Abdominal Doppler: Protocols and Tips - SD

Introduction

I am Kathleen Carter, rn, RVT.
I'm a vascular sonographer.
I live and work in Norfolk, Virginia, affiliated
with Eastern Virginia Medical School.
And I'm gonna talk to you today about abdominal ultrasound,
specifically the aorta and mesenteric systems.
I'm gonna talk about the abdominal doppler protocols
and tips specifically about the abdominal aorta
and the mesenteric system.

Anatomy Review

A little review of anatomy, the celiac trunk comes off just
below the diaphragm, giving rise to the hepatic
and splenic and usually within one to two centimeters.
Below that is the takeoff of the superior mesenteric artery,
followed within another centimeter
or so by the renal arteries.
The inferior mesenteric artery is usually located just
above the iliac bifurcation, prior to the division
of the iliacs and the common iliacs.
Then, of course, divide into the external
and internal iliac arteries.

We're gonna talk about aneurysmal disease
that affects the abdominal aorta, aortic iliac,
occlusive disease, a little bit about dissection,
and then we'll go on and talk about the mesenteric vessels.

Aneurysmal Disease of the Abdominal Aorta

The adult abdominal aorta tapers normally tapers
as it traverses distally.
It is normally about two centimeters in diameter.
When ectasia is present, the diameter may range
between two and three centimeters.
So let's look at what this looks like.
A normal aorta has smooth walls.
You can see the takeoff there
of the superior mesenteric artery
and the abdominal aorta tapering as it traverses distally.
When ectatic aorta is present,
then you see you have irregular walls, some dilation
that is less than an aneurysmal dilation.
Irregular borders to the wall of the aorta.
Once dilations become greater than three centimeters,
and some literature says greater than three
and a half centimeters, that's usually considered
aneurysmal disease.
Once that now becomes greater than about five, five
and a half centimeters intervention is usually indicated
in the iliac arteries.
We usually look at a increase in the diameter of the artery
by one and a half times the normal diameter
to call that aneurysmal.
When the iliac arteries exceed three centimeters,
that's when intervention is usually indicated in that,
in the iliac arteries, it's very important
to measure these accurately, particularly since we're going
to be measuring
and following patients serially
for increase in size of any aneurysm.
So you need to be perpendicular to the vessel,
in both the transverse and longitudinal views.
And we're going to look in whatever,
we're gonna look in transverse, sagittal,
and perhaps coronal planes.

So this is a transverse view of fusiform aortic aneurysm.
We'll look and evaluate that measure carefully
and estimate the amount of thrombus
that might be present within the within the lumen.
The iliac arteries generally
are about 15 millimeters in size in men
and a little smaller in women.
And the externals are a little bit smaller than the common
iliacs when an iliac aneurysm is encountered.
And this is a very large iliac aneurysm,
almost four centimeters.
We need to measure that. Again, estimate the amount
of thrombus within that.
You can see there's a smaller lumen,
residual lumen in this very large iliac aneurysm,
and it's then evaluated both in transverse
and longitudinal views.
And you can see that this one actually extends down into the
bifurcation of the iliac internal iliac
and external iliac arteries.
When we encounter these, we need
to measure them again carefully with a perpendicular,
orthogonal plane so that we're sure
that we're measuring accurately.
Aneurysms are usually fusiform. They may be saccular.
It is good for us that the most of them are fusiform
because those are easier to measure accurately.
A true aneurysm involves all three layers
of the arterial wall.
Pseudo aneurysms or false aneurysms are usually caused
by injury or a hole in the arterial wall
with flow maintained into a hematoma
and do not involve all three layers of the arterial wall.

So here's an example in both in longitudinal
and transverse view of fusiform aneurysms.
You wanna make sure again, that you're truly perpendicular
as you're doing these measurements.
Saccular aneurysms produce a little bit more of a challenge
to figure out exactly where to measure.
It's usually an outpouching as seen here,
and may be easier seen in the long axis.
So we're gonna measure in both the longitudinal
and transverse views for accurate measurement,
and they should be somewhat similar.

