Renal Sonography: Renal Lesions Hiding in Plain Sight - HD

Introduction

Hi, I'm Dr. Beverly Hashimoto. I'm section head of ultrasound at Virginia Mason Clinic, Seattle, Washington. And today I'm going to be talking about renal sonography.

Renal sonography is a very unusual topic in that although for ultrasound it's very easy to see the kidneys. In fact, renal lesions are commonly missed because they're very difficult to spot. And this cheetah, it's very important that an imager, as they're looking at the kidneys, looks at them very, very carefully in order not to miss lesions.

Why do we miss lesions in the kidney? I'm gonna divide this talk into four different topics because these are the major reasons why we are missing lesions. And they include sonographer training issues, non visualization of kidney lesions, pitfalls in hydronephrosis, and then the pitfalls we see in imaging real masses.

Sonographer Training Issues

Sonographer training issues are critical. Part of the reason why we miss, frankly, any kind of abnormality in the abdomen. And some of the reasons are that the sonographers inexperienced, in other words, they're a kind of imager and that they see but don't observe. So they just take pictures instead of actually taking pictures which are diagnostic. And in doing so, they may miss lesions. And if they miss lesions, then you as a radiologist will also miss these lesions. It's therefore very important that your sonographers are well versed in renal abnormalities and can spot these abnormalities readily.

The normal appearance of the kidney is generally something that all sonographers and all radiologists are very well familiar with. That is its renal formm object. It's between 10 to 14 centimeters in length. The kidney should be symmetric in size with media echogenicity and a cortex greater than or equal to 10 millimeters.

How do we make errors in appearance? Sometimes the kidneys are normal appearing to us, but in fact they're really abnormal. And the reasons why we miss this abnormality are, first of all, if the size of the kidneys is abnormal and yet measurements are not present or we don't remeasure the lesion. And when we're looking at the kidneys, it's very important that your sonographers have either made measurements or that you are very aware of what the estimated length of each kidney is in order not to miss an abnormality due to renal size.

We also miss renal abnormalities because there are standard renal pictures which are just omitted from the actual exam. And for example, if you have an abdominal ultrasound and you're missing the picture of the right kidney with respect to the liver, you may not realize that the echogenicity of that kidney is in fact abnormal. Abnormal orientation is a more difficult problem to miss because unless you're actually scanning the kidney, you may not realize that the kidneys are abnormal in orientation. And it's important that if you are not directly scanning the patient, that you are aware of what that orientation is by your sonographer. And then finally, it's very important that whenever you see the kidneys in an image, you're able to see all the borders of each kidney.

Here's an example of a 36-year-old woman with pelvic pain and this is the right kidney and is it normal? In fact, it's too large. It measures 15.3 centimeters in length and this woman only has one kidney. So it's very important in this case to have had that measurement so that if you don't see the left side, you have a good reason as to why you're missing that left kidney.

Here's a 70-year-old man with bacteremia and the reason he came to us was to rule out gallstones. My sonographer said that the exam was normal, but as I was looking at the exam, I thought that the echogenicity of the kidney was abnormal compared to the liver. And I called that and later on reviewed the patient's chart and found that in fact this patient did have an elevated creatinine.

Here's another case, 44-year-old woman with possible hydro necrosis. If you look at these kidneys, there's no hydro necrosis, but do you see any other abnormality? In the right kidney you might say, maybe there's a cystic lesion here. In fact, there's another important problem with both kidney images and that is that you don't see the lower poles. And one of the critical aspects of a kidney examination is that you see every single border and in fact, this kidney was a horseshoe kidney. And what that stenographer didn't tell you was that the orientation of both kidneys was abnormal. And the lower poles aren't seen because she originally missed the fact that they were connected to each other.

Non-Visualization of Kidney Lesions

Sometimes the sonographer will come to you and say, I don't see one of the kidneys. And when this happens, it's very important to have some kind of differential in your mind in order to problem solve why you may not be seeing that kidney. And possibilities include the fact that perhaps the sonographers using poor technique or the patient's just difficult to scan. Another reason may be that there's a congenital abnormality here so that for example, the patient has agenesis of the kidney, sometimes the lack of a kidney is acquired. For example, if the patient had a nephrectomy and your sonographer has asked the patient if the patient's had surgery, if the patient has renal disease, then the kidneys may be extremely echogenic and small and therefore blend into the retroperitoneum. In that case, it may be very difficult to see either kidney in this situation. And then finally, if you're not able to see a kidney, it's very critical that you look all over the abdomen to make sure that you're not missing a kidney that's in an abnormal location.

