Renal Transplant - HD

Introduction

My name is Wei Chong.
I am at MD Anderson Cancer Center, Houston, Texas.
And I'm going to talk about renal transplants.

Renal Transplants

The one year survival rate for renal transplants is now 80%.
80% of transplants are from cadavers, and 20% are from living donors.
Transplants are placed extra peritoneal in the contralateral iliac fossa.
And this is a graphic showing how a left kidney is placed.
It's usually in the right iliac fossa, and in this particular case, the anastomosis is an ide, renal artery to the external iliac.
Here is an alternative way of anastomosis the renal artery.
Here it is going into the internal iliac artery, and the anastomosis is here, is going into the external iliac vein.

Sonographic Assessment of Renal Transplants

First point I want to make is that Al Dola ultrasound is the first line imaging modality for evaluation of renal transplants.
We use gray scale, first of all to look at renal parenchymal echogenicity.
We look at the collecting systems and ureters for hydro nephrosis to diagnose obstruction.
We look for pararenal fluid collections.
We look at, we use doppler to look for flow in the renal artery and the renal vein to look for obstruction.
Then we look for peripheral resistance in the renal artery bed as a marker of graft dysfunction.
And the metric we most commonly use as the resistive index or ri it's, I will refer to in the rest of my presentation.
And we use color and power doppler to assess renal perfusion.

Doppler Assessment of Renal Transplants

The resistive index or ri, is the main parameter for peripheral resistance.
We use the acceleration index and the acceleration at time obtained from the main segmental and accurate renal arteries.
We obtain angle corrected velocities from the main renal artery and iliac artery.
And if main renal vein stenosis is suspected, we obtain angle corrected velocities from the main renal vein.
And most, but not all of the problems related to vascular obstruction, occur at the anastomotic site.
So that's where you want to focus your attention.

Resistive Index

A couple of words about the resistive index.
The reive index is a measurement of peripheral resistance within the renal artery bed.
It is independent of angle correction and high resistance indicates renal dysfunction.
A normal reive index is less than 0.7, between 0.7 and 0.8. It's indeterminate and above 0.8. It's abnormal.
These are not hard and fast numbers.
This is a kind of soft categorization.
And it's particularly important to observe the trend in the resistive index on serial scans, rather than rely on a single measurement, IE you should see if the ris are rising on serial measurements or falling.
And the most severe form of per, elevated peripheral resistance is when the diastolic flow is reversed as on this image here where you have forward flow in sly, but reversal of flow in diastole, this indicates very high resistance, and it's a sign of severe abnormality.
The color doppler analog of this is what I call a red blue flashing.
Basically, you see the renal artery in red during systole and blue in diastole.
It flashes red, blue, red, blue power Doppler allows visualization of smaller arterial branches and parenchyma, and you can do a certain extent assess cortical perfusion.
Here you see a normal renal transplant, colored, with beautiful colorization with the power doppler, and you can see flow all the way to the edge of the cortex.

Complications of Renal Transplantation

This is a brief review of the complications of renal transplantation.
Vascular complications can be in the artery or the vein, and you can have false aneurysms and arterial venous fistula.
You can get ary obstruction, fluid collections, extrinsic compression.
So these categories and overlap to a certain extent.
So extrinsic compression can lead to arterial and venous obstruction.
There's an entity known as compartment syndrome, which I'm going to talk about a little bit.
And then there's renal parenchymal disease, which is a catchall phase for rejection and acute tubal necrosis and immunosuppressive drug toxicity.
And then finally, we'll talk briefly about transplant related malignancy.

Vascular Complications

So the vascular complications starting in the renal artery, you can get a stenosis in the renal artery that usually occurs at the anastomosis, and that presents on doppler as elevated velocities at the site of narrowing and tardis parvis wave forms distal to the point of stenosis.
A renal artery kink is a folding or twisting of the vascular pedicle due to malposition or lack of space.
So if the renal artery is a little bit torturous and the surgeon packs it into a kind of small space, it might kink.
And this is a form of compartment syndrome.
It usually presents immediately post-surgery and has the same sonographic signs.
In terms of doppler as RAS, it's easily correctable, so it's important for us to pick it up.
The renal artery can thromboses, the renal vein can be thromboses and also stenosis, and you can get AV fistula and false aneurysms.