Accurate Measurements and Aortic Angulation

Now, I talked about how important it is
to do accurate measurements,
and we know that maximum aneurysm diameter measured
by ultrasound and standard axial CT is not equal,
and that's due to aortic angulation.
Many times as people get older, the aortic neck
will angulate, particularly when people begin
to get a little bit shorter,
it almost becomes redundant.
So, a study was done at the institution where I
was working in Norfolk, Eastern Virginia Medical School,
and that study was published in the European Journal
of Vascular Surgery.
I'll give you that in a moment.
But the important thing is, is that we compared
the ultrasound measurements to
3D reconstruction CT scans in which a perpendicular line
could be mechanically dropped in and measured,
and then compared that to axial ct.
And in the presence of aortic angulation,
there was significant difference in the measurements,
and that's because the axial CT is doing a
transverse cut through to the body.
And when the aorta is angulated, you end up
with an oval measurement,
which is slightly larger on axial ct,
the orthogonal CT
or 3D reconstruction cts in which a true perpendicular line
was placed correct for that angulation.
As does ultrasound
and as sonographers, we can correct for that angulation
and perform these measurements perpendicular to blood flow.
And again, this was published in the European Journal
of Vascular Endovascular Surgery in 2004
with the main author of Richard Sprouse.
Good orthogonal measurements look like this.
You make that fusiform aneurysm as round
and large as you can,
and they should be fairly symmetrical,
and that's what a good measurement should look like.

Abdominal Aorta Spectral Doppler and Protocols

Let's talk about the abdominal aorta spectral doppler.
When we encounter the aorta proximal to the level
of the renal arteries, SMA
and Celiac in that region, you're going
to have more diastolic flow
because the aorta is feeding partially the
celiac artery, the renal arteries, which have a,
they're feeding a lower resistance vascular bed, such
as the kidneys, the liver, and the spleen.
So you're gonna get more diastolic flow once you are
below the level of the renal arteries.
The aorta is pretty much just feeding a high resistant
peripheral vascular bed
and has a much higher resistant flow pattern.

Aorta, iliac, duplex can localize disease.
We're gonna be doing direct assessment of the aorta
and iliac vessels and careful color.
Duplex ultrasound can determine a number of things for us.
We can decide if the disease is focal,
figure out the length of any focal disease,
or is it diffused throughout the entire arterial tree.
And this piece of information may impact whether
or not the patient gets surgical treatment,
endovascular treatment, or just medical therapy.
So we can determine the exact location of disease,
estimate the severity, determine the length of stenosis.
We may even be asked to measure the external diameter
of the vessels and the residual lumen,
and that may assist in sizing
of any appropriate endovascular devices such
as catheters and balloons.
We need to use high resolution duplex ultrasound
that has good spectral and color doppler.
We're gonna use a variety of transducers
that are based on the patient's body habitus.
Usually we keep these patients NPO for eight or 12 hours.
They usually do not need a bowel prep.

So the crux of the protocol is going to include examination
of the aorta iliac segments in transverse
and sagittal planes, the entire abdominal
aorta and the iliacs.
And the iliacs is usually best imaged in the long axis.
And I occlude a picture here of a 3D reconstruction ct just
so that you can see how tortuous these iliac arteries can be
in many of these patients.
And it is very difficult to maintain a 60 degree angle
around a lot of the bends that you're going to encounter.
So it becomes a bit of a challenge.
Color flow can really be helpful in these exams
because the iliacs are tortuous, they're deep.
You may have overlying bowel gas, so you may need
to use different approaches.
And the lateral decubitus approach can be very helpful
sometimes to change the approach
and lay the vessels out in a more opportune approach
for achieving that 60 under 60 degree angle
for spectral doppler.
Waveform collection need to recognize
that there are some limitations
and challenges to this exam, which would include patients
who are obese, poor patient cooperation,
and the ever present abdominal bowel gas,
we're gonna look at the aorta iliac,
or the aorta first in proximal mid and distal
and collect samples there.
And then the iliac, we'll look at the common iliac.
The external iliac, the hypogastric
or internal iliac in both transverse
and longitudinal views using imaging color flow and doppler.

Special attention can be paid when there are changes.
If you have your scale
and your PRF set correctly, the color flow can give you a clue to where there are
areas of increased velocity that you might need to investigate
sample at less than 60 degrees,
with your spectral doppler being parallel
to the vessel wall at proximal, mid
and distal in each segment of the artery
as you go all the way down to the groin.

When we evaluate the abdominal aorta here,
you can see this is the proximal aorta sample being taken
parallel to the wall, and you would do proximal, mid
and distal if there are any increases in size in the aorta
as you go down, obviously we're gonna measure those.
We wanna be as in this example
of the external iliac artery parallel
to flow at an opportune doppler angle
to get the optimum wave form.
When you do encounter a stenosis
as seen here in a common iliac artery, we want
to sample prior to the stenosis within the stenosis
and document the peak systolic velocity,
and then also document the post
stenotic turbulence that's present.

