Aorto-iliac Ultrasound - SD

Introduction

I am Kathleen Carter.
I'm from Virginia Beach, Virginia,
and I'm going to speak to you today about aorta iliac
ultrasound, including following placement
of aortic endograft and how to assess those.

Indications for Aorta Iliac Ultrasound

The reason that we perform aorta iliac ultrasounds is
usually to follow up aneurysmal disease
or to identify it, we're looking
for atherosclerotic disease and stenosis.
Sometimes physiologic testing will indicate
that there's inflow, aortic iliac disease,
and we wanna define that more precisely or to follow up
after open or endovascular repair.
Other indications would be claudication that interferes
with the patient's occupation
or lifestyle, usually one that would indicate
that there's inflow disease such
as the hip or the buttock area.
Abdominal bruery
or decreased femoral pulses may prompt an exam of this sort
or postoperative findings of after angioplasty
or stent to look at that and how that is faring.
It may be emboli in the ischemic digits
that prompt the exam
or again, follow up to any kind of revascularization.

Aortic Aneurysm

So let's begin with aortic aneurysm
and just quickly talk about that.
The incidence of aortic aneurysm in the general adult
population is about 60 per 1000,
and it is the 13th leading cause
of death in the United States.
15,000 patients die annually from ruptured aneurysms,
and there are more than 50,000 aneurysm repairs,
both surgical and endovascular annually.
This occurs more often in men than women.
It is mostly infrarenal, but can be senal
or of course thoracic.
It is usually defined as a focal dilatation of greater than
or equal to three centimeters.
Some literature says three
and a half in AP diameter in general,
if they're under four centimeters,
most centers will observe those.
Once they reach about five centimeters, they're a candidate
for elective repair, and once they get larger than five
centimeters, usually patients
that are candidates are offered surgical
or endovascular repair.
Of course, if there's rupture,
then they would require immediate attention and repair.
Aneurysms are usually in two forms, either fusiform
or sac fusiform.
Aneurysms are fairly easy to turn and,
and get into an orthogonal or perpendicular plane
and measure sac a little more difficult,
and sometimes it requires the plane of either the,
the sagittal or the transverse
to accurately measure those.
Here's normal aorta. You can see the walls are nice.
There's no ectasia associated with this as opposed
to this image in which there's aortic ectasia as well
as the dilation in the distal aorta.
The most common sites
for aneurysms are aortic femoral popliteal,
and those are bilateral about 50% of the time and iliacs.
And the most common complication associated
with the aneurysm is distal embolization and thrombus.
And again, these can be fusiform or sac,
but most of them are fusiform.

Iliac Aneurysm Case

Let's look at an iliac aneurysm case.
We often see iliac aneurysms associated
with aortic aneurysms.
This is a patient who had
an infrarenal abdominal aortic aneurysm on CT scan
with left common iliac artery involvement
and had an ultrasound
to confirm the hypogastric artery prior to embolization.
And this was to be done prior to an intervention.
So here's the iliac aneurysm.
You can see that a large portion of it is thrombo
and you can see the thrombus in it.
It's a very large aneurysm over three
and a half centimeters.
And in the sagittal view, you can see it extends all the way
to the level of the bifurcation.
So that is why they want to address this patent
hypogastric artery.
And we need to define the size, document the flow through
that so that we know post hypogastric coiling,
what will be going on with that.
So here's the documentation of the spectral waveform
of the hypogastric in preparation for that coiling.

Other Pathologies: Dissection, Stenosis, and Occlusion

In addition to aneurysms, we're looking
for dissection disease.
Here you can see the intimal wall of this aortic dissection.
Here's another example in transverse,
and then that same artery in the longitudinal view.
Here's an interesting aortic dissection.
You can see that this is curved up in this direction.
This patient had recently undergone
a renal intervention in which a catheter was approached in this direction.
There's a large mo of plaque here,
and when the catheter hit that plaque,
it was forced downward and lifted the tima.
And this was during certain portions
of the cardiac cycle waving and opening and closing.
It was not causing enough of a hemodynamic impact
to address it at that time.
We're going to also look for aortic stenosis.
We're gonna look for iliac stenosis, aortic occlusion
or iliac occlusions.
Here you can see an occlusion at the level
of the terminal aorta with collaterals coming off.
We are confirming with spectral doppler that
that was actually occluded
and as well as with color and B mode.
Now, iliacs, once they've been chronically occluded,
are very difficult to see.
They begin to blend in with the surrounding tissue,
and so you really need to use your vein as your landmark
to help you see it and find it.
And then you can put your spectral doppler in
where you see the sort of a retic artery
and confirm that there's no flow
when you suspect occlusion.

Role of the Vascular Laboratory

So now that we've talked about the types of disease
that we're going to be looking for, let's talk about how we
do that and what the role
of the vascular laboratory would be.
We're gonna determine whether
or not there's disease present, how severe is it precisely
where is it located?
And we may be able to assist in determining therapeutic
options for those patients with stenosis or disease.
The pre-intervention, we're gonna talk pre-intervention,
post-intervention, and then we're gonna talk
about aortic endograft.

