Ultrasound of Renal Masses (and mass-like renal lesions) in Neonates and Infants - SD

Introduction

Hi, my name is Richard Bella.

I'm a pediatric radiologist from the Children's Hospital of Philadelphia.

I'm the director of the Division of Ultrasound, and I'm gonna be talking about ultrasound of renal masses and mass like lesions in neonates and infants.

I'm gonna be talking about ultrasound of renal masses and mass like renal lesions that occur in neonates and infants.

The objectives of this talk will be to review ultrasound findings and common and uncommon masses and mass like renal lesions that occur in neonates and infants.

And I'll describe the CT correlation in given cases.

Fortunately, to start with, I must say that renal masses in neonates are rare.

The renal masses that I'm gonna talk about include mesoblasts nephroma, neph neuroblastoma ptosis, and the mass like renal lesions that I'm gonna talk about include cystic renal disease, which in and of itself you could dedicate an hour's lecture to without question, and renal venous thrombosis.

I'm also gonna show a few mimics of mass like lesions that affect the kidney, namely the upper pole of the duplex kidney and adrenal hemorrhage.

Normal Neonatal Kidney

I think it's worthwhile starting by reminding everybody about what the normal neonatal kidney looks like.

Very briefly, how it differs from the adult kidney.

It's lobulated, it has these very large hypoechoic areas that we refer to as the renal pyramids, not to be confused with cysts or masses or hydronephrosis.

When we see that it's a good thing as we describe the ability to see the cortex against these hypoechoic pyramids as good cortico-medullary differentiation.

Notice also that the neonatal kidney has a paucity of renal fat, also known as the normal adrenal here.

Imaging Modalities

Imaging modalities that we can use for renal masses in the neonate include ultrasound and CT.

MRI obviously both have their advantages.

Ultrasound being for tumor characterization, bilaterality, you can look at Doppler flow and vascular invasion.

And in many cases, when you find a mass, a CT or an MR then ensues to get an idea about the overall tumor extent and the renal reserve.

Mesoblastic Nephroma

The first tumor we're gonna talk about is the mesoblast nephroma, which is otherwise referred to as the fetal renal hamartoma.

This is a tumor that occurs typically in the very young infant, frequently less than six months, with a mean age about three to four months.

This not uncommonly, there may be antenatal maternal history of polyhydramnios.

There is an association of hypercalcemia with these infants.

This sort of tumor is a very solid homogeneous tumor.

Here's an example of a fetal ultrasound where you can see a mass within the region of the renal fossa, which was subsequently found to be a mesoblastic nephroma.

Notice. It's a very solid, fairly featureless looking tumor.

And notice that the patient also had, or at least the mother had polyhydramnios as well.

They're usually typical.

In the typical case, these are very benign tumors.

They're locally invasive and they require nephrectomy, and they do well with nephrectomy.

There are rare cases where you have atypical tumors, which are large cellular, can be more locally invasive, and even in rare cases metastasize.

As I mentioned, they're very featureless tumors.

They almost have a very muscle tumor look with a histology that has multiple spindle cells.

It almost looks like ITS in some ways, not very vascular.

And as you can imagine by CT, they also have a very featureless looking appearance and they can be quite variable in size, sometimes being quite large.

This is an example on your lower image of a more atypical form in this coronal plane where you see the IVC, the aorta.

Here's the spleen here, and you can hardly see any bit of left renal tissue that's left, but it's really been pretty much engulfed by this very large heterogeneous tumor, which by CT looks like this.

Very heterogeneous, very necrotic looking.

This was also an atypical form of mesoblastic nephroma.

Notice, again, unilaterally, the right kidney being normal.

I don't think if anybody just sees that particular tumor, they can just slam dunk and say that that is a mesoblastic nephroma.

I think there is a differential, one of which is a rare neonatal Wilms tumor.

Wilms tumor typically occurs in a slightly older child, not typically in the neonate, but it does occasionally occur.

The other tumor, which is also a very rare, very malignant tumor, which can occur with synchronous cerebellar tumors.

