The Aorta and its Branches - HD

Introduction

Hello, I'm Dr. Mary Frady from Brigham and Women's Hospital in Boston, Massachusetts.

Today, I'll be speaking to you on the aorta and its branches.

What we'll cover in the next 40 minutes or so are the aorta itself, the mesenteric vessels, including the celiac, SMA and inferior mesenteric artery.

A few cases involving the splenic artery and a little bit about renal artery evaluation.

At the end, when we talk about aorta and its branches, the pathology that can affect the aorta and the branches is stenosis, patency of indwelling stents, vascular occlusions, aneurysms of any of the vessels, again, defined as 1.5 times the normal diameter of the vessel and vascular malformations.

Abdominal Doppler Technique

It's good to start with a conversation about how we do abdominal doppler.

So for most studies in the abdomen, when we're looking at blood flow, NPO status is desirable.

We have to remember to optimize all three techniques, gray scale, color, and pulse techniques.

And usually this requires using lower frequency probes for the penetration that we need and for the best doppler evaluation.

So that brings you to probe choice, and as with every study in ultrasound, we always have to play penetration versus resolution against one another.

And for abdominal doppler work, we really need penetration and low frequency to get the good pulse doppler evaluation of the vessels.

Remember, whenever you're using doppler to assess velocities in vessels, angle correction is required and should be under 60 degrees.

The rate limiting step in abdominal doppler work is often patient body habitus and breath holding ability.

It's kind of easy to remember that the aorta and all of its branches all have normal peak systolic velocities between 80 and a hundred centimeters per second.

That's kind of an easy number to remember that 100 centimeters per second doesn't matter if you're talking about a renal artery or an inferior mesenteric artery, that's where you would expect the velocity to sit.

Most atherosclerotic disease in these branches occurs where the branches are or where the vessels are arising from the aorta.

And we'll look at those areas with gray scale.

After the gray scale evaluation on goes the color Doppler, and with color doppler, we're looking for focal areas of aliasing.

The aliasing giving us a sign that we have a high velocity area there.

Then the pulse doppler comes on a pulse doppler interrogation right at the area of color aliasing to look for a peak systolic velocity.

And then it's important to look at the vessel beyond the level of the stenosis and where we're using pulse doppler and waveform analysis.

So as we're doing this pulse doppler waveform analysis, what are we looking at?

Well, what we're looking for to define a hemodynamically significant lesion is the presence of a tardis parvis waveform.

Tus meaning late parvus meaning slow.

And when you see this wave form, it implies that there's distal ischemia beyond where you're measuring the tracing.

The tissue at that end, for example, in the kidney, needs more oxygen.

It's not getting enough blood flow.

So there's vasodilatation in that end organ, which will allow more flow to come into the structure during diastole.

But remember, we still have a focal stenosis and that causes less flow at peak systole.

So that brings us to a lower peak and a shorter or more sloped upstroke to get the flow out to the end organ.

This type of flow is typical of flow that we see through vascular collaterals anywhere in the body.

Again, back to terminology structures.

It's important to use the correct term for what you're describing when you see abnormalities in the aorta.

Remember that ectasia or an ectatic vessel is diffusely dilated tortuosity refers to the curve of a vessel.

An aneurysm is a focal dilation, which should be either over three centimeters or one and a half times larger than the proximal aorta.

Aneurysms can be fusiform so long and subtly or slowly increasing or sac a little round sac or bulge off the wall of the aorta.

And certainly a aortic dissection is another term that refers to a split of the media from the wall.

Aortic Aneurysms

Starting with aortic aneurysms, remember that most aneurysms are silent and they are non palpable.

We do have a little bit of a running joke in our department that whenever patients are sent down to evaluate palpable pulsatile abdominal masses, it usually means that the patient is quite slender and the clinician is feeling the normal abdominal aorta and the aortic aneurysms are not usually palpable and the patients are usually quite a bit larger.

The majority of patients with aortic aneurysms are male over 75%.

Again, most are asymptomatic and most aneurysms start to evolve between the ages of 60 and 70.

One of the biggest risk factors for the presence of an aortic aneurysm is smoking.