Okay, how do you go about doing this kind of problem solving technique as you're actually doing your exam? First of all, as I stated, when you're told that there's no kidney visible, the first thing to think about is, is it technique? So when you look at your images, one of the things you can evaluate is does it look like there's too much air or gas? Or you ask your sonographer, why don't you see the kidney? And they may just say, there's overlying gas. In that case, one of the suggestions you may use is to have the patient lie on their stomach because using a posterior approach you can almost always see a kidney.

The second technique is to make sure you're looking at the contralateral kidney very carefully and see if you can tell why it is that the other kidney is missing. Because this contralateral kidney that you see commonly has clues to the missing kidney. First of all, is the contralateral visualized kidney large? If so, then you can anticipate that the other kidney, the one you're not seeing, may be very small a trophic or may be missing. Could there be a congenital abnormality? That's very important to think about is the kidney. CRO is for example, a cross fused utopia. The kidneys would be on the same side. And then finally, if the contralateral kidney, the one you visualize appears very normal, then look for a kidney that's perhaps in the wrong location.

As you're doing your problem solving and looking for kidneys that are in locations other than in the upper quadrants, the pelvis is probably the first place to look. And when you're looking in the pelvis, it's important to put a lot of pressure against the pelvic brim. When you do this, you can generally push away any air and see a kidney against the pelvic brim in the female pelvis. Sometimes you can see associated gynecologic abnormalities and that will give you a clue as to why you're not seeing the kidney because congenital abnormalities in the pelvis and a female are commonly associated with congenital problems in the kidneys. And then finally look at the renal arteries. Sometimes the renal artery on the non visualized side will give you a clue as to the location of the non visualized kidney.

Here's a patient who came in with had a stent previously and for UPJ obstruction but now has U sepsis and the sonographer came up to the radiologist and said, I'm not sure, but this is the only thing I see in the left upper quadrant. I'm really not sure it's the kidney. And if you look at it, it looks like it perhaps isfor, but it's very, very difficult to see. So is this a technique problem? In this particular case it's not a technique problem because this patient has semus pyelonephritis. Here you see a plain film where there's a large amount of air which has infiltrated the entire kidney and a CT scan emphasizing the same findings with this air interspersed throughout the kidney. Then it makes the image, the ultrasound image of the kidney very distorted.

Here's another man, 48-year-old with elevated creatinine. He doesn't have a kidney which is visualized, his left kidney looks normal however. So what should we be thinking about? Normal appearing kidney on the visualized side, again, think about a contralateral, non visualized kidney in a wrong location and that's where it is in this case. In this case it was deep in the pelvis. In fact, it was a transverse kidney here you see here with the great vessels, deep to them to the kidney. And this kidney had two renal arteries.

Next patient, 36-year-old woman with pelvic pain, no left kidney visualized. Why is that? Here's the right kidney, notice the size, 15.3 centimeters. Here's the appearance of the uterus and here's the right ovary. So do you think there are gonna be any other findings in this pelvic ultrasound? In fact, if you don't see a kidney in a woman, in which you're doing a gynecologic exam, think about the fact that they may have a congenital problem and in this case, this woman has an absent leftover that was confirmed over two different examinations. It turns out about 37 to 60% of women with renal ssis have genital abnormalities.

Pitfalls in Hydronephrosis

Okay, now we're gonna turn to the next topic and that is pitfalls and hydronephrosis. So there are four reasons why we miss hydronephrosis and frankly this is a pretty depressing topic because hydronephrosis is probably one of the most important and easiest indications for ultrasound. But sometimes we miss it. And why is that? First of all, we may miss hydronephrosis when it is actually present. And I'll tell you the reasons why. Sometimes when hydronephrosis is present, we can't identify the obstruction. In fact, that's fairly common. If there's hydronephrosis and hydro ureter, we commonly can't tell where in the ureter the obstruction is located. Hydronephrosis may actually in fact be reflux, it may not be obstruction at all. And then finally, para pelvic cysts can sometimes be difficult to differentiate from hydronephrosis.