Renal Artery Stenosis in Transplants

Renal artery stenosis in the transplants, it is less common with ca c cric allografts because a cuff of aorta is harvested during a cate vari, transplant, allowing larger caliber anastomosis.
Doppler ultrasound is essentially a kind of screening tool because it's highly sensitive for renal artery stenosis, but it tends to be less specific.
So if you have got a positive doppler ultrasound finding, then the patient will proceed to CTA or MRA.
So the doppler criteria that are out there are peak systolic velocity of greater than three meters per second renal artery to iliac artery, peak systolic velocity ratio of 1.8 to one greater than 1.8 to one, and tardis parvis waveform with an acceleration time of greater than 0.1 seconds.
There is some early data out there to indicate that contrast ultrasound may be as sensitive as doppler, but with higher specificity.
And we are probably gonna see a lot more of that in the years to come.
So here is an example of renal artery stenosis.
Here we have the doppler cursor at the anastomotic site, and we see a peak very high peak velocity of 7.7 meters per second, and a very turbulent waveform.
This is the same patient.
And now we have our doppler spectrum from the intrarenal arteries, and this is the classic tardis parvis waveform with a slow rising early systolic spectrum.
And this is another patient showing how the tardis pars waveform can change or improve after treatment.
So here's a patient with renal artery stenosis on the left.
This is the intrarenal artery wave form showing tardis parvis the same patient after successful angioplasty, and the tardis parvis has gone away.
You've got a nice sharp upstroke in early stoly.

Renal Vein Thrombosis

Renal vein thrombosis presents with the following signs.
The kidney may be enlarged.
You may get reversal of diastolic flow in the renal artery, and you may get absent or monophonic flow in the renal vein.
In the example I have here, you see the cursor and doppler cursor is on the renal artery, and you have reversal of flow in diastole very high peripheral resistance.
And the arrow here is pointing at the thrombo renal vein, which is this hypo coic structure over here with no, with clot.
Inside it.

Renal Vein Stenosis

Renal vein stenosis presents with elevated velocities, and in this case we see a stenosis at the renal vein IVC anastomosis, and we have a peak velocity here of 2.1 meters per second.
You may also see elevated ris within the renal artery caused by the outflow obstruction.
Here, there aren't any precise figures for renal vein stenosis as they are for a diagnosis of renal artery stenosis because it's a relatively rare entity, but it's something you want to look at if you have someone who has a very high ri, there with no visible cause.
And you see on K doppler an apparent focus of elevated velocity in the main renal vein at the point of anastomosis.
In fox in the transplant kidney may show up as filling defects on power doppler.
This is a case here of an infarction, which shows up as a wedge shape filling defect on this power doppler image.
Power doppler is more sensitive than color doppler for low flow states, but generally speaking, we are not that good at picking up infarct with our standard ultrasound techniques, although contrast may change that in the future.