The big concern with an aortic aneurysm would be spontaneous rupture, and that rupture increases over a measurement of five centimeters.

If rupture occurs to an abdominal aortic aneurysm, the mortality rate outside of the hospital is 85 to 90%.

Because of that, the threshold for intervening or for repairing an aneurysm is five centimeters for men and five and a half centimeters for women.

Measuring Aortic Aneurysms

Well, that means it's important to measure your aneurysm correctly if you're going to talk about intervening in the aneurysm when it gets to a certain measurement.

So again, we're measuring aneurysms defined as anything over three centimeters.

Should you measure it in a sagittal plane or a transverse plane or a coronal view, it turns out you can use any of those three imaging planes.

But the measurement that we're most interested in is the anterior posterior measurement of the aneurysm.

That's the most reliable measurement because the posterior wall of the aorta bumps up against the lumbar spine.

And so you are held firm at that back wall.

And once you identify where the back wall is, you can then go directly across and get a true AP measurement and not be worried about being too oblique or too angled.

Aneurysms are measured outer to outer.

In other words, the wall of the aorta is included in the measurement of the aneurysm.

You are not simply measuring the lumen.

You should describe as best you can, the level of the aortic aneurysm.

And the most important thing in describing the level is the relationship of the aneurysm to the renal artery.

Is this aneurysm starting above the renal artery?

Is it at the level of the arteries or is it a completely infrarenal aneurysm?

Don't forget to look at the common iliacs because extension into the iliac arteries is quite common, and an aneurysm of the iliac artery would be defined as a measurement over 2.5 centimeters.

We will monitor aortic aneurysms for growth every six months.

In aneurysms that are over 4.5 centimeters, under four and a half, once a year is sufficient.

A true change is considered anything over five millimeters over the course of a year.

Examples of Aortic Aneurysms

Let's look at a few examples.

Here's a 70-year-old man who is a smoker, and we can see on transverse view of the aorta that you're including the wall on the measurement.

Here's the spine back here with some retroperitoneal adenopathy incidentally noted, and the measurement is up around 6.7 centimeters.

So clearly time for intervention on the sagittal image, we're able to pick up the hypoechoic or low level echoes in the anterior part of the aneurysm.

And color Doppler shows us that this is a partially thrombosed aneurysm with flow in the posterior aspect.

It's important when you measure aortic aneurysms that you try and get the aorta as round as possible.

So here is a transverse image.

Here's the spine here, and the measurement says the aorta is 3.0 centimeters across same patient shortly thereafter, oblique the probe just a little bit, and now we have a measurement of 5.7 centimeters in the transverse plane.

So which is it?

Well, you've gotta get the largest roundest image that you can and then measure anterior to posterior with the spine in the back.

And we can see that the true measurement of this aneurysm is 3.6 centimeters with, again, the area of partial thrombosis anteriorly and the patent lumen posteriorly, there's a different kind of an aneurysm.

This is the saccular aortic aneurysm seen on the sagittal image, a small rounded bubble coming out anteriorly off the surface of the aorta.

And with color doppler, we can see that this saccular aortic aneurysm is completely thrombosed.

Screening for Abdominal Aortic Aneurysms

Now screening for the presence of an abdominal aortic aneurysm has been mandated by the United States Congress.

What screening does is provide one study to look at for the presence of an abdominal aortic aneurysm in any male patient who has a history of smoking and who is between the ages of 65 and 70 years old.

The other qualifier besides smoking would be any patient over the age of 65 with a family history of an abdominal aortic aneurysm.

And both of those categories of patients are eligible for a one time screen of their abdominal aorta.

Well, has this been a good idea?

Did it help at all?

Has it reduced the death rate from aortic aneurysms in the United States?

And as a matter of fact, it turns out that one for every 200 or so screening aortic studies, a life is saved, so certainly well worth the investment of a single image.

Here's a patient who came in for just that such.

He was a smoker and he came in for screening.

And our abdominal ultrasound of the transverse of the aorta shows that we have a 7.0 centimeter abdominal aortic aneurysm in here.

It is seen sagittal with a little bit of patency in the back and a large thrombosed area in this patient who was completely asymptomatic.