Pre-Intervention Duplex Ultrasound

The pre-intervention duplex compliments the physical
assessment done by the physician on the patient, as well
as any physiologic testing
or angiograms done prior to the duplex ultrasound.
This is more specific localization
of the disease than the physiologic test,
and we can determine it primarily, is
that disease focal or diffuse?
Where is the exact location of disease?
How severe is it in terms of percent stenosis?
What's the length of the stenosis?
If there's going to be an endovascular intervention to this,
that might help them determine the size
and of the balloon
or the catheters that they're gonna use.
And if there's adequate visualization,
you can measure the external diameter and residual lumen,
and that may assist in determining
what appropriate endovascular device
to be used to address this problem.

Equipment and Technique

What do you need? You need high
resolution duplex ultrasound.
This is not a study that's probably best done with one
of the smaller laptop type systems
because you need really strong, good robust color
and spectral doppler deep in the abdomen.
You're going to use lower frequency transducers
and perhaps use several of the transducers may be a curved or a linear,
and you may have to go to a phased array
or an annular array based on the patient's body habitus.
We usually keep these patients,
NPO don't normally do a bowel prep for them.
So the technique would involve a thorough examination
of the entire aorta and iliac segments in both transverse
and sagittal planes.
However, the abdominal aorta
and the iliacs are usually best imaged in their long axis,
but transverse will help you identify the
course of those vessels.
Lower frequency pulse doppler transducers, high resolution,
always less than 60 degrees in the center stream
of the vessel to document the velocities.
Color flow is very helpful.
Iliacs are often very tortuous and deep,
and of course, we always have to deal
with overlying bowel and gas.
You may need to turn the patient, you may need
to use differing approaches to be able to
access each segment of the iliac arteries.
And we found that the lateral decubitus position is
really a helpful approach.
This picture is a 3D reconstruction of a one millimeter ct.
And you can see here
that this is quite an angulated aorta
and you can also see how tortuous these iliac arteries are.
And even though a standard axial CT would drop the plane this direction,
we're able to put a plane in these CT scans in a orthogonal or perpendicular approach.
And that's what we do with ultrasound to be able
to accurately measure the residual diameter here.

Limitations and Challenges

You need to recognize that there are some limitations
and challenges to this examination.
Obviously, obesity, poor cooperation,
and it's sometimes very difficult due to this tortuosity
to obtain adequate angles under 60 degrees.
So it requires some due diligence to do that,
we're gonna use imaging color flow and doppler
and use sample a spectral doppler throughout usually,
proximal, mid
and distal in the common iliac, proximal, mid
and distal in the external iliac, the origin of the internal
and then the femoral bifurcation.
You wanna be parallel to the wall
and you want to make sure that the Doppler cursor
is parallel to the wall.
And as you go through each segment,
and as I said, that is gonna take some manipulation
to be able to do that adequately at under 60 degrees
in tortuous vessels.
So we'll look at the aorta proximal, mid and distal,
and then the iliacs, including the hypogastric
or internal iliacs,
and using the image B mode, image, color flow
and doppler, we're gonna assess this thoroughly.
Spectral waveforms are collected throughout the
aorta iliac segments.
And then I normally would collect the runoff vessels
of common femoral SFA and PFA origins as well.
Special attention is then paid to color flow patterns
where you can see if there's elevated velocities
that suggest a stenosis.

Normal and Abnormal Waveforms

This is what we want to see.
This is a nice normal phasic high resistant iliac waveform
with a nice spectral window and return to forward flow.
After the reverse flow component, you can see
that this is parallel to flow nicely parallel
and an appropriate angle.
This is the kind of disease we want to document.
You can see there's a huge aortic common iliac brewery here that is causing all of
that color speckle within the area,
but this is from a severe common iliac stenosis.
We can see here
that this is over 500 centimeters per second,
certainly a hemodynamically significant stenosis
by anyone's criteria.
In order to determine that there's at least a 50% stenosis,
we have to have a doubling of velocity
plus post stenotic turbulence documented from.
So we would have a doubling of velocity from the segment
of the artery prior to the stenosis as compared
to the highest velocity within the stenosis.
And then we'd wanna document that post stenotic turbulence.
Here's another example
of a severe common iliac artery stenosis over
600 centimeters per second.
It's aing and the loss of the reverse flow component,
certainly a very s stenotic.
Here's an example of an external iliac stenosis.
So here's what I was talking about.
Here's the pre stenosis waveform.
It is monophasic, it doesn't have a diastolic component.
Then we get into the highest velocity
and then document the post stenotic turbulence
distal to the stenosis.
And you can see here
how color will help you place the doppler in the highest
velocity segment where that's aliasing.
Don't forget about B mode.
B mode can show you also where the plaque is
and you can sort of get an idea of
where you're gonna be putting your spectral doppler
to confirm whether
or not this is a hemodynamically significant lesion.

