Contrast Enhanced Ultrasound of the Kidney - HD

Introduction and Disclosures

This is Dr. Ed Grant. I am the chairman of the Department of Radiology at the University of Southern California.

I'm gonna be speaking for the next hour or so about contrast enhanced ultrasound of the kidney.

I do have a few disclosures, grant support. I have from General Electric Incorporated, and this entire lecture will deal with the off-label use of an approved drugs, kind of.

Sonographic Contrast Agents in Renal Masses

I'm gonna talk about sonographic contrast agents in renal masses.

What is it that we can actually do with these agents?

First of all, if we'd like to just basically look at the assessment of internal vascularity for various reasons in the kidney, these are excellent ways to do that.

It's obviously far more sensitive than Doppler, either color or power.

Evaluation of Pseudo Lesions

One of the other things that we can do is look at or evaluate pseudo lesions.

Basically pseudo lesions are things that look like tumors in the kidney, but in fact are not.

Examples of this would be, for example, a column of bertan.

Sometimes they're scarring or infarct that can actually look like masses.

And, the contrast enhanced ultrasound is an excellent way to determine if in fact these represent true or pseudo lesions.

Evaluation of Complex Cysts

Probably the most common thing that we do with these, agents is to evaluate complex cysts.

Obviously these are very common, in the kidney.

And the obvious problem is that a percentage of these will actually be cancers.

So we look for such things as flow in the wall, flow in septi, nodularity in septi.

And again, the contrast ultrasound is far more, sensitive for flow in these things than would be classic color or power doppler.

Characterizing Indeterminate Masses

Contrast ultrasound can also be useful, useful in characterizing indeterminate masses that have been identified on CT or mr.

This is particularly useful and there are several recent publications showing how superior contrast ultrasound is in characterizing masses in patients typically who have chronic renal failure or who for other reasons can't have contrast.

So there's very little question in my mind at least that contrast enhanced ultrasound is a far better way to evaluate masses, than just basically going with a non-contrast CT or mr.

There are also occasional cases where even after contrast administration, the a degree of enhancement may be insufficient to classify a lesion as benign or malignant or containing, flow.

And the contrast ultrasound can sometimes help to clarify that.

Identifying Additional Lesions

Occasionally we will be able to identify smaller or additional lesions with contrast ultrasound, although this is certainly not something that we typically use it for.

Characterizing Benign vs Malignant Masses

And in general, I think we can characterize masses, benign versus malignant and in some cases even as to the type when it comes to the type of malignancies such as one form of renal cell carcinoma versus another.

Semi-Quantitative Analysis

One of the other interesting things that we're not really going to get into particularly, but is possible with contrast ultrasound is semi-quantitative analysis.

So you can actually construct, enhancement curves and in some cases this may be a value where the visual diagnostics are in question.

Phases of Contrast Enhancement

Like other imaging techniques with contrast.

There are various phases that we look for after we inject the contrast.

Early on, for example, there is the nephro graphic phase and then later on, we turn into the medullary phase.

The important thing about very early on as is shown here, is you can see that right after the injection, the pyramids stand out as being almost completely avascular.

These should not be confused based on the anatomic position and the triangular shape.

These should not be confused with hydronephrosis or other abnormalities.

Clearly, as you can see very shortly after the injection, these things fill in and become iso intense to the surrounding, per renal parenchyma.

So just a point out that this is a normal variation that we see during the early phase after injection.

Assessment of Blood Flow in the Kidney

Now I mentioned you can look at, blood flow in the kidney.

You can see in this normal kidney shown on the left that there is very rapid enhancement.

You can see the pyramids are standing out.

This was a relatively young man who came to us, with a history of an aortic dissection, and this is his right kidney.

You can see that in the left kidney there is essentially no flow except for a small amount of enhancement in the upper pole here, and you can actually see some of the individual vessels that are left.

This gentleman came in with this ct.

You can see that there is a, membrane here typical of a, dissection in this particular case.

And one of the complications is that they may actually affect blood flow to the, origins of the arteries that arise from the aorta and can actually cause infarction of the bowel of the kidney and other structures.

In this particular case, the clinicians wanted to know what to do with him since it was now 48 hours after the initial ct.

And you can see that the contrast ultrasound was confirmed, very confirmed that the findings that were seen on the original ct, remain and that basically the kidney was non-viable after 48 hours.

