Renal/Adrenal/Retroperitoneal Ultrasound

Introduction

My name is Dr. Ethan Halper, and I'm from the ultrasound section at Thomas Jefferson University Hospital in Philadelphia.

The talk that we'll be giving today is the renal adrenal and retroperitoneal talk.

Today we'll be talking about the kidneys and the adrenal glands, and this is a basic lecture on the most important organs that we'll use ultrasound for in evaluating the retroperitoneum.

We're gonna start with the topic of renal ultrasound. And there we're gonna look at the normal kidneys and normal anatomy as well as variations in normal anatomy. Then we'll look at the appearance of parenchymal disease, the appearance of obstruction, and one of the major causes of obstruction being renal stones. We'll look at renal cysts and different types of renal masses, and finally look at some vascular pathology.

When we move to the adrenal glands, we'll look at the normal adrenal and the appearance of adrenal hemorrhage and various neoplasms in the adrenal gland as well.

These are the two major issues that we're gonna address in evaluating the retroperitoneum with ultrasound.

Renal Ultrasound: Normal Kidney Anatomy

Starting with the kidney, when we evaluate the kidney, we use a two to five megahertz transducer. Usually we image the kidney both in the long and the short axis, and the views generally include a portion of the liver or the spleen to allow for comparison of echogenicity.

In this slide here, one can see that the liver is seen on top of the kidney and one can see that the kidney is relatively similar in echogenicity to that liver.

Here is a short axis slide of the same kidney, once again, liver on top and kidney under it, and one can compare the echogenicity. Again, a longitudinal view of the kidney. The cortical echogenicity of the kidney is similar to or perhaps slightly less than that of the adjacent liver.

The pyramids here appear hypoechoic and the central sinus in the kidney is fibrofatty and has vessels in it. So it appears echogenic.

The normal length of a kidney is somewhere in the range of nine to 13 centimeters, being slightly longer on the left side as compared to the right side, such that the right kidney can normally be approximately a centimeter shorter than the left kidney. If it's more than two centimeters shorter on the right or more than one centimeter shorter on the left, then we start to be concerned about things like renal artery stenosis.

Neonatal and Infant Kidney

Before we go on to look at the adult kidney, I just wanted to take a minute to talk about the neonatal and infant kidney. In the first year of life and sometimes up to the first two years of life, there's increased echogenicity in the cortex of the kidney. And here this is a normal finding, increased cortical echogenicity and then decreased renal sinus echogenicity because of a paucity of sinus fat. And so the kidney actually may be more echogenic than the surrounding organs.

And once again, this is shown here in long axis and in short axis in a normal neonatal ultrasound.

Anatomic Variations of the Kidney

Now there are various anatomic variations that we should be aware of when we evaluate the kidney. Often at the junction of the upper and the middle third, or perhaps the middle third and the lower third of the kidney, there is a junctional defect. And the junctional defects are related to the fact that there are many fetal lobes that coalesce to form a kidney and as they coalesce, there could be a junctional defect between those lobes.

And you can see it as a focal defect shown in the upper image here, or you can see it as multiple lobation as shown in the lower slide. These are both normal variations of kidney anatomy.

Now a column of Bertin is another normal variation of kidney anatomy. We see here the normal cortex, which is relatively hypoechoic, we see the echogenic renal sinus. But there is a small amount of parenchyma which dips into the renal sinus. And this is a normal column of Bertin.

When we have a duplication of the kidney, this renal parenchyma actually splits the entire renal sinus. So there's renal sinus above renal sinus below and there is renal parenchyma going down through. This is a duplication of the kidney.

A dromedary hump being yet another variant is often seen on the left side where the spleen is above the kidney here and the spleen seems to indent at the upper part of the kidney. And there's sort of a hump in the mid portion of the kidney that's known as a dromedary hump. This congenital abnormality is very common, and it should be known for what it is as a normal variation.

Other relatively less common abnormalities include crossed fused ectopia where both kidneys end up being on the same side. And we have what looks to be like a normal kidney except for the lower pole of that kidney is fused to an ectopic kidney that came from the other side.

And then agenesis being another relatively uncommon variation where there is no kidney in the normal renal fossa or ectopic kidney. Now kidney can be someplace other than in the renal fossa in other is not under the liver, not under the spleen, but perhaps in the pelvis. And here is a right kidney that is ectopic in the positive pelvic kidney.

Horseshoe kidney, yet another variant where the two kidneys from both sides are combined in the lower pole. So there is a union of the two kidneys and there actually is only one kidney that comes up on both sides. The union here could either be a parenchymal union as you see here with renal parenchyma joining the two sides, or it can be just a fibrous connection between the two kidneys, but it crosses anterior to the aorta and the cava we see the spine aorta and cava and transverse, and this is the horseshoe kidney crossing over the midline.