Diagnostic Criteria

This is an example of diagnostic criteria.
Some centers will use greater than
or less than 50% stenosis.
Others will break that down further into 50 to 75
and 75 to 99 based on these criteria.
Occlusions, of course, you have to identify,
confirm the absence of flow,
and normally we'll hear a pre occlusive thump just proximal
to the site of that occlusion,
and then confirm that it's occluded within the vessel segment that is occluded.

Case Study: 75-Year-Old Male with Bilateral Lower Extremity Claudication

So let's look at a case.
This is an aorta iliac case of a 75-year-old male
with bilateral lower extremity claudication.
He had calf pain at two to three blocks.
He had the other usual comorbids
and was a prior smoker.
The study was prompted by decreased femoral pulses
with absent distal pulses.
Although he had patent doppler signals at both the DP
and pt, he did undergo a physiologic study
that showed likely aorta iliac disease
and an aorta iliac duplex was ordered
to define the extent of this disease.
So let's just walk through what we would normally collect.
In a complete exam of this type.
We would look at the proximal aorta, the mid aorta,
and the distal aorta.
We would be looking for any aneurysmal dilatation
or as well as any stenosis.
While we are assessing this in both
transverse and longitudinally.
Then we look at the origins of both common iliac arteries,
and you can see that there's quite a bit
of difference in the waveform here.
This is a much more normal waveform on the left
where there is some reverse flow component as opposed
to this on the right where there it is a monophasic waveform
and there's no reverse flow component.
So we're gonna be keeping an eye out on that.
The right common iliac was patent throughout with about a hundred to 125 centimeters per second.
As we come down into the right common,
we see the bifurcation of the hypogastric or internal iliac
and then the proximal or proximal to mid external.
As we get just a little further out in the external iliac
artery, we see a step up in velocity
of almost 500 centimeters per second with additional
increase in velocity at the origin of the internal iliac artery.
Again, over 400 centimeters per second.
Here's a depiction of where that is by color flow.
You can see in the external iliac right where
that lesion is occurring.
And then distal to that,
we have the post stenotic turbulence
and decrease in amplitude and velocity,
and the wave form is quite disturbed which confirms
that that's a hemodynamically significant stenosis.
Finishing out that side of the exam is documentation
of the right common femoral artery
and the runoff vessels, PFA and SFA.
All of these vessels then are monophasic.
We then go to the left
and we again see the left common iliac artery origin,
and there is some step up in velocity there,
but it doesn't double from the previous segment,
and there's no real post stenotic turbulence
associated with that.
We continue on down the rest of the common iliac
and then get into the left internal iliac artery,
which similar to the right also has an elevated velocity
and continue down the rest of that segment as well.
When we got down to the level of the femoral, we noticed
that the left SFA is occluded
and confirmed that with the spectral doppler,
and here is a left profunda adjacent to that.
That's 251 centimeters per second.
Here's the PFA distal to the origin.
And so the question is, is this PFA stenotic
with this step up in velocity?
Well, the answer to that question is there's no post
stenotic turbulence here,
and this PFA is simply compensatory for the occluded SFA,
so it's not really stenotic.
The impression on a case like this would be hemodynamically
significant stenosis of the right proximal to mid external.
Remember, we had that very high velocity
with post stenotic turbulence, bilateral internal iliac
or hypogastric stenosis, bilateral patent,
common iliac arteries
and left iliac artery external iliac artery without any sign hemodynamically
significant stenosis, the occluded left SFA
with the compensatory profunda or deep femoral.

Summary of Pre-Intervention Aorta Iliac Duplex Ultrasound

In summary about pre-intervention aorta iliac duplex
ultrasound, it compliments the routine diagnostic workup.
It's good for selective use in pre-intervention assessment, and it may assist
and determine appropriate intervention, particularly
for endovascular interventions.
And it may be able to predict the success
of endovascular procedures, specifically
by looking at is the disease diffuse focal.
If it's really vastly diffused that he may not,
this patient may not be a candidate
for endovascular intervention.
We can also determine if more focused
or limited angiogram is appropriate rather than a
full diagnostic angio.
Many of these patients have other comorbid problems like
marginal kidney function, and it may be helpful not
to give them a full download.
We may be able to determine the suitability
of the endovascular repair versus an open surgical repair.
Just looking at the anatomic structure,
if it's focal versus diffuse disease
and what the hemodynamics are within the segments.
This role in patient selection
and procedural planning prior to intervention
can be accurate, cost saving and time saving,
but it does require high quality resolution equipment
and experienced examiners and interpreters.