And that is the malignant rhabdoid tumor of the kidney.

Nephroblastomatosis

The next tumor I'm gonna mention is a tumor that we refer to as nephroblastomatosis.

And what this refers to is when you have multiple or diffuse nephrogenic rests, rests of metanephric renal blastema that persist beyond the fetal life into infancy.

And these are pre-malignant lesions, which are known precursors of Wilms tumor.

Beckwith has described them histologically as being either intralobar or perilobar, and their fate can be of these nephrogenic rests quite different.

Some can remain dormant, some can mature to normal kidneys.

Some become hyperplastic and overgrow while others form Wilms tumor through neoplastic induction.

There are a group of infants for whom we routinely screen for the presence of nephroblastomatosis because they are at risk for this particular tumor.

And they would be infants with Beckwith-Wiedemann syndrome.

Classically macroglossia, hypoglycemia, macrosomia.

Patients who have so-called WAGR syndrome, Wilms tumor, aniridia, genitourinary abnormalities, retardation.

Here's an example of sporadic aniridia infants with trisomy 13 and infants or children who have hemihypertrophy.

These are children who are at risk for nephroblastomatosis, and are screened at periodic intervals for the development of that tumor and the potential for development of Wilms tumors.

Hyperplastic nephrogenic rests or nephroblastomatosis can sometimes be difficult to be seen with ultrasound.

They can be unilateral, they can be bilateral, they can asymmetrically or symmetrically enlarge the kidneys.

Here's a case here where you can see the solid mass here, quite isoechoic to the remainder of the kidney here, better seen by CT.

In addition to that mass, you have multifocal masses of variable sizes.

This is an image taken from a child who had WAGR syndrome with aniridia.

Again, he had a solitary lesion, a little more cystic actually appearing in the kidney.

But by MRI showing multifocal areas of high signal.

Again, these particular modalities being a little bit better for showing the multifocality of the lesions.

A little bit easier to see by those modalities.

And then on rare instances you can have a rather diffuse form of nephroblastomatosis, where these rests of primitive metanephric blastema just absolutely cake each kidney and enlarge each kidney.

Here's the corresponding CT here that's functioning; the kidney's functioning well, but you can see how both kidneys are markedly enlarged and caked by rests of metanephric blasts.

A diffuse form of nephroblastomatosis.

Multilocular Cystic Nephroma

I mentioned this particular tumor, not so much that it's seen in neonates.

It's certainly seen in young childhood as well as in older children because it is sort of a relative of nephroblastoma and it's called the multilocular cystic nephroma.

That's certainly a mouthful.

And the reason I mentioned it is because it has a fairly classic appearance when you see it in that given age group.

They're well circumscribed cystic masses with multiple thin septations that enhance on CT.

And some people refer to these as cystic nephroma and some people refer to them or also known as cystic partially differentiated nephroblastomas.

And they refer to the latter case when they actually have rests of metanephric blastema that are found in the septa.

So that's the only way they can differentiate these two is based on the histology of what they find in the septa, and this is what they look like.

Again, they can be multifocal, but often they're solitary, large, well encapsulated multiple fine septations.

Here's the CT correlate of that same patient with enhancing septations here.

Here's the CT from another patient.

Notice how large this particular lesion is here.

This would have to be differentiated from a necrotic Wilms tumor.

Mass-Like Lesions: Renal Cystic Disease

Now another topic to talk about.

Now I'm getting off the topic of renal mass lesions.

I'm gonna be speaking about mass like lesions of the infant and neonatal kidney.

And I'll start by talking briefly about renal cystic disease because renal cystic disease in many ways can mimic renal masses.

We're gonna mention ARPKD, autosomal recessive and autosomal dominant polycystic kidney disease, those you see with malformation syndromes.

And then the genetic and non-genetic forms of cystic kidney disease, namely the multicystic dysplastic kidney.

Multicystic Dysplastic Kidney (MCDK)

The multicystic dysplastic kidney, the classic form is with pelvicalyceal atresia.

