 Thank you. Thank you again for the kind information. Today, I'll be speaking on Pirates and also staging of prostate cancer. It's quite, you know, a bit lengthy topic, but we will go pretty, say, a concise manner. So let me first give you an object to what we'll be covering in this topic. So basically, I'm going to provide a brief overview of ACR Pirates' scoring system. Then followed by, we'll see some illustrations of anatomical and imaging principles related to local staging that includes EPE, SV involvement, and also tumor-involving other key surgical landmarks in the pelvis. And then we're also going to discuss how this local staging and staging of prostate cancer impact management in terms of radiation or surgical. So as we all know, ACR actually adopted Pirates over the past couple of years now. So with the introduction of Pirates, basically they started giving a structured report in terms of having a clinically significant disease in the prostate gland, especially when you have focal lesion. So in order to help and have a uniform language across the radiologist and the clinicians, and who refers to these cases for us, have a uniform reporting standards, Pirates basically helps us to speak a lexicon that is uniform and across the board. So when we talk about the Pirates' reporting system, we basically divide the gland into various segments and sectors. So if you look at the gland, basically we have apex, mid-gland and apex. I mean apex, mid-gland and base, and also we have seminal vesicles. Again, at each level, we have a peripheral zone and transition zone that is again segmented into a anterior zone, posterior zone, especially in the TZ. Whereas for peripheral zone, we have anterior haunts, posterior and posterior medial segments at the base. Basically the area around the seminal vesicles is central zone at the mid-level and again apex level. We'll come more when we see the illustrative cases. In order to maintain uniform reporting standards, Pirates also specifies what kind of technique we should follow when we're actually imaging prostate for localized disease or localized lesions. So basically we have a small FOV sequence and also we have a large whole pelvis staging sequences. Small FOV prostate-specific sequences has basically helps us to identify focal lesions in the prostate gland. So that includes after opening and localizing sequences, we obtain a small field of T2 in a three orthogonal plane that is T2 sagittals, T2 axioles and T2 kernels. And we also obtain same field of view DWI, including ADC maps. And we also have a post-contrast sequences with pre and post-contrast injection. Especially for the DC sequences, we need to have some technical parameters to achieve a good temporal resolution. We say at least 10 to 15 seconds and also having to go over two minutes, a little over two minutes. So this is a simple protocol, but again it varies between the institutions, between the vendors. So the key things to consider here is having a small field of view for a prostate-specific sequences and having a small slice thickness without any space between the sequences. That's a key thing to achieve, especially for anatomical sequences. So as I said, Pyratz is a like-art score, basically having from Pyratz one to Pyratz five. Pyratz one being a very low suspicion for having any clinically significant prostate cancer, versus Pyratz five is very highly likely having a clinically significant prostate cancer. In order to achieve this or to get this scoring system, we basically utilize key sequences for both peripheral zone and transition zone and derive a composite figure that basically tells us a risk certificate, risk assessment. For example, when you look at the T2 weighted images, we use a different scoring system for peripheral zone and transition zone. Many of you might have already seen this in the ACR Pyratz document. I'm going to quickly look at the high risk or high likelihood of disease. So in the peripheral zone, when you call it as a Pyratz four for a T2 weighted sequence, it's supposed to be having a circumscribed homogenous moderate high point in its focus. It should look like a nodular lesion and it should be less than 1.5 centimeter in the greatest dimension. And if it's anything more than five centimeter and having the same features, it characterized as Pyratz five on T2 weighted sequences. Whereas in the TZ, it's a little different. Especially if we have a BPH changes that basically tells us it's as two or three depending on how the nodules are. But if the lesion is non circumscribed homogenous and has a moderate high point in signal of less than 1.5 centimeter TZ lesions we could classify that as four. And again, typically again, lenticular shape lesions that is especially along the surgical capsule also qualify to be called as Pyratz four on the TZ on T2 weighted sequences. So that's a key thing to remember especially when you're scoring on sequence based. So and again for DWI on DWI sequences signal abnormality is characterized on both PZ and TZ in the very similar way. So basically when to call it as a Pyratz four on DWI sequence is supposed to have a focal high point intensity on ADC and mark the hyper intensity on high V value. And that basically qualifies a high suspicion score on DWI. If anything less than that that means if you see only hyper intensity on ADC but do not see hyper intensity on high V value or vice versa those will be classified as Pyratz three on DWI sequences. Again, anything linear, wedge shaped looking like a sequelae of prostate is they all come under two and again, no