Renal Transplant Ultrasound - SD

Introduction

Good afternoon ladies and gentlemen.

Let me first introduce myself. I'm Alex Ward.

I'm a physician and nephrologist at Lancashire Teaching Hospitals NHS Foundation Trust in Preston in the northwest of England.

My interest in renal transplant ultrasound stems from eight years of performing renal transplant ultrasound myself from my training in Germany.

I'm also formally certified according to step one of the guidelines of the German Society for Ultrasound in Medicine.

I also perform regular courses on renal and renal transplant ultrasound for junior and middle grade nephrologists.

Now the menu of today's talk is given.

In this slide we will first discuss what transplant ultrasound can do and what it role is in clinic and more importantly, we'll also discuss what transplant ultrasound cannot do.

We'll then move on to common findings in B mode ultrasound and then progress to the more advanced duplex and doppler.

Ultrasound of the renal transplant will go over common findings and start with the not so difficult things such as measuring the renal resistive index and then move on to the more advanced evaluation of transplant renal artery stenosis.

And finally, I'll try to formulate a standard of what a proper renal transplant ultrasound should cover.

Performing Renal Transplant Ultrasound

Now when I perform renal transplant ultrasound, I sometimes feel like the man on this beautiful painting by Hi Bosch, the imposter.

Now the imposter, that's me in this allegory.

I perform the renal transplant ultrasound.

The others are watching.

Some of them can't quite believe what's going on.

Some of them come closer to try and understand what's going on.

Others look away entirely.

Some look up to the sky and just don't believe what's going on.

What Transplant Ultrasound Can Do

What can transplant ultrasound do?

What it can do very importantly is exclude obstruction.

And that's actually probably the most important thing that renal transplant ultrasound is good for.

We can exclude obstruction in a transplant that is deteriorating and that's actually quite easy.

Every renal registrar and every junior renal doctor can do that with a little bit of training and a bit of supervision and experience.

We can also provide evidence for or against an acute problem in that we can measure the renal resistive index.

Again, that is not as easy as excluding obstruction, but it's not really difficult and can be done with a bit of experience and supervision.

We can also prove patency of the transplant artery and vein postoperatively.

That is actually very important in an acute transplant unit.

So if you work in an acute transplant unit, then you will know how important it is to know that the transplant artery and vein are patent.

If, for example, a transplant deteriorates in the first 24 hours after surgery, what we can also do is diagnose or exclude transplant renal artery stenosis, although I think it's fair to call that advanced and that needs a fair bit of experience and supervision.

And that is for the advanced ultrasound wizard.

What Transplant Ultrasound Cannot Do

What it cannot do is equally important.

Transplant ultrasound can't diagnose or exclude rejection.

The best we can do is provide evidence of an acute problem by measuring an increased renal resistive index.

But to diagnose or exclude rejection is actually still the role of the transplant biopsy.

Anatomy of the Renal Transplant

Now what do we expect to see?

It's worthwhile to spend a slide in a couple of minutes on the anatomy of the renal transplant.

Most transplants are fitted into the right isli fossa.

The vessels connected usually to the isli vessels in this case.

The common ILI artery and the common ILI vein can also be connected to the external ILI artery or vein.

And then we have the transplant ureter that is connected to the recipient's bladder.

As shown in this cartoon, it's worthwhile to know if the patient has had his transplant or her transplant in childhood.

In that case, we can expect the transplant artery to be connected directly to aorta and the transplant vein probably connected to the inferior vena cava kidney pancreas transplants.

Slightly different in their anatomy in that the kidney graft is usually in the left ILI fossa and it's not retroperitoneal as in the isolated kidney transplants but intraperitoneal, however we can't visualize that on ultrasound as the peritoneal folds are usually not visible on ultrasound.

The pancreas transplant usually on the other side, on the in the right ILI fossa.

Although pancreas transplant ultrasound is largely unknown territory and will not be covered in this talk, it's a nice challenge for the advanced ultrasound practitioner, but we have yet to learn the meaning of, for example, the resistive indices in the pancreas transplant or measuring the volume of the pancreas transplant that is unknown territories, no, its meaning is not yet known how to get started well in a fresh and well-functioning transplant.