First case, 73-year-old woman with fever and was sent to the department to rule out hydro necrosis from the er. So here's the left kidney. Frankly, the right kidney looked the same. And from our point of view, we thought the kidneys looked normal, the bladder was empty. What did we find? Patient symptoms persist. And later in the day the patient had a CT scan which showed severe left hydro necrosis with a UVJ stone. So why did we miss this hydro necrosis? The most common reasons for missing hydro necrosis on ultrasound when it in fact is actually present is first of all patient dehydration. If the patient's highly dehydrated and commonly if they're super sick, they are because they're vomiting, they're not taking anything orally, they're not making urine. And if they're not making urine, there's no urine to back up for us to see, in the kidney itself. So one of the important factors is if hydro nephrosis is your primary indication, make sure that patient is well hydrated. And in the ER for example, they're coming in and they look very, very dry. We ask them to start an IV at the time that they order the exam so that by the time we see them, which is anywhere between 15 minutes to 30 minutes, they've at least had some hydration.

Very distal or mild hydro necrosis or partial hydro necrosis may also be a situation in which we don't see a lot of urine in the kidney. And again, this may be another reason that we miss hydro nephrosis.

Here's a 66-year-old man with acute renal failure and the indication was rule out obstruction. So here is the right kidney and the left kidney was normal and there was a normal left ureteral jet. No right ureteral jet. So what do you think is there right hydronephrosis? In fact in this case, my sonographer saved the day for me because I would've said, yeah, there maybe is a little bit of hydro. What she did, if you remember looking at this picture of the bladder, the bladder was extremely full when she started the exam. So she had the patient void and after voiding there was no urine in the kidney. And in fact what we were seeing was just some reflux into that right kidney. So it's really important that if the bladder is highly distended that it be emptied before you make that diagnosis of hydro nephrosis.

Here's another man, 71-year-old with chronic hydronephrosis, which side? Unfortunately this patient came in from an outside hospital. I didn't have any of his outside records. Urologist wasn't available for discussion. And I basically had to guess. And here's the appearance of the right kidney and take a look at it. This is longitudinal, this is transverse, and here's the left kidney longitudinal transverse. So what do you think, which side do you think has hydro? It turns out in this case there were bilateral ureteral jets. I made the diagnosis of right hydronephrosis. In fact, it was left in fact, it was the left side that had severe para pelvic cysts and had, the left side had hydronephrosis and the right side had severe para pelvic cysts. So this is an example of how para pelvic cysts can sometimes be very deceptive. Most of the time it's not a big deal if a patient has para pelvic cysts, we can definitely tell the difference between that and hydro, but once in a while it can be a challenge.

Pitfalls in Imaging Renal Masses

Now I'm going to turn to a very troublesome topic one, which we all know is a challenge and that is pitfalls in imaging renal masses. And the reasons why we miss renal masses are varied, including the fact that the masses may be iso coic with the kidney masses may be exophytic and we may miss them. Sometimes normal variants look like masses. And then finally it's really critical that whenever we're doing a renal ultrasound, if there are previous other cross-sectional imaging that we cross correlated with, such as ct.

Now many a times all of us are extremely busy and we're doing numerous exams and we're sort of saying normal, normal, normal, normal, normal. And as we're going through our day, we quickly look at the kidneys and we pass 'em because they look basically normal. If that's the way we practice, unfortunately something's going to catch us up and there's going to be something that is actually not normal or not usual as in this sign. And we're gonna miss it because these commuters, they're sort of immune to looking at their environment and they're just saying, oh, it's the same old, same old, same old thing and they're gonna bypass this sign and not realize that it is very unusual.

