 Now, we will move on to lesser common neoplasms which are infrequently seen very rarely. Some people will see this once or twice in their career. Again, brain tumors in itself are rare, of the brain tumors, the glial tumors are the most common ones. The other tumors are unique that they arise from each specific cell line and according to the cell line, we will move from one tumor to another and I will just enumerate the most common of those. There are other tumors that I will not get into which are more rare tumors and are very unusual form of tumors which can be treated just as a general holistic approach of how you would approach a brain tumor based on my first lecture. But the most common of the rare tumors, I will go cell by cell in each different category and talk about them. Now, that we will first approach the epitominal lining. This is the big lining which lines the epitominal system right from lateral ventricles down all the way through the fourth ventricle apolaminoplusica. These are all lined, the ventricles are lined by oscillated epithelium called epitominal cells. Now, when a neoplasm arises from these cells, they can be classified as epitominal cell tumor. There are two types of this. One is epitomal and the second is subepitomal. The more malignant is the epidemoma and more benign is the subepidemoma. Both these arise along the epidemomal lining. So let's start with the subepidemoma which is more benign. Now the picture over here is of an epidemoma. The subepidemoma is a more solid tumor. It is a very slow-growing tumor. Some people almost classify it as a benign tumor. It is a WHO1 classification tumor. It does not metastatize very infrequently, if ever will metastatize. It is confined just as this description is. It is subepidemomal in location. It is iso-to-hypointense on T1. It will be as I mentioned earlier, masses have mass effects. So this will be a mass lesion with a very narrow zone of transition, iso-to-hypointense on T1. Sly hyperintense on T2 examination, generally a solid. It may approach heterogeneity if it gets very big and is almost never associated with enhancement. Once resected, it is almost like treated. The second form is which is the more malignant one is the epidemoma, which again arises from the ciliated cells epidemomal lining, which can arise anywhere from the lateral ventricle, superior frontal horn aspect down to the fourth ventricle. Now both epidemoma and subepidemoma frequently arise from fourth ventricle. Common location about greater than 50% are in the fourth ventricle. And epidemoma happens to be the more aggressive one, which is generally low intensity on T1. Hyperintense on T2, frequently associated with cystic foci or micro-cystic foci, can have fine calcifications, which are not clearly are obviously seen, but can be appreciated on SWI images, not so frequently seen on CT images and is associated with intense enhancement in its solid component. Now this solid component is the main tumor and this solid component will show enhancement and may frequently show areas of restricted diffusion because of its cellularity. It is also associated with areas of hemorrhage, again, which will be appreciated on the SWI images. This is classified as WHO2 and frequently as WHO3 as far as the tumor, just because of its aggressive nature. When it abuts the extents into the brain parankyma, it causes a significant vasogenic reaction. It has T2 hyperintensity, wide zone of transition, frequently associated with a hydrocephalus, which may both be related to cell debris, metastasis, like as in seen in coroate plexus papilloma or papillary carcinoma, or may be related to obstructive hydrocephalus. Both of these conditions entities can do that, causing hydrocephalus. Now the important thing about this is it breaches the epinema lining. So it is directly exposed as a neoplasm within the ventricular lining. It can cause drop metastasis. It can metastatize anywhere along the neural axis. So our job when this patient comes in and we see a mass lesion in a lobulated fashion extending into the ventricular lining. Now this may be not specific for epinema. It will be common for medial blastoma, coroate plexus papilloma, coroate plexus papillary carcinoma, or even if you see a central neurocytoma, which generally does not cause any drop metastasis. But once it is there, extending into the central cavity of the CSF, our job is to do imaging of the entire neural axis. The patient should not go home from the MR scanner without getting a full neural axis examination and to all wait for drop metastasis, which will be seen as leptomeningal enhancement, nodularity along the corpus callosum. So these kind of things. So we will have to image the entire neural axis pre and post contract. So this is a case