 So I'm coming back to talk about kidneys, current guidelines and recommendations. So first we're going to talk about the imaging technique and then go over current guidelines that help us manage these renal masses. Talk about differential diagnosis based on imaging features and hopefully provide you with some tips and pitfalls. As Dr. Fishman mentioned, renal masses are commonly detected in asymptomatic individuals as incidental findings and the majority of these renal masses are benign cysts and the prevalence increases with age, such that they can be seen in up to 40% of patients on CT. And the clinical challenge is really in trying to balance the benefits of early RCC detection versus workup or treatment of a lot of these benign or small malignant masses either with the treatment or serial follow-ups that really aren't necessary. There are several guidelines that help us manage these renal masses and I'll mention the highlights including the ACR management guideline in 2018, appropriateness criteria for indeterminate renal masses, the revised Bosnia classification in 2019 and also recommendations for active surveillance. When we think about the appropriateness criteria for the initial imaging of indeterminate renal masses, if the patient has no contraindications, the best choices are really exams performed with IV contrast, be it CT, MRI or ultrasound with contrast. In our practice, usually we do either CT or MRI, renal protocol. If the patient has contraindication to CT and MRI contrast, then ultrasound with contrast becomes a modality of choice and also ultrasound of the kidneys and MRI without contrast. And if the contraindication is to CT contrast only, then usually we would end up doing an MRI with and without contrast and at some institutions they may prefer to do an ultrasound with IV contrast. For renal mass protocol, we still do a traditional IV phase protocol with non-contrast, arterial phase, venous phase and delayed phase images. Some institutions like to do a dual phase CT and that may improve the differentiation between non-enhancing cysts and low-level enhancing tumors and also theoretically you can get rid of the non-contrast phase because you can use the dual energy capabilities to give you virtual non-contrast. In our practice, we are still sticking with the traditional IV phase protocol because we find that the measurements are a little bit more reliable with the traditional protocol. And also with the CTs, it's important to look at multi-planar reconstruction because small lesions at the upper pole and the lower pole of the kidney, if you're just scrolling through the axial images, you can easily walk by it and miss them. And the coronal are really helpful in showing those lesions at the upper pole and lower pole to advantage so that you don't miss them. And 3D reconstructions are very helpful for the vascular mapping so you can see the vascular blood supply that can help the surgeon plan the surgery. And also these 3D images also help us appreciate the extent and also characterization of the lesion. And they are also helpful in distinguishing real masses from pseudo masses, such as in this example here. So this patient was referred in for renal mass biopsy. Superficially, when you look at this lesion, sure, it does look like a heterogeneously enhancing mass on the axials, but when you look at the coronal, you almost get the impression that the more central hypodense area is the unopacified renal calluses. And the reason it looks weird is because of distortion by this big renal cyst. So instead of doing a biopsy, I recommended the patient to come back for delayed phase images. And lo and behold, we can appreciate on the delayed phase that there's contrast or pacification of the calluses, and this is just normal renal parenchyma and not a renal mass. And when we think about renal mass characterization, we need to pay attention to the size, attenuation, whether the lesion is homogeneous or heterogeneous, any internal enhancement in a complexity of the cystic masses, and priors are always helpful in looking for growth and morphologic change over time. There are several features that indicate lesion heterogeneity, including wall thickening, septations, neural nodules, measurable or visible attenuation differences between phases, and also within the lesion, and internal calcifications. And what are the criteria for enhancement? On CT, if there's a change of 20 household units or more in the pre and post contrast, that is considered definite for enhancement. Between 10 to 20 household units that's considered equivocal, the difference of 10 household units or less that's considered no enhancement. And on MRI, because we don't have absolute units, it's more a relative increase of 15% or more on the pre and post contrast that's considered enhancing lesion. And often it is also helpful to get subtraction images on MRI to see if there is any internal enhancement. Dr. Fishman already went over some of the rules on how we deal with these incidental renal masses, but I will also review them because I think repetition is helpful in helping us remember. So first off the bat, if we see a renal mass of non-contrast CT without any fat, we first want to look at whether the lesion is homogeneous or heterogeneous. A heterogeneous lesion is considered indeterminate and should be further worked up with renal protocol CT or MRI. With a homogeneous lesion, we need to look at the household units. If it's low, less than 20 household units, it's considered a benign cyst and no further work up is necessary. 