abnormality is usually typically normal. So once we derive these scores on T2 weighted sequences and DWI sequences it's again to apply a kind of algorithm to basically get to the final score. So in the peripheral zone our dominant sequence is DWI. Basically we give a final score based on DWI. So if you have DWI one, it basically one overall Pyratz score vice versa. But if you look at Pyratz three on T2 weighted sequences DCE basically helps us in this category. If it's a DCE positive and had a Pyratz two, Pyratz three on T2 weighted sequences we can upgrade it to on overall score as four. And whereas for other sequences or other lesions any other sequence findings may not matter actually. In terms of again, transition zone again, focus on T2 two scores, three scores where we again have to look at again in transition zone our dominant sequences T2 weighted sequence. And again, if you have a mild suspicion or intermediate suspicion always look at DWI. If DWI is scoring high that's where you upgrade them to three if it is two have abnormal DWI it becomes three if it is abnormal I mean three score on T2 weighted sequences and you have abnormal DWI you upgrade it to three I mean it's remains three especially in the T2 TZ lesion of three. So these are the key little bit of a confusing scoring system that often gets in the clinical practice. So now again, I just want to show here peripheral zone dominant sequence in DWI and for a TZ dominant sequence T2 again, these are the key areas where other sequences matters especially when there is a intermediate score here. This basically if you're reading it workstation keep this at one slide at your desktop it's help you to actually come to a final score just looking at all the information at one slide. So let's review some examples. So in the peripheral zone this is just a normal gland we don't see any abnormality maybe some linear abnormalities it just sequelae of prostitutes we don't see any other abnormalities in the corresponding areas in the other sequences. Again, this is a linear orbit shaped focus in the peripheral zone and we do have some abnormality on the sequences but because of the shape it's again, I've been in finding overall pirates three here peripheral zone lesion we have a focal abnormality that is non circumscribed and maybe some ill-defined margins and has abnormality in only one sequence. So only ADC has a little bit dark but also on high B value and I think there's not much even mild enhancement again, overall category is pirates three here. Pirates four as told clearly is a focal lesion has a redistricted fusion and also enhancement. Pirates five as in size wise it's bigger than 1.5 centimeter that's why it's qualified as pirates five. And again, the TZ lesions again, this is a normal central gland central gland is basically TZ and CZ at the mid gland level central gland is only TZ. Here we see diffuse hyperplastic changes maybe some heterogeneous nodule here and again, all these changes are just to be patient nodules and so it's a TZ pirates one. Again, here we can see some nodules maybe some thickening of septa in between nodules but again, this is again called without any focal abnormality on other sequences it is pirates two on TZ sequences. Here it's a three mainly you can see we see a focal abnormality in the transition zone anterior on left side corresponding area has some redistricted fusion but not much of a high B value abnormality against enhancement this again, not significant especially when scoring TZ lesions. So based on having only on one sequence it's again categories as pirate three on TZ sequence. These are the atypical nodules. Basically it looks like a B patient nodule with circumthrived margins and having a maybe partially encapsulated margin and has a high signal intensity and high B value and also this is diffusion that's why it becomes a though it looks like a T2 on T2 weighted sequence it looks like a two but because of its high signal abnormality features on DWY and ADC it's again upgraded to overall pirates three. Very similar case with in this time this is more of a lenticular shape long base atypical capsule with a restriction diffusion that becomes four very thing by just by size criteria. So again to summarize pay attention to sequences when you're characterizing them depending on the zone. So DWY is our main sequence peripheral zone lesions and transition zone lesions it is T2 and again DWY makes a much difference when assessing TZ lesions and again DCE sequence plays a role when you have intermediate T2 weighted and peripheral zone lesions. Again there are some cancer mimics and pitfalls while interpreting focal lesions and the prostate especially using the pirate system. So those are basically anatomically we can have a hypertrophic fibromus stroma that is especially antiretlant they can have a thickened asymmetric thickening of surgical capsule that can also can sometimes mimic periprostatic venous plexus and fat lobules sometimes have a tissue diffusion and may mimic like extra prostrate extension or if the lesion that exists next to it sometimes neuroversal bundle posterior pseudo capsule lesion tear drop sign those things and also help you some of the these pitfall anatomical pitfalls to avoid. Again BPH depending on the amount and the extent they also can mimic some of the aggressive features. Informatory infectious pathology such as chronic prostratitis abscess, ground limitous prostratitis can sometimes mimic as a prostate cancer if we are interpreting them in a blind way without having to know any prior histories or any BCG