Post-Intervention Assessment

We'll move on now
and go from the pre-intervention
to the post-intervention assessment.
This is done with selective use.
We're gonna use both imaging
and doppler data, just like we did in the pre
pre-intervention and look at that pre-op for comparison.
If there was a stent placed along the course
of this intervention, we're going to look very carefully at
that stent alignment in the relationship to the vessel wall.
The rationale for looking at patients in the
aorta iliac segments
after intervention is knowing that identification
and treatment of re-stenosis prior
to complete occlusion may improve long-term patency.
We know that stenosis are technically easier
to manage than occlusion, and that PTA
and stent procedures are associated
with a pretty significant re-stenosis rate,
and we wanna find those and intervene prior to losing
and having that segment go down.

Endovascular Interventions

Well, beginning first with endovascular interventions.
This is a standard aortic stent for stenosis.
This is not an aortic stent graft.
This is a simple stent structure,
like a stent anywhere.
And you can see the linear stent structure
within this aorta.
We're gonna walk the Doppler through this.
In this particular case, there was some flow defined outside
of this stent, and that would not be so unusual
because this is it can go through the interstices
of the metal of the stent.
What we wanna do is make sure
that there's no stenosis through the stent.
Look at the treatment length.
So we're gonna look at the inflow, the outflow,
and the entire treated segment of that.
This is an example of iliac stents.
Now these are bilateral kissing stents.
You can see in transverse here
that they are in the common iliac right up to the level
of the distal aorta.
And we're gonna look for good wall opposition
and make sure that these are symmetrical
and that they're fully deployed.
We're gonna get all the velocities that we need to get
through all that segment.
Usually if the patient has had a full aorta iliac,
and this is just a follow up to a post-procedure stent,
we would just do the terminal aorta
and then look at the whole segment of the iliac.
Since both iliacs were treated,
we would walk the doppler right on through the segment
of the treated portion or of the stented iliac
and confirm all of that
with spectral doppler in several areas.
Most stents in the United States are nitinol
and most stents in Europe currently today
are stainless steel.
And even though most stents are
nitinol that we see depending on
what the manufacturer is and
how those stents are put together,
they do image quite differently.
You can see that these two have a very different imaging
profile, but they're generally pretty easy to see.
And if you rotate your hand back
and forth, you can see where they begin and end.
'cause those end points are important.
You can see in this stent
that there's still a plaque burden.
This has crushed the plaque,
but not all the way to the wall of the artery.
So that leaves the end of this stent kind of hanging loose here and not quite all the way opposed
to the wall.
And that's something I'd want to note
and keep track of as we follow that patient.
Again, we're gonna be looking for opposition
to the wall of the artery.
And you can see here another segment
of plaque burden underneath this.
The plaque has been crushed as far
as it could crush towards the wall, and
but this is still a widely patent stent.
These have a higher level of or less of compliance, a higher stiffness level.
And so there's going to be gen in general.
We expect some higher velocities
through stented segments like this than we
get in native vessels.
And again, we're just really paying attention to this stent
and the opposition to the wall of the vessel.
Color is helpful to walk through there
and you can, again, just like in a native vessel, look
for any AAL listing or
places where you wanna place your spectral doppler.
So we're gonna assess the entire length of the stent
with Doppler, looking at the pre stented segment,
the origin, the proximal mid and distal portions,
and then the outflow portion of that as well.
Here's an example of a common iliac artery stent stenosis,
and you can see very easily where
that is narrowed within the lumen.
We document the elevated velocity associated with that.
This one happens to be over 500 centimeters per second,
and then document the post stenotic turbulence
and the decrease in velocity after the stenosis.
This is an example of a subintimal
angioplasty with stent.
This is where they tunnel underneath
and in between the intimal medial segment,
create a new lumen in occluded segments,
and then they may
or may not place a stent within that
to keep that segment open.
And we have to walk the doppler throughout
that stented segment just like we do with any stent.
Here's an evidence of a distal stent
where you can see the stent structure quite nicely up here,
and then some turbulence associated right at the distal stent
and then going out into the native vessel itself.

Case: Routine Graft Surveillance Leading to Iliac Stenosis Discovery

Here's a case example that's kind of interesting in looking
for iliac disease.
This is a routine graft surveillance
and for inguinal graft surveillance.
The patient had had the graft for many years
and came back in for follow up,
and we noticed that the velocities in the graft were in the
impending failure range.
The graft was pristinely clean all the way through.
There was no areas of stenosis.
These velocities had dropped
precipitously from the previous study.
So we knew based on the waveform morphology
of a delayed systolic rise time
that we had an inflow problem.
The outflow was wonderful, there was no problem with it,
so we just went up and followed
because this was at the anastomosis at the common femoral artery.
We went on up until we found the problem,
which was located in the very proximal portion
of the common iliac,
a very severe stenosis over 330 centimeters per second.
And this was then addressed.
You can see the lesion here on angiogram.
And this was addressed with a stent and
repaired his graft was fine afterwards.
And this was, since this was threatening his graft,
it was good that this was identified early
and repaired prior to him losing
that very nice vein graft.