Finding the Transplant

That should be a piece of cake to find the correct side.

Usually there will be a well delineated scar and we will just place the transducer in parallel to the scar.

It is important as a bit of ultrasound etiquette to be gentle.

Many patients have hyperesthesia in their IC foil that contains the transplant.

This is because nerve damage has occurred during surgery and quite a few patients are very sensitive there.

So be gentle and the patient will be your friend.

There should be no problem in finding a functioning transplant and by this stage you should have found the transplant.

All right. In a non-functioning transplant, the patient who has already returned back to dialysis, that may be quite a bit more difficult to find and the following rules may help all that pulsates, all that has peristalsis and all that changes shape with flexion of the leg is probably not the allograft.

So that will allow you to differentiate between the transplant, the old non-functioning transplant and for example, bowel or muscle.

Using these rules, it's usually possible to find even an older non-functioning transplant, although after years of returning to dialysis that may be a challenge and something for the more experienced ultrasound wizard.

Size, Length, and Volume of the Transplant

Size, length, and volume of the transplant.

I'll spend quite a few minutes and several slides with this.

As many mistakes are made there in clinical practice, we first have to appreciate that there's a difference between renal length and renal volume.

Most ultrasound reports of transplants provide the renal length, although actually what correlates with the patient's body weight is the renal volume.

The kidney is an ellipsoid body, so there is a mathematical formula to approximate the volume of an ellipsoid body such as a native kidney or a kidney transplant.

And this is the formula. It will be length times breadth, times depth times P divided by six.

The mathematical number P divided by six usually equates to roughly 0.5, so A times B times C times 0.5 is a gut estimation of the renal volume and the normal renal volume in a native kidney relates to body weight in that the normal renal volume should be body weight of the patient times two plus minus 20%.

However he alerts the major problem because in native kidneys, obviously the kidney volume relates to the patient's body weight and in transplants the transplant volume will obviously relate to the donor.

So if a six foot tall muscular man receives a tiny transplant from a adolescent tiny girl, then the volume of that transplant will not relate to the six foot muscular man but to the body weight of the tiny adolescent donor.

So in a nutshell, there is no normal size in transplant as the volume relates to the donor.

So the correct wording in a transplant renal ultrasound report would be the renal volume is appropriate or not in relation to recipient, not the renal transplant has a normal size.

So what we can do is we can measure the renal transplant volume, relate that to the recipient's body weight and then call the renal transplant volume appropriate or not.

In relation to the recipient, how to measure the renal volume first, obviously we need to measure the length of the transplant.

That needs a bit of patience.

We need to obtain several readings until we are convinced we've actually found the longest length of the transplant.

To measure B and C, we need to apply the 90 degrees trick.

How is that done? That is done by placing the transducer on the longest length of the transplant as shown on the left hand side and then rotating the transducer by 90 degrees.

This is what beginners usually find extremely difficult.

The best way to do it is usually to look at the transducer and your hand that holds the transducer and not look at the screen.

And actually in my ultrasound courses I will usually cover the screen with a cloth to make it easier for the beginner.

So what you do is identify the longest length of the transplant, have your transducer, alongside the longest length of the transplant, rotate the transducer by 90 degrees and then you will usually see this picture, 90 degrees to the longest length.

So a nice transverse cut of the transplant and you've already found the hili by convention we measure B and C at the level of the hili where the vessels come in and even without applying doppler and duplex, you can see that this is the transplant artery and vein coming in and this is just spot on.

So then you've obtained A, B and C and you can calculate the renal transplant volume and relate that to the recipient's body weight and call it appropriate or not.

Parenchymal Width

Parenchymal width can be measured at the same spot where you've just measured A and B as detailed before.

Obviously there are several measurements that can be obtained and indeed a good transplant ultrasound report should then provide several readings.

So for example, in this case you would say that the parenchymal width is between 10 and 13 millimeters.

