 All right, so let's go ahead and get started. Hello, welcome to the first of many live stream noon conferences hosted by MRI online in response to the changes happening around the world right now, on the shutting down of many in-person events. We have decided to provide free daily noon lectures to radiologists worldwide. To learn more about future lectures and webinars we have coming up, please visit our website. Our software can accommodate the first 500 attendees to make sure you register and show up on time. The link is provided as a first come first serve basis and we will be putting them on the course after we sign off. Today we're joined by Dr. Mohan Mathur, associate professor of radiology and biomedical imaging at Yale School of Medicine, associate program director for diagnostic radiology residency and director of medical student education and radiology. Awarded four times the Yale Radiology Teacher of the Year. Please join me in welcoming Dr. Mathur. I'll let you take it from here. Thank you very much, Ashley. Let me just share my screen. Okay, does everyone hear me okay? I'm assuming that's a yes. Well, welcome everyone. As mentioned, let's see, people said yes, perfect. Thank you. My name is Mohan Mathur. I'm a radiologist at Yale. You can read my credentials over here. I'm really honored to be here today and I really wanna thank MRI online for putting this together and really leveraging technology in order to bring us together in this hopefully temporary era of social distancing. So for the next hour or so, let's forget about what's going on and let's sit back and learn from each other and enjoy learning about the retroperitoneum. We have a couple of objectives that hopefully you'll be able to obtain at the end of this hour. The first is you'll be able to review and explain the normal anatomy of the retroperitoneal compartments. Secondly, you'll be able to describe key imaging and clinical features of both solid and several cystic retroperitoneal neoplasms and we'll finish off by talking about imaging and clinical features of some non-neoplastic retroperitoneal processes. Now, as of now, we had over 100 participants, 128 to be exact and so everyone's probably gonna be at a different stage of training. Some people may be experts in this, some people novices and so we can all get what we need out of this talk and so hopefully within these objectives you can find something that you can learn from. Well, let's start. Before we get going, I wanna show you five unknown cases and this is something that I just thought about doing about 45 minutes ago. I will show you five unknown cases and you can jot down the answers if you want on a piece of paper. You can think about the answers and if you want, you can chat and text us the answers as well and we'll see if we can give bragging rights or something else to the person or people who get all five of them right. So this is the first case. I'm not gonna describe anything. I'll give you a couple of seconds to look at it, see what you think. Come up with one answer. This is the second case over here. Give you a couple of seconds to look at it. Again, one right answer for this. Case number three, move on to case four. These are MRI images. The sequences are named over here and last but not least, case number five. All right, so we'll revisit these cases through the talk and I'll give you the answers at the end of this session. All right, so first objective is to talk about anatomy and so the anatomy of the retroperitoneum is really built around this tricompartmental model and this has sort of been established at least since the 1960s and it's a great model to explain sort of how the different components fit into the retroperitoneum and it's really built around what I like to call the flagship organ of the retroperitoneum which is the kidney and you can see the kidneys over here in this schematic and around the kidneys you have different spaces, you have the space anterior to the kidney, the anterior peri-renal space, the space around the perimeter of the kidney, the peri-renal space and finally of this space posterior to the kidney, the posterior peri-renal space. Now the anterior peri-renal space is delineated anteriorly by the posterior layer of the parietal peritoneum. Here this is highlighted in blue. Posteriorly it's delineated by the anterior renal fascia. It's also known as charotus fascia is highlighted in red over here and laterally it's defined by the lateral conal fascia here highlighted in green and this contains several organs of the retroperitoneum including the ascending colon, the descending colon, the second and third fourth portions of the duodenum. It contains the maturity of the pancreas but we're not really going to talk about these organs today we're going to talk about the spaces in between and what grows in the spaces in between within the fat within some of the vessels here and fibers tissue. The peri-renal space is the space immediately around the kidney and is delineated anteriorly by the anterior renal fascia or charotus fascia posteriorly by the posterior renal fascia or sacro candles fascia here highlighted in purple and this of course contains the kidneys and the adrenal glands which are not imaged on these images here but also variable amount of fat, lymphatic tissue, lymph nodes and other things that we'll talk about a little bit later. And finally my favorite space is the posterior peri-renal space it's my favorite space because it really just contains fat so there's not much I have to remember about that and it's delineated let's go back to the last slide anteriorly by the posterior renal fascia or sacro candles fascia posteriorly it's delineated by the transversalis fascia there's really really thin layer that sort of surrounds some of the muscles over here and goes out laterally and then laterally this extends as the lateral conal fascia and this fat actually extends laterally and you can see it as the pro-peri-neofat stripe on the plane films. And so that's the tri-compartmental model and if that's all you kind of want to glean out of the anatomy portion of the talk I think that's sufficient that's sufficient to explain most processes. However, it turns out that these fascial layers that I talked about Gerota, sacro candle, lateral conal fascia are not a single layer but rather they're laminated made up of multiple layers that are fused and as a result they can expand and form these expansile planes and so if we kind of want to push our limits of knowledge to the vocabulary that we've already established it's important