This is that single vessel that you could see going to the upper pole that we showed on the recent ultrasound.

So again, there are various vascular abnormalities such as infarct, in this particular case, that can be used, that the contrast ultrasound may occasionally be of value For, further clarification

Mass-Like Lesions and Pseudo Lesions

moving into mass type lesions, which again represent the vast majority of, things that we evaluate With contrast,

I mentioned pseudo lesions.

Pseudo lesions again are areas in the kidney that have a mass like appearance, but that in fact are normal parenchyma, again, column of buran scarring and, post infarction may give you these pseudo lesions.

We see them commonly on gray scale evaluation.

Here you can see in this gray scale, image, this large mass like area in the central part of the kidney.

We were certainly not comfortable with blowing this off as a column of bertam and we're concerned that this could represent malignancy.

You can see in the early or nephro graphic phase that there is equal intensity of this area to the surrounding regions of the cortex.

And that the timing, although you'd need real time for that, the timing of this actually was similar.

So originally we were suspecting that this probably does represent a column of britan or one of these so-called pseudo lesions and clinching.

The diagnosis is this image which actually shows a pyramid within, so you wanna look for similar enhancement, you wanna look for similar time of arrival, and you can make the diagnosis cleanly by actually observing the presence of a pyramid in the central portion of these suspected pseudo lesions.

Differentiation of Cysts from Solid Lesions

Differentiation of cysts from other lesions, from solid lesions or from partially solid lesion, again, is probably the most common thing that we do with contrast ultrasound.

This is particularly useful again in patients who have chronic renal failure, but may also be useful in other situations where the patient can even get contrast since actually the resolution of contrast enhanced ultrasound is superior to that of CT or of mr.

Example: Polycystic Kidney Disease

This was a patient who obviously had adult type polycystic kidney disease and a history of chronic renal failure.

You can see these multiple cysts identified in the enlarged kidneys on the non-contrast T two weighted mr, but you can also very easily see that there's one of these cysts that clearly has a very different signal intensity and, was of concern on the non-contrast ultrasound.

I think our concerns, grew in in that.

You can see here that there are various thick and nodular septi.

There's a large mass like area centrally, the walls of this area of the structure are shaggy.

So this was again, further suspicion that there could be something going on here, but was nicely confirmed as a hemorrhagic cyst on good old contrast ultrasound.

You can see that within it, none of the solid material that we were seeing on the gray scale ultrasound actually proved to have vascularity.

And this is the hallmark or typical picture of a simple hemorrhagic cyst in a polycystic kidney.

Pre-Transplant Workup

One of the other common examinations that we do in patients with renal failure is that of a pre-transplant workup.

So all the patients in our institution who are going to undergo a, kidney transplant evaluation will go on to have abdominal ultrasounds.

A lot of these patients will have been on dialysis for a long period of time and there is an increased incidence of renal cell carcinoma in these patients.

You can see very nicely that there is this multi septate cyst in the upper pole of this, kidney.

You can see that the kidney is abnormal and small and has other cysts around it, but certainly there is a large amount of solid material within this kidney that would, again, on gray scale ultrasound, make this of concern.

Again, you can see here after the injection of contrast that there is essentially no flow within this lesion.

There are a couple of small septi identified here.

This is perfectly fine.

Again, remember that the resolution of contrast ultrasound is better than that of CT or mr.

And that therefore you may see fine benign septi in these patients with an occasional bubble flowing through them.

They should not be thick or shaggy.

So this again, confirmed for us that this probably represented a hemorrhagic cyst in this pre-transplant patient.

Bosniak Classification

Now, when I think in terms of true cystic lesions of the kidney, the BOSNIAC classification comes to mind and the bosniac classification was actually made for ct.

It has since been adapted for use with mr.

And I think a lot of us are now starting to think in terms of how the bosniac classification would be applied to contrast ultrasound.

And this is a chart from an article that we wrote, several years ago, showing the CT findings and kind of similar findings on contrast ultrasound.

The bosniac classification basically goes from one to four, one being an koic or totally benign, cystic lesion all the way up to four where there's a expected or high incidence of cancer in an otherwise essentially solid mass.

2 3 2 2 f and three of course lie within the middle.