It would be abnormal if that was below 10 millimeters.

That's worthwhile to keep in mind.

Parenchymal Changes

Now moving on to parenchymal changes.

For that unfortunately we don't have the luxury of normal values.

We can only rely on experience obtained with measuring and seeing hundreds or thousands of transplants.

This is how a normal transplant parenchymal should look like.

And please note that there's a clear cut border between the transplant parenchyma and the surrounding tissues.

And please also note that the transplant parenchyma is smooth and has a straight lining and is well demarcated against the surrounding tissue.

Now if we compare that to another transplant, I think it's very obvious that there are parenchymal changes compared to the previous picture to start with.

There is no clear cut delineation between the transplant parenchyma and the surrounding tissue that has been lost already as a sign of parenchymal changes and also the parenchyma itself is in homogenous with echo dense and echo poor areas and that is what we would classify as at least moderate parenchymal changes.

Moving on to the next picture, a transplant that may even be difficult to find in a patient who has already returned to dialysis, no clear cut border to the surrounding tissue at all and very in homogenous parenchymal.

So this is what we would call severe parenchymal changes.

Another important finding in the parenchyma prominent medullary pyramids are seen in this transplant medullary pyramids.

Very obvious in this picture as echo poor areas and if you compare that to the pathology findings of such a kidney, then it's very obvious that these are indeed the medullary pyramids as in this transplant, kidney from the patient with acute transplant failure, this is unfortunately what we call a soft sign.

It can be seen even in some healthy transplants.

It occurs in acute transplant failure regardless of the course.

It can also occur in acute rejection, so prominent ary pyramids, a soft sign of acute transplant failure but important to remember that it can also be seen in healthy transplants.

Obstruction and Its Variants

Moving on to obstruction and its many variants, I've said that excluding obstruction is one of the most important things of transplant ultrasound.

We will start with something that is not obstruction as seen in this picture.

So what we can see in this picture is merely a dilated transplant pelvis.

This the transplant here, the transplant pelvis and note that the calluses are not dilated at all.

It is merely the pelvis that is dilated.

This is act pelvis, of the transplant or also called lactase and not relevant obstruction.

So this would not in itself warrant further tests or referral to a urologist.

This is merely a variant of the normal as long as the callouses are not dilated.

Also worthwhile to remember that we are not permitted to diagnose obstruction with a full bladder.

So if this was seen with a full bladder then the next reasonable step would be to send the patient to the toilet and the repeat the transplant ultrasound.

Very often these signs would then disappear.

So do not diagnose anything that is connected to obstruction as long as the bladder is full.

Another variant of the norm in this case segmental dilatation of the calluses here.

The transplant in the left ILI fossa and what we can see is dilated callouses but not proper obstruction.

If we would have a look at another section of the transplant, there will be no visible calluses at all.

So this is just segmental dilatation of the callouses, again, a variant of the norm and does not necessarily warrant further investigations.

This is often seen in patients who have experienced recurrent urinary tract infections and scarring and does not necessarily imply any abnormal pathology.

Now moving on to proper obstruction and again, people's preferences as to the grading of obstruction, differs between countries and continents.

There's a grading for obstruction obtained from first from children's native kidneys, and also used in adult neph, nephrology and urology.

Some people would just say mild, moderate and severe obstruction, which I prefer because I think the grading sort of gives the illusion of a more precise classification than than we actually have.

Now in this picture you can see severely dilated pelvis of the transplant extending into the calluses.

And this is proper obstruction, at least moderate I would say.

And we can also see the ureter of this transplant dilated and in this case it was a stenosis of the transplant ureter close to where the transplant ureter enters the urinary bladder.

If you are not sure how bad the obstruction actually is, the best thing is to have a look at the transverse view where it usually becomes very clear the pylon, the renal pelvis dilated and extending into the calluses.

This is particularly helpful if you don't know whether the calluses are dilated, then the best thing is obtain a transverse view and that will often make things very clear.

Another variant of the norm, not necessarily abnormal, not necessarily should this prompt.