to add a few other things this is the retro mesenteric plane which is the plane that occurs when the Gerotus fascia expands you have the retro renal plane which is the plane of the sacro candles fascia when that expands and the lateral conal plane when the lateral conal fascia expands these meet out laterally in something called the fascial trifrification and that extends out inferiorly as something called the combined interfacial planes so if you look at these sagittal images on this CT scan you'll, and with the retroperitone process you know I'm going to show you a few in a bit you may often end up seeing a Y shape as the combined interfacial plane goes downwards forming from the union of the retro mesenteric and the retro renal planes if we look at on axial images this is the CT scan with intravenous contrast it's very tough to see where the combined interfacial plane is but if I click on the next slide you can see that it's going to roughly correspond to a very thin layer about two to three millimeters at most that occurs over here and everything sort of behind this is going to be part of the retroperitoneum and everything medial to this over here will be intraperitoneal as we go down inferiorly again it's very hard to see that plane when it's normal you hardly see it but if you scroll and imagine where it could be you'll see that it sort of goes along these dotted yellow lines over here this is where the combined interfacial plane goes downwards as you go down even more inferiorly very tough to see but it roughly follows this trajectory and you can see that it allows processes to go inferiorly and communicate with the pre-sacral space over here and so if we look at a few examples we can see over here that this person think had and all served the second portion of the duodenum that perforated and had some complications related to that and as a result had lots of fluid that were tracking on the retro mesenteric plane in this instance so this is not technically the anterior peritoneal space it's a very well delineated plane that goes out laterally allowing processes to sort of communicate from the right side of the retroperitoneum to the left side over here this is a patient with diverticulitis that was sort of the descending colon and as a result the inflammatory change sort of drained and expanded the retro mesenteric plane the retro arenal plane over here as well as portions of the lateral conal plane that allowed the inflammatory process to sort of decompress through these different planes. This is another case of diverticulitis where the descending colon gets inflamed and that inflammatory process is sort of decompressing through the presence of these retro mesenteric, retro arenal and lateral conal planes which are expanded and this was that Y shape that I showed you over here a sagittal CT scan with intravenous contrast we can see that the retro mesenteric plane is expanded the retro arenal plane is expanded and downwards you can sort of see that Y shape as straining through the combined interfacial plane and again the presence of these planes allows one to perhaps appreciate and understand how processes that sort of start off in the abdominal retropaginocompartments can communicate all the ways down to the pelvis. So this is a patient with pancreatitis and that advanced pancreatitis with necrotizing collections and you can see that the inflammatory process and the collections are expanding the retro mesenteric plane over here the retro arenal plane expanding the fascial trifurcation and all of this is going downwards expanding a combined interfacial plane on the left side. On the right side we hardly see that plane because it's normal. If you follow this downwards again you can see that it's following the expected location of the combined interfacial plane and finally going down to that pre-sacral space so all of a sudden we can appreciate how something that started off in the pancreatitis is now communicating with that pre-sacral space. And as we sort of finish off the anatomy portion of this the perirenal space also has ways that it sort of communicates with the other retro mesenteric and retro arenal planes and it turns out that the perirenal space contains these lamella which are really channels and that allow for processes to decompress within the perirenal space into the retro mesenteric and retro arenal compartments. And so we can see that in this case over here this person has a subcapsular hematoma compressing the left kidney over here and causing mass effect in the body itself is trying to decompress it by opening up these different channels and allowing some of that hematoma to communicate with both the retro mesenteric and retro arenal planes and that communicates inferiorly to the pelvis via the combined interfacial planes. This is another case that I just saw last week that sort of demonstrates some of these findings nicely. This patient, an older study on the patient had history of lymphoma had infiltrated the left kidney has adenopathy over here but the processes that also sort of expanding these conduits within the perirenal space allowing the retro arenal plane to be nice and lumpy bumpy as you can see over here and the retro mesenteric plane to be lumpy bumpy so you have soft tissue that's sort of exiting and the perirenal space through these different planes. Again, you can see on the sagittal image that Y nicely delineated much more thick within the retro mesenteric plane and it goes down and it communicates inferiorly via the combined interfacial plane which is very, very thick into this instance. So this is a case of lymphoma of the left kidney that's sort of decompressing through these channels and expanding all these different planes. And so we've achieved our first objective going through the normal anatomy of the retro perineal compartments. Remember to try compartmental model if that's all you want to remember that's probably sufficient but once you've mastered that it's important to sort of add to your vocabulary the different planes that we've talked about the retro mesenteric, retro renal, et cetera because it allows us to understand how different compartments in the retroperidium communicate with each other from right to left and from cephalic to caudal. So now move on to talking about retroperitoneal neoplasms and there are a lot of retroperitoneal neoplasms and really no talk or paper would be exhaustive enough to cover every single little thing that can occur. So I'm just going to touch upon several of them and we're going to talk specifically about sarcomas primary