70 household units or more, it's a proteinaceous or hemorrhagic cyst also does not need any work up. It's the lesions in this kind of intermediate household units that really require the renal protocol CT or MRI. Let's look at this example of a man coming in with flank pain. So clearly we can see a low density cystic lesion in the right kidney, but also in the left kidney, it may be hard to appreciate that there's a subtle lesion that's almost the same attenuation as the background kidney that's very hard to see. You can appreciate that a little bit better on the coronal with that contour deformity. And this patient was referred for MRI and we can appreciate that the right renal lesion does not enhance so that it's a simple renal cyst and the left renal lesion shows heterogeneous enhancement and it's a renal cell carcinoma. So just be aware that the renal cell carcinomas tend to have this intermediate attenuation that's similar to the background kidney that's actually hard to pick up on these non-con images. Another patient coming in with multiple lesions of different attenuation, some are low attenuation, some high and some of that intermediate attenuation. So the next appropriate step obviously it's a renal protocol exam and on the multi-phase images we can appreciate that the right anterior lesion does not change so it's just a simple cyst. This middle lesion here also doesn't change on multiple dynamic phase images and it's a hemorrhagic or progenacious cyst whereas the left renal lesion shows avid arterial enhancement with washout and that is a renal cell carcinoma. What about if we find an incidental renal mass on contrast and hidden CT? Again, if the lesion is heterogeneous it is indeterminate and needs to be further worked out. If it's low attenuation then it's we can call it a benign cyst and doesn't require any follow-up and anything that is more than 20 house units on a contrast and hidden CT are technically indeterminate and would require renal protocol CT or MRI. So look at this example here. So there's a posterior lesion, zero house unit so if that was the only lesion we can confidently dismiss that as a benign cyst. The anterior lesion here 57 house units that is indeterminate and we need to work it up whether it's an enhancing lesion or a hyper dense cyst. And we got an MRI that showed that the posterior lesion surely does not enhance and it's a simple cyst whereas the anterior lesion is intrinsically bright on T1 and on the subtraction images there are there is no internal enhancement and that is just a protonation cyst. But sometimes people mix up the rules. So this was an outside case and it was a young lady with flank pain. This lesion was 48 house units on a contrast enhanced exam and they just flat out called it a Bosnian two-cyst and didn't mention any follow-up. Patient had persistent pain and came to my hospital and on ultrasound you can immediately appreciate that this does not look like a cystic lesion. It's very heterogeneous in echo texture. So I recommended an MRI to further work this up and it is a T2 hypo intense lesion with internal enhancement and this was confirmed a papillar carcinoma. So just keep in mind that on a contrast enhanced exam in lesion of more than 20 house units is technically considered indeterminate and we should not just blow these off as Bosnian two-cysts. And this was a trainee of ours that made a similar mistake that he was confusing the rules. That we saw this lesion 91 house units on a contrast enhanced scan and he told me well since it's more than 70 house units it's a protinacious cyst right and then I asked him well you don't really know if we had a noncon whether it was a low density lesion that enhanced or if it was a bright lesion that stayed at 90 house units on the pre and post. So when you encounter these high density lesions that are more than 20 house units you really ought to work it up with a proper renal protocol exam and we obtained an MRI for this and again heterogeneous on T2 with enhancement and this was confirmed a chromophobe RCC. When we think about solid renal tumors we the differential includes renal cell carcinoma, oncocytoma, angiomyelopoma, renomegulary carcinoma, ureothelial carcinoma, lymphoma and meds and the growth pattern and also the tissue characteristics can help us figure out what type of tumor it is. Clear cell renal cell carcinoma is the most common type of renal cell carcinoma and cystic degeneration can occur in up to 15 percent and when we think about clear cell renal cell these are heterogeneously enhancing masses and we may see the heterogeneity due to central necrosis, internal hemorrhage and also microscopic fat and because these are aggressive tumors we may also see renal vascular invasion. This is a typical example of clear cell renal cell in which you see a very heterogeneously enhancing mass with some renal vascular invasion so this is very typical for renal cell. Papillary renal cell is the second most common type as opposed to clear cell which is avidly enhancing on arterial phase these tend to be hypoenhancing masses and also tend to be T2 hypo intense as opposed to clear cell which is T2 hyper intense. Chromophobe is the third most common type of renal cell carcinoma these tend to enhance more slowly and more homogeneous so this is a lesion that is homogeneous and hypoenhancing mass so very typical for chromophobe. So this is the early example that I showed of the chromophobe carcinoma so kind of low level in hypo enhancement more homogeneous than what you would expect for a clear cell. So based on the enhancement characteristics and how it looks on MRI you can help try to figure out what kind of subtype it is. Clear cell tend to be hyper vascular and also these are more aggressive tumors so you would expect to see vascular invasion hemorrhage necrosis and the classic syndromic associations include VHL and tuberous sclerosis. Papillary subtype classically T2 hypo intense and that helps distinguish between clear cell and chromophobe. Chromophobe RCC are classically associated with Bertholdt-Dubay and it's also important to remember that sometimes abscess and renal cell carcinoma they can have overlapping appearances. This lady came in with hematuria and this was read as an abscess but when you look at it more carefully this looks like intrinsically bright on the non contrast so it looks much more