Further investigations is the visible transplant ureter as in this case transplant in the right ILI fossa transplant with parenchymal changes and here you have the visible transplant ureter but nothing else.

The renal pelvis not dilated. The callous is not dilated.

Again, that's not proper obstruction, that is a visible transplant ureter and that has uncertain significance.

It needs to be mentioned in the report but it should not in itself trigger further investigations.

This is something that we sometimes see in the early post-transplant period.

This is a dilated pelvis of the transplant with the pigtail catheter.

In situ of the pigtail is what the transplant surgeons tend to put inside to allow healing of the ureteric anastomosis and the pigtail catheter is usually seen as a double contour within the transplant pelvis.

Obviously the pigtail will be removed six or eight weeks after transplantation.

So if you see this a couple of months after transplantation, that will usually imply that someone forgot to take the pigtail catheter out.

We've spent the last couple of slides on obstruction and on variance of the norm regarding the transplant ureter and the transplant pelvis.

This is another finding that is commonly seen in transplants, a renal transplant in the transverse view, the renal transplant pelvis, but within the renal transplant pelvis we see a thickened urothelium of 2.4 millimeters.

This is often seen in recurrent or chronic urinary tract infection of the transplant.

However, we need to appreciate that this stool is a soft sign, meaning that there is no clearly defined upper limit of normal for the thickness of the transplant.

Urothelium another common finding in transplant ultrasound but the lympho seal here in a picture from Christoph Hamer's review article, the transplant in a longitudinal view next to the transplant, a large cystic structure echo free.

This is a typical lympho seal. How does a lympho seal occur?

The lymphocy is caused by transection of lymphatic vessels by the surgeon at the time of the transplant surgery.

This will then lead to accumulation of lymphatic fluid, indirect vicinity to the transplant.

If we switch on the color duplex, then the lymphocy may look even more frightening.

We can see the transplant artery and the transplant vein traversing the lymph seal.

This looks frightening and may cause unnecessary fear and some juniors will then try to mobilize the vascular surgeon or a transplant surgeon to intervene.

However, these junior doctors can usually be reassured.

It looks frightening but catastrophic bleed into the lympho seal is unheard of.

So although the transplant artery is in direct vicinity, to the lympho seal or transverses, the lympho seal bleeding is almost unheard of.

Another classical lympho seal the transplant in a longitudinal view next to it a cystic structure no interior, echoes.

That is another small lympho seal and again that would not need an intervention.

The only reason for intervention in a lymphocy will be if it's so large that it will compress the transplant ureter cause obstruction in that case, surgical intervention is usually necessary.

Cysts in the Transplant

Moving on to another common finding in transplant ultrasound, the cysts here I've brought you a 12 millimeter simple cyst with an renal transplant.

A clearly defined hairline wall and no interior echoes.

A simple cyst. It's worthwhile to spend a couple of minutes on the classification of renal cysts.

I reckon that most of you will be familiar with the Bosnia classification of renal cysts that I've brought here.

It's worthwhile to remember that the bo nut classification at its extremes has the class one cyst as I showed you just now a B nine simple cyst hairline thin wall, no scepter, no interior solid components.

At the other extreme of the spectrum, the class four bosniac lesion a clearly malignant cystic mass with soft tissue components.

These will need surgical exploration and a tissue diagnosis.

The classifications in between from two two f to three are somewhat more controversial and it's probably fair to say that even seasoned ultrasound practitioners may find it difficult to differentiate between a class two and a two F lesion.

Part of the controversy stems from the fact that this classification is actually not an ultrasound based classification.

It is in its very roots a CT based classification.

So it's not validated for ultrasound nor for that matter for transplant renal ultrasound.

Many people therefore prefer to speak of simple cysts, clearly suspicious cysts or mildly or moderately atypical renal cysts.

Instead of using the Bosnia classification.

