So You Found a Renal Mass With Ultrasound – Now What? - SD

Introduction

Good morning.
I'm John Jay Cronin.
I am chairman of radiology at Brown University in Rhode Island Hospital.
And I do ultrasound.
And today I'm here to talk to you about ultrasound and the assessment of renal masses.

Assessment of Renal Masses

Today's topic is the assessment of a renal mass that you found on ultrasound.
What is that mass and what is the significance of that mass?

Overview of Renal Masses

First of all, renal masses.
The vast majority of these are found incidentally, they are not part of their directed search.
Half of patients over 50 years of age have at least one renal mass, so they're fairly ubiquitous.
The vast majority of these masses are benign.
Most of these are also completely asymptomatic, whether they're cysts at one extreme or a renal cell cancer at the other extreme, they are not manifesting any symptoms which leads to their incidental findings.
Benign, solid renal masses, such as an angiomyolipoma, really need to be excluded because the mindset has traditionally been that all solid masses are bad.
And in reality, as we'll see in this discussion, a good portion of these solid renal masses are not surgical lesions.

Renal Cell Carcinoma

Let's just talk a little bit about the solid renal mass that most typifies our concern.
And that is a renal cell carcinoma.
2% of all cancers are considered to be renal cells.
There's about 30,000 new cases per year.
It leads to 12,000 deaths.
Unfortunately, renal cells, we don't have a real good treatment.
They are resistant to radiation and fairly resistant to chemotherapy.
So your ability to treat these depends upon finding them early and removing them surgically or destroying them with some sort of thermal ablation technique.

Incidence and Detection Trends

Most renal masses, as I mentioned, are going to be found completely incidentally, the number of renal cell cancers in the country has been increasing very steadily.
Initially, this was attributed to cross-sectional imaging.
We're finding a lot more masses, but this, there is a reason much beyond that and we're unsure of it, but there clearly is an increased incidence of renal cell cancer.
As a matter of fact, the increase has been considered about 38% increase over the last 25 years and it seems to be that the incidence is continuing to go up about 3% a year in blacks, the incidence is even higher.
So renal cell is really increasing in the population, which is why we find so many incidentally this chart, you'll see demonstrates on the left hand side, the increasing incidence of renal cells over a 25 year period.
And in that same 25 year period, a decrease in transitional cell cancers.
So in the kidney, the amount of solid parenchymal tumors has gone up significantly.
And the same patient population.
The amount of transitional cells has gone down

Prior to the development of cross-sectional imaging, renal cell cancers were detected when they became symptomatic and that was about eight centimeters in size.
That's a huge size, I mean, so basically a softball size mass in the kidney.
And even at that stage, probably the vast majority of these masses were found at autopsy rather than during life.
Today, most renal cancers are less than four centimeters when detected.
So we're detecting them much earlier than we had previously.
This is important because the staging scheme really depends upon the size of the mass with the success of which you're going to have in getting the mass out of the patient and having the patient survive.
So a stage one tumor being less than seven centimeters versus the larger than seven centimeter mass and the mass getting into the cava with lymph nodes where you're not likely to be able to affect the patient's survival.

Imaging Techniques for Qualification

Now the optimal techniques for actually qualifying or quantifying these masses is CT and MRI.
They really do a great job in telling us what the characteristics of these masses are.
Ultrasound is involved more in the incidental detection of these and to separate masses which may be either cystic from solid less effective in actually telling us what is the solid mass per se.
And you'll see from this chart how poor we are with all types of imaging in delineating and finding renal masses with utmost confidence, you'll see that a renal mass under five millimeters, we really don't run a very good chance of finding that on an incidental search.
And the masses are up to about two centimeters before you confidently detect on CT all the time and pushing almost three centimeters if you confidently will always find a renal mass on ultrasound.
So the detection of these is not a is not very great really unless you have a directed search.
And these numbers are really for incidental detection.