False Aneurysms and AV Fistula

False aneurysms and AV fistula.
Now, I've put them together because they have some features in common, although they're quite separate entities in terms of eti of the flow dynamics.
First, they're most commonly secondary to transplant biopsy, although they can be a surgical complication.
You can get this multicolored or mosaic appearance where you have red, blue, green, yellow, a kind of red, blue, green, yellow blob in the area of the aneurysm of or av fistula.
This is caused by turbulence.
This is the color analog of spectral broadening.
And they may be di it may be difficult to differentiate a false aneurysm from an AV fistula if it they may be difficult to distinguish from each other if they are small.
So this is an example of a false aneurysm, and this is a particularly dangerous one because it is outside the kidney.
So here is the transplant kidney, and we see a cystic area on the gray scale outside the kidney.
And when we turn on the color doppler, this is the renal artery heading into the hilum.
And we see the classic yin yang wave form in filling the cystic area here.
And this is a ular aneurysm of the renal artery.
This one was a surgical complication, not post biopsy.
And this kind of aneurysm i i is more like this kind of postsurgical false aneurysm is more likely to rupture because it's unlike the false aneurysms that occur inside the kidney as a result of biopsy, there's no renal parenchyma to buffering.
This is a postrenal biopsy arterial arteriovenous fistula.
These are very common in that they occur in 10% of biopsies.
The doppler findings are focal high velocity, low resistance, and turbulent flow.
And you on color doppler, you may get the tissue reverberation artifact.
That's something that Dr. Klu mentioned during his talk.
Basically you get a false Doppler signal due to tissue motion from the adjacent turbulent flow.
So here you have the mosaic pattern, that multicolored area represents the A VF, and you get all this false color, which is the tissue reverberation artifact around the A VF.
And you may see arterial waveforms in the renal vein.
And in this case, we see a turbulent doppler spectrum.
No treatment is required if the patient is asymptomatic, but embolization may be necessary if there is hematuria or renal failure.
Here is another example of an arterial venous fistula.
And this patient here we have the Doppler spectrum on the renal artery, you can see very high velocities in the that renal artery branch, six meters per second, spectral broadening and very high flow during diastole.

Urinary Obstruction

Utary obstruction in a transplant has a multiple causes by its most commonly occurs in the distal ureter at the anastomotic site due to ischemia or fibrosis.
It can be caused by external compression from fluid collections or hematomas from kinking fungus balls, pape or calculi.
And there's an increase incidence of calculi in transplants.
Hydronephrosis is not always synonymous with obstruction because hydronephrosis due to reflux from a full bladder is commoner in transplants than in native kidneys because the UVJ valve doesn't exist to the extent that it does in a native kidney and ureter.
So hydronephrosis does not always imply obstruction.
One of the complications of retary obstruction at the anastomosis is that can it can lead to leak at the anastomosis and a oma.
So here we have a transplant kidney with hydronephrosis and a dilated ureter down to the level of the anastomosis where there is a stricture.
And here is the bladder here.

Causes of Elevated Resistive Indices

I'm just gonna briefly cover the causes of elevated reive indices or elevated peripheral resistance inside the transplant kidney.
You can put them in two broad categories.
There's parenchymal disease, which is rejection, a TN, immunosuppressive drug toxicity and pyelonephritis.
And the take home point here is that ultrasound cannot distinguish between these different, generally speaking between these entities.
Then there are the morphological causes, renal vein thrombosis, urinary obstruction, extrinsic compression due to hematoma or compartment syndrome.
And what ultrasound can do is it can distinguish a morphological cause from the parenchymal causes.