If used in ultrasound reporting, one should probably say something like this is a simple cyst 12 millimeter equivalent to Bosnia class one to emphasize the fact that the Boston classification is not directly applicable in ultrasound, I've brought an example of one suspicious cyst, a transplant and the longitudinal view in the right Alec fossa at the upper pole of the transplant, a cystic structure with hairline thin scepter within.

But in addition to that, a solid structure within this cystic structure on high resolution ultrasound with a linear transducer that becomes even better visible.

We can clearly appreciate the scepter that we've seen before and the solid structure within the cystic component.

Further evaluation of this abnormal cyst and clearly suspicious cyst will also comprise power doppler ultrasound looking for increased vascular supply and in this case, I'm sure you will agree that this suggests increased vascular supply in the vicinity of the lesion.

Although reassuringly the solid components within do not have increased vascular supply and again, increased vascular supply is of course a very suspicious sign in renal cysts in this case.

Second imaging was requested in the form of an AM R scan where the lesion looks even more worrying with this solid component and an irregular wall.

Unfortunately this patient declined further surgery and further interventions.

As far as I know, the patient is still well, two or three years after this diagnosis was made.

So we can be reassured that this was probably not a renal cell carcinoma.

Obviously the decision for surgical intervention is not an easy one as it may lead to not only removal of the cyst but potentially loss of the transplant.

Color Duplex and Doppler Ultrasound of the Renal Transplant

Moving on to color, do duplex and doppler ultrasound of the renal transplant.

Let's first start with the renal resistive index.

The renal resistive index was devised by a man called poral according to this formula, also known as the poral index.

Not surprisingly, Celeo was double qualified as a medical doctor, as a radiologist and also as an electrical engineer and it's probably fair to say that he was one of the forefathers of today's doppler ultrasound.

If we, go away from the formula and just look at these wave forms then the easiest way to remember the resistive index is to say that the renal resistive index is a measure of the diastolic flow that is good and proper diastolic flow as in this wave form equals a normal renal resistive index.

In a transplant that would be between 0.6 and 0.8 Poor diastolic flow as in this wave form equals high resistive index.

As I said before, the upper limit of normal is probably 0.8 and a renal resistive index of 0.86 is clearly elevated.

What does that indicate?

It merely indicates that the transplant is acutely unwell.

It does not provide a tissue diagnosis.

This can be caused by acute rejection but also by acute urosepsis and urinary tract infection or acute renal failure of the transplant of any other cause.

In contrast, a renal resistive index between 0.6 and 0.8 broadly speaking indicates that the transplant is well.

So this is a good way to remember The renal resistive index.

High renal resistive index indicates poor diastolic flow due to parenchymal swelling due to the transplant having an acute problem.

Proper diastolic flow results in a normal resistive index between 0.6 and 0.8.

It's also important to remember that if the transplant renal reive index is very low as in below 0.6, this may indicate transplant renal artery stenosis and we'll come back to that later.

Another example of a very high renal resistive index in this case resulting in a renal resistive index of 0.9 and how to calculate the renal re resistive index.

I will show you that in the next couple of slides.

However, also worthwhile to remember that the renal resistive index is actually a marker of transplant and recipient outcome.

This was nicely shown in the very large study by my ex-colleague yada mahar, published in the New England Journal of Medicine 2003 showing that actually the renal resistive index is the strongest marker of outcome, meaning that the lower the renal resistive index the better the outcome.

High renal resistive indexes indicate a poor outcome for the transplant and the recipient where to measure the renal resistive index.

Actually, it's very important to become familiar with one's own ultrasound machine and the algorithm that the machine uses, but it's still very important to know where to measure.

And that is shown in this picture.

It's very important to measure the renal resistive index in the distal segmental artery.

Why is that? That is because the renal resistive index changes along the course of the arterial vascular tree.

Therefore, by convention the renal resistive index is measured in the distal segmental artery.

We don't want to measure in the main transplant renal artery.

We don't want to measure in within the parenchyma, no, we want to measure at the level of the distal segmental artery.

Also important is to do repeat measurements.

So a seasoned ultrasound practitioner will probably do three or four repeated, renal resistive indices at the same site.