of epinema. It's a pretty aggressive neoplasm, has a solid cystic component, has intense enhancement. This is another case. Again, this is projecting into the brain. Parenchyma has a solid and a cystic component, intense enhancement of the solid component. And here, if you see the periphery of the cyst is also enhancing. That means this is not an cyst as seen with hemangioblastoma or juvenile palo septic astrocytoma, but the cyst is not component of neoplasm. The solid component is the component of neoplasm. In this case, the entire cyst is enhancing. The cyst is also a component of the neoplasm. And when the surgeon goes in, he has to distinct the entire cystic as well as solid component, unlike what we see in hemangioblastoma, where only the solid component needs to be dissected. So this is a very aggressive form of ependemoma projecting into the brain parenchyma. And in this case, there was no leptomineal enhancement. There was no drop metastasis. But once you see this condition extending into the ventricular lining, in the last sagittal and coronal sequences, you can see it extends and abuts the ventricular lining. So this is an ependemoma. Can be confused as an glioblastoma multiforme, but this turned out to be an ependemoma. Once you see this, you do an entire neural access examination. Once again, the important thing in this case when the patient is in the MR scanner is to call the clinician and tell him about the herniation, because that is what is going to kill the patient. Not this tumor immediately, but this mass effect and herniation can decompensate and kill the patient within a matter of a day. So this is what we have to mention and call the clinician and see what he wants, whether he wants the patient to go to the ER or to his clinic, but this patient should not go home from this point. So these are the two main entities arising from the ependemol lining, which is ependemoma, which is the emellignant one. Some ependemoma, which is a benign one. Moving on to the next tumor cell line, we would be talking about the choroidal cell lines. This is the cells which are lining the choroidal matter. So this is, as we know, the choroid plexus extends from the lateral ventricles, passing through the foramen monorho and then through the third ventricle into the fourth ventricle and from there into the foramen of Lusca. So as by definition, a tumor rising from these choroidal cells can arise anywhere along the choroid plexus. These two. So a cauliflower sitting in the left atrial region, lateral ventricle, intense enhancement, associated hydrocephalus. This is not touching the ependemol lining. This is arising from the choroid plexus. So this would be a classist choroid plexus papilloma or papillary carcinoma, but in this case, the choroid plexus papilloma. Now another one, this is a pediatric patient, iso-intense to gray matter signal intensity, iso-to-hyper-intensity to signal in the same area, lob-related cauliflower type of lesion, intense enhancement, clearly associated and attached to the choroid plexus, severe hydrocephalus, unless proven otherwise, this is going to be choroid plexus papilloma or papillary carcinoma. And again, this is a situation just like we talked about in ependemomas. You see this thing? It is our moral responsibility to image the entire neural axis and look for drop metastasis and that is what we will be using to differentiate between choroid plexus power versus papillary carcinoma. So this is an aggressive form. This is not WHO-1. This would be WHO-2 or WHO-3. It's an aggressive neoplasm. It can invade the surrounding soft tissue. It can invade the brain, pattern, chima. It can be associated with areas of hemorrhage. It is frequently, in fact, almost very, very commonly associated with drop metastasis. Can be evaluated by CSF evaluation. By imaging, it will still be a large cauliflower shaped intensely enhancing lesion, sitting inside the ventricular system anywhere within the atrial region which is the most common area in children or within the fourth ventricle which is the most common area within the adult patient. Now, choroid plexus papillary carcinoma almost exclusively happens in children. Very rarely does it happen in adult patients. So this thing would be shedding tumor cells into the CSF. Moving on, I would like to mention another tumor which is arising in the ventricular system. Although we talked about conditions such as appendemoma, sub appendemoma, choroid plexus papilloma, papillary carcinoma. There are many other lesions that can arise from the ventricular lining or ventricular system such as center neurocytoma or SEGA or some giant cell astrocytoma which is frequently seen in tuberous sclerosis or meningioma or some normal variants like K1 septum palusidum, K1 verge, K1 