And finally, a pancake kidney is an unusual variant where the kidney is sort of splayed out like a pancake, as opposed to having its normal bean shape, which we associate with the normal kidney anatomy.

Normal Echo Texture and Diffuse Parenchymal Disease

So now that we've gone over some of the gross anatomic appearance of the kidney in terms of its contour, we need to talk about the normal echo texture. And as we said before, the normal renal echo texture is hypoechoic compared to the adjacent liver. So the kidney here should be darker than the liver. And in this case we see a kidney that is brighter than the liver.

Now when we have diffuse parenchymal disease, that's often associated with an increased renal echogenicity and there are many causes that one can see for increased renal echogenicity, we list a few here. Glomerulonephritis early on can cause a hypoechoic kidney and a large kidney, but later on can cause a bright kidney glomerulosclerosis, sclerosis in the glomeruli can be associated with increased echogenicity and this is often a result of diabetic nephropathy, which in the long term can cause glomerulosclerosis.

Hypertensive nephropathy can also result in some form of glomerular sclerosis and can be associated with increased echogenicity. Various collagen vascular diseases such as lupus, scleroderma and amyloid may also be associated with increased renal echogenicity.

Additional causes include chronic pyelonephritis, though acute pyelonephritis is most often not visible. And if it is visible, it's often hypoechoic, but chronically can result in an echogenic kidney. Sickle cell disease can be echogenic in large kidneys, interstitial nephritis, analgesic abuse or AIDS nephropathy.

And here once again, we see this large kidney here, which is echogenic and we know it's not chronic renal disease in this situation because it's a large kidney. And here we see again increased renal echogenicity within a normal size kidney. Notice how the kidney is much brighter than the adjacent liver here and here as opposed to this case where the kidney is actually rather small.

So here we have a small echogenic kidney and look how thin the cortex is. We've got loss of parenchymal thickness and this is starting to look like end stage renal disease. And we see here some ascites often associated with renal dysfunction and end stage renal disease. And the slide on your right here, this is also end stage renal disease and what's actually happened is the kidney is so echogenic that it begins to blend in with the perinephric fat and we actually can't pick the kidney out that well. This is often seen in end stage kidney.

Renal Obstruction

Moving now to perhaps the most common cause or reason for renal ultrasound, renal obstruction, the reason this is such a common indication is because ultrasound is a great way to evaluate for obstruction and this is the number one treatable cause of renal failure.

So here we see a kidney seen in long axis, and here's the collecting system and it all hooks up into the renal pelvis. This is pelvis, upper pole calyx, mid portion calyx and lower pole calyx. And notice that they're all distended, they're very dilated. Normal calyx should be cupped so that it has sharp points at the tips of the cups. But this is sort of a clubbed calyx. So this is marked hydronephrosis and we know these are calyces because they all connect to the renal pelvis in the setting of obstruction.

One often sees a dilated calyces if there's obstruction together with infection. That's a reason for emergent decompression of the kidney. And the main ultrasound finding for obstruction is hydronephrosis.

Now there are many causes of obstruction, we'll look at first. Some of the uncommon causes here is a duplicated collecting system. The upper pole here is obstructed and blown out. The lower pole is also mildly hydronephrotic because there's reflux and there's a famous rule called the Weigert-Meyer rule. When there are a duplicated system and there's ectopic insertions, usually the upper pole inserts more inferiorly immediately and it tends to obstruct while the lower pole tends to reflux.

And here's another example of a case with a dilated upper pole secondary to obstruction and with a lower pole, which is mildly dilated secondary to reflux. And we often see this on an IVP as something called a drooping lily, because the upper pole becomes invisible, it doesn't enhance with contrast and the lower pole is dilated and pushed down by the obstructed upper pole.

Here's another reason for a hydronephrotic kidney. Here we see the bladder and the distal ureter, which is dilated. Going into a structure here, there's a round thin wall structure at the orifice at the UVJ at the ureterovesical junction, and this is a ureterocele and this results in dilatation of the ureter and in fact also dilatation of the collecting system within the kidney. So we see hydronephrosis associated with a dilated ureter and a ureterocele.

Now, as we said before, when there is infection, that's the cause that's an emergency basically. And associated with hydronephrosis infection is a reason for emergent decompression. And often the findings are in addition to hydronephrosis, you see low level echoes within the collecting system. And that's what we see here. And this is probably the most common finding with pyonephrosis. So we're looking at pus in a dilated collecting system here and here again, in this case.