Renal Transplant Compartment Syndrome

Renal transplant com compartment syndrome is something that's not well recognized in many places.
But it is a recognized entity and it is defined as graft failure from extrinsic compression due to confined space at the transplant side.
Basically, the kidney is too big for the space that this transplant surgeon is trying to fit it into.
So he packs it in, and the kidney is under pressure and it usually presents immediately post op, and it is defined as pressure of greater than 20 millimeters of mercury on the transplant kidney.
The Doppler findings are variable.
It depends on which part of the kidney and the vessels is getting is being pressured the most.
So if the entire kidney is being globally pressed, you might get elevated Reive indies indices because of increased resistance to flow.
If the renal arteries being squeezed and kinked, you might get focal narrowing in the renal artery and elevated velocities, as I described bef earlier, you generally get reduced renal vein velocities.
So this is now becoming more and more well recognized.
And in fact, there's actually a society dedicated to this entity of abdominal compartment syndrome.
It's called the World Society of abdominal compartment syndrome.
And they actually have ambassadors to get go around the world and spread the gospel about a CS.
So I thought if I wasn't a radiologist, I might like to be an ambassador and go to a party and introduce myself as the ambassador for the World Abdominal Compartment Society.
They so it is a very well recognized entity, and they have a convention.
Next one is in gen in Belgium.
Okay, so how does it look?
Well, if the kidneys being compressed, you're gonna get elevated ris.
And but when you turn on the power doppler, you should look for something like this.
Here's a patient with RA 1.0 because the kidney's being squeezed.
And on power doppler, you can see that the p the the orange color does not extend all the way to the capsule, unlike in this patient here where the RI is normal.
And this is a sign usually that you are dealing with a situation of elevated peripheral resistance, and that prevents the color from the power doppler from going all the way to the edge.
And this is of course, an extreme case when the artery is completely occluded and you have no power doppler signal at all.
Here's another type of another variation of compression if you like.
This is a subcapsular hematoma compressing the kidney.
Here's your the transplant kidney here is kind of bode in a kind of arch like manner.
Here's the collecting system or collapse.
And it is in this it is caused by this lenticular fluid collection, which has a fluid fluid level.
It's actually a hematoma that has partly liquified.
And when we put the doppler on the renal artery, we see reversal of diastolic flow in the renal artery due to renal compression.
And this is called a page kidney.
Because the this is a subcapsular hematoma, it's pressing on the kidney and it is causing a high resistance to flow within the renal artery.

Renal Parenchymal Disease

Okay, so I'm gonna just briefly cover renal parenchymal disease.
Acute rejection, this manifests as a rapid rise in creatinine greater than 25% over 24 or 48 hours.
Decrease urine output and definitive diagnosis requires biopsy.
There are some features of on gray scale ultrasound, renal you might see features of renal edema.
The kidney may be big, you can get thickening of the collecting system, the thickening of the urothelium, and you get thinning of the renal sinus fat.
The pyramids may become more prominent and you may see increased or decreased cortical echogenicity.
The resistive index can go up, but remember that rejection can be present with normal ris.
So this is a patient during his rejection phase and after he had his treatment.
So in low, the kidney when it was being rej rejected, was much bigger.
This loss of the cortico modality differentiation, it's much more echogenic.
The urothelium is thickened, and this is how he looked after he had been given anti-rejection medication.
So this is a sign of renal edema.
This is the thickening of the wall of the renal pel of the renal pelvis.
Normally it's pencil thin.
Here you can see it's at least several millimeters.
And this is just a feature of the global edema that you're seeing in the kidney that extending into the collecting system.
Chronic rejection is defined as slow deterioration occurring over months or years.
And this is something we cannot diagnose generally on ultrasound.
And usually no morphological changes and resistive indices may be normal.
Acute tubulin necrosis is characterized when acute decrease in glomerular filtration rate, an increase in creatinine and anuria that is maintained for several days, followed by spontaneous recovery.
It occurs in the immediate post-transplant period.
It almost always occurs in ca transplants and is directly related to the length of graft ischemia period prior to the transplant.
It does not affect ultimate graft survival on ultrasound.
The kidney may appear normal or may demonstrate hyper coic renal cortex with elevated ris.
So this is an example of acute tubular necrosis.
And the only thing that we could see that was the abnormally elevated ri with reversal of flow in late diastole.
So the renal transplant patients get drugs to prevent rejection, but these immunosuppressive drugs themselves are nephrotoxic and they these drugs are now are the calcineurin inhibitors of which the most commonly used are cyclosporine and tacrolimus.
So although they have markedly improved allograft reject or survival by reducing rejection, they pro they have a nephrotoxic effect that appears as a art uropathy and a microangiopathy.
The nephrotoxic effect is occurs even when the serum concentration is within the therapeutic range.
And the nephrotoxicity may be acute, subacute, or chronic.
Acute and subacute are dose related while chronic nephrotoxicity occurs 60 days after the transplant and is not dose related.
On ultrasound, we see echogenic normal kidneys with elevated ris and the definitive diagnosis requires renal biopsy.