intrepositum or you can see arachnoid cysts or infections such as neurosis to surfaces. All these things arise in the ventricular lining but all of these I would like to mention the choroid cyst over here at this point. So choroid cyst is basically a primitive neuroepithelium arising neoplasm that contains mucin, blood, old blood products, cholesterol, ions in different combinations. And depending upon these combinations it gives you a different picture on MR sequences. So it is a very variable picture. It can be T1 hyperintense to T1 hyperintense. It can be T2 hyperintense to T2 hyperintense and can give you any signal on MRC. So in no specific signal is characteristic of a choroid cyst but what is very classic is it is almost always almost 100% of the time positive on CT as a hyperdense lesion. CT is much, much more sensitive where it is 95% positive on CT and only 60 to 75% sensitive on MRI examination. So the study of choice in a choroid cyst would be a CT examination, not an MRI examination. Now this presentation is somewhat classic for a choroid cyst where this is a pedunculated lesion that is adjacent to the foramina mondra. So occasionally depending on which side the patient is lying it causes occlusion of the foramina mondra and hydrocephalus or headache. So it will present with position headache. That with this hyperdense focus in this area is pathognomic for a choroid cyst. One thing that you have to differentiate is an aneurysm arising from an anterior communicating artery which is projecting superiorly. That is the critical thing. You don't want to put in a needle without knowing that this is an choroid cyst definitely or it is an aneurysm arising from the anterior communicating artery. So that is one test you want to make sure that you do. The important thing about this is it can cause positional instant occlusion, complete occlusion of CSF drainage and severe hydrocephalus which can potentially kill the patient. So this is a potentially fatal entity. Even though it looks very benign, most of the time almost majority of the time it is incidentally detected. Patient doesn't come specifically with headache or that generally depending on the size it can be associated with mild moderate or severe hydrocephalus. Majority of the time when we see it incidentally it is not associated with any hydrocephalus. Classic presentation, hyperdense cyst situated at the foramina mondra on CT examination. MR is somewhat unreliable here. We see an example of that. It can be very, very variable on intensities almost never associated with enhancement internally may have a mild form of capsular enhancement if at all but enhancement is not any special attribute to this region. It is not associated with restricted diffusion. It is not associated with any pulsation artifact which would be differentiating it from on the face direction on an anterior communicating artery. So moving on, how do we, when we see an intraventricular mass how do we approach it? So if it is a solid completely intraventricular mass lesion intensely enhancing not associated with any of the coroeplexus lining or the ependymal lining associated with restricted diffusion unless when otherwise it would be a meningioma. If it is an entirely cystic component complete cysts, CSF intensity or mixed signal intensity the differential would be arachnoid cyst when it is CSF intensity, cysticercosis when it is CSF intensity, neuropithelial cyst within it is CSF intensity, colloid cyst which we just talked about would be variable intensity. Then most of the time what we'll be seeing is mixed signal, mixed appearance both solid and cystic component. Now then we talked about this when it is attached to wall or coroid lining that is what we'll differentiate it. When it is attached to the wall then it will be ependymoma or subependymoma when it attached to the septum palusidum then it is going to be a central neuropsychoma if it is associated with foramidum mandro a lobulated mass in a patient with tuberculosis we will call it a SEGA or subependymal joint cell astrocytoma when it is not attached to the periphery when it is centrally located attached to the coroeplexus it is going to be a coroeplexus tumor or a coroeplexus metastasis. Now coroeplexus metastasis we could generally tend to underrated there are very, very common coroeplexus metastasis in a patient with diffused metastatic disease if you do the histology more often than not we will find tumor cells within the coroeplexus also. So we should not disregard this at an entity and the other would be a blood clot associated with the coroeplexi hematoma formation that would be the thing that we would and once it gets organized it can potentially enhance and give a mass like epigenes so this is how you would interpret tumor.