Grading of Hydronephrosis

When we talk about hydronephrosis, we have a grading system for hydronephrosis. Normal means that there's no visible collecting system within the kidney when we see just minimal dilatation of the calyces here, that's grade one hydronephrosis. There's some mild dilatation. You can clearly see the calyces are dilated, but they're still somewhat cupped. And that's this is mild hydronephrosis.

As you start to lose the cupping in the calyx, that's a moderate hydronephrosis here all the calyces are collecting into a dilated renal pelvis. And finally, the severe hydronephrosis is a totally blown out set of calyces where we lose all cupping and in fact they're convex instead of being concave up here. And this is severe hydronephrosis.

Other Causes of Obstruction

So moving on to some other causes of obstruction. We talked about ureteroceles, we talked about duplicated systems. Another interesting cause is UPJ obstruction and 80% of UPJ obstructions are related to crossing vessels. So the white here is the collecting system in the ureter, and here's a vessel that's crossing in front of the ureter at the level of the ureteropelvic junction and causing obstruction.

If there is no vessel seen with a UPJ obstruction, those patients are amenable to an endopyelotomy. When the vessel crosses posterior to the renal pelvis, they can have a dismembered pyeloplasty also called the Anderson-Hynes procedure. And when the vessel crosses ventrally, as we see in this case, they need a non-dismembered pyeloplasty or the Y-V plasty.

Just to show you an example of what you might see. So here's the IVP showing a dilated collecting system on the right side, normal left collecting system with normal left ureter. Here's the ultrasound, there's the dilated renal pelvis. Doppler evaluation first demonstrates nothing but with contrast enhancement. There is a vessel which is visualized here to be crossing right at the level of the dilated renal pelvis. And here's the MRA and one can actually see here's the main renal artery and there is an accessory renal artery here coming down crossing in front of the renal pelvis to go into this lower pole. And this is resulting in the UPJ obstruction.

False Positives Mimicking Obstruction

Now there are many false positives which can mimic an obstructed system. And here we're looking at a kidney where the system is dilated. So here's the kidney with a dilated collecting system, but there's really no obstruction and the reasons that could happen include a distended bladder. So here's your very distended bladder. And this patient just is unable to empty all the urine out because the bladder has a high pressure and is distended.

Patients who are given diuretics are an active diuresis. They may also have a dilated collecting system, an obstruction that's been relieved. It takes some time for the hydronephrosis to resolve then a reflux. So reflux nephropathy can be associated with a dilated system even though it's not obstructed. And finally, diabetes insipidus is another form of diuresis. So there's so much urine being made that it dilates the collecting system.

Papillary Necrosis

Now papillary necrosis is an interesting category because that's a disease which has several etiologies, but the end result is that there is a necrosis within the renal pyramid and usually of the tip of the pyramid or the papillary tip of the pyramid. So that's called papillary necrosis that can actually result in cystic spaces in the region of the sloughed papilla. And that can give an appearance of the clubbed calyx and could actually mimic hydronephrosis.

However, you should be aware that it's also possible for papillary necrosis to be a cause of real hydronephrosis because the sloughed papilla may go off and actually obstruct the renal pelvis at the UPJ or somewhere in the ureter and can actually be a cause of hydronephrosis. But usually when you see papillary necrosis, this is not an issue. It can be a mimic of hydronephrosis. And I'll show you some examples.

The tips of pyramids often can calcify and they can look like echogenic foci and they as a typical they can break off and appear in the renal pelvis. So here we have an example of a patient with some hydronephrosis. This actually is true hydronephrosis. And here we see some papillary necrosis identified by the echogenic tip inside this pyramid.

Yet another case here's a renal pyramid and here is this echogenic focus here and here. And this is a patient with known papillary necrosis, does not have hydronephrosis in this case.

Doppler Evaluation for Hydronephrosis

Now doppler evaluation can actually be useful for the evaluation of hydronephrosis because as we said, hydronephrosis can be obstructive or it can be a false positive or non-obstructive. Turns out that the resistive index will increase in a post-obstructive hydronephrosis. So several hours after the hydronephrosis onset, if you do a doppler, you'll see elevated resistive indices often over 0.7 and a delta RI. That's just the difference RI between the two sides is usually greater than 0.1.

So if you have a case like this with hydronephrosis, you get a resistive index out here and you compare the two sides. And if it's more elevated on the hydronephrotic side by a greater than 0.1, that is a sign that we're dealing with obstructive hydronephrosis.

So for example, here we have a distended renal pelvis. But here if you look, the RI is normal and this RI less than 0.7 suggests that this is not an obstructive hydronephrosis, but perhaps a residual of previous obstruction or perhaps related to increased diuresis or something along those lines.