Peri-Transplant Fluid Collections

Peri transplant fluid collections can be classified as lymphocy, which is a leak of lymph oma hematoma or abscess.
So this is an example of a a perinephric fluid collection anterior to the transplant hematomas usually occur immediately after surgery or biopsy, and they look occur.
They look like hematomas ev everywhere.
Heterogeneous, partly solid, partly cystic masses.
Here we see a large perinephric hematoma anterior to the transplant.
Lymphic seals are the commonest fluid collection.
They occurred a different on a different timescale.
They classically happen four to six weeks after transplantation.
They may be asymptomatic or compress or obstruct the kidney and may contain debris or septations on ultrasound, they frequently recur after percutaneous aspiration and they may require surgery because of this recurrence.
Omas tend to occur in the early post-transplant period.
They're causes as I mentioned earlier, by a leak at the utary anastomosis, and they are associated with urinary obstruction.
They're usually transonic, but may they contain debris and they tend to grow because the as the urine continues to leak out, abscesses are infections of preexisting hematomas, lymphic seals or omas.
They usually contain internal echoes.
And the appearance of debris or gas in a preexisting echo free collection is suspicious for abscess.
So remember, your all these patients are immune suppressed, so they may not show classical signs of fever or pain, so you have to be on the watch out.
This is an example of renal abscess.
We see a hypo coic area.
We inside the low pole of this transplant kidney and it's got internal echoes and that this has no internal flow on doppler.
So it's not a mass.
And this is the MRI showing a lot of enhancement and internal septations.
And this turned out to be an abscess in the inferior report of the transplant kidney.

Transplant-Related Malignancy

I'm just gonna briefly mention transplant related malignancy.
It's all in your handout here, but patients who have transplants have a much high incidence of RCC six times high.
It's mainly in the native kidney.
They can also get transitional cell carcinomas and non-Hodgkin's and post-transplant lymphoproliferative disease, which is a B cell lymphoma associated with the Epstein VA virus.
This usually occurs outside the transplant.
They may get massive adenopathy and you may see hypo coic masses and they also get increased incidence of sarcoma, kaposi sarcoma and skin cancer.
This is an RCC appearing inside a native kidney.
The kidney itself is markedly echogenic and shrunken, but so the RCC stands out quite well.

Ultrasound Guidance for Renal Transplant Biopsy

I'm gonna spend just a minute talking about ultrasound guidance for renal transplant biopsy, which is something that most transplant centers offer to other nephrologists.
We tr try and biopsy the upper or the lower pole and we find a track where there's no bowel or major vessels in the needle path.
So this is the biopsy guide here.
These two dotted lines and the needle will traverse between them.
We use spring loaded automated biopsy needles and the trajectory should pass through the cortex like this and avoid the hilum.
So we tell them, avoid the white stuff in the middle of the kidney.
You have to explain that to the nephrologist.
The complication rate is low with reported graft loss rate of 0.4 to 1%.
This is how not to do a renal biopsy.
You can see that the nephrologist needle has gone right into the into the white area, which is what we tell them not to do.
And this is what you don't want to see.
And this you try not to hit the panic button when you see this kind of thing, but you can see an active extravasation from the lower pole.
And here some of the other things that will happen when your bio when you your biopsies bleed, you can get a perinephric hematoma here.
You can get rapid appearance of hydronephrosis.
That's always a bad sign due to clot inside the collecting system.
And you look in the bladder and there's huge clot inside the bladder.

Conclusion

In conclusion, doppler ultrasound is the first line imaging modality for evaluating renal transplants.
Doppler can diagnose renal artery and vein obstruction.
Elevated resistive in disease are non-specific and can be caused by parenchymal disease.
And morphological causes definitive diagnosis of renal transplant Disease requires biopsy, rejection can be present with normal resistive indices.
Thank you.