There is a rare hydronephrotic form, but in the typical case of pelvicalyceal atresia, there's absence of the renal sinus in the sense that there's lack of a normal developed pelvis and a normal developed calyces, such that what you result with is really hardly any discernible renal parenchyma and just multiple variable sized cysts.

Whereas in the hydronephrotic form you have a central cyst around radially arranged cysts.

Most people recognize what the MCDK looks like, but I think what we have to concern ourselves with is with the contralateral kidney because it's prone to reflux obstruction as well as variable degree of dysplasia as well, which may be hallmarked by the presence of cysts.

Here are two examples of the classic appearing multicystic dysplastic kidney variable cysts of variable size echogenic intervening tissue here.

Here's another one as well here, but notice on the contralateral left kidney for this particular patient, this kidney is certainly robust and relatively large, but unlike the normal kidney that I'd shown you, there's no corticomedullary differentiation here.

In fact, there may be small cysts within the parenchyma indicating that this patient probably has some element of cystic dysplasia involving the contralateral kidney.

Now this is in contradistinction to this patient who has the more hydronephrotic form of multicystic dysplastic kidney on the left where you have the central cyst with these radially arranged cysts around the perimeter here.

This being the normal right kidney, not to be confused for this, which is again, normal right kidney here where these dilated areas here don't represent cysts but are actually dilated calyces in continuity with the renal pelvis, which is dilated a classic appearance of UPJ obstruction.

Autosomal Recessive Polycystic Kidney Disease (ARPKD)

The second inheritable form I'm gonna talk about, I talked about a non-inheritable form that's MCDK; inheritable form of cystic renal disease is autosomal recessive polycystic kidney disease, which can result in mass like enlargement of the kidneys in neonates and the hallmark being the kidneys being enlarged, dilated collecting ducts or renal tubular ectasia, biliary ectasia is an important part of that condition.

And you may also see elements of hepatic fibrosis, not usually so much in the young, but more often you see in the child who presents at an older age.

In fact, as we know about autosomal recessive polycystic kidney disease that in the perinatal or neonatal period, the kidney predominates over the liver disease.

Whereas in the older form of autosomal recessive polycystic kidney disease or the so-called juvenile form, the kidney sort of takes a backseat while the liver in the way of hepatic fibrosis and subsequent portal hypertension comes to the forefront.

Now here are three examples of autosomal recessive polycystic kidney disease in the perinatal neonatal period.

And the only thing I wanted to show you here is again, notice how on these plain films here they have mass effect where the bowel is centrally located.

So they really do present as if they were abdominal masses with central location of the bowel.

In this case, there was a unilateral mass and this baby had a solitary enlarged kidney, which is by ultrasound, autosomal recessive polycystic kidney disease.

And of course the other feature is that you have this echogenic medullary portion of the kidney here it's quite expanded, compressing the cortex and the sort of so-called cortical rim sign.

But this appearance here and here as well as these multiple lucencies here are all compatible with what you might see with renal tubular ectasia and autosomal recessive polycystic kidney disease.

In some cases where the kidneys are not quite as large as one might expect, but you look rather heterogeneous, you can actually use high resolution ultrasound like we're doing here and looking at this one area here with a linear transducer.

And you can actually see the manifestation of tubular ectasia using high resolution ultrasound.

Now the other important differentiating feature for autosomal recessive polycystic kidney disease in terms of differentiating it from autosomal dominant disease in the child is looking for biliary ductal ectasia because there's a clear known ductal plate malformation with this condition.

And what you look for in the liver would be evidence of dilated intrahepatic bile ducts.

These babies are not jaundiced, this is just a malformation of the ductal plate and it's quite variable the degree of dilatation that you might see.

And this was probably the most striking example of biliary dilatation that I'd ever seen in a child who had autosomal recessive polycystic kidney disease.

This was an older child who had very dense echogenic liver likely due to hepatic fibrosis.

But some of these holes that you're seeing in the liver here are not vessels; in fact they're actually evidence of biliary ductal ectasia with a central portal vein here.

Now here are two patients.