Also important is to measure the renal resistive index at the upper pole of the transplant, the lower pole of the transplant and the middle pole of the transplant.

Why is that? Some patients may have several transplant renal arteries.

For example, a main transplant renal artery and an accessory upper or lower pool transplant renal artery.

In this case, the only way to pick up an abnormally low renal resistive index indicating stenosis of one of these multiple arteries is if you actually measure the renal resistive index at the upper pool, the middle pole and the lower pole.

Measuring the Iliac Vessels

Moving on to measuring the pelvic vessels.

Here you can see the transplant and below that in black and white, the IIC artery and if we use power doppler, that becomes very clear the IIC artery and the origin of the transplant artery.

What do we want to measure in the ILI artery?

We want to check the ILI artery behind the origin of the transplant artery.

The easiest way to do it is to place the transducer alongside the ILI artery and measure very close to where the ISLI artery, the external ISLI artery becomes femoral artery because that will surely be very much behind the origin of the transplant artery.

We expect to see aphasic normal signal as shown in this picture very commonly.

We also see a biphasic signal in elderly recipients or if there is atherosclerosis monophasic, signals are abnormal and also seen in atherosclerosis a dampened arterial signal in the arterial in the ILI artery.

A dampened and monophasic signal indicates stenosis of the ILI artery.

This is what referred to as the clamp stenosis.

The clamp stenosis is caused by the surgical clamp that the transplant surgeon applies to the ELI artery When the transplant surgery is performed, this is a predilection site for stenosis of the ELI artery hemodynamically.

The clamp stenosis behaves like a transplant renal artery and is equally important to pick up on transplant ultrasound.

Therefore it's imperative that we always check the IIC artery.

Arterial Anastomosis Variants

Moving on from the IIC artery to the arterial anastomosis, it's important to spend a bit of time on variants of the arterial anastomosis.

Now this is obviously a very, very delicate structure in theater.

There are several variants.

Most commonly the transplant arteries anastomosis to ole artery with a aortic patch that is in cric transplantation.

Also possible multiple arteries without a patch or on the right hand side multiple arteries with one patch originating on one patch.

Now for obvious reasons, live Don anastomosis is different.

Most donors are very reluctant to give away part of their abdominal aorta.

So the live don anastomosis has no patch.

If we look at that, on ultrasound, the ILI artery seen here, duplex ultrasound shows the origin of the transplant artery.

This is a very simple situation.

One transplant renal artery, probably with a aortic patch but normally we can't see the aortic patch.

So IC artery transplant artery originating in a 90 degree angle from the ILI artery and there's only one of them.

The simplest, situation that we can possibly encounter.

Along the cartoon that I've shown initially.

Another possible situation. Two transplant renal arteries.

Again this the ILI artery one transplant renal artery.

Second transplant renal artery probably because they're so close originating on the same patch but the patch again cannot be seen on ultrasound.

Very often the transplant renal artery can be visualized if the patient is slim even without duplex ultrasound As in this situation, the this is a transverse view, the ILI artery, and originating from the ILI artery, the transplant artery vis visible even without color duplex it is sometimes difficult to visualize the transplant artery, especially if the patient is a bit more obese.

Something that can help a great deal as power doppler as shown in this case is the power doppler as the great advantage that it's more sensitive to flow than the conventional duplex at the expense that it cannot show the direction of the flow.

So power doppler will only show one color, but is a lot more sensitive in picking up, the flow.

Very helpful in obese patients as seen in these pictures.

The ILI artery seen here and clearly defined the transplant artery originating from the ILI artery or on the other side.

ILI artery transplant artery originating here.

So to remember, whenever it's difficult to find the course of the transplant artery, especially in obese patients, power doppler may help transplant renal artery stenosis.

Transplant Renal Artery Stenosis

A few words on that, although as I said before that is advanced renal transplant ultrasound and needs a lot of experience transplant renal artery stenosis is an important course of hypertension in transplant patients and therefore it's worthwhile to check for transplant renal artery stenosis.

In almost every transplant patient there are mainly two forms.