Significance of Renal Mass Size

Now what about renal mass and size?
What's the significance of the size?
Well, certainly less than three centimeters.
The definition is this is a small renal mass and the feeling was up through the eighties and most of the nineties these didn't even metastasize.
That is not an absolute rule, but frankly three centimeters is a safe number to feel a mass is not gonna go anywhere.
There is a direct relationship between malignancy and the size of the mass.
And anything above three centimeters you must consider fairly likely to be malignant less than 1.5 centimeters.
You sort of say, it's hard to actually characterize this mass and to tell you what the mass actually is.
It may be cystic and solid and we can tell you it's a solid mass, but the type of solid mass is gonna be more difficult.
So that's where we are with imaging.
We're sort of stuck that under three centimeters is less likely to be of concern for metastasis, but the actual characterization is not that good.
And we actually have from Silverman's article on characterizing small renal masses.
The definition that any mass under 1.5 centimeters may actually be too small to characterize accurately.
Certainly the small renal mass, the more difficult it is to characterize.
And that is led to the concept that while many of these are gonna be benign so we can engage in surveillance imaging, follow the patient for a period of time so that we can then characterize the mass better.

Role of Renal Ultrasound

Now, renal ultrasound has a very important role in the kidney, but it's role in this characterization of solid masses may be less important.
And we all recognize that for hydronephrosis obstruction assessing the size, looking for stones, it is pristine.
It does a phenomenal job in separating renal masses which are cystic from solid, which is the Bosniak one type lesions.
Great success there.
It has a much more difficult task in separating out the different types of solid masses and that's where we rely on CT or MRI more so here you are, you're doing an ultrasound incidentally and you find a renal mass on the left side here you see the masses.
There's two renal masses and they clearly are benign.
They're cyst and you'd have no trouble with that.
And on the image on the right you see this mass and it's clearly solid and you now have a solid renal mass and your degree of concern has to be there significantly raised on this renal mass and you would order additional imaging in an attempt to characterize this.

Confirming the Presence of a Mass: Pseudotumors

So when you have the question, is there a mass, let's just back off and say are you certain there's a mass?
Can it be you're imagining there's a mass, is it possible that the mass is really a pseudotumor and not a real tumor?
Could it be a scar or could it be, is it really a solid mass?
Pseudotumors are very common and that's normal renal tissue which is present in increased amounts.
It looks like a mass as you scan, particularly if it gets funny angles with the ultrasound probe, you can actually accentuate it quite dramatically.
It is best defined with CT with contrast and you can delineate this as a normal tissue ultrasound with contrast would do the same.
It's just that at this point in time we don't have ultrasound contrast readily available.
And this image shows you a pseudotumor, which is the classic subcapsular pseudotumor, also known as a splenic bump.
And it's on the left side just below the spleen.
And here's the tip of the spleen right here and you see the mass and it and it's just normal tissue.

The other type of pseudotumor, which is very common is the septum or column of Bertin, which is the increased normal tissue which indents into the renal pelvis can actually display the collecting system to some extent.
And you see that mass here frequently, these are a little less hypoechoic than the rest of the renal tissue.
And the contrast material, you see this is all collecting system in white and this is the same as the other renal tissue.
It has tubular function and looks exactly the same.

Another area that presents frequently with some confusion is the Bertin's column or the junctional parenchymal defect, which is an area of fusion embryologically between the lobes of the kidney.
That's a normal variant, occurs usually on the right and extends from the surface down to the renal sinus and it can mimic a scar.
And here's a transverse imaging and you look at this mass and here it is and you see it.
And that's the classic Bertin's column or junctional parenchymal line should never be confused with the renal mass.
And it's important to know that and not dictate it also as a scar.

Cystic vs. Solid Differentiation

So if you have a renal mass, you're pretty comfortable.
Now the question is, is it cystic? Is it solid?
Is it mixed or can you not tell?
Very important differentiation and clearly ultrasound, if the mass is a pure cyst, ultrasound is as good as anything in telling you it's a pure cyst, avoids radiation, avoids a contrast.
And the vast majority of renal masses a cyst, 95% plus of all renal masses are cysts.
So ultrasound should be able to discriminate these very simply and quickly the criteria, anechoic mass paper thin wall increase through transmission and the bending of the ultrasound beam.
Creating the acoustic shadowing is sort of a secondary finding.
These are all useful findings and should have no difficulty in separating the renal mass.
So that's a very binary assessment.
But one that's very effective because if it's a cyst you're done with it, there's no further action that needs to be carried out versus the non cyst which is gonna require further imaging.