The one on your left is a fetal ultrasound and the one on your right here is a neonatal ultrasound, both of which are demonstrating very large echogenic kidneys.

It turns out on the left here it's a fairly classic example of renal enlargement mass like enlargement secondary to autosomal recessive polycystic kidney disease.

The patient on your right had a very similar appearing kidneys, eight centimeter kidneys each, but this one had parents who had a history of autosomal dominant disease.

So the point is that they can look quite similar in the neonatal period, autosomal dominant polycystic kidney disease.

You don't have just cysts of the renal medulla portion of the kidney, but you have the entire nephron as well as the tubules.

Again, they can present as an abdominal mass in the neonate; in older children can present with hematuria or hypertension.

The liver disease, unlike autosomal recessive disease, is usually rather rare.

Autosomal Dominant Polycystic Kidney Disease (ADPKD)

Now there are several gene loci that have been identified who are responsible for the phenotypic look of autosomal dominant polycystic kidney disease.

And again, if you find yourself with a neonate with large mass like enlargement of the kidneys, take a good look at the liver here.

This liver was normal, had no evidence of biliary ectasia, whereas there are multiple small somewhat sonographically resolvable cysts, actually more cortical than medullary location.

This would be more typical for ADPKD as it was in this baby here who again who had a positive family history for ADPKD mass like and renal enlargement of the kidneys and multiple small cortical cysts evidenced by this fetal MR.

Now I mentioned that they have identified the gene locus for ADPKD on several gene loci.

It turns out that there is a neurocutaneous condition or one of the multiple malformation syndromes classically tuberous sclerosis where the locus for TS is contiguous with that of the PKD1.

So in rare cases, the phenotypic manifestation of the kidneys of TS early in life and neonatal and the young child could present very similar to what you would see in an adult with autosomal dominant polycystic kidney disease.

This was a child who presented with mass like renal enlargement, found to have multiple huge cysts in both kidneys.

Obviously this would not be a multicystic dysplastic kidney because if the child had bilateral MCDKs, he would not be alive.

This was the same patient's CT.

You can actually see the kidney functioning renal parenchyma, but then large huge cysts within this kidney.

Very much what you would expect to see classically with ADPKD.

And this was the same child's brain CT showing the hematoma here in the left frontal region.

Neonatal Renal Venous Thrombosis

Now another condition I'm gonna mention and lastly and talk about is neonatal renal venous thrombosis, which can also cause mass like renal enlargement of the kidneys.

We see most of this occurring very young in life.

The classic way they present is hematuria, hypertension, mass like renal enlargement.

And the point I want to make is that the renal venous thrombosis that occurs in neonates and sometimes even in utero, begins in the intrarenal small veins of the kidney and works its way through the interlobar veins into the main renal vein.

And even occasionally into the IVC, there is an association that you should remember between left renal venous thrombosis and adrenal hemorrhage.

As you would expect with renal vein thrombosis, the kidney early on would become enlarged.

The architecture would be altered entirely, it would look quite patchy.

Sometimes the medullary portions where the veins are sitting look rather hyperechoic with streakiness over time, as the thrombosis evolves or as collateral circulation develops, the kidneys decrease in size become relatively more hypoechoic, but they still continue to have poor corticomedullary differentiation.

Those pyramids are still not well seen.

And then over time the kidney may or may not atrophy depending on the amount of collateralization that takes place.

Sometimes we'll find that the kidneys are small and echogenic and sometimes we'll find small calcifications within the kidney in the same places where the thrombi had occurred within the veins of the kidney.

Now let's look at some cases.

Here's a classic example of an acute or early neonatal renal venous thrombosis.

This is the adrenal here, here's the liver here.

And notice this very large patchy architecture of this enlarged right kidney.

Again, this baby is a three day old would have had hematuria.

Here's another patient. Notice again, this is the left kidney spleen over here, large echogenic kidney, a little bit of streakiness in the medullary regions here, but very featureless, no pyramids.

And this patient actually had, as I mentioned earlier, an associated left adrenal hemorrhage.

Now here are some of the late findings with neonatal renal venous thrombosis.