Okay, here's a 42-year-old woman with epigastric pain. So this case I called normal. However, is it normal? CT scan was later done again because the patient's symptoms persisted and in fact this patient had an abnormal renal mass, turned out to be renal cancer. This in retrospect was the picture, the closest picture we have to that area. And you notice one of the things in retrospect that I really should have keyed in on is that this area of the kidney certainly is asymmetric compared to the rest of the kidney. Now if you're going fast and this is the only picture, which it was in this abdominal ultrasound, it's easy to just sort of pass it and say, the sonographer was just slightly asymmetric. But it's really important in fact to be very careful. And if you see asymmetry in terms of what looks like cortex, renal cortex, it's important that you send your sonographer back, take a closer look, make sure there are no renal masses.

Here's another patient man comes in with bloating, right upper quadrant pain. In this case, here's the right kidney, it was echogenic, but the radiologist and sonographer did notice the fact that there was asymmetry of the cortex and in fact this turned out to be a renal cancer. And color doppler can be very useful if you're not sure you have an iso coic, mass collar doppler is a very useful way to delineate these renal masses and separate them out from the rest of the cortex.

The 74-year-old woman came in with abdominal pain and here's her left kidney to see anything unusual. Is there any reason to take another look? Look at it carefully because this pitfall was one I showed you earlier in that notice lower border we don't see it well and in this case, if you don't look carefully, you're going to miss this renal mass. So again, all the borders on your kidneys have to be well-documented. If you're missing a border, you have to send your sonographer back. Take another look. Okay?

There are other pitfalls that one runs into when one sees renal masses and one of the biggest problems is that benign masses and malignant masses have very similar appearance. Second of all, koic versus hypo coic masses can be very difficult to differentiate. So it can be difficult to tell whether something's a cyst versus a solid, especially depending on the imaging of the patient. Third problem is circumscribed margins. You see a mass, it has circumscribed margins. Do you always call it benign? If you look at a hypo or anti coic or hypo coic mass and it doesn't have color doppler, does that automatically mean that it's a cyst? And then finally it's really important to look at the patient's clinical history and review any previous exams. If you see an unusual renal mass,

Here's a 69-year-old woman and she had left kidney area pain and this was her left kidney. And notice there appears to be some thickening or asymmetry in the mid kidney. So the question was, is this a mass? We had no other comparison imaging and so we did ask for a CT in this case, or an MR and what did we see? In fact, there was no abnormality. This was a normal column of ene and column of enes occur in 6% of adults. One of the ways to differentiate column ene from abnormal renal masses is the fact that there's no outer contour abnormality.

Here's a 71-year-old man with chronic aortic dissection and in the kidney we notice this sort of echogenic area. So is it a mass, is it scarring? When we looked at the patient's previous CT scan, we noticed that in fact there was some thinning here. And this is just again a congenital abnormalities, junctional parenchymal defect. This is a fusion defect when the anterior and posterior nui of the kidney's fuse and it's located anterior and superior in the kidney. So if it generally it's in the junction of the upper one third lower two thirds of the kidney in the anterior aspect. And if you see that think junctional parenchymal defect.

Here's another patient, unusual looking kidney, sort of sticks out here. Has renal arterial flow? Is this a mass? Luckily we had had previous imaging available and this unusual loation had been present for seven years and this is just a fetal ululation.

65-year-old man with back pain. And this is the left kidney. First of all, this is not a normal kidney, right, this very echogenic kidney, but in the lower pole there's a hypo coic mass. So is this a renal cancer? It turns out in this person that it's a heavily calcified lesion, which turned out to be renal tb. So this illustrates the fact that benign lesions of the kidney really are indistinguishable from malignant ones, ignorant ones.

This is a 93-year-old man, he had just had renal lithotripsy earlier in the day. He went home and then came back through the ER when we saw him that night. This is the way his right kidney looked and there was a big mass in the upper pole. Is this malignant? Is this benign? Again, renal history is very important. And in fact this was just a large hematoma which had occurred as a result of renal lithotripsy.

The 66-year-old man had a cyst on the CT and the cyst on CT was too small to be characterized. So this patient was sent for ultrasound. On ultrasound we found that the mass was hyper coic and exophytic sort of difficult to see the borders. So what do we say? Is this benign? Do we think this is an angiomyolipoma? It didn't have fat on the ct and the borders are ill-defined at least possibly irregular. And in fact, this was renal cancer.