Renal Stones

Now the most common cause for obstruction is renal stones and stones have a very classic appearance. There is an echogenic area, very echogenic usually with posterior acoustical shadowing and usually stones throw a clean shadow. So it's a well-defined hypoechoic shadow in back of the stone.

And here we see in the kidney one stone shadowing nicely. Here we see multiple echogenic foci, kidney shadowing, so multiple stones in the kidney.

Now in addition to solid stones, sometimes one can see sort of a milk of calcium type of appearance where there is echogenic material that appears to shadow. But if you the curate patient, it will move around. And so we see this stone appears to be changing positions. So this is actually not a solid stone, but this is milk of calcium or basically a lot of gravel in the collecting system that can be moved back and forth similar to what one might see with gallstones in a gallbladder changing in position as the patient changes in position.

Now finally, sometimes it can be difficult to see that echogenic focus in the kidney. So looking here, it's very difficult to pick up whether there's a stone in here. But when we turn the doppler on, there's a twinkle on here. This is aliasing with color doppler and this tells you that in fact there is a calcification here and a twinkling sign is an artifact that's created by calcification.

Notice again. So here in the lower pole of the system right here, it's not very obvious that there's a stone, but when you put the doppler on, there's clearly a twinkle sign here. And perhaps in this image is seen even to better advantage, there is a twinkle sign, which is a marked aliasing on the Doppler signal behind the stone.

So just to point out the difference between the normal vessel here in the lower pole and the adjacent stone with a twinkle sign, you would not confuse this doppler signal, which is a normal vascular velocity from this doppler signal, which is highly alias. This is on color doppler and here's a spectral doppler. Here is the arterial signal from the regular vessel and here is the aliasing that one sees from the stone.

What happens is there's multiple reflections within the stone which confuse the Doppler analysis on the system. And so it looks like aliasing on the doppler signal. Here again, this is a twinkle sign and here is the aliasing that one sees the doppler of that stone.

Distinguishing Calcifications from Stones

Now having introduced a topic of stones, not all calcifications in kidney or stones. So first off, some of the calcifications are going to be vascular and it's important to try to distinguish vascular calcifications from stones. The vascular calcifications will follow the typical course for a vessel and often there'll be two lines corresponding to the two walls of the vessel.

But the other type of calcification it's important to distinguish is parenchymal calcification. And so whereas stones or nephrolithiasis are calcifications in the collecting system, nephrocalcinosis is calcification that distributes within the parenchyma. And that basically comes in two flavors, the one being cortical nephrocalcinosis, and the second being medullary nephrocalcinosis. And the vast majority of patients have medullary nephrocalcinosis.

The etiologies of medullary nephrocalcinosis are overlapped with the etiologies of nephrolithiasis. So people with nephrocalcinosis are at increased risk for kidney stones and vice versa.

So an example here of medullary nephrocalcinosis, here's the renal cortex, normal architecture, but here are the pyramids. Remember normally these are supposed to be hypoechoic pyramids, but in this patient they're echogenic, they're increased echogenicity.

There are several causes that one can enumerate medullary sponge kidney can result in echogenic pyramids, renal tubular acidosis as a metabolic abnormality as is hyperparathyroidism with increased calcium. Those are all causes of medullary nephrocalcinosis. Anything that causes an elevated serum calcium can cause medullary nephrocalcinosis, cortical nephrocalcinosis as demonstrated here is a much less common entity.

Here we see the hypoechoic, relatively speaking pyramids with the markedly echogenic cortex. The two major etiologies here are cortical necrosis and hyperoxaluria, both relatively uncommon, but if you see this as a much more limited differential diagnosis as compared to medullary nephrocalcinosis, which can be due to basically anything that causes increased serum calcium.

So just some examples of the difference between the normal. The hypoechoic pyramid here is starting to see medullary nephrocalcinosis with some surrounding echogenic appearance around this pyramid. Here are some pyramids that are more uniformly echogenic here. Remember they're supposed to be hypoechoic, not echogenic, and here they're markedly echogenic in this medullary nephrocalcinosis case, which is more progressed.

So we look at stones, we can see the stones in the kidney as we've shown, but we can also follow the stones down. And it's important if you don't see a cause of obstruction up high. And remember, kidney stones are the most common cause. So if we don't see an obstructing stone at the UPJ at the ureteropelvic junction, we should look down near the bladder at the UVJ or the ureterovesical junction.

And here's the ureter coming into the bladder and we see the stone here. Echogenic focus with shadowing here, it's in sagittal, here it is in transverse stone with shadowing. Here's one on any other side, a stone in the in the left UVJ with some shadowing.

Now sometimes you can't see the stone, the ureter looks obstructed and the question is, is it really obstructed or is it just dilated? Another very good way of looking at this is by looking at ureteral jets. Now a normal well-hydrated individual should have two to three ureteral jets per minute. I would say that if you look for two minutes and don't see ureteral jet, there's something abnormal about that.