sarcomas of the retroperitoneum. We'll also talk about neurogenic tumors. We'll also touch base on metathesis and lymphoma which are actually very commonly seen in the retroperitoneum. And I'll finish off with talking about a few cystic neoplasms. The starting with sarcomas. Now, good news is that sarcomas are very uncommon. You can see that incidence of cases of one to three cases per million but the bad news is that when they do occur they almost always are malignant, about 80% of them will be malignant. They tend to present in patients around the fifth or sixth decades of life and they're rather large on the present oftentimes more than 10 centimeters on presentation. The five year survival is not great. A lot of this depends on the histologic rate of the individual neoplasm that is the degree of de-differentiation. It also depends on the type of sarcoma that you have the histologic subtype. But also, even if it's something that's relatively benign or indolent the survival rate may not be great because as I said, they tend to grow very large and it is very difficult for surgeons to get tumor free resection margins. So the main state of treating these retroperitoneal sarcomas is surgery have to try to take it out if possible but because they get so large and because they can grow in this space in the retroperitone for a long time before they come to presentation it's very tough to get tumor free resection margins. So that also plays into the overall prognosis. We're gonna talk about sarcomas again there are many different types of sarcomas but only gonna touch base on the three most common ones. Lipo sarcoma is the most common it'll account for about 40% of all primary retroperitoneal sarcomas and it's also consists of different histologic subtypes and to be honest, I don't typically like committing these things to memory but the only times I do commit it to memory is because if there are some imaging findings of them or some clinical significance. So within liposarcoma you have different group the first group consists of an atypical lipomenous tumor ALT well-differentiated liposarcoma and de-differentiated liposarcoma. The second group's often includes mixoid and round cell tumors well the third is pleomorphic. And so one thing you need to know is as you go from one to three the prognosis gets worse. And the other thing I'll point out is that these two entities of atypical lipomenous tumor and well-differentiated liposarcoma are essentially the same histologic entity. So why do we have two different names for them? Well it turns out this is more a pathology differentiation or pathologist differentiation I should say in that when they see tumors that look the same but when they occur within the extremity they'll call it an atypical lipomenous tumor. When it occurs in the retroperitonium they're prone to calling it a well-differentiated liposarcoma and that simply is because the same tumor occurred in the extremity will have a much better prognosis. It's much easier for the surgeons to take it out. The likelihood of recurrence of that site is very, very low and so they chose to give a different name to it. And also some pathologists have their own prepfans thinking that something like a well-differentiated liposarcoma as we'll talk about is a tumor that does not metastasize and so because it does not metastasize it doesn't warrant the name sarcoma. So they like to call it atypical lipomenous tumor. All that you need to know is that if you see this in your reports ALT or well-differentiated liposarcoma it's essentially the same entity. Lyomyrosarcoma is the second most common primary retroperitonium sarcoma at an instance of about 30%. The third most common is what we used to call malignant fibrous histiocytoma. Now the updated terminology is actually undifferentiated pleomorphic sarcoma. I'm sure many of you people on the call will know that, but I do find that when I was training it was called an MFH and so just I'll use both in this instance just to sort of make that connection with anybody who's used to hearing it as a malignant fibrous histiocytoma. So liposarcomas, well-differentiated are the most common and as you can imagine on imaging they contain fat. Mostly composed of fat. They may have a few septations but if they're present they will be very thin. You know we're talking about millimeters hair line thin. They may have a few nodular components but again the nodular components are gonna be small typically less than a centimeter and it'll exert mass effect upon the organs around it. I mentioned it's a very low grade tumor and it does not metastasize. The only problem is if you don't get tumor free resection margins there's a good chance of local recurrence. You do need to monitor these patients periodically even once resected. Now some of you on the call may think well you know you have a mass like this looks like it contains fat why don't we just call it a lipoma and that would be a very good question or very good consideration. Except it turns out that pure lipomas are exceedingly rare in the retroperitoneum. So this is a case of a lipoma and the reason I know it's a lipomas because they actually resected this out. The point here is that when you see a fat-containing lesion in the retroperitoneum even if it's simply containing fat no other complexity within it it needs to be evaluated as a well differentiated liposarcoma to approve it otherwise because lipomas are very very rare and if you biopsy these lipomas you could miss out on the small component that would make this a well differentiated liposarcoma therefore biopsies often not encouraged if you can take it out it suggests that you do take it out. This is opposed to de-differentiated liposarcoma. Now this can occur de novo but can also occur in up to 15% of well differentiated tumors over the course of about seven to 10 years a well differentiated tumor could potentially become de-differentiated in up to 15% of patients. And as you can imagine these just look more complex. They will contain some fatty components as you can see over here they're gonna have much more soft tissue they're gonna have some calcifications they're gonna have nodular components that are greater than a centimeter in size. Why does de-differentiation matter? Because these tumors can metastasize. So well differentiated tumors won't but de-differentiated tumors can. And so this is an example of a patient who over a decade was unable to get resected for their liposarcoma but was followed to make sure it didn't metastasize or get too large in size. And over 2005 you