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Hi! This is Siva P. Raman. I am an assistant professor of radiology at Johns Hopkins. And over the course of this lecture, I'm gonna talk a little bit about the CT imaging of solid pancreatic masses.
Now we're going to begin with a very brief introduction, talking a little bit about protocol optimization and specifically, how we at Hopkins choose to image patients with a suspected pancreatic mass. But we're gonna spend most of this lecture really going into two major types of pancreatic masses,that I think come up most often in clinical practice.
We'll start by talking about pancreatic adenocarcinoma which I think is probably the most important, and something you all should be familiar with in your day to day practices. And then we'll talk about pancreatic neuroendocrine tumors, the prototypical hyper vascular pancreatic mass. Now for each of these lesions, we're gonna talk about staging, how you can help the surgeon determine what's resectable and what's not, as well as a few mimics that potentially could look a lot like an adenocarcinoma or neuroendocrine tumor.
Now as far as I'm concerned, having proper CT technique is absolutely critical when you're imaging a pancreatic mass. Now I'm gonna help you in terms of identifying the lesion, but if you don't have the right technique, you're not gonna be able to tell what that mass is. Is it an adenocarcinoma? Is it neuroendocrine tumor? And moreover, you're really gonna have trouble telling whether you're dealing with a pancreatic or a peri pancreatic lesion.
But once you've identified the lesion and figured out what it is, having that proper technique is critical in terms of local regional staging, identifying distant metastatic disease, and providing your clinician that critical information as to whether or not a lesion is resectable or not. Now our standard pancreatic protocol at Hopkins is a dual phase study. So any suspected pancreatic pathology, not just a mass, but things like pancreatitis are gonna get a dual phase study. So typically that entails an arterial phase at roughly 25 to 30 seconds, and then a venous phase at roughly 50 to 60 seconds.
Now note that we do not give these patients positive oral contrast, not only will that interfere with your 3D post processing, which we put a lot of emphasis on at Johns Hopkins, but you can also end up with streak artifact and beam hardening artifact, that I've seen examples where that artifact can actually obscure lesions on the pancreas.
Rather, patients with suspected pancreatic pathology are just gonna get a neutral contrast agent, either water or volumen, typically about a liter of water or volumen, including some immediately prior to injection. Now it is critical that you give a brisk injection of IV contrast, at least 3 to 5 cc's per second, and we give Omnipaque or Visipaque depending on the patient's renal function.
Now why exactly do you need two phases? Now what's the point? Why not just do a single venous phase like we do for a lot of other things? And there's a couple of reasons for that. First of all, the arterial phase is critical in terms of differentiating vascular tumors, especially neuroendocrine tumors from pancreatic adenocarcinoma, which tends to be hypodense and most conspicuous on the venous phase. It's also important in cases of neuroendocrine tumors, in terms of identifying vascular metastases,whether it's lymph node Mets or liver metastases from a neuroendocrine tumor, they're going to be most evident on the arterial phase.
Now even though arterial phase imaging is most important for neuroendocrine tumors, it is worth noting that there are rare cases where adenocarcinoma will be more conspicuous on the arterial phase, and having both of those phases together increases your odds of catching a subtle tumor.
On top of that even once you've identified the lesion, vascular mapping techniques are gonna help you determine vascular tumor involvement. And that's critical for adenocarcinoma, right? The distinction between a lesion with just subtle abutment of the SMA, or full 360 degree encasement of the SMA, is quite significant in terms of whether or not that patient is resectable.
Now the venous phase images of course for pancreatic adenocarcinoma are going to be the most important. The vast majority of adenocarcinoma will be most conspicuous on the venous phase. And identifying metastatic disease, especially to the liver and local regional lymph adenopathy, again for pancreatic adenocarcinoma, is going to be best done using the venous phase.
Now on top of that, determining the tumor's resectability will always entail looking at the portal veins and the SMV, and that's best done on the venous phase images.
And of course you're not just looking at the pancreas, right? Anytime you're looking at a CT scan, you have to evaluate all of the different solid organs of the abdomen, and that for the most part, is gonna be best on using the venous phase.
( to be continue.....)
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