installations in the bladder any of such histories will definitely help us to identify or narrow down the nutritional diagnosis. Variant histopathology also is very difficult to apply pirates routes because again, musinus or ductal or neuroendocrine differentiation all this atypical histopathology variants have a different morphological features on MRI and may not follow pirates routes. Of course, hemorrhage and calcification sometimes can also compromise image quality and also cause pitfalls in interpreting. So again, a pirates has a good performance is one metanalysis pooling about 13 diagnosed accuracy studies since it is over 80% and again specificity is over 70 with Irish 2.1 we are much higher than this especially at the high volume centers. Moving on to the second half of the talk on staging. So when you talk about the first part was about when you see a focal lesion when you are screening a prostate for identifying cancer that's where you apply pirates but again, if you know that there's a cancer exist in the gland based on your pathology, biology biological assessment then the key is to stage tumor. So there are different prognostic factors to actually assess prognostic significance. As we know, Gleason score is one PSA values and of course, T staging is the one that mainly helps us to categorize our prognostic factors. Looking at the T staging itself so we have a localized disease I mean, T1 disease we don't see an MRI if it's a T2 it's basically how much it is involving the gland with the focal tiny T2A on behalf of the gland it's T2B if it is more than I mean our majority of the gland both sides if you come T2C and again, if the tumor is gone beyond prostate it is T3A if the tumor is beyond prostate it involves some vesicles it becomes T3B T4 is basically going beyond prostate involving a bladder wall or rectal wall or geodaphram so these are the things that becomes T4 disease. Again, there are some nuances depending on microscopic, platonic invasion all those things especially pathologists if you have a detailed analysis I think that way the pathological staging that helps actually further prognostify after the post prostate to me. Based on these factors again, NCCN group actually further risk-statified and their prognostic value on that we have basically very low to very high depending on T stage depending on PSA values depending on again, at least in grade grouping on the biopsy pathology. So coming to the treatment options depending on the what stage and what risk factors you obtain so we have various options we can remove the gland entirely by surgical techniques or we can give the radiation and combination of ADT and the radiation therapy and of course depending on again variant pathology and variant Mr. Pathology these may also get some chemotherapy as well. The goal here is to match the treatment intensity to the level of aggressiveness. If you have a glistened six disease and you are treating them very aggressive with surgical and radiation that's okay. Then if you have a glistened eight disease and treating them with active surveillance or watching them or giving them ADT is again a overkill. So we have to match the intensity of the tumor in the gland with appropriate treatment options. And again, the goal is to avoid over treatment and under treatment. I won't go into details here radical cross-sectional basically we remove the gland and again there are different techniques nerve sparing and non-nerve sparing depending on functional outcomes that surgeon or patient would want to preserve after management. So basically if they remove the all nerves that is non-nerve sparing that has a side effects in terms of retinal dysfunction and incontinence. If you're sparing it again the chances of you spreading the tumor especially beyond prostate. And there's reason the nerve sparing to be performed with very caution also very good surgical staging or with a pre-surgical MRI. The key thing to note here is to avoid positive surgical margin and that basically increases having to have a recurrent disease. The key areas that actually prone to have a positive surgical margin are postulatory based apex in the bladder neck. So those are the areas that we as radiologists also pay attention and inform the surgeons if you see the tumor at these locations. Of course, radiation therapy we need to be a very, very clear about tumor extent especially the tumor involves some of the vesicles or surrounding structures surgical management is somewhat contraindicated and try to go towards radiation therapy and medical management versus surgical management. So here again choosing various different options having to have a pre-treatment MRI is also very helpful to decide on these different options. The goal again, he is to identify when you have a staging MRI the goal here is to identify primary lesion and also extent of the tumor. When you again identify the tumor in the gland key is to have how well we can reset the tumor without leaving any tumor behind and then how well we can achieve functional outcomes that is in terms of maintaining erectile function and also a continence of the bladder. So because sometimes the patients would prefer to have these functional outcomes versus having to have aggressive treatment. So that need to be always factored in when you are counseling or providing the various treatment options to the patients. That's where pre-surgical MRI plays a very important role in terms of deciding on those treatment options. Of course, especially when you have intermediate incision risk groups patients there are multiple