Bosniak Classification

Now Bosniak's classification of masses or cyst type masses was actually done with CT, but ultrasound does very effectively associate these same findings and the simple cyst, the Bosniak one and even the minimally complicated cyst, it can handle the more complicated the types threes and fours, it has the same issues as CTs.
Fairly complicated and CT imaging was how Bosniak classified it.
But you with ultrasound you can do much of the same thing.

Enhancement Patterns in Malignant Masses

The hallmark of a malignant renal mass is that you're going to get partial enhancement.
So on CT and multi detected CT you got 20 Hounsfield units or greater enhancement and MR about 15% enhancement.
This indicates that this mass in the kidney has a lot of blood flow to it but necessarily the renal tumors don't have tubular enhancement.
So this is an early phase enhancement pattern.
And here you can see on this renal mass on the left kidney on delayed imaging here we're three to four minutes out.
So this is not the arterial phase.
This enhances from pre contrast to post contrast 25 Hounsfield units but doesn't match the rest of the kidney 'cause it because it doesn't have tubules in which to actually store contrast in.

Now if we had contrast material for ultrasound, we could do the exact same thing and here's a renal mass precontrast at beginning of a contrast injection on an ultrasound and later the intense degree of vascular flow in here would indicate that this is a renal mass.
And here's another different patient who has a renal mass mid portion of the kidney and you see it's exophytic and by ultrasound.
And when you give the first bolus of contrast and look at it initially it enhances rapidly characteristic of a renal cell and then continues to have some enhancement but wash out later on which is very consistent with a renal cell cancer, that very quick burst of neovascular and then the little bit wash out.
But persistent flow and this was resected and this was renal cell cancer.

The CT assessment of a renal mass would do this exact same thing.
You get a non enhanced image, you give a cortical image phase in the first 25 to 80 seconds and then you would get the nephro phase out at a minute and a half to two minutes.
You look on the more complicated renal masses, you start to look at septations wall enhancements, high density et cetera.
And here's the classic minimally complicated cyst.
You have a little bit of a thin septum running through it and by CT you see that same septum with cyst and you're very comfortable if that this is just a minimally complicated cyst does not require surgery.

Solid Renal Masses: Benign vs. Malignant

Now if you've established that it's a solid renal mass, the teaching up to 10 years ago was, that was a surgical lesion.
Today 25% of solid renal masses have been shown to be benign.
So these are the masses we're talking about in the three centimeter range or smaller, they are solid and you hate to take the kidney out or perform radical surgery because it turns out these are not even malignant.
So they require some further evaluation and ultrasound can be helpful here.

The concept here is that these masses may be lymphoma, they could be metastasis so they're solid masses, true but they don't require surgery.
Could be focal pyelo nephritis and abscess an infarct more commonly an angiomyolipoma or even an oncocytoma benign tumors that do not require surgery.
So 25% of renal masses are now felt to be benign processes which has led us to do more imaging on these masses and also to do biopsies to establish which of these this is.

Role of Biopsy and Ablation

So renal biopsies clearly has a role in renal mass assessment, particularly true for these small masses.
They can differentiate primary for metastatic lesions and in these small masses in the right age population in the right sense, you can actually do ablation procedures under ultrasound and cure the patient of this mass without any interoperative procedure really.

And here's a patient who was actually going to be screened to have a lung transplant and on the renal ultrasound we saw this mass in the kidney and it was very small.
You can see it was only a two centimeter mass left kidney and we biopsied that mass 'cause it was solid and we saw nothing specific and people were really concerned what was it?
And it turned out to be a clear cell renal cancer.
So it was a renal carcinoma and it was two centimeters in size so it was a bad player.
It indeed.

Angiomyolipomas

Now angiomyolipomas account for the majority of this 25% of benign lesions.
These are fatty masses on CT, they tend to be very echogenic on ultrasound.
They can look a lot like a renal cell and it is best to have a CT with and without contrast via confirmation.
And you can see the ultrasound has a characteristic echogenic appearance.
The problem is there are some renal cell cancers which can also be echogenic.
The mass is just about four centimeters in size and when you look at it on CT it's -30 to -3400 units.
It's a fatty mass, it's an angiomyolipoma.
It does not require surgery and that's important.
So your thought process here is how can you help in this?