So here's the transverse view of the bladder and here's the jet from the left coming in and flowing out to the right side. Here's the jet from the right going in and going flowing to the left side. So you just look at the bladder and transverse at the level of the ureteral vesical junctions and you just keep watching it for a couple minutes and you should see alternating jets from the left side, from the right side to left side and the right side.

But if you see multiple jets on one side and you fail to see a jet on the other side, that side is probably obstructed and that's why there's no jet. Alternatively, if you still see dribbling of urine coming in from one side, that's a sign of obstruction.

Characterization of Renal Masses

Okay, so moving now from the topic of obstruction, which is probably one of the more common reasons for doing renal ultrasound to another common reason for doing renal ultrasound, and that is for characterization of masses. And so when a mass is identified, for example, if a mass is identified by CT, often one cannot tell on CT if a low density mass is cystic or solid. So an ultrasound is a very sensitive way of distinguishing a cystic from a solid lesion.

Renal cysts have to fulfill three criteria. They're anechoic, that is, they have no internal echoes, they have thin sharply defined walls and they have enhanced through transmission of sound. This is a simple cyst. So a simple cyst is anechoic thin walls and good through transmission make that diagnosis. There is no need for further follow up.

This of course is a stone, nice echogenic focus with posterior shadowing.

Now it's important to distinguish parapelvic cysts from hydronephrosis. So here's two cases where there are dilated structures, and this is long view of a kidney dilated fluid filled structures, dilated fluid filled structures. But in this case, whenever you did, you could not connect these structures. These are parapelvic cysts. In this case, if you tried you could connect all the cysts together into one renal pelvis. And so this is hydronephrosis.

So important to make that distinction between hydronephrosis and parapelvic cysts because this is a leave me alone type of situation, whereas hydronephrosis may need to be treated.

Now the differential diagnosis of renal cyst, what we talked about parapelvic cysts, we talked about hydronephrosis. How about calyceal diverticula? So here we can see a dilated fluid full structure in the upper pole of the kidney. This in fact is just an obstructed upper pole and that can also mimic a renal cyst. So you have to think about that.

And finally, a vascular lesion can do it. And here's an example. This is a renal transplant and this looks for all the world like a cyst in the lower pole that renal transplant. But we knew we had just biopsied this patient and we turn on the doppler. This is actually a pseudoaneurysm in the lower pole of the transplant and we'll see the AV fistula here with an artery coming up and a vein draining from it. And here we see the AV fistula flow on the spectral doppler and the filling of the pseudoaneurysm on the color doppler.

So this, be careful when you see a cyst use of doppler is very useful to distinguish the cyst from a vascular lesion.

Polycystic Kidney Disease and Acquired Cystic Disease

Now there are some patients who have lots of cysts. The adult version of polycystic kidney disease, certainly is characterized by large kidneys with multiple bilateral cysts. It's seen in a relatively younger age group than a standard senile cysts. These people tend to present early on, they may have cysts in their liver and pancreas as well. They may have cerebral aneurysms and sometimes they present with cerebral bleeds. And also they often present with renal failure that is as distinct from acquired cystic disease, which you just may get as the people get older. They may get cyst in their kidneys, or patients who've been on dialysis for several years. They also tend to have an increased incidence of cyst in their kidneys.

And this is an echogenic kidney filled with cysts. This is obviously someone with some chronic renal failure and these cysts are likely secondary to chronic dialysis.

Complicated Cysts

Now we talked about the criteria for a simple cyst and they were clean and anechoic with sharp walls and good through transmission. Now this is a patient with a clean cyst in his kidney goes skiing and after a traumatic incident with skiing has echoes within the cyst. And so this is hemorrhage within a cyst. Hemorrhage within a cyst in and of itself is not problematic as long as you knew that was a clean cyst and you had a good explanation for the hemorrhage.

However, if someone presents with a hemorrhagic cyst, one has to worry that perhaps there's an underlying etiology for that such as tumor, but other things that can cause a cyst with solid tissue, tumor and infection or the major things need to be excluded it.

Now what about these cysts that aren't quite simple? So here's a long view of a kidney and here's a cyst with a single thin septation. So a single thin septation is probably nothing to worry about. However, as you have multiple septations or as the septation starts to become thicker, these cysts should be followed because then we're starting to get a little worried. Could these be early cystic neoplasms?

And in fact, here's a patient with a relatively thick septation, a couple thin septations. Here's another patient with a cystic lesion and some nodularity. And these are both cystic renal cell carcinomas. So it's very important to realize that there's sort of a spectrum of simple cyst, which is leave me alone cyst with one thin septation, leave me alone. But as the septation starts to become multiple and thickened, one has to follow them and be concerned about the possibility of cystic renal cell carcinoma.