Case: 70-Year-Old Male Aorta Iliac Stent Case

So here's an aorta iliac stent case.
70-year-old male referred for evaluation
of lower extremity arterial disease.
He had calf claudication
and ended up with bilateral common iliac
and external iliac PTA with stents.
So here's what we would see.
We've imaged and identified where the stent is.
This is the pre-sent, the origin of the stent,
and then walking through the stent, all of the doppler velocity profiles that we need to capture to make sure
that we thoroughly have assessed that stent.
Then there's another stent in the external iliac.
So here's the origin of that,
and then proximal stent, mid stent and distal stent.
And then the right hypogastric
or internal iliac is documented as well.
As we went further down,
there was some increase in the peak systolic velocity at the
proximal right external iliac artery
and internal iliac artery with turbulence.
But there wasn't a doubling of velocity
and there wasn't a lot of post stenotic turbulence.
So this was probably not hemodynamically significant.
As we went further down into the groin at the level
of the femoral bifurcation,
there was a large collection noted.
This was measured, it was doppler to make sure
that there was no flow within it.
And this was probably associated
with the original procedure at the time
of stent placement, not affecting any
of the hemodynamics of the vessels.
Moving on to the left side,
the left common iliac artery origin, mid stent,
distal stent, and then the distal vessel all
with relatively normal profiles.
There isn't much reversal of
diastolic flow,
but there's some as we go on down, we look at the
external iliac and then the external stented segment, the
mid external iliac artery
and mid to distal external iliac artery.
And we've lost the reverse flow component completely
by the time we get down that far.
And then right as we get down to the interface
with the common femoral artery,
we see this very tight lesion by color.
There's a lot of aliasing
and we see that the common femoral distal to
that has an elevated velocity of 264 centimeters per second
with post stenotic turbulence documented.
And here is where we see that the tightest portion,
the highest velocity collected within
that was 455 centimeters per second.
So this was a hemodynamically significant lesion.
We evaluated then on the runoff for that,
the common femoral, the SFA looking at the lesion.
Now, your report on this would be bilateral patent common
iliac and external iliac artery stents
with a hemodynamically significant stenosis
of the left distal external iliac artery,
right at the origin of the proximal common femoral artery.
An incidental finding of that groin complex where we measured it with no associated flow
and likely consistent with a hematoma.
And this patient underwent an endarterectomy
with vein patch angioplasty to address that lesion
that we saw that was so stenotic.

Summary of Duplex Assessment Following Peripheral Interventions

So duplex assessment following peripheral interventions.
We know that identification
and treatment of these re-stenosis may
improve long-term patency.
It's technically easier to manage a stenosis than wait
for it to occlude, and we know that there is a
significant stenosis rate associated with PTA and stent.
We're gonna use our imaging and doppler data.
We're gonna look at the pre-op or baseline comparison
and really pay close attention to the stent alignment
and relationship to the vessel walls.

Duplex Ultrasound Following Endovascular Aortic Stent Graft (EVAR)