can see the tumor over here mainly composed of fat a few imperceptibly thin septations and just over time the tumor gets larger but more concerning certainly in 2008 you start to get soft tissue components form and these soft tissue components start to get larger and larger and larger. There are new and enlarging calcifications that also form during this period of time. And so this is an example of a well differentiated liposarcoma that over a decade has undergone de-differentiation. Another example over here coronal CT scan this is over a course of three years mainly fat containing tumor with some soft tissue and calcified component. Probably that component was de-differentiated at this time but certainly over a period of time three years grew much larger with the calcium also growing larger. So typically when I'm looking at well-differentiated liposarcomas on the surveillance imaging I'm not so much looking at the fat as looking at the soft tissue components and seeing how they're doing over a period of time. Mixoid liposarcoma is another category of liposarcoma and this is an interesting tumor in that it contains an abundance of mixoid gelatinous components. You can see this tumor over here in the pelvis on the CT scan has low density certainly looks like fluid density has some interspersed areas of fat. So we should be suspicious that this is a liposarcoma. If we were to just look at the T2 weighted imaging it looks quite bright. And so you would think that this is maybe a cystic neoplasm but unlike any cystic neoplasm when you give contrast this enhances. There's heterogeneous enhancement it doesn't have to be hypervascular even low level enhancement is fine. When you see a tumor in the retroperitoneum with T2 hyper intense components which enhance and has sliver of fat in it you got to think of a mixoid liposarcoma. So this here is a patient with liposarcoma you may be familiar with this this was our unknown case number one. You can see a large liposarcoma centered in the perirhenal space pushing the kidney cephalate to the right. And this here is also a fat containing mass looks very complex and you could be mistaken to call this liposarcoma. But of course this is a renal angiomyelopoma you can see a claw sign and this little knuckle of tissue that's emanating from the kidney. And so these two are vastly different tumors that are treated differently. So it's important to sort of recognize and see if you can see whether it's coming from the kidney in which case it's gonna be an angiomyelopoma. Another potential mimic on this axyl CT scan a fat containing mass in the retroperitoneum you may be tempted to call it liposarcoma but always look at every available plane when you're evaluating these cases this is a super renal mass you don't see the right adrenal gland this is a myelolipoma of the right adrenal gland. Again benign lesion that is treated and evaluated very differently than the liposarcoma. Lyomyisarcoma as you recall the second most common primary retroperitoneal sarcoma and what you're gonna look for in lyomyisarcomas is contiguous involvement of vessels. So you can see this lesion over here heterogeneous mass that's inseparable and expanding the inferior vena cava you gotta think that could this be a lyomyisarcoma. Cystic changes and internal necrosis have been described within these lesions but calcifications are quite uncommon. So if you see involvement of the vessel with areas of necrosis in the mass think of a lyomyisarcoma. This is a case this is our second unknown case which is a lyomyisarcoma you can see that in this instance there's actually quite a large component that's extravascular but it is contiguous and involves the IVC. So an intra and extravascular component in this instance of a lyomyisarcoma it can be completely intravascular as seen in this case over here where it's involving the renal vein and IVC. And they've also described them as extravascular in this instance is probably some vascular involvement that of some vessels that we're not seeing but when you look at them on imaging it's hard to find that component. And so this was a patient who had a history of breast cancer and had these nodes sort of or this mass sort of pop up in the retroperitoneum and we thought that was unusual because there was no disease elsewhere and for nodes to pop up here in the retroperitoneum or breast cancer would be unusual and over time you can actually see that it grew and this was actually resected in her net to be a lyomyisarcoma. This is another interesting case to show how subtle these findings can be. This patient had a renal cell cancer and it was being monitored over a period of time. There was an exophytic mass arising from the right adrenal gland or at least we thought it was an exophytic mass arising from the right adrenal gland over here very close to the IVC. We presumed it was an adenoma and we just followed it over a period of time but you can see that over a period of time you have a knuckle of tissue that starts to invade the IVC here. That knuckle becomes more nodular and more invasive. This was resected and this turned out to be a lyomyisarcoma separate from the adrenal gland and this turns out to be a lyomyisarcoma that arose in the adrenal vein. So the point here is that sometimes these sarcomas as you know can grow quite large when they present and it may be just very difficult to know where this is coming from. So we thought this could be a primary adrenal cancer like an adrenal cortical carcinoma. Turns out the adrenal gland was okay over here and this was a tumor that was arising in one of the adrenal veins. So sometimes when it gets quite large these things can be quite challenging. And the last sarcoma that I'll talk about is the undifferentiated pleomorphic sarcoma formerly known as malignant fibrosisctoma of NFH and the imaging features here are really non-specific. Calcifications have been described as being more common in these tumors up to 20% of these tumors. But overall this just appears very heterogeneous. Cystic changes possibly due to some necrosis. There's often hemorrhage in it. So we'll see bright signal or T1 weighted images. The enhancement will be quite irregular. And somewhere in the literature someone saw this and thought this looked like a bowl of fruit. And so that's also been described. But the point here is that you're not gonna be able to make a specific diagnosis and this often is a diagnosis of exclusion at least based on imaging. And so if we review the sarcoma clues and just to break it down very simply if you see a retroperitoneal mass a