And as you go up in the number on the bosniac scale, the expected percentage of cancer obviously rises.

Bosniak Category 1 Example

Here is a patient in whom there was a photonic area on a recent PET CT scan.

This patient has a history of lung cancer.

On the non-contrast ultrasound, again, you can see that we have an koic structure and very nicely illustrated here as a sort of bosniac one, simple cystic lesion that really needs no further follow up.

Bosniak Category 2 Example

Again, as you go up in the bosniac numbers, the more solid these lesions become, bosniac two is typically also considered to be benign.

You can see here following the injection of contrast, the walls of this are smooth and there is a single fine septum within this.

And again, this would qualify as a bosniac two or benign lesion probably does not need follow up afterwards.

Bosniak Category 2F Example

These are the lesions where I think we still need to work harder on what is and what is not, suspected of being malignant.

When it comes to contrast ultrasound,

you can see in this particular case that that there are a relatively large number of septi to my eye, I think that there is a bit of nodularity to these septi.

We would classify this probably as a bosniac two F.

These lesions can be followed.

This one did, actually wind up being removed because there was another relatively large tumor in this kidney and this one did in fact turn out to be benign.

So again, I think this is the type of lesion where we need to look and have more experience with contrast ultrasound to determine if we can further break more of these down as being definitively benign or highly suspicious for cancer.

Bosniak Category 3 Example

As the septi become thicker and more nodular, I think the likelihood that we're going to be dealing with a bosniac three or a highly suspicious lesion increases In this particular case, I think after we injected the contrast, you can see relatively thick septi here, a little bit of nodularity along the wall, and this was a surgically proven cystic renal cell carcinoma in this particular case.

Bosniak Category 4 Example

Again, the more solid material you have, obviously the worst the prognosis in this particular case, you can see the entire upper outer portion of this lesion, is solid and enhancing.

There is nodularity, there is a thick septum here with abundant flow.

And one of the things that retrospectively, I, think I, if you look at the gray scale on this, there's a lot of artifact in this and sometimes, I'm finding myself a little more paranoid about just calling cysts based on the gray scale appearance alone because again, a lot of times there is fill in and background noise, but I don't think anyone would have a problem, suspecting that this would represent or should be classified as a malignant lesion based on the enhancement pattern following contrast injection.

Solid Renal Masses

Now, solid renal masses are another sort of, this would be the bosniac four, but there is a, a very different set of diagnostic possibilities when it comes to solid renal masses.

I think the general approach to solid renal masses is that they are renal cell carcinomas until proven otherwise, unless they're brightly echogenic, in which case they may represent angio.

My lipomas and we'll talk a little bit more about that in a moment.

Types of Renal Cell Carcinomas

When it comes to renal cell carcinomas, there are two types to two common types.

There are others, but the two most common types would include clear cell versus papillary carcinoma.

And there are relatively suggestive or specific features that with contrast ultrasound we should be looking for to differentiate between the two.

Angiomyolipomas

Again, angio my lipomas, those that contain fat, most of them do.

Are, something we should keep in our mind when you see an echogenic lesion.

But again, do keep in mind of course that renal cell carcinomas may present as echogenic masses as well.

Oncocytoma

Oncocytoma are unusual renal masses, typically they are solid.

Most of these will actually be diagnosed not by imaging, but at surgery or biopsy.

Since the imaging features in general are quite nonspecific,

I think most are familiar with the fact that transitional cell carcinoma is another lesion that may occur in the kidney.

Of course, it may occur in the ureter in the bladder, but when they occur in the kidney, again they will present as usually a central mass.

But the differentiation between garden variety renal cell carcinoma and transition cell carcinoma may be difficult.

Metastasis to the Kidney

Remember, metastasis may affect the kidneys or may be found in the kidneys.

This is unusual. Typically it occurs late.

And of course it's the bloodborne metastases which will most commonly go to the kidney.

Lymphoma of the Kidney

Finally, lymphoma, again, both primary and more commonly secondary or metastatic, spread of lymphoma may also affect the kidneys as well.

Comparison Studies and Case Examples

As I mentioned, there are two recent articles that have been published just this year, looking at the comparison of non-contrast CT or MR in characterizing renal masses and clearly contrast ultrasound outperformed non-contrast CT or mr.

And of course gray scale ultrasound as well at characterizing renal masses.