One is early on due to swelling of the arterial anastomosis or if the, if there is preexistent stenosis that has been overlooked in c donation or overlooked.

On the MR scan in live donation there is the second variant of late transplant renal artery stenosis and that is largely due to atherosclerosis of the anastomosis.

The transplant renal artery stenosis can occur early on in life donation transplants.

That is basically because there is no aortic patch ultrasound Diagnosis of transplant regional renal artery stenosis needs a lot of experience as emphasized before the criteria for diagnosing transplant.

Renal artery stenosis remains somewhat controversial as reviewed nicely again by Christoph Hamer from Switzerland.

In his review in, 2007, most people would say that maximum velocities in a healthy transplant renal artery are up to 250 centimeters per second.

A proper transplant, renal artery stenosis most people would agree will need velocities around 400, 300, 400, 500 and above centimeter per second.

This is an example, the transplant renal artery and during the course of the transplant artery in area of LEA or also known the con as the confetti phenomenon.

If we interrogate with the doppler probe, we can see markedly increased velocities, in this case up to 440 centimeters per second.

That is a proper transplant.

Renal artery stenosis, there are formulas that help us to gorge the severity of transplant renal artery stenosis that unfortunately slightly beyond the scope, of this torque, but the formulas can give us an idea of the degree of transplant renal artery stenosis.

The formulas will need measurement of the veloc within the stenosis as well as beyond the stenosis or at the at the hilum of the renal transplant.

If you have those two velocities, you can calculate by a formula the estimated severity of the stenosis.

Another example, maximum velocity 426 centimeters per second.

That is clearly abnormal within the transplant renal artery.

Moving on to indirect signs, we've discussed the direct signs that is, to demonstrate increased velocity within the stenosis in the transplant renal artery stenosis.

Indirect signs, pertain to signs that can be obtained within the transplant beyond the stenosis and this is the classical sign called the tent sign.

Meaning due to a severe and hemodynamically relevant stenosis, there will be delayed, increase of the systolic velocity as seen here.

So whereas a normal flow signal will lead to a sharp increase of the systolic velocity in transplant renal artery stenosis, there is a delay in the increase in velocity and that is called a tent sign.

And I think you can, see that this signal broadly re resembles a time, a tent.

We can also measure the acceleration time.

That is the time from the beginning of the systole to the systolic maximum systolic velocity.

That is called the acceleration time that can be measured as well.

I've mentioned before that we need to check the ILI artery to detect clamp stenosis.

This is an example of a clamp stenosis, the transplant here, the ILI artery here and here the INE in a ILI artery stenosis, prior to the origin of the transplant artery, again hemodynamically that will behave like a transplant renal artery stenosis and it's just as important to pick up but more difficult.

Another, rare finding in, duplex, enterprises of the transplant.

Is this a thromboses pseudo aneurysm of the transplant artery.

So you can see the, thromboses pseudo aneurysm here without any flow on duplex measurement.

And this is the transplant renal artery.

This was a sequel of, surgical catastrophe with, bleeding and pseudo aneurysm of the transplant artery, which, fortunately went well and the aneurysm thrombosis by itself and could be seen years later on ultrasound.

As this thrombose pseudo aneurysm, sometimes the transplant renal artery is anastomosis to aorta or there are variance of the arterial anastomosis as shown in the first katoon.

In this example, this is an a transverse view of the abdominal aorta, the distal abdominal aorta and they're originating from the distal abdominal aorta.

The transplant renal artery with marked leasing and the confetti phenomenon and a markedly increased velocity in this transplant renal artery of 600 centimeters per second.

So this was a moderate transplant.

Renal artery stenosis in a transplant renal artery Andes osis to aorta that was not a pediatric patient.

This patient had received, his transplant after long history of retroperitoneal fibrosis and the transplant surgeons felt that, an arterial anastomosis to aorta was the only anastomosis that was technically feasible.

Another thing that helps if the an anatomy is not straightforward as in this case, before embarking on hours of duplex ultrasound to try and find the exact course and possibly the number of transplant arteries.