In order to call a 50% diameter reduction
that you might encounter across the course
of an iliac artery, you need
to have at least 100% increase in the peak systolic velocity
from the adjacent segment
and document the post stenotic turbulence.
There are some other criteria in the literature for,
for if you wanna break down anything between 50
and 99% stenosis.
And sometimes a
ratio greater than 4.1 is used
to suggest a greater than 75% diameter reduction
or a peak systolic velocity greater than 400
centimeters per second.
The severity of lesions distal
to a high grade stenosis may be underestimated, so
that may be a limitation of the exam as you go through.
So if you have a high grade stenosis
and then encounter further stenosis downstream,
those stenosis may be underestimated in their severity
because the head of pressure isn't going to be enough.
Another sort of
hampering of this exam is that in the a iliac segments,
you can have a very severe stenosis in the iliac
or even in a short segment occlusion.
And if it's really well compensated with collaterals
at rest, the a BI may be normal
and the common femoral artery being near normal,
and the only way you'd really uncover that is with exercise
or reactive hyperemia.
So that may be a limitation of
looking at this exam.

This is an example of when it is clear
that there is not good compensatory flow.
This is a common femoral distal, so severe iliac disease.
You can see that there's a very delayed rise to peak.
There's a lot of diastolic flow when you normally would see
no diastolic flow
and a dampened waveform where the peak velocity is.
A peak systolic velocity is only in the thirties.

Occasionally we will identify aortic occlusion.
When that is done, you want to see where the runoff is,
where the collaterals are coming out.
Document the occlusion
with spectral doppler and follow down.
Here you can see this is occluded all the way
to the terminal aorta
and no flow present within that segment by spectral doppler.

Aortic Dissections and Pseudoaneurysms

When we talk about dissections,
sometimes you can identify new dissections
or even old, more healed dissections.
You can see the intima here in both transverse
and longitudinal views is lifted away from the wall.
You may or may not get two channels of flow within this.
It just depends on whether
or not the dissection has begun to heal down or not.
But this should be documented in its length.
And if there are two channels of flow,
certainly should be documented
with spectral doppler in both areas.
The extent
of the aortic dissection should be determined.
These can spiral up
and dissect into the visceral vessels as well.
Here's other examples of where
plaque was present.
And there is di a short segment dissection
that is curling up in certain portions of the cardiac cycle,
and then laying down in certain
portions of the cardiac cycle.
And in transverse here, you can clearly see
where the aortic dissection is.
You wanna have your PRF
or your scale set so that if you do have any
cavitations into the wall of the aorta, as in this case
where you have a short dissection that became aneurysmal,
if there's a small amount of flow going into this
cavitation, then you wanna be able to pick that up.
And so make sure that the color scale is set appropriately.

You can have pseudo aneurysms,
and in this case, a multilobular pseudo aneurysm associated
with the aorta does not involve the layers of the wall
of the aorta, as you can see.
And that should be measured.
Color doppler
and spectral doppler can identify
where there's any flow within those pseudo aneurysms
also should be measured in size
and what the residual lumen is.
That is still patent.

Mesenteric Arteries

We're gonna go on now
and talk about the mesenteric arteries
that come off of the aorta.
We're gonna talk about the celiac.
The, we're gonna talk about the superior mesenteric
as well as the inferior mesenteric arteries.

Anatomy of Mesenteric Arteries

Again, the review of the anatomy, the celiac trunk
is the first branch off of the aorta
after the diaphragm followed within one to two centimeters
by the superior mesenteric artery.
And then the inferior mesenteric artery is located just
above the common iliac bifurcation.
The celiac axis is the first abdominal
branch off of the aorta.
It is about two to three centimeters in length
and gives rise to the splenic common hepatic
and left gastric branches.
This can be evaluated in either
longitudinal or transverse views.
You get that sort of y division there where the hepatic
and splenic form a seagull
or y approach, some people call it.
This again can be evaluated in either longitudinal,
transverse, whatever works out best to see the bifurcation
of those replaced.
Hepatic artery can
occur when the hepatic artery arises from the SMA instead
of the celiac, and that can happen about 40% of the time.
It is very rare for there to be a common trunk
of the SMA and the celiac.
So replaced right hepatic can occur about 17%
of the time, a common celiac
and SMA trunk about 1% of the time,
and a separate hepatic off
of the aorta about 1% of the time.
And here is the celiac artery seen in transverse.
So you see the aorta in transverse giving rise to that
two to three centimeter length of celiac artery,
and then the origins of the hepatic and splenic artery.