Basically about all you can really say in this particular case is yes, there are two mass like areas in the upper pole of the right kidney, which you can see here and here.

This was a patient who was 74 years old history of chronic renal failure.

So, contrast injection was out of the question.

And so further characterization of these areas was essential.

In this particular case, you can see following the injection of contrast, there are two lesions which correspond to the masses identified on the recent CT following contrast injection.

Here you can clearly see that these masses enhance less than the surrounding parenchyma through all phases of the examination, but very importantly are nonetheless vascular as opposed to those hemorrhagic cystic lesions we saw, on the earlier patients.

The fact that these are hypovascular compared to the surrounding parenchyma in all phases is important to observe and is typical of papillary carcinoma, which both of these turned out to be at surgery

of interest in this same patient.

When we looked around the kidney, you can now see that there is actually a third mass, which was not obvious on the non-contrast ultrasound at all, but that the enhancement pattern of this mass is quite different than the other two.

You can see that literally from early on through the entire examination or at least this part of the examination, you can see that this mass is actually more vascular than the surrounding renal parenchyma.

And this is typical of a clear cell carcinoma.

This is important in that the prognosis of clear cell versus papillary is different.

Clear cell is usually a far more aggressive tumor than is papillary carcinoma.

So if you can see these characteristics on a contrast ultrasound study, good idea to let the clinician know that this is probably the cell type that you're dealing with.

If you have a question, this is an example here of a time intensity curve, illustrating the typical or expected findings of a clear cell carcinoma.

The blue represents the blue line represents the enhancement characteristics of the mass.

The green line represents the enhancement characteristics of the surrounding parenchyma, and here you can clearly see that the clear cell carcinoma enhances earlier than the surrounding parenchyma and enhances at peak more dramatically.

In this particular case, you can also see that in the delayed phase that there is actually washout where the two curves actually cross.

And in that particular timeframe, the clear cell carcinoma would actually become less vascular or less echogenic than the surrounding uh, parenchyma.

This is another, 69-year-old woman.

Again, you can see the glomerular filtration rate is 30, which is abnormal, precluding her from having, contrast either with CT or mr.

Again, this was performed for back pain and this was an incidentally found low density mass on the ct.

She was sent for mr and you can see again on the T two weighted image there appear to be several cystic spaces, but importantly there appears to be or there, yeah, there appears to be, regions of solid material within this mass as well.

On the contrast ultrasound, I think you can very nicely see here is the normal parenchyma.

This is obviously early in the nephro graphic phase.

You can see the pyramids are standing out.

There is that cystic area that was seen on the mr, but importantly on the edge of this mass you can see there is a solid structure which is again hypervascular to the surrounding, renal parenchyma and clearly suspicious for a renal cell carcinoma.

This was a cystic renal cell here on the clip.

I think you can very nicely see that this thing enhances earlier than the surrounding parenchyma and as was shown on the static image is clearly more echogenic in the early phase of the examination.

Indeterminate Lesions on Contrast CT/MR

Now I mentioned so far the cases that we've seen have all been comparing contrast ultrasound to non-contrast CT or mr.

There are occasionally cases where after the injection of contrast there is a renal mass which may not enhance sufficiently to be confidently called a renal cell or to confidently be stated to have intense arterial enhancement.

Such was the case in this particular patient.

You can see here that there is a structure along the lateral edge of this kidney.

It's somewhat hypervascular or not hypervascular, hyperdense when compared to the parenchyma and following injection of contrast, it did not enhance more than the expected cutoff of 15 hounds field units.

So this was an indeterminate lesion.

On contrast enhanced ultrasound, going back to my comment about blowing off cysts as being, just cysts rather than solid lesions.

If I had just seen this non-contrast version of this patient, I would've just basically called that assist and moved on.

Interestingly, when we provided contrast in this particular case, you can see here that there is an area of clear cut enhancement in this lesion.

There is this, the, the gray scale version here is the post contrast and this did turn out to be a clear cell renal carcinoma.

And again, an article published now several years ago by Bert Lotto actually confirmed that the contrast enhanced ultrasound can be of value when you have indeterminate lesions.

On contrast, enhanced CT or mr, when renal cell carcinomas become large, they will frequently undergo infarct.