We're gonna move on now from talking about endovascular
intervention with PTA and stent
and talk about duplex ultrasound following endovascular
aortic stent graft or EVAR.
This is a increasing frequency
of repair for aortic aneurysms in this country
and across the world.
And duplex ultrasound is a very good way
of following these patients.
There seems to be some recurrent, some resurgence
of interest in duplex due to frequent CT scans causing
an increased download
and nephrotoxicity problems as well as radiation dose.
So it's something that can be done.
It's a valuable, reliable tool
for postoperative surveillance of aortic endograft as long
as you use a proper protocol.
It is a much more complex
and detailed exam than standard aortic ultrasound for say,
following up an aneurysm.
And it is more sensitive to endoleak than in some cases than CT or even angiography
because it's real time and not
tied to any kind of timing of contrast
that has to be administered.
The advantages of an endograft placement over open repair is
that it's transluminal, small femoral incisions.
The patients have a shorter hospital stay,
there's less stress on the cardiopulmonary system,
and there's less risk of impotence for the men
because there's no per aortic dissection.
However, there's a huge trade off for these advantages,
and that is that patients need more frequent surveillance
and lifelong surveillance.
We don't know what the long-term efficacy is.
We know that there are different complications associated
with this procedure than with the open repair,
and we're gonna talk about that.
So in the surgical repair,
there's a large transabdominal incision.
Patients have to stay in the hospital for a good while
to recover from this very large surgery as opposed
to the endovascular repair where there is small femoral incisions made in cannulation
with a rather large introducer, which is taken up.
And then the device is deployed.
The contralateral femoral is also used
to deploy any extender cuffs
or extra limbs associated with these devices.
So there's a lot of patient acceptance for this.
The problem is they don't always hear that the follow up
that they're going to have to adhere to.
The complications we're gonna look at
with ultrasound are those that are associated
with any catheter based intervention, such as hematomas,
a pseudo aneurysm, animal flaps, animal dissections,
or AV fistulas.
But the main things we're gonna be looking
for is aneurysm enlargement, which is very important because
after all, putting the device in is supposed to prevent the patient from having an aneurysm enlargement
and hopefully have it shrink.
Endoleak is a common complication that's associated with all
of the devices that are currently available.
And then limb dysfunction
or thrombosis, we'll talk briefly about that.
You need to know which complications
to anticipate complications can occur early on in the course
of the patient's follow up
or anywhere along the course.
We've seen patients who had absolutely no complications
and no problems for eight or more years,
and then suddenly due to changes in morphology
or recurrence of aneurysmal disease or being placed on anticoagulation,
suddenly develop new complications many years out.
Be aware of the unique complications associated
with the different graft designs.
Different devices will have different complications
associated with them.
Our purpose of looking
with ultrasound at these endograft is really to monitor this aneurysm size and make sure it's not enlarging
because aneurysm contraction ultimately determines the
operative success of these.
And we know that we can follow the aneurysm size accurately
to follow these serially.
Endoleak is common with all of the devices,
and we'll talk quite a bit about that.
And then limb dysfunction is any anatomic
or hemodynamic impairment that's going
to threaten the function of that graft.
You need to know the surgical or
endovascular details
of this device placement prior to looking at it.
You need to know the type of device, whether it was modular,
whether it was single body construction,
if they did any concurrent procedures such as coiling
of the IMA or hypogastric
or any of the additional stenting,
any additional limbs that they had to put in.
And in some centers, they try
to measure the distance inferior to the renal artery to look
for migration of the device as well.
The device design comes in different configurations.
The bifurcated stent graft is the most common one
that you're going to see, although there are configurations
of a straight tube stent graft that doesn't have limbs.
And there's also not approved
for FDA use in this country in the us
but there are devices out there that have been put in
through trials of uni iliac stent graft
that requires occlusion of the contralateral iliac
and then a femoral femoral bypass to supply the contralateral limb.
These come in a supported unsupported modular
and single body construction configurations.
So they're they can be very different in the United States.
There are only four currently FDA approved for use.
That's the anex device, the Gore device,
the Cook Zenith device, and the Endologix device.
All of these have different configurations
and image quite differently.
Some of them are modular and some of them are not.
So you really need to know what you're looking at
and follow those appropriately.
The graph design is really important.
We're gonna use appropriate equipment, high definition,
high resolution at depths appropriate for the aorta.
This is not a study that again that you wanna do with one
of the smaller laptop type systems
because we need robust good color
and spectral doppler very deep in the aorta.
Many aortas are 15 to 20 centimeters down.
We're gonna use low frequency transducers.
We're gonna use the B mode color and spectral doppler,
and we may need to reposition the patient several times
during the course of the exam.
One tip I can give you is if you can push down on the
patient's abdomen to bring the aorta into about the 10
centimeter depth range,
you'll have much better imaging quality
and much better identification of endoleak.
We usually do these patients in the morning
so they don't swallow air all day
for the same reason we keep them fasting and no smoking
or gum chewing prior to the exam.
Ask them to have a light low fat supper
and not eat anything that would normally produce gas
for them the evening before.
Use the supine and decubitus views whatever view works for
that particular patient
and always look at it both in transverse
and sagittal planes.
The examiner should be very familiar
with visceral vessel anatomy,
particularly the IMA and iliacs.
They should be very comfortable scanning in the abdomen,
and I found that experience with a lot of renal studies,
renal vascular studies helps them in singing to this exam.
There's a longer learning curve than most studies.
And again, it's more complex than standard aneurysm
ultrasound, but this is a study the examiner really has
to wanna do and want to do completely
for this to be successful.

Aneurysm Size Measurement

The first thing I would say is that size matters.
We really need accurate B mode measurements,
and we can do that in either transverse
or longitudinal, preferably transverse.
In the center in which I worked in Norfolk, Virginia,
we looked at this and did a study that was published
and I'll give you that reference in a moment,
but what we found was we compared standard axial CT
to orthogonal CT and ultrasound,
and what we found is that axial CT is going
to overestimate the size of the aneurysm,
directly proportional to the angulation, the amount
of angulation in the neck of that aorta.
So here you see that
if we drop an orthogonal plane into this,
where we can truly be perpendicular to the aorta,
we're gonna get a smaller measurement than the axial CT is
gonna get being transverse to the patient's body.
There was no statistical difference
between orthogonal CT measurements and ultrasound.
So we know that sonographers and
can correct for angulation with their hand
by making the fusiform aneurysm round
and measuring appropriately.
And this is what I mean by that.
So you can see that this axial CT on that angulated neck of
that with an angulated neck, you can see that the
an the residual aneurysm is ovoid not round where
with an orthogonal cut, it is round just like an ultrasound
where we can correct for aortic angulation with our hand
by making it perpendicular
to the aorta, not to the patient's body.
Here's the reference I was talking to you about.
This was published in 2004 in the European Journal,
a vascular and endovascular surgery with the main author of Richard Sprouse.
Looking at all of this data,
this is a good orthogonal measurement.
This is what we want to see, a nice round residual aneurysm sec in which we can measure appropriately for
that follow up of those serial studies.