Another patient 63-year-old with postmenopausal bleeding. And incidentally we noted this well circumscribed genic mass, this incidental finding. What do we do? In this case we had no previous imaging and we felt that even though circumscribed, that it was important to take a look at it with another imaging modality. In fact, it was not fatty and it turned out to be a renal cancer. Here it is the intraoperative image of that cancer,

55-year-old man with history of renal stone. And here we have a circumscribed mass, exophytic mass, no color doppler. Do you think that this is a cyst? In fact, it turns out to be solid. People who saw it the day of the ultrasound made a good call and it was sent to CT and that was a renal cancer, 71-year-old woman. Now this really did look like a cystic mass. And the question is, do we just pass it? Does she need any other follow up? Notice that this cyst is irregular in contour and that some of the septations are thickened. And as a result of this, this patient was sent for a CT and those findings were confirmed and this turned out to be renal cancer. And when we're looking at cyst, it's important to remember the BOSNIAC criteria in which if we're going to not follow up, really we're thinking about cyst with one to two thin septations and a thin wall. Any other deviation? And then we have to really think about it. The Bosniac F category two F category. There are more thin septations and there may be some calcification. Anything beyond two F though definitely needs to be worked. Up here is a 59-year-old man with right upper quadrant pain. And again, is this a renal cyst? It sort of has a hyper coic rim cystic center. Is that something we're gonna pass? No, it's not completely simple, right? The wall is not thin. This turned out to be renal cancer.

Ultrasound-CT/MR Co-Registration

Before I end this talk, I'd like to discuss a topic which I think is really important and that is a new technique, relatively new technique which I think will help us in evaluating renal lesions. And this is ultrasound, CTMR co-registration. It's now available on all major vendors and it's I think a very important technique because it really allows us to be more operator independent. What this technique does is it allows the ultrasound machine to download a previously obtained MRI or CT and then to superimpose that CT or MRI data on an ultrasound. The CT or MRI images are reconstructed in real time in the same orientation as ultrasound.

What are the applications? The first thing is if you're a teaching institution, it's a great teaching tool because many times residents are not as familiar with ultrasound, cross-sectional anatomy because our anatomy is skewed. We can look at organs in many different angles, but they're very familiar with CT or MRI anatomy. So if they have them side by side, it's much easier for them to understand and learn ultrasound anatomy.

Secondly, just as a very practical aspect of day-to-day work, it's great way to document lesions. And when lesions are documented this way, one, as a radiologist, you don't have to double scan because you know that the sonographer has been examining the correct lesion.

Thirdly, let's say you have a very difficult case. You're sent a case in which there's some abnormality on CT or mr and you're asked to characterize it by ultrasound. Something like a very subtle renal lesion. Many a times these are difficult cases and unfortunately my sonographers may not be able to find the lesion. And it means that I have to go in the room. And since I'm busy, it's really important that I don't take a lot of time scanning. And having this technique really does cut down on the scanning time of anybody who has to cross correlate between subtle CT and MR lesions and ultrasound.

And then finally having this technique and using it to document your exam really helps you communicate better with your referring physicians because just like residents referring, physicians many times can't read ultrasound, but they can read or understand a CT or mr. So when you have these pictures side by side, that is the ct next to the ultrasound, then they can understand that you have actually looked at the correct area.

Here's a case in which you can use it as a teaching situation. And normally, we don't think about the adrenal as being something that we teach readily by ultrasound and especially in many patients, it's difficult to see the adrenal. However, on CT you could virtually always see the adrenal. So if you can use against, here's the CT of the same patient with the ultrasound. If you have the CT next to the ultrasound, you can then show the resident side by side. Here's the IVC, here's the adrenal, here is the diaphragmatic slip. Same thing IVC, adrenal diaphragmatic slip. And it's a great teaching tool.

This was a clinical problem in which ultrasound co-registration really helped. And what happened was this patient was sent to ultrasound to characterize this hyper hyperdense CT cyst. The patient was sent into a room initially without co-registration. And the sonographer looked, thought he had the cyst, and it turns out he didn't. You could tell obviously that it wasn't the right location because it turned out this was the only cystic mass in the inferior pole and he was actually looking at something in the upper pole. And I had him go back into a room with ultrasound co-registration and re-scan, and he was able then to find the correct cyst and document the fact that yes, in fact it was a cystic lesion and it was in the same location as the hyperdense cyst.

