be gravitational. Look for the busy clustered nodularity. And remember that atolexus and consolidation enhance differently. Thank you very much.