Aortic Stent Grafts

So we're gonna now move into discussing a little bit about aortic stent grafts.

So an aortic stent graft is a method of treatment for aortic aneurysms, and the graft is placed inside the abdominal aorta and anchored at each end.

It starts above the level of the aneurysm and has two overlapping limbs which go down into the common iliac arteries and are anchored at the end of the common iliac arteries.

And this essentially bypass graft reduces pressure on the wall of the aortic aneurysm because now there is no flow going into the bulging part of the aneurysmal sac.

The stent graft is placed via groin access and it's less invasive than open abdominal aortic surgery.

However, there may be a higher complication rate and these stent grafts are being used with increasing frequency in the United States.

Now, over 60% of patients with aneurysms are being treated with stent grafts.

This is what the graft itself, or one example of what a graft can look like.

And this piece here is placed through the right common femoral artery and it includes this lumen that goes down the right common iliac, and then a short piece that will stick into the left common iliac.

And then the common piece which will sit in the distal aorta just above the level of the aneurysm hooked on with those little grabby things at the top.

This piece of the graft will come up the left common femoral artery and slide inside the sort of short segment of the left side here.

And then when this piece is expanded up here, you're left with a common lumen and then two separate lumens to head down each leg.

So again, we can do endovascular or open surgical repair of the aneurysms.

The perioperative mortality and the rate of immediate complications is lower with endovascular stent placement than it is with open surgical repair.

However, the long-term mortality is similar for both, and there is some concern that these endovascular repairs will have a higher risk of complications downstream 5% of patients versus one and a half percent at eight years.

Once the graft is placed, the patients are monitored for growth of the excluded sac because by definition this graft should take all the flow away from the aneurysm and there should be no pressure on that sac.

The aneurysm should completely thrombose and eventually even start to shrink.

So if the sac is enlarging, by definition there's been failure of the graft.

So we monitor these graft either with CT with contrast and then 3D reformatting, or you can use ultrasound as a reasonable alternative.

It's nice.

There's no radiation, there's no contrast.

And a lot of patients with aortic aneurysms have an issue with renal insufficiency.

The ultrasound is not as sensitive as CT with contrast, but it has very good specificity.

So just to sort of have a sense of what we're talking about, this is a 3D an ultrasound with 3D reformatting of a patient who has an indwelling stent graft.

So here's the outside of the aneurysm and here are the two limbs of the aneurysm here.

And you can see the limbs heading down into the iliacs on both sides.

And this is just a little bit of calcium because this patient was not given contrast.

And on the 3D reformatting image, you can see the lumen of the stent and then the bifurcation down each iliac.

And this sort of helps you understand why this portion of the aneurysm should not have any flow, should not continue to grow.

And if you measure the transverse diameter of this aneurysm, there's no way it should be growing if the stent is doing its job.

Endoleaks

So if the stent is not doing its job, if there are leaks from this graft, this is considered an endoleak.

It's not a leak into the rest of the body.

It's a leak within the aneurysm sac.

And if there's still blood flow or still increased pressure within the sac, the risk for rupture remains.

This is the major cause of graft failure and typically it's due to incomplete sealing of the graft against the aortic wall or the presence of persistent collaterals.

The types of endoleaks, type one and type three are both surgical emergencies.

One end of the graft is not sealing or the graft pieces did not overlap, or the graft has ruptured.

Type two endoleak indicates persistent flow through collateral vessels.

So what happens is the inferior mesenteric artery comes out of that abdominal aorta and you've cut off its blood supply and the lumbar arteries are coming out of the abdominal aorta and you've cut off their blood supply.

So sometimes those vessels create themselves a pathway and you'll get reverse flow in a lumbar artery tracking through the aortic aneurysm and then out the IMA or vice versa.

Reverse flow in the IMA tracking out a lumbar artery, two patent vessels are necessary, but they create a channel through the aneurysm, which again will put the patient at increased risk for rupture.

So how do we look at an aortic stent graft?

Well, a graft has very high velocity flow.

It's carrying the abdominal aorta, all the blood flow of the abdominal aorta.