like a subcapsular hematoma than an abscess. It's a very heterogeneously enhancing mass and this turns out to be a renal cell carcinoma so when someone comes in with spontaneous bleeding really be on high alert that it may be a renal cell carcinoma and look alike for or on the other differential for solid renal neoplasms would be an oncocytoma and the classic feature is a central stellate non-enhancing scar. This is about the best central stellate scar that I can find in a renal mass so when you have something like this you can be fairly confident that it's an oncocytoma but realistically it can be difficult to differentiate between renal cell carcinoma on both imaging and biopsy. More examples of oncocytomas on the top left I can perhaps convince you that this is a nice looking central scar and it's an oncocytoma but as we move to the top right example the central scar is a little bit less obvious and the bottom example I can't really see the central scar at all but regardless when you encounter solid renal mass if you're even thinking about oncocytoma I think it is helpful to include that on your differential because there are other tests like nuclear medicine tests that the clinicians can pursue to try to distinguish between oncocytoma and RCC. Next we'll talk about angiomyelolipoma. It is composed of dysmorphic blood vessels smooth tissue and fat. 80% of them are sporadic and you have the classic AML, fat-poor AML and also epithelioid AML and 20% of them are syndromic with the classic associations of tuberous sclerosis and lymphangiolyomatosis. So the algorithm for renal mass that contain fat next we want to look whether or not there's internal calcifications. If there are calcifications then we suspect renal cell carcinoma if not then we think it's an AML and then with an AML then we want to look whether it's solitary or there's multiple in the size because for small AMLs they don't really require any more workup but for AMLs that are four centimeters or more we need to refer them for management and that is because of the risk of bleeding. So this is a classic AML similar to the ones that Dr. Fisherman has shown so you see a fat in soft tissue attenuation mass so this is very classic so no real differential for this mass and the importance of the four centimeter criteria is because beyond four centimeters these patients are at high risk of bleeding and so we want to avoid this bleeding complication and refer them for embolization. Another example of a small classic angiomyelopoma and sometimes with these small smaller AMLs it's easier to pick up the fat component on the non-con because on the post contrast the whole thing is enhancing and it can be harder to pick out the small fat components. With the fat poor AML there's actually no evidence of fat on unenhanced CT so that they look like hyper or iso attenuating masses relative to the regular venoparenchyma. These are very difficult for us to diagnose preoperatively and you just have to accept that sometimes you're going to be wrong. Like this example here we have this soft tissue attenuation mass that enhances so most of us would think that it's a venosal carcinoma but on pass it turned out to be a fat poor AML. This other example similarly you have a soft tissue attenuation mass with no discernible fat and then it enhances but so most of us again would think that it's a venosal but it turns out to be a fat poor AML. There's also an epithelioid subtype of AML which they don't even see in few or fat or few or no fat cells even on pathology so it's almost impossible for us to identify any fat. These tend to be hyper attenuating on non-contrast, heterogeneous enhancement and they look aggressive due to hemorrhage and they can be cystic and potentially malignant and this is an example of an epithelioid AML in which we have a very complex cystic mass with very thick irregular looking septations no discernible fat so I would say that AML is not really on our radar screen but just be aware that AML can take these very atypical looking forms. Now when we think about a fat-containing retroperitoneal mass the differential would include angiomyelopoma. Renosal carcinoma I put in asterisks here because we expect to see intracellular lipid with renal salcarcinoma but not so much the macroscopic fat. The retroperitoneal liposarcoma and also adrenal myelolipoma would be on the list so the way we distinguish is to look for that claw sign so here with the angiomyelopoma we can see that there's this defect in the renal cortex and this fat attenuation mass is mushrooming out of the kidney so we can tell that it's a renal origin therefore an angiomyelopoma. This adrenal myelolipoma is quite large and when you look at it it can be hard to tell the precise organ of origin whether it's arising from the kidney or the adrenal gland so it's also on that differential for fat-containing retroperitoneal mass and in this case you have a very heterogeneous fat and soft tissue-containing mass that looks like it's more wrapping around growing around the kidney and you don't really see any defect in the kidney with the claw sign so this would point you more towards a retroperitoneal liposarcoma. Coincidentally, patient also has a coexisting clear cell renal salcarcinoma that's enhancing quite avidly and that wraps up the solid renal masses the well circumscribed growth pattern but we can also get more infiltrative looking renal masses and on this list I would consider renal cell carcinoma, renal medullary carcinoma, uroothelial carcinoma and lymphoma. This is an example of a clear cell renal cell with IBC invasion so when we see an aggressive looking mass with vascular invasion I think renal cell carcinoma is at the top of my list and similar to the liver talk the arterial phase is very helpful in showing the internal enhancement of the tumor thrombus that helped distinguish that from the bland thrombus. Renal medullary carcinoma is an aggressive renal malignancy in young patients