Endoleak Detection and Types

Endoleak is a very common complication
after EVAR, it's reported in up to 50%
of endovascular repairs in the two major trials, FDA trials
that were done in the United States, there was a 30% end
leak across all time points.
This is defined as flow outside the endograft,
but within the residual aneurysm sac
and exposes the aneurysm to continued hemodynamic stress
that would lead to potential expansion with the risk
of rupture, it's most commonly originating from residual
branch vessels type two like the lumbars and the IMA.
All of these references document that we can find,
endo can find endoleak in up to 50%
of patients following EVAR.
The protocol for looking for endoleak is to use B mode.
There are a lot of clues with B mode that can tell you where
to look for endoleak.
We're of course gonna use color flow within the graft
and within the residual aneurysm sac,
looking at all potential leak sites, so if any attachment
or fixation site or a modular connection sites
where the IMA would normally come in and looking for lumbars
and then that has to be confirmed with spectral doppler
because there can be some very convincing looking color flow that isn't truly a leak.
And you have to confirm that with spectral doppler.
If you're scanning and you see B mode clues
and you've got a real strong suspicion
that there's an endo leak
and you're not able to identify it really easily,
reposition the patient to a flank position,
re-scan in those suspected areas
and you may be more successful.
We're gonna look also in B mode for several things.
We're gonna look at the attachment site so you can see
where the device begins and ends.
Here's an inferior, you can see
that strut structure quite nicely.
We're also gonna look at the B mode appearance
of the residual aneurysm sac.
We know that normally thrombus is homogeneous and here you see this little hypoechoic area.
I would really strongly investigate that for a leak area.
If you ever see in an unsupported graft wall motion
during the cardiac cycle, that means
that there's more pressure out here
outside the graft in certain portions
of the cardiac cycle than within the graft.
And that's almost always associated
with an endoleak graft affirmation that looks like this
during certain portions of the cardiac cycle.
The other thing that we published about in 2005 was the
appearance of a spongy like texture
to this thrombus within the residual aneurysm sac.
This was usually associated in a small series of patients
with very pressurized sac
and very low flow endoleak that created aneurysm expansion
of up to a half a centimeter a year.
So it was significant aneurysm expansion associated
with this particular B mode characteristic.
So here are some examples of those spongy sacs
that were likely to lead to aneurysm expansion.
And you can see that they are very heterogeneous
and almost have this sort of thread of flow going
through wherever it can kind of seep in around
the thrombus.
And these were the ones
that did result in significant aneurysm expansion.
When we're looking with color, we want
to use real-time color flow that
will identify the source of the endo leak
and the flow direction.
Your PRF has got to be set very, very low.
Your wall filter's low, your gain set high
because sometimes the these are very low flow states so you really need to optimize your system for that.
Then you confirm the spectral waveform of that endoleak
and make sure it's not an artifact.
We do know that some of these very small leaks can cause
systemic pressure within the residual aneurysm sac
and we know that from direct pressure measurements at the
time of explanation from some of these patients.
We for the color sensitivity should be very high
and we're gonna image slowly from proximal
to distal from one attachment site to the other.
Optimizing for looking for endo leak
and looking at the thrombus
and making sure that that is a thrombo site, we need
to be aware of those potential sites of peri graph leak.
A true leak we'll have usually different arterial waveform
characteristics than that of what's in the graft
unless the graft is what the origin of the leak is.
This is an example of a biphasic graph flow in general.
Biphasic flow is associated with something
that has an inflow and an outflow.
Whereas the bidirectional flow as you see in
this picture is associated
with something more similar to the waveform characteristics
of a pseudo aneurysm where there's flow in in systole
and drags back out in diastole.
That's usually representative of a leak
that only has one source.
Occasionally we'll see two colors within the limbs like this
and you think, well these are supposed
to be going in the same direction.
Why are they in two colors? Well, frequently they will cross the limbs and you will see one of them more angulated
and in the transverse view like this, it's going to appear
that it's going in a different
direction when it's actually not.