But these endoleaks that we're looking for from a lumbar artery can be quite slow velocity because we've got reversed flow well downstream from the cardiac output.

So you have to make sure that you're not distracted by the high aortic velocity from looking for these slow flow structures in the aneurysmal sac.

So keep the graft itself out of the color blocks, use a low PRF or scale and check the gains go up, go down, try different gains to make sure that you're getting enough sensitivity but not being distracted by all the flow in the aorta.

On gray scale, you can look for motion in the aneurysm, which would suggest flowing blood.

And it's possible that in the future with the approval of ultrasound contrast that will help us make these diagnoses.

Examples of Stent Grafts and Endoleaks

Here's a 79-year-old patient with an elevated creatinine and a doozy of an aneurysm.

His AP measurement is somewhere around 6.7 centimeters.

And here's the stent graft in the middle of this large aneurysm, and you can see that there's a what looks to be a thrombosed residual aneurysm sac.

When we turn on color, we can see flow down the right limb towards the transducer away from the transducer.

Normal arterial flow down the right side, normal arterial flow down the left side, but on the transverse image we see the red color indicating flow in both of those limbs.

But look at this blue vessel running along horizontally behind the two limbs.

There shouldn't be any flow out there.

The flow should end right on the edge of the graft.

So investigating a little bit farther, we're able to see that there's a vessel in blue here that's got flow coming from anteriorly directed posteriorly.

What could be going on?

Keep following it.

And we can see that there's a little tiny high velocity vessel coming out the back of the aortic aneurysm.

So that's a lumbar artery.

And with pulse doppler, we can see that it's got two and fro flow there that probably is coming up here on the top left from this still patent IMA with reversed flow creating this two vessel channel.

A different patient 67-year-old in for surveillance of his indwelling stent graft.

Here's the two lumens of the stent, again, patent on the sagittal view, but look at these vessels up here.

There's vascular flow outside of the stent graft in the region of the excluded aneurysmal sac on the video clip here, you can see that there's flow coming in from the IMA and going across through the excluded sac.

And while we couldn't find the exit vessel, we know it has to be there.

If it was just a one-way flow in it would self thrombose sagittal.

We can see the IMA coming out anteriorly from the excluded aneurysmal sac.

Here's the pulsed waveform again, this two and fro flow showing that the IMA and presumably a lumbar artery are shooting blood in and out of the excluded aneurysmal sac.

Aortic Dissection

Moving on to aortic dissection.

Dissections of the aorta are different mechanisms than aortic aneurysms.

A aorta that dissects is not necessarily enlarged at all.

What happens in a dissection is that there's an intimal tear that often has continued down from the thoracic aorta, and when that tear happens, either a false lumen is created where flow gets into that false lumen and then comes back into the aorta, farther down the abdominal aorta.

Or once the tear occurs, hematoma, the flow ceases in underneath the tear and there's an intramural hematoma.

For a dissection to occur, cystic medial necrosis has to be present in the vessel, otherwise the intima will not tear.

The presence of an aortic dissection weakens the wall and these patients are prone to pseudoaneurysms.

It can be very hard with abdominal doppler and color or pulse to determine which is the true lumen and which is the false lumen.

And the most important thing, or a very important thing for us to figure out is which branches of the abdominal aorta are affected by the aortic dissection.

Here's a patient with an aortic dissection and we can see the sagittal view of the abdominal aorta and the dissected intima running right down the middle.

And with color doppler, we can see that one lumen has beautiful antegrade flow and then each of the lumbar arteries are being fed from that true lumen across the hematoma, which is now sitting intramural hematoma in the false lumen and on gray scale, you see this as this distinct flap or division right down the middle of the aorta.

This is a different patient whose this was found incidentally on an abdominal ultrasound for to evaluate the liver.

And you can see that there's a calcified structure running right down the middle of the abdominal aorta.

But when we get to the end, the lumen has recreated and the flap has disappeared.

We pulled up a prior ct and indeed it was there on the prior ct, although not appreciated at the time.

And with color doppler, we can see that we have flow on both sides of this small aortic dissection.

Mesenteric Vessels

Well, let's talk about some of the vessels of the abdominal aorta.