options for them to choose depending on what kind of lifestyle they prefer to have after main treatment. And of course, if you're looking for overall staging we work with other motorists for metastatic work beyond pelvis that especially PET CT or bone scan things would help to identify disease beyond pelvis. Our goal here is to have a local staging, lymph node staging and bone staging as I mentioned local staging preferably with MRI lymph node staging MRI plus PET or CT. Sometimes PET is more preferred especially with the PSMA being widely available now in the US. Bone staging preferably usually done with the bone scan but always get again a PSMA scans as well to define on depending on the aggressiveness of the tumor that was identified both in biopsy and also on prior images or MRI. Going into key local staging features that exist now for MRI to identify that maybe one is extra pressure extension that we need to be clearly identifying define it and locate it that basically helps us to help the surgeons to actually have a nerve sparing surgery or nerve sacrifice and surgery. Again, similar surgical involvement as I mentioned it is again key factor to decide on surgical versus radiation management and other key side surgical landmarks or the pelvic floor involvement or rectal involvement or pelvic sidewall involvement sort of see each one of them. So EPE is basically the tumor extends beyond the surgical capsule I mean so beyond the pseudo capsule there's no true capsule on the prostate so basically it's basically a pseudo capsule. If it goes beyond the pseudo capsule we usually call them as extra pressure extension every extra pressure extension will have a lot of base that usually involves some of the physical if it is involving the periprostatic fat or neurovascular bundle that we call them as involvement of neurovascular bundle here we can see neurovascular bundle as a small tiny dots with a T2 dot signal. EPE is a spectrum of finding it's not a yes or no or in a presenter absence it's actually a spectrum invariably begins with a microscopic extension beyond the prostate and then you can start seeing them on MRI as a various direct and indirect science and then obviously when it's really beyond prostate that way it's actually a DRE examination you can actually identify it so that's a spectrum depending on where the findings exist we should be able to identify it either by MRI or by DRE examination. Here is one case where very subtle imaging findings in one case if you look at the MRI they look very similar there's a tumor on the left side peripheral zone and maybe have a capsule abutment but obviously we don't see anything beyond but one had a positive model in this case there's no EPE on histopathology and this case had a histopathology positive EPE so that basically tells us especially when there is no proper disease outside prostate gland we should be very, very cautious in terms of calling it as EPE and preferable to have a ligar score again to give you a likelihood of suspicion. In this case we can see the peripheral zone ending here but there's a tumor going beyond peripheral zone that's where the clear obvious typical EPE that exists beyond prostate gland. This is a spectrum I sold so direct sign is when tumor is extended beyond prostate margin and involves a very prostrate tissue whereas other signs are all indirect signs depending on what you see your ligar scoring system will affect so just a bulge or just capsule abutment that's very early sign of having to have a microscopic extracurricular extension what's a scapsular bulge having a contour irregularity depending on the amount of tumor and obviously this tumor is beyond the prostrate margin so those are indirect signs and direct signs there are different scoring systems usually the one first introduced was a European society heurologic radiology scoring system almost like about a decade now but combining some of these factors NCI actually proposes another gradient system based on multiple factors just having to bulge or multiple bulge and irregularity and obviously over disease outside prostate so especially when you have these findings you are having a risk of EPE is about 66% and they are caught then it goes less and less as they have only one finding versus multiple findings and again some of the key locations as I mentioned those are high risk for surgical positive margin pay attention especially when you see the tumor these locations they are prone to have a extra prostrate extension and positive surgical margin the one is you have a posterior lateral aspect of it in the apex you know anteriorly and also this is something called invaginated extra prostrate space around the senile vesicles ejaculate ducts, sorry so these are the key areas to be paying attention especially when you see the tumor at these locations clinical implications as I mentioned if it is a gone beyond prostrate we don't do a nurse paring at that site and if it's again involving senile vesicle it impacts the decision on tradition management a few words about positive surgical margin it's again a tumor that exists on inked margins you know usually if you've seen the grossing of pathology prostrate specimens they basically ink them on both sides to identify the site and if anything is beyond inked margin or touching the inked margin that's where you call them as a positive surgical margin depending on how well the surgeon intersected very prostatic fat you can actually identify them going beyond prostrate margin but invariably usually we see them as a inked margin positive and again