And that's to be distinguished from another form of a cystic lesion. This often seen in either young boys or older women, multiple numerous cysts of various sizes spread throughout a kidney. And this is called a multilocular cystic nephroma. There are various different names that have been given to this entity, but this is a benign cystic tumor of the kidney And it should be recognized as such with these multiple cysts and just treated as a benign lesion.

Solid Renal Masses

Now as opposed to the most common solid lesion seen in a kidney, which is renal cell carcinoma. And although I showed you some cases of cysts, which were cystic renal cell carcinoma, renal cell carcinoma is much more commonly a solid lesion. It's basically the most common solid lesion in the kidney in an adult. It can be hypoechoic, it can be hyperechoic. Here we see a hyperechoic lesion. It's bright. Here we see a hypoechoic lesion. Here we see a larger hypoechoic lesion, large hypoechoic mass. This is renal cell carcinoma. This is hyperechoic mass, also renal cell carcinoma.

They can be calcified in about 20%, and they are in fact the first thing one should think of when one sees a solid mass in an adult in a kidney.

Now how do renal cell carcinoma spread? The staging follows the spreading and usually it's they first start within the kidney, then they can spread transcapsular and they can spread to local lymph nodes and to the vessels. This is the renal vein. And here we see tumor starting to invade into the right renal vein here. And here we see the IVC in sagittal view. This is the liver hepatic vein into IVC and here's tumor coming up the IVC.

So first the tumor spreads into the vein, then it can spread into the IVC, it can spread locally. This is tumor spreading through the capsule toward the liver, toward the gallbladder. This is the mass, which is sort of invading into the liver here from a kidney. And they can also spread into local lymph nodes in the periaortic region.

What does a doppler signal look like in renal cell carcinoma? Well, here is a renal cell carcinoma, which is suboptimally visualized here, but there's a slight difference in echo texture and the vessels going into it have very high flow with relatively low resistance. That's the classic appearance of the doppler for renal cell carcinoma.

But here's another example of what can happen. Here's a renal cell carcinoma, which is actually compressing an adjacent normal vessel and the mass effect here is resulting in a pulsatile tardus in a normal vessel alongside the renal cell carcinoma.

Contrast material can sometimes be useful in terms of seeing vascularity in a renal mass. So here is a solid solitary mass within a kidney and here it is post contrast administration. With doppler, you can see flow within the mass, with this kind of mass. Usually one would not wonder whether or not this was benign or malignant. But there is some data to suggest that very small renal masses, which one is following, the vast majority of small masses below a couple centimeters in size are gonna be benign. And it may be true that contrast enhanced ultrasound is helpful in distinguishing such that if we see flow in the mass, it's more likely to be malignant mass.

Differential Diagnosis of Solid Renal Masses

So what is that differential diagnosis of solid renal masses? So we said that renal cell carcinoma is probably the most common cause, especially for a large mass in the adult kidney. A fat containing mass would commonly be an angiomyolipoma. Oncocytoma is considered a relatively benign variant of a renal cell and it's somewhat debatable. Not all pathologists agree to the use of this term. Not all pathologists agree that there is such a benign variant, but most people do.

Transitional cell cancer is cancer that relates to the urothelium. So it comes from the collecting system, but it can be seen in the kidney as well. One can see lymphoma or metastasis to the kidneys and one has to distinguish these tumors from hematoma or infarcts or focal pyelonephritis. And we'll look some examples of all these things.

So here's an echogenic mass and this could easily be a renal cell carcinoma or an angiomyolipoma. And here is one that is an angiomyolipoma and this this is the most common benign renal neoplasm. It can present as a solitary lesion or as multiple lesions. Often one sees the multiple lesions in younger males and that's an association with tuberous sclerosis. In older females or middle-aged females, one can see either a single angiomyolipoma or multiple angiomyolipomas.

They're homogeneous, they're well-defined and they're echogenic. When they get large, they have a risk for bleeding and so sometimes they're embolized or treated because of that risk. Here again, angiomyolipoma. Here's a huge angiomyolipoma exophytic from this kidney.

It's very difficult to make a definitive diagnosis on ultrasound, but there are some things that can help be helpful. Here we see the line of the diaphragm and here's the angiomyolipoma, which is a fatty tumor because it's a fatty tumor, actually the speed of sound is changed as it transmits through here and the diaphragm back here looks like it's posteriorly displaced. So it looks like it's not contiguous with the diaphragm here. That change in sound is the clue that this is a fatty lesion and there's really nothing else it could be, but angiomyolipoma.