primary retroperitoneal mass contains fat there'll be a liposarcoma. And then you can look for other clues to see if you can kind of place it within one of those histologic categories. If you see a tumor that has involvement of vessels and or with extensive cystic changes and necrosis you're gonna think of liomyosarcoma and undifferentiated pleomorphic sarcoma is gonna be very tough to call on imaging. If you don't see fat if you don't see involvement of vessels the mass has some calcifications perhaps it's an undifferentiated pleomorphic sarcoma but again very tough to make that call on imaging. So that covers our sarcomas let's move on to neurogenic tumors. And one of the reasons I wanted to talk about neurogenic tumors is it's often something that I still just forget to put on a differential diagnosis and then it comes back as a neurogenic tumor and I think, oh yes, that's what it could have been I always forget it. And so I like to sort of make a point to include it and talk a little bit about it in this retroperitoneum talk. And so these neurogenic tumors can arise from the nerve sheaths it can be schwannomas, neurofibromas, you have malignant nerve sheath tumors as well we'll talk a little bit about those. They can arise from the sympathetic ganglionic cells you have a family of tumors there neuroblastoma ganglion neuroblastoma these are seen in pediatrics and adolescent population will touch base on ganglion neuromas that are seen in adults. And finally the parasympathetic ganglionic cells which give rise to paraganglionis we'll talk a little bit about that as well. We'll start off with schwannoma and unfortunately schwannoma does have a nonspecific appearance but I think it's something good to sort of just think about and whether you include it or not in your differential is really based on the lesion itself but it's important to think about when you see a pair of vertebral mass it can have a variable amount of calcification and necrosis this lesion here none of us could have thought it was a schwannoma in fact we may think of the liomyosarcoma because you don't see the IVC perhaps it's invaded this turned out to be a schwannoma. So a pair of vertebral mass possibly when you have expanded neuroferaminal canalis ball I think schwannoma is a good thing to think about. Neurofibromas can be isolated or they can be seen in the context of neurofibromatosis one which case you'll see multiple or a plexiform neurofibroma seen in this case and one of the clues you can see with neurofibromas and you can also sometimes see them with schwannomas is this target sign on MR imaging where the central nerve is relatively T2 hypo intense and the periphery has a mixoid matrix and we talked about mixoid matrix and the mixoid liposarcoma so the periphery is bright on T2-weighted imaging so when you see that sort of target sign that's also been described on ultrasound and other modalities gotta think about could this be a nerve sheath tumor. Compared to schwannomas, neurofibromas and certainly plexiform neurofibromas have an increased risk for malignant degeneration and speaking of malignant degeneration this is an example of a malignant peripheral nerve sheath tumor you can see on the plain film bunch of distended loops that an opacity of gas on the left side of the abdomen looks like these loops maybe even being pushed away maybe there's a mass effect. If you look at the imaging on the CT scan looks a predominantly low density mass quite complex on the MR images has T2-hyper intense components lots of thick septations within it this turned out to be a lignant peripheral nerve sheath tumor these can arise to NOVO they can also be associated with NF1 and they can also be seen occasionally status post-radiation treatment so particularly if you have young patients who got radiation in the belly perhaps for a tumor like lymphoma when they were young over the course of a decade or so they can potentially develop these peripheral malignant peripheral nerve sheath tumors unfortunately based on imaging it's very difficult to differentiate this as a benign or a malignant nerve sheath tumor mass but you know you can kind of use common sense to suggest that it may be more malignant particularly if it's rapidly increasing in size if clinically the patient has new neurological symptoms or just in general the larger it is certainly greater than five centimeters and if the margins are oldified if internally it looks more complex you're going to suggest that potentially it could be a malignant peripheral nerve sheath tumor ganglioneroma comes from the sympathetic nerve cells again a very difficult tumor to call prospectively on imaging it's been described as having sometimes lobulated in origins tends to be low density in its appearance a world appearance has been described on T2-weighted imaging on MR we have concentric circles within this lesion they may occasionally have some calcifications this has a relatively good prognosis you can see this mass over here adjacent to the IVC tough to call that prospectively as a ganglioneroma but potentially given its paravateria per location and potentially given its somewhat world appearance internally we can consider that this may be of neurogenic origin as I mentioned ganglioneroblastoma neuroblastoma well these are seen in the pediatric at the lesion population and unfortunately they tend to be more aggressive neoplasms this tends to have a relatively good prognosis this is an unusual case of a ganglioneroma that I'll just share with you but as quite a typical features large mass looks actually quite low in its density it's displacing the right iliac vasculature anteriorly it's squeezing the left internal iliac vein over here if you look at the coronals you can see the right external iliac vein looks patent and the left one is actually thrombo so this is a large ganglioneroma with mass effect causing a thrombus in the left lower extremity paraganglioma these are for the parasympathetic ganglionic cells when they arise in the adrenal gland we call them pheochromocytomas elsewhere we call them paragangliomas and it turns out that extra adrenal paragangliomas are more aggressive than pheochromocytomas and only about 40% of them may have elevated calicolamine levels on imaging they tend to be very hypervascular so you can see this lesion over here is quite hypervascular and if they do appear heterogeneous it may be because they sometimes have internal hemorrhage within them and so these sometimes have been described at least in the adrenal gland as having light bulb signal and I don't know how