Here is another situation, 63-year-old woman with hematuria, another hyperdense cyst. Again, this is show how fusion is useful for cross correlation. You notice if you have these pictures as part of your documentation, it's no problem any clinician, anybody can look at it and say, oh yeah, of course you looked at the correct cyst because the orientation of the CT and the ultrasound is the same. And you see that the simple cyst with the through transmission matches the hyperdense cyst on ct.

Here's another case, 64-year-old woman with intra papular mucinous neoplasm. And this is a situation to show that you know what it, you don't have to have beautiful pictures to make a point. And in this particular case, my sonographer came to me and said, I can't find the CT lesion because it was such a small lesion. It's this thing here on CT that they were asking us to take a look at it to tell whether or not it was cystic or solid and she couldn't find it. So I went into the room and again, I can't spend a lot of time looking for these lesions. I used ultrasound co-registration and I quickly started scanning and I immediately found this hyper coic area which matched this CT lesion. So I could definitely say, yeah, it looks like an angiomyolipoma. So in this woman who had a neoplasm elsewhere, it turns out there was an incidental angiomyolipoma in the kidney. And these aren't beautiful pictures, but that's okay. You know, it proves the point. And that's what you need. You need documentation which is compelling. So fusion saves time for difficult cross correlation cases. And here is just a still image showing that angioli lipoma. 'cause once you find it quickly with the ultrasound co-registration, then you can improve your window and sort of optimize it for the still image.

Here's another case in which ultrasound co-registration saved us. A 60-year-old woman had two renal abscesses had actually been followed by CTS multiple time. But the clinicians finally realized, maybe we should reduce the patient's radiation exposure and follow this patient up with ultrasound. One of my most experienced sonographers took the patient into a room and what happened was he found one of the abscesses, but he couldn't find the other one. And he didn't use co-registration because he was pretty confident he was gonna be able to find it. He's a very experienced sonographer. He comes to me with this result and I said, That's not good enough. We gotta find both abscesses. So I sent him back and said, use the co-registration. And once he did that, he immediately knew he could find it. And here it is. So the lateral abscess is yellow, medial abscess is red. We could definitely see both of them. Okay. And then once we could see where we were, we could then optimize the image and look for and make a better picture for the report itself. So here's an example where co-registration, without it we would've missed that second abscess and really looked silly. So here's an optimized image of the abscess, which we could not find once we knew where it was located by co-registration.

Alright, what are the disadvantages of ultrasound co-registration? First of all, it's important that when it's set up that it's compatible with whatever digital network or PACS you're using. And therefore, before you have your vendor, leave your department, make sure that it works. Make sure that the cts and Mrs readily download into the machine. Second of all, different vendor software options differ. And depending on what, how you're gonna use it, it's really important to demonstrate it to use it in your department at least for a short time or look at it because some types of co-registration are gonna be better for interventional purposes and others are gonna be better for diagnostic purposes. This particular feature does generally cost extra. It's an option. So you have to decide whether it's worth the money for your department, but at least in our department, it really has been worthwhile. It does take some time to learn the software and just make sure that you have adequate training time set aside for your sonographers and radiologists so they feel comfortable using the technique. And then finally, depending on your circumstance, the CT or MR. Download time may take a while. In our department it's not a problem to download a CT or Mr. Most of the time, but during our very busy periods it can take a few more minutes. And what we tend to do is we preload our exams. If we know that a patient has a previous CT or mr, we just have that preloaded before the patient arrives.

Conclusion

So in conclusion, there are many problems that we face in renal sonography. However, if we prioritize sonographer training and monitoring, if we realize methods that we can use to address problems such as non visualization of the kidney or hydro nephrosis. And then finally, if we're very careful about looking at our images so that we don't miss renal masses, then we can at least optimize the way that we look at the kidneys and reduce the number of lesions that we miss in those organs.

Just like these pictures, as imagers, we pride ourselves on being able to spot differences in pictures, but sometimes the picture differences are very subtle. And it's important as we go through our daily life and we see numerous pictures of the kidney that we look very carefully as in these pictures to spot any discrepancies that might give us a hint that something is wrong.

Thank you.