with the cocell trait usually is centrally located infiltrative mass and again it is an aggressive lesion that can show renal vascular invasion and also usually we see retroperitoneal lymphatinopathy or even metastatic disease at time of diagnosis. This is an example of renal medullary carcinoma in which you have this very infiltrative growth pattern centered more centrally in the kidney already had liver metastasis and also a lot of lymphatinopathy at the time of diagnosis so a very aggressive looking lesion. Another example it's a diffusely infiltrative tumor that basically replaced much of the kidney with extensive necrotic lymphatinopathy so when you see something like this especially in the right population with this patient with sickle cell trait this is a great thought for that population. Urocelial carcinoma they arise from the renal pelvic urocelium and you can also get this infiltrative growth pattern with obliteration of the renal sinus fat also known as the faceless kidney but urocelial carcinoma can also have other growth patterns such as enhancing filling defects within the collecting system, subtle thickening and enhancement of the renal pelvis. An important thing with urocelial carcinoma is that once you see one you need to carefully scrutinize the entire collecting system due to the high prevalence of secondary foci of tumor. This is an example of a urocelial carcinoma in which you have a very infiltrative looking mass that's replacing much of the kidney. You have some hydronephrosis and that would be a clue of the collecting system involvement and this is a classic example of urocelial carcinoma. This is a different look for urocelial carcinoma in which you see this polyport filling defect within the right renal pelvis and sometimes these lesions can be a little bit hard to see on the non-con or the arterial and venous phase images but you can see them very well on the delayed phase images and that is why we include the delayed phase images in our four phase renal protocol so that we can catch these urocelial neoplasms. While this is a fairly obvious example, this other case is a much more subtle example so on the non-con you can barely appreciate anything on the renal pelvis and the venous phase if you're looking very carefully maybe you can appreciate a little something but it's a lot more obvious if you have delayed phase images and then here's the corresponding retrograde urogram so that you can see the filling defect so again the delayed phase is key for these urocelial neoplasms. Next we'll talk about lymphoma. Lymphoma is usually secondary to systemic disease and we can see bilateral renal involvement in up to 70% of patients and lymphoma can look like single or multiple masses, diffuse renal infiltration or peri renal infiltration and usually we would also see associated systemic lymphatinopathy which would be also a clue. In the top row we can see that diffuse enlargement of the kidneys with preservation of the normal renal form shape and that is very classic for lymphoma. In the bottom example it's a little bit more heterogeneous in which we have some cystic degeneration so lymphoma can have a variety of appearances and in this other case is more primarily a peri renal growth infiltration pattern. This other case bilateral involvement extensive peri renal growth pattern and also soft tissue infiltration throughout the retroperitoneum lymphoma and other metastatic disease would be good thoughts for a case like this. And when we see that peri renal infiltrative growth pattern we can think about certainly lymphoma, retroperitoneal sarcoma, extra medullary hematopoiesis, lymphatic malformation, retroperitoneal fibrosis and hemorrhage, basically anything that can sneak into those nooks and crannies in that peri renal space. This is actually a case of airtime chester so all those lymphoproliferative diseases would also fall into this category. And not everything that is a renal lesion is a renal cell carcinoma so obviously whenever we interpret these we also need to keep in mind a clinical presentation. If we have the right clinical presentation and a lot of soft tissue stranding around it that would lean us more towards abscess than a renal neoplasm. Lastly I'll just touch on active surveillance. In the past anything that's enhancing in the kidney would end up coming out. But these days there's more of a push for active surveillance as an alternative for immediate management. And these patients are followed clinically and with serial imaging. And this is recommended in patients in whom the treatment outweighs the the risk of the treatment outweighs the benefits. And the reason is because a substantial proportion of small solid renal masses are benign along with the vast majority of cystic renal masses. Small RCCs are typically indolent with low potential for malignancy and they are usually in older patients so they are more likely to die from other diseases than from the renal cell carcinoma. And also the RCC treatment have potential complications and they may reduce the renal function and increase the overall mortality. So basically for small solid renal neoplasms one centimeter or less those are usually followed. And then if we see any tumor growth or changes in the morphology that may trigger a change in the management. Cystic lesions in the Bosnia 2F and three categories are usually followed also until we see a morphologic change or reclassification for as a Bosnia 3 or Bosnia 4. In conclusion renal masses are common incidental findings and we have ACR guidelines for the further evaluation of incidental renal masses based on size, attenuation, heterogeneity, enhancement, complexity and growth to help us figure out what to do with these masses. The renal protocol CT or MRI are modalities of choice for the evaluation of indeterminate renal masses and we can form the differential diagnosis based on the specific imaging features and patient characteristics. And thank you very much.