accurate that always is but one thing that we do see somewhat consistently is their hypervascularity this is the case I show my trainees from time to time and they look at it and there's quite a large tumor here but on the axial sometimes it can be tough you know this is the aorta you may be tricked into thinking this is the IVC and then this is just something else adjacent to it or you don't notice this turns out that this tumor is between the aorta and IVC on the coronals and this is a paraganglioma again notice the hypervascularity within it a key feature of paragangliomas and they can be single they can be multiple you can see in this instance in the retroperitoneum another hypervascular mass there are areas of heterogeneity but by and large quite hypervascular hypervascular another mass seen more posteriorly over here and this one of course we look at it and oftentimes we consider this one a not many we see a large mass over here right at the bifurcation of the aorta you can see it on the coronals as well peripherally hypervascular internally not so much this turns out to be another paraganglioma at the famed organ of zucca candle right at the aortic bifurcation just beneath the infirmary centric into your mesenteric artery you see something like this you gotta think of paraganglioma an extra adrenal paraganglioma if you want a nuclear medicine confirmation in this case MIBG is the best test to get you can see over here uptake of this paraganglioma on the MIBG images so that covers neurogenic tumors the nerve sheath tumors sympathetic and parasympathetic tumors move on to medicine lymphoma and we look at lymphoma it's the most common retroperitoneal tumor we can maybe recognize this case is one of our unknown cases case of lymphoma there are two categories hotkins and non-hotkins and there are certain image includes that we look for to make a prospective diagnosis of lymphoma we notice that lymphoma often when it involves when it's involved in the retroperitoneum we'll lift the aorta off the spine called the floating aorta sign sandwich sign has also been described where you have masses of lymphoid tissue that are essentially surrounding vessels with the vessels appearing as the condiments or the contents of the sandwich and the lymphoma masses as the bread another key feature of course is that it tends to encase vasculature without causing any organ damage so if you see over here the artery is completely encased but this is perfused perfectly over here the artery is completely encased but again the kidney is perfused perfectly this is lymphoma and we can see in the perivinal space has a reasonably distinctive appearance it can appear as one mass it can appear as multiple masses surrounding the kidney can also have this very ill-defined sheet-like appearance when you see that sort of soft tissue surrounding it you can think of potentially lymphoma always like to look at the occasional plane film to see what I'm missing retrospectively so this was a plane film here and this is the left kidney you can see kind of the outline of it the right kidney looks a little bit more dense if we look at it on the CT scan we can see that there's a mass in the perivinal fat this turns out to be a mass from melanoma so melanoma can certainly metastasize anywhere and certainly the retroperitoneum will not be spared in this instance and this is an important cancer to remember in terms of metastases and that's a particular cancer and so this is a patient who had a known choreocarsinoma and testicular cancers like to have nodal metastases to the retroperitoneum typically at the entry point of the gonadal veins this was a little bit lower down a very aggressive tumor actually that invaded some of the vessels causing some collaterals to form and in fact invaded the bowel as well this was choreocarsinoma mets and this was an interesting case of a young gentleman who had been doing a lot of sit-ups had some pain, got an ultrasound they saw hematoma or they thought was a hematoma told him to go back home he came back a few days later with more pain this time they got a CAT scan it turns out that there's actually a thick rimmed mass in the retroperitoneum and you know if you were considering primary retroperitoneal tumors maybe Lyoma, sarcoma maybe a good possibility but it's a young gentleman with retroperitoneal mass and no other history you got to think about testicular tumor as a primary neoplasm and so when we did the ultrasound we actually see that there's a coarse calcification in the patient's right testicle this was all removed and this turned out to be a burned out testicular tumor quite an uncommon entity where the thought process is that the patient had a testicular tumor it did metastasize but for a variety of reasons the primary tumor regressed but the metastasis persisted and so this was a burned out testicular tumor we'll move on to cystic neoplasms now and you know just like solid neoplasms there are lots of different varieties of cystic neoplasms I'm only going to go through these three because they're relatively common I would say but again the list is exhaustive so lymphatic malformation we do see these from time to time it's a developmental abnormality where the lymphatic tissue fails to communicate and it results in these low density masses that are cystic but they may have some variable signal in MR imaging due to the Kyle content it can have fluid fluid levels within them one of the key features is that it sort of insinuates between multiple structures and multiple compartments and so when you see a lesion that sort of insinuates is low in density maybe fluid fluid levels got to think of lymphatic malformation patients are often asymptomatic however if it gets very large it can result in pain and distension and this is an example of lymph angiomatosis where you have a very large lymphatic malformation and really multi-system lymphatic malformations involving again multiple compartments and so it can be more infiltrated in its appearance can occasionally have foci of calcium but again we have a large mass involving multiple compartments got to think of the sort of spectrum of lymphatic malformations and this is the answer to one of I think it's the fourth unknown case a tailgut cyst and this is something that you know we see not uncommonly and the literature would suggest it's not very common we do see it from time to time and it's almost always an incidentally found lesion and the key finding here is that it's in the pre-sacral location again you look at the literature they'll describe it more often in