So angiomyolipoma in young males associated with tuberous sclerosis, which is an autosomal dominant transmitted genetic issue. There's a classic triad of seizures with mental retardation and adenosebaceous, which looks like bad acne. And they also have these angiomyolipomas in the kidneys. Basically what an angiomyolipoma is, is it's a hamartoma. And so these kids who have angiomyolipomas in their kidneys basically have hamartomas in the brain and in the skeleton as well.

We mentioned before oncocytoma oncocytoma is a variant of a solid renal mass, which is considered relatively benign, 5% of renal neoplasms. The problem is it's a non-specific appearance. Someone can almost never make a definitive diagnosis of oncocytoma on ultrasound. The classic appearance is said to be a central scar with a stellar appearance. So if one sees this, one can suggest oncocytoma, but it's probably gonna need to be taken out anyway for the pathologist to look at it and to make this diagnosis.

Now we mentioned the transitional cell carcinoma was arise from urothelium. So here's a kidney with a collecting system that's dilated and here's a mass in the collecting system. Here's another kidney though where the mass is in the collecting system as well. But this is the masses inside the intrarenal portion of the collecting system. So just like this is a transitional cell in the renal pelvis, this is a transitional cell within the calyces of the renal sinus.

Lymphoma can rarely involve the kidney. Usually we're talking about a non-Hodgkin's type of lymphoma. It can be solitary or multiple masses or it can be infiltrative. And here we see multiple little masses. And this is lymphoma in a kidney. And here we see this diffusely enlarged kidney with a heterogeneous texture. And that's also lymphoma. And in some cases it's the perinephric space that's involved with lymphoma. So those are all different possibilities.

Here's a patient with multiple masses in the kidneys. This is renal lymphoma. Here is a lymphoma lesion, which actually looks so anechoic that was mimicking a cysts.

Other Mimics of Solid Masses: Hematoma, Infarct, Pyelonephritis

Okay, moving now to some other things we've seen in the kidneys, subcapsular hematoma. So this can be seen post-trauma can be seen in people in anticoagulation, and it can be seen with people who have tumors that bleed. So you have to be careful, you know, thinking of what the cause of the bleed is. But here's the kidney. And here we see early on a very echogenic lenticular shaped collection, which is compressing the kidney. It deforms the renal contour and it changes with time.

So a few days later it's anechoic now because the blood cells here have been degraded and dropped to the bottom or been taken away. And what's left is sort of the fluid here. And so it changes with time and in the end result here can be a smaller shrunken kidney that's been compressed known as a Page kidney and that can be associated with long-term hypertension.

Other things that we said could cause the appearance of a solid lesion of kidney include a vascular injury or infarct. And here is an echogenic appearing area in the upper pole of the kidney. And in fact if you look, there's flow here below it and there's flow here toward the apex of that kidney. But there's no flow in this echogenic area here. And this turns out to be a renal infarct.

There are many causes of renal infarct that can be embolic. They can be related to a vasculitis, but just realize that that is one of the potential etiologies of an abnormal echo texture.

Now pyelonephritis we said most often looks normal and most often there are no gray scale findings. However, when there are findings, usually it's a hypoechoic appearance. Here we see a focal area of pyelonephritis, which is hypoechoic. Sometimes the whole kidney can be enlarged. Sometimes it can sort of be heterogeneous or patchy in its appearance. Doppler flow is often increased. So for example, in this case we see flow around an area of focal pyelonephritis.

And the complications of pyelonephritis is something we really look for in ultrasound more than the actual diagnosis. So the diagnosis tends to be a clinical diagnosis, but the complications are things here like an abscess in his kidney. And once again, it's a fluid containing structure with low level internal echoes.

Another sign that one can sometimes see with pyelonephritis, if there's a little bit of dilatation in the collecting system, one can see that the actual urothelium, which lines the collecting system looks thickened. Now in the normal patient the urothelium is paper thin, but here we see the slight amount of mild hydronephrosis with a thickened urothelium. And here again in the renal pelvis, a thickened urothelium. So this would be a sign of inflammatory process and possibly pyelonephritis to be distinguished from transitional cell cancer, which tends to be more focal and more irregular in its appearance.

So here's another case, nice smooth urothelial thickening. This is probably related to an inflammatory process. Most likely pyelonephritis can be seen with obstruction and a transplant can be seen with rejection, can be seen with ischemia and as we said before, needs to be distinguished from tumor, which tends to be more focal and more irregular.

Okay, so that basically wraps up what we wanted to talk about as far as the kidney goes.