risk factor as I said for having a positive surgical margin is a tumor location it's relationship with the prostate and again volume of the prostate volume depth of the tumor depth of the gland in the pelvis because sometimes if the pelvis deep and the prostate is deep in the pelvis it sometimes is difficult to dissect and also with the technical difficulties of resecting it we may leave or we may some tumor in the pelvis itself so all these factors combined with the surgeon's experience volume of the tumor pathological stage at least in grade you know PSA levels and all these are the other factors that were modeled into the risk stratification next one is similar physical involvement as you see the tumor involving some of the vesicles here MRI has a good sensitivity specificity in terms of over 60 percent sensitivity and over 95 percent for specificity again T2 weighted sequences corresponding DT2-BY and enhancement pattern helps us to identify ISV involvement so key is to again identify ISV involvement by looking at multi sequences multiple sequences and planes so for example a few cases I'm going to show future will show you as agile images and these are corner images this one example just show various patterns of ISV involvement so one is direct spread if the tumor is at the base level it can directly spread into the adjacent pediplastric fat and get involved in some of the vesicle in this case tumor is through the capsule and again involving going beyond and involving these other vesicles this is asynchronous that means you know tumor is in the similar vesicles this is an agile images DT2-BY tumor is in the similar vesicles bilaterally DT2-BY and DC sequences but whereas there's nothing exist at the level of base so tumor the bulk tumor was at the apex but the tumor deposits were in the similar vesicles so these are the atypical and again discontinuous tumor involvement of similar vesicles these are the common patterns but this is the most common one this is the second most and this is one of the greatest one again this year you can see the tumor at the level this is a coronal image you can see the tumor at the level of base that upwards the ejaculate ducts and similar vesicles this is agile images the same tumor may be surrounded by SV and if you look at this again very similar findings you can see here as well but when you look at the histopathology here one was positive this was actually having a similar vesicle involvement on pathology this was did not have so basically that basically tells us just abutting the similar vesicle on sastral and coronal MRI is not a direct sign of similar vesicle involvement so again on pathology to call it a similar vesicle involvement they're supposed to have a muscularis property involvement so all these things are nuances that you know you get to see as you see the advanced cases and seeing the more cases of similar vesicle involvement and again analyze them on multiple planes impact depending on the extent of involvement VPE and SV they may not qualify to get a especially brachy and EBRT there are other additional landmarks that we need to be paying attention that is extra urethral sphincter at the apex level blood and neck at the base level neurovascular bundle posterior laterally and bilaterally anterior muscle stroma anteriorly that's again from the common pitfall as well to interpret rectum posteriorly and gudiform inferiorly around the apex so quick link going on some of the findings here this is external urethral sphincter that basically at the level of apex this is coronal image we can see a normal strated muscles that and the long parallel manner and we can also see a donut shaped or if the south Indians are around what are shaped structure here in the apex that basically compromise normal external urethral sphincter this is key surgical and radiation on college related landmark because having to spare this anatomical part will improve much outcomes in terms of unary symptoms so if the surgeons can spare a good amount of apex and have a good anestomosis they can actually maintain a good functional outcome after surgery and if the radiation oncologist can avoid this area of implanting radiation seeds or radiation they will be seeds they can actually avoid burning iteration things of a that nature and they post radiation life so that's reason this is one of the key relevant anatomical sequence that people need to be identifying and helping the surgeons and radons to avoid any overprevent and treatment of it bladder neck this again critical structure difficult to identify sometimes on sequence on imaging I mean involvement of bladder neck I mean so on anatomical images definitely you can see it but because of lack of any tissue planes between the prostate and the bladder it is very difficult to identify bladder neck involvement prospectively when especially when it is settled the tumor as you can see here this is normal bladder wall T2 dark signal and glands also extends into the bladder neck but if the tumor signal exist in the bladder when at the base and if you have a discontinuity of the bladder wall that's one of the signs of having the bladder neck involvement again this is very difficult and prospectively to identify especially when you have a abnormal signal in all sequence in the tumor is at the level of base and extending into the bladder neck again it's something to call and again help surgeons to avoid positive syndical margin as I said neurovascular bundle that exists postural laterally on both sides again there's a lot of anatomical variants there are again theories