middle-aged women but we've seen it in males and females it's from an embryonic hindut remnant and the key is the location which is pre-sacral the fact that it looks multiloculated it's on the T2-8 images I was trying to show you that there's you know one cystic component here one here one here one here one here and they may have variable signal because of the variety of internal hemorrhage or protein content and they won't enhance internally the peripheral aspect of the cystic lesion will enhance and so what do you do with these when you see these you know you call it as such it's a tailgut cyst the other name for this is a retro rectal hematoma so some people gave that answer you'd also be correct you do need to actually take this out because there's a small risk of malignant degeneration one series that I read was up to 14% and that that seems quite large to me but that's what's out there in the literature and oftentimes it's quoted that squamous cell cancer is what it degenerates to but I've seen it degenerate to all sorts of tumors and so I suppose it's not as important to know the exact histology that it differentiates to but know that it can and so when you see this and somebody asks you what should I do with it well they should see a surgeon and see if they can take this out safely so that covers their neoplasms and one last objective to get through some non-neoplasmic retroperineal processes and these are the four that I'm going to talk about most of these here are going to be very very very uncommon but you may see it in your practice occasionally rarely and hopefully I can give you some clues to to make the right diagnosis so I'll start with retroperineal fibrosis and it's actually a disease that encompasses you know a range of findings and diseases and ultimately what happens is you have proliferation of a fibro inflammatory tissue that sort of the epicenter of which is around the inferrenal abdominal aorta it can also involve the IV senileiac vessels and it likes to involve the ureters now there's a laundry list of things that can cause retroperineal fibrosis but most commonly it's idiopathic and up to 60% of cases and this is really rare all right some studies suggest that it's probably maybe a little bit more common than we thought but ultimately this is a rare diagnosis we don't see this every day maybe once or twice a year it's seen more often in males and it's seen often in the fifth to seventh decades of life but I want you to remember about this disease and something I didn't appreciate till a little bit later on is that it's actually a dynamic disease in that you know it's called fibrosis but in the early stage of the disease it's actually consists of very edematous tissue that's highly vascular and that that fibrotic component really becomes more manifested in the late stage of the disease we have a reduced inflammatory ill-filtrated more avascular hyalogenized collagen content and so why is that important? well the reason is that if we can detect the stage the early stage perhaps this is more amenable to medical therapy or if it's in the late fibrotic stage medical therapy doesn't work as well and you may have to do some surgery to sort of free up the ureter from the disease free up vessels from the disease so this is what it looks like on on imaging on CT imaging it's an ill-defined sheet-like mass the borders of which are irregular now this is not always true but I like to remember that involves typically the anterior lateral borders of the aorta that it likes to spare the posterior border you can see this mass over here sheet-like mass forming the epicenter of which is around the anterior lateral aorta going down the iliacs posteriorly looks pretty okay over here and it can involve the ureters because they go right in this location and you'll often see medial deviation of the ureters that's a characteristic finding when it wraps around the ureters and quite a large number of patients can actually present with obstructive uropathy because of that obstruction this is another case of retroperine fibrosis on a reformatic coronal image how you can see that the ureter is being pulled immediately this one's also being pulled immediately but this kidney is not working as well so we don't see the excreted contrast here so it likes to pull the ureters and occasionally it'll also encase vessels resulting in collaterals and deep vein thrombosis so this was another case of retroperine fibrosis you can see the soft tissue over here you can see that somewhere more inferiorly it's obstructing the ureter we can see a lot of collaterals that are developing because it's also enveloping the IVC in some of the venous vessels and you can see there's a DVT as a result of that as well and we talked about the early stage and the late stage and so how does one go about potentially differentiating that it's quite hard on CT imaging PET imaging may be a little bit more promising in that early stage will have a little bit more FDG avidity on MR imaging chronic disease tends to be T1 and T2 hypo intense as you can see over here when you give contrast there'll be minimal enhancement and I want you to sort of compare that to what active disease looks like where you know it looks sort of on a non-contrast CT like soft tissue on T1 weighted images relatively hypo intense but on T2 weighted images does look quite markedly hyper intense compared to the other case and noticeably hyper vascular on post-contrast imaging so if we can catch in the early stage and let our referring providers know about it potentially this is a minimal to some of the medical therapies that they have out there this is always a nice thing to remember how do you differentiate this term of common retroperitoneal tumor that's lymphoma well retroperitoneal fibrosis as I said spares the posterior border as I mentioned with lymphoma it lifts the order off the spine typically and retroperitoneal fibrosis obstructs ureters can obstruct vessels lymphoma as seen in these two cases well lymphoma does not tend to do that lymphoma will envelop vessels without causing obstruction potentially can cause that if it gets very very large and bulky but by the most part it doesn't cause any sort of obstruction to vessels or the ureters so that's rp fibrosis we can start to get to some more exotic diseases as we finish up this session this is a case of erdheim chester disease it's a non-long hand cell histiocytosis clinical presentation is variable patients can be asymptomatic they can have bone pain weight loss malaise fever and on imaging you get characteristic bony