 Our next case is a 38-year-old man, no history given, but he has an obvious mass located along the inferior aspect of the fourth ventricle near the foramen magnum. We have a T1 non-contrast and contrast image with a little bit of enhancement along the inferior aspect of the mass, and on an axial T2-weighted image, the mass is kind of boring. It's gray and somewhat smooth, but does fill out the inferior recess of the fourth ventricle. The differential diagnosis of intraventricular lesions is legendary, but limited, and we're not going to give it here just for the sake of time, but let's talk about this lesion so that we can hone in on a specific diagnosis. First, it's bland. It's gray. Second, the enhancement is scant, and sometimes with this lesion there's no enhancement whatsoever. It's a little bit lobulated. It fills out the fourth ventricle. In fact, it likes the fourth ventricle a lot. 90% of these lesions occur in either the fourth ventricle or the lateral ventricle, and this is a sub-pendymoma. So if you have an intraventricular lesion that isn't in one of those two ventricles, you better start thinking about another diagnosis. But here's another clinical, what I call pro-scan pearl. When you think about ventricular lesions in and around the fourth ventricle, you're usually thinking about pediatric patients, endopendymoma, megaloblastoma. Unfortunately, this lesion occurs after age 15. In fact, 80-82% of them occur after age 15, and most megaloblastomas occur before age 10, and endopendymomas also occur in the juvenile or pediatric setting. So age is very helpful. Lack or paucity of enhancement is very helpful. But let me ask you a question about these lesions, which are usually less than two centimeters in size. This one's about two, and when they're two or less, they're usually asymptomatic. When they're four or more, they may produce obstruction, and then, as a neurosurgeon, your hand is forced, you may have to shunt them or take them out. What would you do with this lesion? Yeah, this one, often these are incidental findings. The history is totally something unrelated, so it's an easy thing to get embarrassed on and miss, right? Sure. I'm embarrassed every day. The enhancement that you mentioned is actually, if you read about them, they're described as being non-enhancing. It's true. But this is the most common location. Second most common is lateral ventricle. If they do enhance, the ones in this location enhance more often. Meaning, in the lateral ventricle, very mostly non-enhancing, but if they're going to enhance, these are the ones that are going to enhance. That's a cool little pearl, too. Now, if this does need to be taken out, usually follow these. I have patients that I've followed for years and just look at it every year. It looks back at you. How often would you image them? Yeah, I usually, when I see a new lesion, I usually look at it at three or six months because I don't know its behavior. If it's nothing's happening in six months, then I'll start stretching it out. But eventually, I'll probably be looking at this one year, maybe even once every two years, if somebody's been stable for quite a while. But you're not taking this one out. I'm not taking it out based on what we know, which is that there's no symptoms directly referable to it. The patient's stable, okay? No evidence of leptomine and geoceding, anything which doesn't usually occur with this lesion. And no hydrocephalus, too. That's correct. So, if there is a reason, let's say it's all of a sudden it's bigger and there's hydrocephalus, it's a great case, right? Suboxypital craniacomy, you're going to be right at the inferior border of the fourth ventricle. You're going to get a plane down here and skim this baby right off and it's going to be a very interesting surgery. So it can be done. Well, great for you, but not so great for him. Well, that's correct. They'd rather do without it, but they're not happy to be seeing a neurosurgeon to begin with. So they have to deal with that. But so it can be treated, very treatable. A lot of times they do well. I've followed a lot of them for years, never had to do anything. Usually the surgery is curative and this is a subapendemoma. It's a classic subapendemoma and it's a very straightforward case. Let's move on to some others.