on how these bundles form some theories that you know basically a focal anatomical structure that exists along the postural lateral aspect superiorly and inferiorly some say it's a diffuse from the base to apex some say that exists across the prostate you know but again depending on the what pattern you see on the particular patient usually it's along the postural lateral aspect of the tumor that exists next to it can actually compromise and extend into it that just because these structures basically pierce the capsule that is pseudo capsule and have an easy weight to a tumor sense to spread along these tracks anti-fibromastom fibromastoma as I said this is again thick T2 high point in signal and anteriorly this again pitfall if you again see standalone finding but often correlate with our disinstructors and see when your tumor signal exists and that exists beyond that and if you have any essentially thickening always call it as a tumor otherwise typically if you have a symmetric finding and it's a especially on the base it's usually a pitfall surgical versus nonsentrical management I briefly told earlier but again when you have a structures like a rectal wall geodiafrome involvement those are definitely you know cases for nonsentrical management in this case at the apex level you're seeing at the bulky tumor here the tumor is involved with rectal wall as you can see muscle property has been pulled here and actually measures in the rectal coil here you can see the tethering of the rectal wall to the apex and the tumor is here so this again direct sign of rectal wall involvement especially when you do not see such a direct signs here it's very difficult to prospectively call in those scenarios always look at sexual sequences both on T2 and T1 weighted sequences especially on T1 fat may appear sometimes bright and have a clear line between wall and the posterior prostate margin that helps you sometimes to identify a clear plane and fat plane this again old case where there is a bulky tumor in the prostate again goes beyond prostate involving the rectal wall tumor also in the rectal lumen that you can see and all sequences and post contrast we can see heterogeneous networking areas as well another lesion where tumor is directly involved in the geodaphram infinitely as you can see apex and transferred apex is compromised tumor is gone beyond here you can see normal levator muscle on the right side but on the left side you can see the compromised signal and the tumor is in the musculoskeletal layer I mean in the muscles here tumor gone beyond and went in ahead and spread into the bladder wall this is a direct bladder wall environment this is the word cases you can easily identify them so in this case tumor is basically traveled along the posterior lateral aspect of the gland and again involve the bladder wall so to summarize basically we have a key anatomical key areas that is extra prostrate extension neurovascular involvements universal involvement rectal wall extra neutral sphincter geodaphram bladder neck and the bladder wall these are the key areas to be in mind when you are interpreting a staging MRI for prostrate cancer and again lymph nodes as said we can definitely identify local regional lymph nodes especially in the pelvis but whereas beyond pelvis we need additional images either CT or pan depending on the risk stratification so here the most common findings we see are the obturator and external lactic chain and again it can go in any chains in the pelvis and again go into retropytonium and commonly I can retropytonal parietic nodes again as I think we heard Dr. Morani mentioning it depends on depending on your aggressive tumor in the prostate if you don't see anything or if you see a very low grade tumor or a very small amount of tumor in the prostate it's again very unlikely to have any node in the pelvis to be called as a prospectively a number node again there are other differential diagnosis including lymphoma leukaemia and other reactive nodes can also sometimes appear bulky and need to be always in the differential diagnosis when you have a low pre test probability of having a bulky tumor in the prostate again bone metastatist we can only see in the pelvis and we have two sequences for staging especially the whole pelvis T2 T1 and in our practice we obtain T1 sequence but some practices in my fellowship we used T2 so depending on what you obtain be familiar with the bone findings and often these findings are difficult especially when you have a limited sequences to evaluate a bone metastatist often these findings are evaluated with a bone scan or with a pad scan and again end up having the biopsy as well especially having a bone disease is a again a significant risk startling factor for management so it excludes all your local treatments so that's the reason they often get them you know undergo biopsy before giving them a definitive local therapy so again to summarize second part of my talk basically on staging so local local regional staging of prostate basically influences in SCN risk certification and which directly informs prognosis and management that's main reason when you are having a talk with a patient about management decisions this plays a very important role and again EPG is not a yes or no question it's a multifactorial likely good scale should always give you all the factors in consultation give them always like at school unless you have a gross EPG again always look for key anatomical landmarks or on the prostate when you have a bulking disease to identify key structures and their involvement