The kidney would have shrunk over time.

This kidney probably only measures about two centimeters in size.

The average newborn kidney being about five, I would say between four to five centimeters on the average, but again, it's sort of a featureless looking kidney.

Here's another example of a late renal venous thrombosis.

Multiple small calcifications scattered throughout this small relatively hypoechoic.

Very abnormal looking kidney, obviously some sort of a renal vascular insult.

Now this is an interesting image that was taken from a venogram from an article by Brill years ago from an infant who had had neonatal renal venous thrombosis.

And when they did this venography, they noticed that there were multiple small calcifications scattered throughout this kidney in a lace like fashion in the same areas where those calcified veins were located.

And I think that if you notice, you can see this clinically.

Here's an example we've had just fairly recently from a plain film.

You can see this lace like calcification here in the kidney.

Similar to that, what you'd seen previously in this baby who had had some hematuria.

This was another child who from an outside CT sent to us.

It's a non-contrast CT.

There's a catheter in the aorta and you can see this lace like calcification within this relatively larger right kidney as well as a calcification in the main renal vein.

This can also be seen by ultrasound here.

Here's the liver here, transverse view, right kidney, these small punctate calcifications.

And in addition, a calcification had propagated into the IVC that you're seeing transversely here, the same calcification you're seeing like the so-called bullet calcification of the IVC here in the same patient.

Mimics of Renal Masses

Finally, there are a couple of mimickers that you should be aware of that can mimic neonatal renal masses, one of which can be the upper pole, the dilated upper pole of a duplex kidney.

Some of these can be cystic dysplastic.

Here's the smaller lower pole.

Obviously you should recognize this as representing that given the fact that this patient had a thin walled ureterocele in the left side of the bladder.

This would be another example of an upper pole mass here.

Indenting the superior aspect of the right kidney here, this large complex cyst, this was in fact an adrenal hemorrhage, which you would follow over time to make sure that it regressed and partially calcified.

Now sometimes even a complex or cystic neuroblastoma could have a similar appearance.

So that would be one of the reasons you would certainly want to be able to follow that.

Summary

So in summary, ultrasound really is the initial imaging modality of choice when you're evaluating the neonatal kidney for many conditions, including that when an infant presents with what seems to be a renal mass or some mass like condition of the kidneys.

And in many cases a CT or MR is actually obtained as well to determine the overall extent in renal reserve.

But fortunately, solid renal masses in infants are rare.

The mesoblastic nephroma, albeit rare, is actually the most common and occurs in the less than six months old.

And again it's a very featureless looking kidney in most cases and is amenable to surgical resection.

Nephroblastomatosis occurs when you have remnants of primitive renal blastema that exist in infancy.

And they can have many different manifestations in terms of being dormant to having potential for malignant development.

They can be asymmetric and in many cases we have to screen a certain group of infants that I'd mentioned to you for the development of those particular tumors.

The multilocular cystic nephroma I mentioned to you.

Particularly the cystic partially differentiated nephroblastoma I only mentioned because that's the only way it can be differentiated is by the presence of nephroblastomatosis within its septa.

That cystic renal disease is one way that kidneys can present in neonates similar to masses that an autosomal dominant and recessive can have very similar ultrasound appearances.

Obviously a family history is important.

Take an ultrasound look at the liver to determine whether there's any evidence of biliary ectasia would certainly help you differentiate ARPKD from ADPKD.

If you see what looks like phenotypically autosomal dominant polycystic kidney disease in an infant, multiple macrocysts, think about tuberous sclerosis like the images I'd shown you.

And finally, that renal venous thrombosis again can present with mass like enlargement of the kidney with hematuria hypertension, you should think about that diagnosis particularly if you see lace-like renal intrarenal calcifications like I'd shown you as well as the calcified IVC thrombus.

And finally, there are some mimics like I'd mentioned in the upper pole such as that which you would see with a duplex kidney.

Think about that, particularly if you look at the bladder, you see ureterocele or the adrenal hemorrhage.

And I thank you for your attention.