We normally think about atherosclerotic disease when we're
talking about the mesenteric vessels,
but this is just an incidence in which we encountered high
velocity turbulent flow within the celiac axis
as it took off from the aorta.
And in this particular case, it was not due to stenosis,
it was due to a dissection.
So just keep in mind that there are other things
besides atherosclerotic plaque
that can cause increased velocity in these vessels.
There was a study at Dartmouth that also suggested
that we wanna note the flow direction in hepatic artery.
And when the flow direction is reversed,
that is usually compatible with severe stenosis
or occlusion in the celiac artery.

And you can backtrack to identify that
the superior mesenteric artery
or originates a centimeter
or two distal to the origin of the celiac artery.
It most often takes off from the aorta at
a very sharp angle.
Almost zero degrees comes up
and then courses inferiorly parallel to the aorta
as it arborizes into many branches.
Color doppler can be very helpful
to identify the distal course of this and its branches.
The normal spectral wave form in the fasting patient is
fairly high resistant
and then postprandially when all the blood vessels in the
mesentery will dilate you get forward diastolic flow
throughout diastole.

The inferior mesenteric artery looks much like that of the
spectral wave form looks much like that
of the superior mesenteric artery.
It is the last major branch off of the abdominal aorta
before the iliac bifurcation.
It originates from the anterior aortic wall
and then curves to the left and inferiorly
and it serves as a source of collateral flow.
Some people have a difficult time identifying the IMA
and inability to identify.
It doesn't mean that it's occluded, it just means
that you were not able to identify it.
But with the practice, it's not
that difficult to identify.

Now these blood vessels are connected
through a rich collateral network through the arc
of Riolan, sometimes called the wandering
artery of Drummond.
And this is very helpful
because one vessel remaining
of the three can supply the entire small bowel.
So, it's very important to know
that these have such a rich collateral network
that's present Normal Doppler spectral
waveform analysis
of the celiac demonstrates forward flow throughout diastole
with spectral broadening expected due to the size
of the sample volume relative the size of the artery.
We expect peak systolic velocities normally
to be less than 200 centimeters per second
in the superior mesenteric artery.
We expect high resistant flow in the fasting state,
with a sharp systolic upstroke.
There may be a little bit of turbulence,
approximately becoming more laminar
or distally as it does that sharp turn off of the aorta.
We expect that normally peak systolic velocities will be
less than 275 centimeters per second,
and the end diastolic less than 45 centimeters per second.

Mesenteric Vascular Diseases

So the mesenteric vascular diseases that
are usually present,
we're not gonna talk much about acute mesenteric ischemia
'cause there's very little role
for the vascular laboratory are doppler
in the diagnosis of this disease.
We'll talk more about chronic mesenteric ischemia.
We may see ischemic colon disease, celiac axis syndrome
or mesenteric venous occlusion.

Acute Mesenteric Ischemia

Acute mesenteric ischemia is relatively rare.
It has a very high mortality.
It requires a very rapid aggressive diagnostic
and therapeutic approach before the bowel begins to die.
Problems that include problems associated
with this disease include delayed
or uncertain diagnosis that leads to death of the tissue,
accurate identification of where the lesions are
and usually intraop where decision making happens.
The etiology of acute mesenteric ischemia is usually
embolic or thrombotic, can be caused
by venous thrombosis.
Duplex has no real proven role in this.
It's not a reliable test in unrepped patients
with acute symptoms, and usually these people are diagnosed
with biplane angiography.
The clinical features associated
with acute mesenteric ischemia is
severe abdominal pain out of proportion.
They're usually elderly with a history comorbid
cardiac and peripheral vascular diseases.
They may have peritoneal signs and symptoms
and bloody diarrhea.