Adrenal Glands

And now we'll talk a little bit about the adrenal gland. So the normal adrenal anatomy is really better visualized in children. So many of these slides come from children. In the adult, the adrenal is relatively smaller compared to the kidney and so much more difficult to visualize. But in kids, relatively easy to see the adrenal gland, it can be the inverted V or a Y shape. With this being an inverted Y this is the body of the Y and is the two, the two arms of the Y and this is the kidney down here.

And the adrenal gland tends to have an echogenic, medullary or inner portion and then surrounded by more hypoechoic cortex. And the classic thing about the adrenal is that it's concave. So if you look here, it's concave. If you look here, it's concave. There are no bulging convexes. If there's a convexity in an adrenal, we're thinking about a mass.

So a normal adrenal concave thin structure, V-shape or Y shaped with a trilaminar appearance, a hypoechoic cortex, and the central echogenic adrenal medulla. This is what you don't wanna see. You do not wanna see a rounded appearance of an adrenal gland. So here is a kidney. And above the kidney we see a rounded appearance of the adrenal gland. So this is basically an adrenal mass.

What that adrenal mass is, we don't know, but look, this is the normal adrenal gland here, a nice paper, thin linear structure. This is the mass. Here's our differential diagnosis. Adenoma adenomas tend to contain some fat, but not enough for us to make that diagnosis. On ultrasound, we can often make the diagnosis with CT or MRI Metastasis can look like that a pheochromocytoma, a carcinoma, and that's the primary carcinoma of the adrenal gland or lymphoma in that area.

A myelolipoma is a fat containing lesion in the adrenal gland and then adrenal hemorrhage and neonates often looks just like that. So if it's a newborn and you're suspecting hemorrhage, most often what's done is they do follow up ultrasound 'cause hemorrhage should resolve while masses stick around.

Adenoma

The most common mass in the adrenal is the adenoma. It's usually asymptomatic, usually less than three centimeters in size. Ultrasound of the adenoma usually shows a homogeneous lesion, similar in appearance to the liver. It may result in Cushing syndrome or Conn syndrome if it's hormonally active. And the bottom line is ultrasound is nonspecific. So there's no way for us to distinguish on the ultrasound appearance this adenoma from a metastatic lesion or from a primary adrenal cortical carcinoma.

Metastasis

So here's a metastatic lesion. This is more characteristic appearance. This is more hypoechoic. It is a relatively common site for metastases, especially when one's talking about lung cancer. Breast cancer lymphoma also go to the adrenal gland. As we said before, it can mimic an adenoma. Usually when they get larger they're more heterogeneous and so they don't really look like the homogeneous echogenic adenoma.

But here's a lesion above the kidney in the lesion of the adrenal fossa. It's heterogeneous. It's got some, perhaps some calcium in it. It's got some cystic areas in it.

Adrenal Cortical Carcinoma

This is an adrenal cortical carcinoma. This is the primary lesion and primary malignancy of the adrenal gland. They often grow large, they have hemorrhage and necrosis. They can invade the adjacent veins and they may also actually be hyper functioning. So they may result in something like Cushing syndrome.

Lymphoma

An example of lymphoma, here's non-Hodgkin's lymphoma, which you see a mass here in the region of the adrenal. Here is another one with the mass in the region of the adrenal. Usually it results of direct invasion from retroperitoneal disease. So the patient has known retroperitoneal disease. Often they're bilateral and they're usually solid hypoechoic masses. They look like lymphoma nodes look.

Myelolipoma

Myelolipoma once again, usually very difficult to distinguish this on ultrasound. But because they're fat containing, they're usually hyperechoic, they may actually attenuate the sound. The only way to make a definitive diagnosis is if there's enough fat here so that this diaphragm instead of being a straight line through, gets displaced because of the differential velocity of sound within a fatty lesion.

If you see that and you see the velocity diaphragm being displaced, as we said before in terms of making the diagnosis of an angiomyolipoma in the kidney, same thing for a myelolipoma here with the adrenal gland. If you can see definite evidence that the speed of sound has been altered because of the fatty content, then you can make that diagnosis. Otherwise, if it's just an echogenic lesion, you can suggest it, but we usually can't be definitive.

Adrenal Hemorrhage

Hemorrhage in the adrenal gland often presents as a complex mass, often as unilateral, as opposed to a tumor mass, which should have flow in it. Hemorrhage is just blood clot, so there should not be any flow in the Doppler evaluation. So here's the mass, here's the doppler in the liver, and here's the doppler in the hemorrhage, which has no flow.

So once again, complex mass for hemorrhage. We see sometimes anechoic areas and sometimes more echogenic areas. No doppler flow. You have to follow it up. So you follow this up and then a few weeks later it looks like this. So we see it's getting much smaller. You'd like to follow it to resolution if you're unsure at all that this is hemorrhage.