So if you see avascular or devascularized areas within, and enhancing mass, this should not dissuade you because again, necrotic renal cell carcinomas are quite common when they become large.

In this particular case, you can see there's a very large mass occupying most of the central portion of the kidney and that the kidney itself has been displaced laterally by this partially necrotic mass.

This patient did have a relatively normal renal function and therefore underwent a contrast enhanced ct, which very nicely confirms the features that we have just described on the contrast enhanced ultrasound.

Here you can see the left kidney is displaced by a large central mass, which has extensive areas of necrosis centrally.

So again, when you see these areas that are nonvascular in the center part of the kidney, this should not surprise you because again, quite commonly these tumors outgrow their blood supply and develop a sometimes extensive areas of necrosis.

Echogenic Masses: Angiomyolipomas vs Renal Cell Carcinomas

Now I mentioned, angio my lipomas versus renal cell carcinomas.

There is literature out there that tells us that a significant number as many as 30 to 50% of echogenic renal masses will be renal cell carcinomas.

This has not been my experience.

I think that they are relatively unusual, but they do occur.

So I think when you see a renal echogenic renal mass that's larger than a centimeter, always keep in the back of your mind that you wouldn't wanna miss a renal cell carcinoma.

Here is a case of a relatively large, homogeneously echogenic mass in the left kidney following contrast enhancement.

There is rapid beginning of of flow in this.

Here you can see, at, at slightly several seconds later, this thing has intensely enhanced, and continues to enhance throughout, the, sequence of images.

Going back to the original ct, you can see that there is a, in the non-contrast ct, you can actually see that this is a, a, a high density mass, which would be the opposite of what you would expect in an A ML an angiomyolipoma.

So I think to review, echogenic masses may represent renal cell carcinomas or angio my lipomas.

Unfortunately, if you look at the literature on this, the findings for AMLs have been contradictory and really are not diagnostic.

And so when I see an echogenic renal mass, although the contrast ultrasound may be useful to look at vascularity, probably the easiest thing to do for differentiating between an A ML and a renal cell carcinoma is a simple non-contrast CT looking for fat.

So in this particular case, although the features are typical, very, very vascular, very intense enhancement, pointing you toward a renal cell carcinoma, I think that in reality these larger echogenic masses are probably best served to be evaluated by non-contrast CT looking for areas of fat and making the clear diagnosis of an A ML.

Whereas as I said on contrast ultrasound, while the findings may be interesting, they are not really going to be diagnostic in most cases

Oncocytoma Case Example

oncocytoma are uncommon tumors, that affect the kidney.

There's a small series, published in the JUMA number of years ago which described this kind of yin yang pattern.

You can see here, with the contrast injection that there's kind of half of this mass actually lights up and the other half is relatively hypovascular.

This is actually very nicely confirmed on the CT as well.

Again, this was a small series and whether this will pan out in general, I doubt quite honestly.

And the other problem with the imaging diagnosis of oncocytoma, whether you're dealing with CT MR or contrast ultrasound, is that oncocytoma is may be mixed tumors, so they may actually have oncotic components and may also harbor renal cell carcinoma.

So even if we were to be a little more specific with the contrast to be able to say, well, this is suspicious for an oncocytoma, I would be kind of, uncomfortable hanging my hat on that diagnosis because again, sometimes there may be oncotic components mixed with renal cells.

So again, most of these will probably need to undergo biopsy or, or remove surgical removal depending upon the size.

I do think that I've probably never seen a renal cell carcinoma that had that kind of yin yang appearance and this one did in fact turn out to be an oncocytoma.

So kind of an interesting finding.

Again, I'm not sure that I would hang my hat on making a definitive or trying to make a definitive diagnosis by imaging of any kind.

When it comes to oncocytoma.

Transitional Cell Carcinoma Case Example

Now I mentioned that transitional cell carcinomas tend to live in the central part of the kidney.

These are urothelial tumors.

In this particular case, this was a CT that was done maybe a month before the ultrasound.

You can see that there was this low density mass like area here that seemed to be isolating a calyx, the upper pole calyx.

This patient presented about a month after the CT with fever and chills and, did have some renal failure at that time.

So we contrasted him, because what appeared to be to us on the gray scale examination almost looked like a large mass in the upper pole, which he clearly did not have previously.

