 Our next case is a 28-year-old with intractable seizures. Let's get right to the images, which show an axial T2-weighted image with some hyperintensity in the precentral gyrus region, anterior to the central sulcus of Rolando. And even the posterior frontal gyrus is involved. More importantly, the lesion is peripheral. It has a heterogeneous character to it, which we'll discuss in more detail. For your own perusal, the flare image is on the right. The coronal flare image is combined with the coronal T2-weighted image with a characteristic that you should acknowledge and identify, a position you should acknowledge and identify, and a zone of transition you should acknowledge and identify. How would you categorize the contrast-enhanced T1MR? Do you think there's intense enhancement, scant enhancement, no enhancement? Let's go backwards again from the axial T1 C plus MRI to the coronal flare and T2 to the axial flare and T2. So you can have another look. OK, question number one. The most likely diagnosis is ganglioglioma A, pleomorphic xanthoastrocytoma D, Taylor's dysplasia C, D net D, or neuroepithelial cyst E. Which of the following is not a characteristic of D net? Because now you know the answer. They are A hypervascular, B bubbly, C may deform the cortex, D, they have a bright flare MR rim, E mass effect is scant. You should be able to get this one just by looking at the case. Which of the following regarding D net is true? And by the way, there's no shame in looking at the case and figuring out the answer or figuring out the answer from the answers given on other questions. But you often will not be able to go backwards and look at the prior questions. So you must memorize those questions and choices that you previously answered. If you can't do that, you probably should quit medicine. Which of the following regarding D net is true? It grows rapidly. A, 30% of gliomas. B, usually under age 20. C, contains fat greater than 50%. D, associated with obstructive hydrocephalus. All right, let's take our answers now. First, the most likely diagnosis. Ganglioglioma, that is a strong consideration. It's a peripheral lesion. It's a mixed lesion consisting of neuronal and glial elements. If you're going to get shown one of these, it's going to be calcified. It's often in the temporal lobe. It's the most common cause of neoplastic temporal lobe epilepsy. But there is no calcium present. They're usually not as consistently bubbly as this lesion appears. Pleomorphic xanthoastrocytoma. Absolutely in the differential diagnosis, but they enhance and they have a dural tail. Not here. Tailor's dysplasia. They don't enhance. They consist of balloon cells. It's a dysplasia, but it's not bubbly. D net. D net is the answer. And we'll discuss why in a few moments. And then finally, neuroepithelial cyst. A bland, cystic lesion that doesn't enhance, nor does our d net very much, but it does not have a flare peripheral rim of hyperintensity. That's characteristic of the d net. Let's go to question number two. Which of the following is not a characteristic of d net? It's hypervascular A. It's bubbly B. It deforms the cortex C. It has a bright flare rim D. Mass effect is scant. Well, that one's pretty easy just by looking at the case. Our lesion is bubbly. The cortical deformity, difficult to appreciate and maybe not present. Bright flare rim, we've discussed, so that's a gimme. And mass effect is scant. That's true in this case. So you should assume that that is part of the disease complex. But this lesion is virtually a vascular or hypovascular. So hypervascularity must be the correct, exceptional answer, not a characteristic of d net, but is a characteristic of ganglioglioma and pleomorphic xanthoastrocytoma, which has a durable tail. Which of the following regarding d net is true? A, grows rapidly. B, 30% of gliomas. C, usually under age 20. D, contains fat greater than 50%. E, associated with obstructive hydrocephalus. Well, it's not associated with obstructive hydrocephalus. It's a peripheral lesion. So that can't be true. It's not ventricular at all. That's an absurd choice. Contains fat greater than 50%. Do I mean greater than 50% of its volume or 50% of the time? It doesn't matter because they're both wrong. Usually under age 20, that is correct. They usually are younger in their teens. 30% of gliomas, the number is way too high. It's a low grade lesion, so it does not grow rapidly. The answer is C. So let's talk about the disembryoplastic neuroectodermal tumor, or d net, also known as the mixed glioma. In keeping with its slow growth, it is well demarcated. It's bubbly. It is in the cortex or gray matter of the brain. It may deform the overlying bone, but not that often. The patients are younger, usually under age 20, with partial complex temporal lobe epilepsy that is longstanding and difficult to control. The location is classically in the temporal lobe, amygdala, and hippocampal formation. That is where you'll get shown one of these on an exam. Less likely parietal, caudate, or septum polycytum. So this one is in a slightly atypical location, not being in the temporal lobe or hippocampus. They are wedge shaped. Frequently, the apex points towards the ventricle, and it does in this case. There's the apex pointing towards the ventricle on our flare image. Sometimes if the lesion is less bubbly, visually the wedge shape may simulate a stroke, which is a big mistake to make. But strokes evolve. Strokes eventually enhance. Strokes are not bubbly. Usually it's part of a gyrus, but it's not large. These are not massive lesions. In fact, the amount of mass effect for lesion size is understated. Take a look at it on the T1 weighted image. Barely any mass effect is present. The lesion has no surrounding edema, except for a little bright flare on the flare. A little bright rim on the flare. Let's take a look again. There's the flare. There's the flare on the flare. The high signal intensity around the peripheral edge. But no extensive edema. Intertable scalloping, a little hard to appreciate, but present. Calcification, 25% of the time, but hard to see on MR. Easier to see on CT and not seen in this case. Faint, nodular, or patchy enhancement may occur on CT or MR. In this case, we have faint to no enhancement. Lesions are going to be very bright in the bubbly areas on the T2 weighted image. Quite self-explanatory. There is no restricted diffusion on MR. There is no characteristic spectroscopy. They are hypometabolic on FDG PET. With C11 methionine uptake, they also demonstrate decreased uptake. Whereas gliomas and ganglia gliomas are going to be more hypervascular than D-net with more C11 methionine uptake. HMPAO, nuclear medicine uptake, and hyperperfusion are only present in the ictal or periictal phase. So let's talk about the differential diagnosis of D-net. The main suitor as the primary competition for the differential diagnosis is PXA. Pleomorphic xanthoastrocytoma, a few features. The dural tal, they enhance more. The enhancement often includes a sub-peel nodule. Short of that, they could look identical. This is another bubbly peripheral lesion. Another bubbly peripheral lesion with a propensity to deform the intertable and cortical bone is ganglia glioma. It's a tumor of young adults. It has a more frequent incidence of calcification. So if you're going to get shown a lesion like this and it's heavily calcified or has chunky calcification, you're going to go for ganglia glioma over these other two. The enhancement is a little more consistent and more intense. But they may have cysts and ganglia gliomas can look bubbly. We already talked about the neuroepithelial cyst, which is an easy one to differentiate. No flare rim, no enhancement. We talked about Taylor's dysplasia, which is a dysplasia, no enhancement whatsoever. It looks like the tuber of tuberous sclerosis and usually expands just one gyrus. The pathology of this condition is basically a glioneronal element that then translates into a tumor. What's another glioneronal lesion? Well, ganglia glioma. You get columns of heterogeneous cells and they are oriented perpendicular to the cortex. So they're oriented this way, in part explaining the wedge shape configuration where it points to the ventricle. The internal architecture is complex. The microhistology shows the generation of neurons floating in a matrix. So in summary, D net should always be a lesion that you like when you see a peripheral lesion in a younger patient with intractable seizures, with mild enhancement at best, without appeal or subpeal nodule, without much or consistent calcification, with a flare rim that points to the ventricle. That's in the hippocampus. That's near the amygdala. That's when D net should be at the top of your differential diagnosis. Let's move on to the next case, shall we?