A good thing is to obtain the surgical notes first.

These will usually detail how the arterial anastomosis is done and equally important, how many transplant arteries there are.

And then after you've seen the surgical, no return to the patient and try to identify the arteries and the anastomosis as detailed in the surgical nos.

Also important is that an accessory transplant artery is easily overlooked.

This can be potentially very important as an accessory transplant artery may carry a stenosis just as the main transplant artery.

Therefore, if in doubt, and if you really want to make sure you've seen all transplant arteries and you've really excluded transplant renal artery stenosis, have a look at the surgical nodes and then go back to the patient if necessary.

The overlooked transplant, renal artery stenosis, transplant artery may have a stenosis as well and that's why it pays to spend a bit of time with the surgical notes.

Other Findings: AV Fistula and Vein Thrombosis

Another finding in transplant ultrasound, is this an AV fistula that usually occurs after a transplant biopsy.

What is it? It is essentially a shortcut between, a transplant artery and vein.

Usually the segmental artery and vein.

It is seen as a large area of leasing within the parenchyma.

These can be very large, up to several centimeters, become hemodynamically.

Significant proof of the fact that this is an AV fistula requires, measurement of the renal resistive index in the distal segmental artery that feeds the AV fistula.

And this will probably be the artery that feeds the AV fistula in this case, in that, artery that feeds the AV fistula.

The resistive index will be low or indeed very low because it is essentially a shortcut with a very high diastolic flow.

These, these arteries that feed the AV fistula may have renal resistive indices as low as 0.5, 0.4.

A very rare finding but important in the early post-transplant period.

Transplant vein thrombosis with a pendulum flow in the transplant.

This is a transplant surgical emergency that requires immediate intervention penal flow in the arterial system.

So this is the arterial system within the transplant.

Penal flow signaling, acute venous thrombosis of the transplant, a surgical emergency.

Standard for a Proper Renal Transplant Ultrasound

Now in the last slide, I would like to propose what a proper transplant renal ultrasound should comprise as detailed in the first part of the talk.

Measure the size, and the volume of the transplant.

Relate the volume of the transplant to the body weight of the recipient and say whether the volume of the transplant is appropriate or not.

In relation to the body weight of the recipient, measure the width of the parenchyma and comment on parenchymal changes, exclude obstruction.

Have a look at the bladder.

We've not covered it in this talk, but it's also important in transplant ultrasound to have a look at the urinary bladder to see whether, there is, for example prostate enlargement.

Have a look at the transplant ter and comment on these findings.

Check the surroundings of the renal transplant for lymphocy and for fluid in hematoma.

Again, something we've not covered in this talk measure the renal resistive index in the upper, middle and lower pole of the transplant each time, repeated measurements are necessary.

For example, three repeated measurements each at the upper, middle and lower pole.

Check the signal of the eyelid artery and beware of the cap stenosis.

Identify the origin of the transplant artery and try to exclude stenosis of the transplant artery.

And finally, check the entire transplant with duplex and look for a post biopsy AV fistula.

This is quite nice to know, especially if you plan another biopsy, then you will know whether the AV fistula has been pre-existent or has indeed been caused by your biopsy.

Conclusion and Acknowledgements

So this was the end of the talk.

I hope this was, interesting for the audience.

I have no con conflict of interest to disclose.

I have some acknowledgements to make.

First and foremost to Professor Gable and Hanover, my, ultrasound teacher.

I'm very indebted to this man for teaching me the basics of abdominal ultrasound and also to, his colleague Dr. Black, who's now in Standal in Germany.

I learned a lot about renal and transplant ultrasound from Dr.

Dr. Marcus hiss, consultant nephrologist at Heno for medical school.

I'm also indebted to my colleagues, and co-organizers of the p renal ultrasound course.

Dr. Schultz and Dr. Faring from Worcester.

And I'm also indebted, and oh, thanks to Toshiba Medical Systems, both in Germany and the UK for many years of excellent technical support.

Thank you very much for.