Types of Endoleak

So let's talk about the different types of endoleak.
We have the anchoring system
or attachment site endo leaks, that's type one.
We have the inner segmental junction modular endo leaks.
That would be type three. The most common kind is
of course is the branch vessel
or type two coming from patent lumbars or IMA.
And then type four is trans graft
or through the porosity of the graft fabric.
Any of these can cause pressurization of the sac
and aneurysm expansion
and we don't know which ones will and which ones won't.
Here's examples of these different types of endoleak.
Here is a superior attachment endoleak.
Here is an IMA endoleak.
Here's a lumbar endo leak with that two frow flow.
This is an inferior attachment leak
and we need to look for all of these.
This is a type one or a distal attachment leak.
There was not a good seal due to calcific plaque at the distal common iliac.
And here you can see flow going towards the foot depicted
here in sort of a pink red color
and then back up towards the aneurysm sac adjacent
in this iliac artery.
In blue you can see retrograde flow
because this was originating from the graft itself,
it had the same wave form characteristics of the graft
and was biphasic.
This is that patient that had the superior attachment leak.
And if you look here, you can see
that not only was it leaking near at the superior attachment
and scooting up adjacent to the device,
but it actually was feeding the existing IMA in the correct
direction going out into the periphery there.
This is a type one endoleak from the inferior attachment.
Here you can see it on angiogram CT as well
as on duplex.
This is a typical type two endoleak.
Here is a whole nest of lumbars that were patent.
You can see it's causing a large endoleak in
between the two limbs of this graft.
And this is about a month later.
A 3D reconstruction CT was done depicting the same
type of endoleak.
No modality is gonna miss a very large IMA
leak such as this one.
This one is very easy to see.
You can see that it's causing some movement
of the graft wall right here.
This much more subtle smaller lumbar leak is the one
that is much more difficult to define and look for
and takes a bit of skill to do.
Here's another IMA that has sort
of bizarre flow pattern entering the aneurysm sac.
This is an example of the lumbar
where you see in both longitudinal transverse
and you can see that lumbar feeding the posterior portion of the sac as well
as the bidirectional flow confirmed on spectral doppler.
So we have all three views that we need to confirm that endo leak type three endoleak, this is a disconnect
of the modular interface here you can see in geographically
and it was causing this big huge leak on
you can see on the doppler here by the color.
Right where this was disconnected here.
Here's another type three endoleak seen on CT as well
as duplex ultrasound confirmed with spectral doppler.
This is a type four before and after a wall graft.
I don't think that we will ever be able
to tell the difference by ultrasound between type three
and type four, but you will know that it's there
and suspect that it's not something associated
with branch vessels.

Pitfalls in Endoleak Detection

The pitfalls in endoleak detection is
that there's a wide discrepancy in the rates of the endoleak that is detected.
Small leaks are often more difficult to define
and we know that leaks more difficult
to define in the supported endograft
and all of the available endograft in the United States
today that are on the market are supported.
So that makes it a little our job a little bit harder.
There are differences in device design
and construction that affect our ability
to detect endoleak
and that's due to wall oscillation and pressure transmission.
But we do know that small leaks can cause systemic
pressure within the aneurysm sac.
So all of them are important until proven otherwise.
There may be a role for ultrasound contrast,
although this is an off-label use.
We used it in our center to help us
to identify those patients in whom we thought
duplex said there was endoleak and CT was negative
and the ultrasound contrast confirmed those that were positive really for endoleak.

Limb Dysfunction

So let's leave endoleak for a moment
and talk just briefly about limb dysfunction.
Unsupported endograft are more at risk
for limb dysfunction
and even though there are no more of those on the market,
there's quite a few patients out there
with unsupported limbs from the an cure device.
We can effectively identify any problem that is going
to threaten the graft patency, twisting, kinking,
bending torches, I iliacs incomplete deployment occlusion
and aneurysm remodeling over time.
So here's an example of limb dysfunction early on.
Here is a stenosis. You can see a high velocity.
This was early in the our experience was re ballooned
and we have a nice normal phasic flow
when we talk about aneurysm remodeling.
When these aneurysms start to shrink, they shrink.
And sometimes this happened to be a uni iliac
graft and it became very redundant
and kinked on several occasions.
And you can see here angiographically how kinked that was.
And remember, if this is an aorta uni iliac,
it's supplying both limbs.
So this is a real problem.
But over time the morphology of
that residual aneurysm sac can change.
And if that graft becomes redundant,
then this has to be addressed.
This is what we don't wanna see.
This is a endo endograft occlusion in this limb.
And here's an example where you see that this limb,
the right limb is flattened occluded
and very different in appearance from the circular normal
left patent limb.

Advantages and Disadvantages of Duplex Ultrasound After EVAR

So the advantages of duplex ultrasound
after endovascular aortic repair is that it provides,
we can provide very accurate
residual diameter measurements of the aneurysm sac.
We can be very sensitive to endoleak detection,
identifying the source of it, the direction of flow.
We can evaluate limb dysfunction,
any other hemodynamic
impairment that might threaten the graft.
It's relatively inexpensive reproducible
and does not require any contrast.
And I believe there's an additive effect of CT
and ultrasound and follow-up of these patients.
The disadvantages is that it does take a time commitment.
It usually takes about an hour
or so to do these studies thoroughly.
It is a technically challenging study.
However, with proper training and desire, most labs or
facilities can do this well.
You do need high resolution
or the more expensive type of equipment
because you need something with very robust
spectral and color doppler.
But the hardest thing I think in the biggest disadvantage is
that making patients understand that they are committing
to lifelong follow-up
and compliance with that follow-up so
that we can identify any complications
that may occur over time.

Conclusion

Thank you.