This actually turned out to be an abscess that had occurred in this amputated calyx and in fact, the transitional cell carcinoma is shown as this low, vascularity hypodense area in this center part of the kidney.

So again, when you think of transitional cell carcinoma, the majority will present as a mass in the region of the collecting system or the pelvis, but they may occasionally amputate a calyx and as occurred in this particular case, they can occasionally turn into an abscess.

Metastatic Disease Case Example

Now I mentioned metastatic disease.

Again, this is a relatively uncommon, and usually late occurrence, but certainly metastatic disease can present within the kidney.

Typically, those lesions that will affect the kidney are bloodborne metastasis, melanoma being a classic lung cancer, breast cancer among others.

You can see in this particular case there was really nothing specific about it, but it was con this, the contrast ultrasound confirmed that there was this relatively small hypovascular mass in the lower pole of this kidney.

This was eventually biopsied under ultrasound guidance and did turn out to be metastatic melanoma.

Again, nothing specific.

Given the location, this could certainly represent a papillary renal cell or even a transitional cell.

Again, given the history, however, of melanoma, metastatic disease would certainly be a consideration.

Lymphoma Case Example

Now I mentioned lymphoma.

Lymphoma can rarely affect the kidney.

It may occur as an intrarenal mass probably in my experience I've seen it as a shell like perinephric mass or even perinephric adenopathy.

This was an interesting patient in whom there had been a heart transplant and presented with this, lower pole renal mass and some renal failure.

Here you can actually see here's this mass.

You can see that there are, enhancing areas internally and at biopsy.

This turned out to be PTLD or post-transplant lymphoproliferative disorder.

So occasionally lymphoma will affect the kidney.

One variety of lymphoma is the so-called PTLD, nothing specific about these masses again, but certainly the vascular internal appearance of this would tell you that this does not likely represent a simple hemorrhagic cyst like we saw in those other initial patients.

Additional Uses of Contrast Ultrasound

Post-Partial Nephrectomy Follow-Up

One of the other interesting uses that we find for contrast ultrasound, is in patients who have undergone partial nephrectomy for renal cancer.

I, think in most institutions, the, our, the urologists have now moved to partial nephrectomy rather than complete nephrectomy, particularly for smaller masses.

Normally these patients are followed up with contrast ultrasound.

A lot of these patients will have issues with renal failure.

And so contrast ultrasound may not be optimum or possible for some of them.

And contrast ultrasound may be quite valuable.

A lot of times the renal failure may be transient and so again, for follow up, contrast CT would certainly be optimum.

In this particular case, you can see there is a mass like area along the lateral edge of the kidney.

There's several clips around it.

And again, the renal failure here made the urologist shy away from contrast ct.

And we injected, contrast ultrasound in this particular case.

You can see clearly that this represents a small postoperative OMA or seminoma.

This is by far and away the most common SQL rather than recurrent disease, but obviously these patients are being monitored for recurrent disease.

And contrast ultrasound can be quite valuable, again, particularly in patients who have had transient or postoperative renal failure.

Guidance for Biopsy

A use that I mentioned a moment ago, for contrast ultrasound both in the kidney and in the liver and elsewhere is guidance for biopsy.

This was a 77-year-old man, you can see that there's this very poorly defined mass like area in the upper pole of the kidney on this non-contrast, CT scan.

Likewise on the gray scale image, there is a mass like area in the upper pole, but again, it's hard to know exactly where the borders are.

And with the injection of contrast, we were able to define this hypovascular area here and actually we're able to biopsy that, better after the injection of contrast.

There you can see the needle in, in the lesion.

So occasionally if there is a poorly defined mass, you can define it better.

And again, we can use the contrast ultrasound to, get a better target, and place our needle.

Publications and Conclusion

Just in ending, we, have published a number of articles.

This was a general article that we published, several years ago looking at contra in, in, radiologic clinics of North America.

Looking at both contrast enhanced ultrasound of the liver and kidney,

more germane to this lecture, was another article on contrast enhanced ultrasound of cystic and solid lesions.

It's, it's a nice review of, of renal masses with contrast enhanced ultrasound.

And finally, an entire article dedicated to the use and explanation of quantitative assessment.

As I briefly mentioned, in some of my slides, with time intensity curves and exactly how we use it.

So, at that juncture, I think we have completed our, lecture.

Thank you very much.