Renal Infarcts

The other aspect of renal masses are these masses created because of renal infarcts, usually secondary to emboli, usually cardiac emboli, multiple throughout the kidneys and spleen.
Very peripheral in the kidney and spleen and they can present with masses.
So here's a patient who shows up with flank pain and they thought he might have a stone in some hematuria, might have a stone.
Here's the kidney and there's this huge, we see this mass three to four centimeter mass in the lower pole of the kidney.
And we said, my god, what is this?
And we did a CT and you can see that there is clearly areas of non flow in this kidney and these are renal infarcts and they can present as masses.
So it is important to put all this together and to think about this and not be afraid to get some additional imaging.
Certainly wouldn't wanna end up by saying the patient has a renal cell.
And this was a patient who had developed atrial fib, been on atrial fib for a long time but for whatever reason was now throwing emboli.
And the renal infarct you would think would have a fairly good clinical presentation of flank pain which the patient had.
So fever and hematuria.
So it should help

Renal Lymphoma

Now renal lymphoma and here's a renal ultrasound and you can see this mass in the kidney, another mass here.
You look in the CT, there's gee, there's a bunch of masses here.
What are these? And you certainly don't want to, you wanna avoid surgery on this.
And this is a patient with lymphoma and about 6% of patients with lymphoma will have renal involvement.
Multiple lesions. There's solid tend to be hypoechoic and ultrasound can present with just diffuse renal enlargement but that's pretty rare.
And when you see those in a patient with lymphoma, it's good to either a get additional imaging and try to characterize it or biopsy.
It's simply established with a biopsy.

Renal Abscess

A renal abscess can also present as a real mass because there's sort of complicated solid masses.
The patient will have fever, some URI and clearly can be treated without surgery just with antibiotics and drainage.
And here's another patient sent to us on the left side flank pain.
And we looked and we saw this mass and ill-defined mass and it didn't have doppler flow in it had no flow in it but looked very solid nature.
So we wondered about an abscess.
We got the CT and we could see this hypoechoic area and we put a drainage catheter in and actually got 50 ccs of pus from this kidney.

Other Cases: Lymphoma and Epithelial-Stromal Tumor

A different patient, 67-year-old presents with back pain and the left kidney has a fairly large mass, seven by four centimeters.
A lot of flow in this, in this renal mass on doppler.
So we put the color doppler in and you can see there's a lot of flow.
So this is a solid mass with a lot of neovascular.
You gotta be kind of concerned about it and you can see on the pulsed doppler, it was really pounding away with a lot of flow and we got the CT and you could see the size of this mass.
It was quite large. And this is a PET study and the PET was intensely enhancing here.
And this was a B-cell lymphoma, which we had a biopsy with ultrasound.

And one of the last cases I'm gonna show you this was a patient who was 41 and had a mass on the chest x-ray in the hilar region and had some flank pain.
And on the CT, the non-contrast CT, we saw what looked like a mass contrast CT.
There was clearly a mass there.
Again, lack of tubular function here.
And on the more delayed imaging you see there's some little bit of contrast enhancement.
So we knew this thing was a solid mass with blood flow.
We did, with ultrasound we biopsied the mass and you can see the mass here with color flow, how different.
It was a normal tissue and while it had flow it, it wasn't the same as the rest of the kidney.
This thing turned out to be a very unusual tumor, an epithelial and stromal tumor, which is not actually malignant, but in consultation the surgeon and the patient decided to remove it and it was very fibrous, kind of a tumor, but it what they didn't do a total nephrectomy and because they had the tissue biopsy ahead of time.

Summary

So in summary, ultrasound has a major role in the detection of renal masses.
Its job is to define the masses which are benign from those which are malignant.
Those cystic from solid.
But not every solid mass requires surgery and many of these can be identified with additional imaging or biopsy.
And I think ultrasonographers are, have a very critical role in the assessment of renal masses.
And I want to thank you.