Chronic Mesenteric Ischemia

Atherosclerosis is about the main cause
of chronic mesenteric ischemia.
About 95% of chronic mesenteric ischemia is caused
by atherosclerosis, and it usually involves the ostial
portions of first one to two centimeters
of the major visceral vessels.
When we talk about the other 5%, that of things
that can cause mesenteric ischemia,
it can be arteritis radiation, the autoimmune disorders,
fibromuscular, intimal hyperplasia,
RQ ligament compression
or coarctation of the abdominal aorta, two
of the three mesenteric vessels.
Celiac, SMA and IMA must be abnormal for that patient
to be symptomatic if one is abnormal.
You have to really try hard to find that IMA
and look for any disease,
especially if the patient is symptomatic.
A single patent visceral artery is capable
of supplying the entire small bowel.
So if that occlusive disease develops slowly,
patients can be asymptomatic
with only one vessel really supplying it.
Remember though that if one vessel is diseased,
there may be elevated velocities throughout the remainder
of the vessels due to compensation.
So that piece of documenting peak systolic turbulence
or post steno turbulence to rule out
compensatory flow as the main cause
for increased velocity is very important.
All three vessels are usually involved when
there is disease present.
One of the three vessels may occlude
and that's usually the celiac axis.
If it does, the SMA is usually the one
that is most involved in narrowing significant narrowing.

Signs and symptoms of chronic mesenteric ischemia can include a gnawing and dull per umbilical
or epigastric pain.
It usually is occurring postprandially after meals
and may persist for one to four hours.
These patients develop a food aversion
because food is what is causing their pain.
They don't want to eat, they have significant weight loss
and may get cramps in the abdomen
that radiates to their back.
Many times they have an epigastric bruit.

The diagnosis can be made for this disease
with either duplex, ultrasound or angiography.
The typical patient presentation is a female in 40
to 70 years old, displaying postprandial pain, weight loss,
food fear, and usually these patients take a long time
to get worked up for diagnosis.
They're usually worked up for many months
for ulcer gallbladder problems, cancer
before the diagnosis is made of
of chronic mesenteric ischemia.

So here are some examples of celiac
and mesenteric stenosis where you can see that
the velocity is so high over 700 centimeters per second in
the celiac here.
That in its aliasing you can see a bruit associated
with it, particularly in the SMA
where the velocity is almost certainly over 500 centimeters per second.
And then in the hepatic distal to that celiac, you can see
that the wave form is abnormal.
It is bowed over. There's a delayed rise to peak
and it's certainly post stenotic.
Here is the splenic in that same patient
where you see the splenic artery again, is bowed over,
has a delayed systolic rise time
and has a transmitted bruit even still within
that splenic artery.

This example is a very high celiac artery flow,
but this was not due to celiac artery stenosis.
This was a patient who had an infrarenal aortic occlusion and critical SMA disease.
So the main runoff from the aorta was going out.
The celiac causing a very high amount of flow within
that stents.

So many times these patients are treated with stents,
and when we're looking at patients
after the stent is placed, we need
to walk the doppler throughout the course of the stent.
You may get higher velocities throughout the course
of the stent as long as there's no focal increase
that may just be due to the decreased compliance
of the vessel because of the stiff
stent that's placed in there.
But we would expect in a certain percentage
of the time that these stents may restenose.
So we wanna walk the doppler all the way
through them from the aorta all the way through to the end
of the course of the stent interpretation
of mesenteric disease.

The celiac velocity should be less than 200
centimeters per second.
If it's over 200 may and has post stenotic turbulence that's consistent
with significant celiac disease.
The SMA velocity should be less than 275
centimeters per second.
Again, greater than that may be consistent with
significant stenosis within that vessel.
And the IMA, there's no absolute number associated with
that, but it should be visualized with normal flow patterns
and any focal increase in velocity documented.
Are the distal wave forms dampened?
Is there post stenotic turbulence?
Is there a lot of collateral vessel development?
All of those that can be clues
to hemodynamically significance stenosis present.

Median Arcuate Ligament Compression Syndrome

Now this talk briefly about median arcuate
ligament compression syndrome.
Celiac artery velocities can be increased due
to extrinsic compression by the median arcuate ligament.
In that instance, the signals will normalize
and decrease in velocity when the patient is examined,
sitting, erect, or during a very deep breath.
So the SMA is almost never involved with this
syndrome and patients usually have a normal arterial
wall and aorta.
So we wanna evaluate these patients both in the supine
and sitting position.
And if you can normalize the waveform
and velocity, then it's not due to intraluminal problems,
it's due to extra luminal compression
by this median arcuate ligament.

Now interestingly, most patients
who have this are not symptomatic.
And about 50% of patients
that have this situation are completely asymptomatic,
which kind of indicates
that the symptom complex may not be due
to arterial stenosis.
Thank you very much.