lesions which are bilateral symmetric and there's thorotic involved in the metaphyseal and diaphyseal areas of long bone this is taken from the literature extraslittle manifestations are seen about 50% of cases and the most common extraslittle manifestation is in the retroperitoneum and it likes to form this perinepric rind of tissue you can see in this case over here around the left kidney on the coronals you can see it over here as well and this was our last unknown case where you can see that rind of tissue that's surrounding both kidneys and a patient who also had bony lesions this was erdheim chester disease amyloidosis is very very very uncommon it may be primary or secondary it's due to extracellular deposition of amyloid and the imaging findings are going to be non-specific it can be localized where you see a soft tissue mass with calcifications but that's not really it's going to help you systemically it can involve the retroperitoneum or again you see a retroperitoneal soft tissue that over time could calcify but again a very very tough diagnosis to make prospectively I'll finish off with extra medullary hematopoiesis now this we see not uncommonly and this is due to ectopic deposition of hematopoietic tissue outside of the bone marrow you often see in context of patients who have hemoglobinopathies perhaps myelofibrosis some things like leukemia where you have the need for developing a bone marrow that's outside of the a bone marrow normal places of bone marrow development it can occur in the liver spleen lymph nodes when it occurs in the retroperitoneum it often looks like para vertebral masses but this pre-sacral space is a is a common location and it can look soft tissue like this in 2007 didn't change it for three years in the patient who I believe had myelofibrosis it can also contain a variable amount of fat as you can see in this case patient with soft tissue and fatty components now there's a differential for this but in the context of this patient this was deemed to be extra medullary amount of poesis and so the key things you're going to look for are any skeletal changes that can be seen with things like myelofibrosis perhaps signs of iron overload that can be seen in patients of leukemia and of course the pre-sacral mass if you see stability over time think that it could be extra medullary amount of poesis so that's our last non-neoplastic entity that I wanted to discuss and let's sort of circle back to the objectives before getting to the unknown cases so over the last 50 minutes or so these are the objectives that we went through we talked about the tricompartmental model of the retroperitoneum that's built around the kidney and to that we sort of added this concept of interfacial planes that allow communication between different compartments we then went through some imaging features of retroperitoneal neoplasms the three sarcomas liposarcoma liomyosarcoma and undifferentiated pleomorphic sarcomas talked about a few neurogenic tumors remember the target sign with neurofibromas and remember the hypervascularity of parasympathetic tumors metastases lymphomas well remember lymphoma the lifts they order talked about the sandwich sign we talked about lymphoma enveloping structures causing damage or obstruction then we talked about a few cystic neoplasms namely lymphatic malformations until we get cysts we finished off with these non-net neoplastic retroperitoneoprocesses what I want you to remember for retroperitoneopibrosis is that it's antrolateral infrarenal aorta okay and it's a dynamic disease has an active stage an early stage or a late stage and we can use imaging potentially differentiate that Erdheim-Chester is always a fun thing to think about when you see these perinephric soft tissues surrounding the kidneys making it look like a hairy kidney with these characteristic bony lesions you've got to think of Erdheim-Chester and amyloidosis I mentioned here but it is quite non-specific in a very tough diagnosis to make prospectively so let's cycle back to our objective's first case everyone who got this writing can pat them on the back liposarcoma large fat-containing mass in perineal space pushing the right kidney anteriorly our second case is liomyosarcoma a mass in the retroperitoneum majority of which is outside of the vessel but you certainly see a component that's invading the IVC here so that's the liomyosarcoma this was lymphoma lymphomas lifting the aorta off the spine enveloping the vessels not causing any degree obstruction within this left kidney over here this is a tailgutsist pardon the spelling over there also retro rectal hematoma so if you got that as an answer you'd be correct this multi-loculated cystic mass in the pre-sacral space enhancement of the septations in the periphery you got to think of tailgutsist remember these can degenerate to malignancies so you got to take them out if possible and last but not least was Erdheim-Chester disease hairy kidney this perinephric soft tissue surrounding the kidneys with sclerotic lesions surrounding the meta-diaphyso regions of long bones so that's a little tour of the retroperitoneum thank you everyone for your attention there's been a bunch of comments and I'll open it up for some questions that people have and we'll see if I can get through them so we have a few people with that answering the cases so thank you so much for your participation there I'll certainly we'll certainly have a look at that and see if we can announce some winners over here so we'll just put that aside for the moment let's see in the Q&A nothing right now to everyone writing and thank you so much you're so kind to take a moment to to thank me I'm so happy to be able to do this one person raise their hand let's see if I'm gonna allow him to talk we'll see if they have a question yeah absolutely and are you here do you have a question that's working if anyone has a question they can add it into this Q&A section or put it in the question or the live chat and also there's my email here so if anyone has a question the later on feel free to you can get in touch with me and I'll I have some free time nowadays so I'm happy to answer them all right perfect as I bring this to a close I want to thank you Dr. Mathur for your time today thanks to all you guys for participating in our noon conference a reminder that this presentation will be available on demand on our website please find it at mrionline.com and sign up for future conferences we have one again tomorrow and the rest of the week also available on our website thanks so much for joining thank you