Mesenteric vessels can have acute ischemia occur, or there can be chronic ischemia related to the mesenteric vessels.

Acute mesenteric ischemia is a surgical emergency.

These patients will require angiography CT or MRI for diagnosis.

This patient should not be coming to the ultrasound division.

This patient should go directly to the operating room.

But chronic ischemia patients ultrasound is a very useful technique and we look at the celiac, the SMA and the IMA for evidence of mesenteric stenosis.

And we can also follow stents if patients have been treated with a stent placed.

So patients with chronic ischemia basically have insufficient flow to meet the needs of their gut after they eat.

They present with postprandial pain, bloating, weight loss, and diarrhea.

So the thing about the mesenteric system is that it has extensive collateral flow between the SMA and the IMA.

So just one vessel being stenotic will not create symptoms at least two vessels.

Two of the three vessels have to have greater than 70% stenosis before the patient will appreciate any symptoms.

Scanning Mesenteric Vessels

How do we scan mesenteric vessels?

Patient must be NPO for eight to 12 hours.

Remember, same as we said earlier, most of this disease occurs right at the ostia.

We'll use color doppler and look for color doppler aliasing angle, correct.

The pulse doppler use the same angle as you follow these patients over time.

And really the sagittal plane is the most useful because the sagittal plane is gonna allow you to see the angle of takeoff from the abdominal aorta.

The celiac system is a low resistance system.

It's low resistance because the liver gets constant forward flow, whether the patient has eaten or not.

The liver doesn't care if you're running a marathon or if you are sitting down to Thanksgiving dinner.

It wants constant forward flow, whether you're asleep or awake, always has flow contrary to that system.

The SMA and IMA are a high resistance system in a patient who is not eating, there is no diastolic flow sent to the gut.

You don't want a lot of flow sent to your gut.

If you're running a marathon, you want the flow to your gut after you eat.

So if we study these patients, fasting, fasting is fasting.

If you've been NPO in December and your NPO in May, that's the same NPO, it's not a big breakfast or a big lunch.

That way we can have inter exam continuity.

Normal velocities should be around a hundred for each of these vessels.

And we can diagnose a 70% stenosis when we have a velocity of over 200 in the celiac and over 275 centimeters per second in the SMA in the IMA, we can also look at the mesenteric aortic ratio.

If that comes out over 3.0, that's an indication of severe disease, even if the velocities are not elevated.

Examples of Mesenteric Stenosis

So here's a normal patient showing you what the normal abdominal aorta looks like with the celiac branching and the superior mesenteric artery branching.

The normal celiac tracing, again, has constant diastolic flow throughout the cycle and contrast that to the superior mesenteric artery that even has a little bit of reversed flow at the beginning of diastole and much less diastolic flow through the cycle.

Here's a 19-year-old patient who we were doing an abdominal doppler on for hypertension and we noticed that the origin of the celiac axis was very difficult to see on gray scale.

The celiac comes out here and branches into the hepatic and splenic arteries and this whole proximal portion of the celiac was abnormal.

With pulse doppler, we identified a velocity of almost 400 centimeters per second.

The corresponding MRA shows a very tight stenosis in the celiac artery of over 90% different patient 24 years old.

And her primary care, her a bruery in the midline of the abdomen, sent her into us for renal artery stenosis study renal arteries were pristine.

So we started looking around and we found an elevated velocity again in the at the origin of the celiac artery with a velocity of almost 240 centimeters per second.

And here's the corresponding CTA and we can see narrowing of the proximal celiac axis.

Another patient a much more disease, much more atherosclerotic aorta.

It's tortuous and the wall is irregular.

With atherosclerotic changes.

This patient, it's harder to see the anatomy, but at the origin of the celiac artery, we can see an extremely high velocity of 570 centimeters per second and a lot of turbulence in that area.

And the SMA also elevated at 310 centimeters per second, two vessels.

Diagnosis of chronic mesenteric ischemia.

Mesenteric Stents

Once stents are placed, there's not a lot of data about what velocities are normal In mesenteric stents, we know that we do know that an optimal cutoff to diagnose a 50% or greater stenosis in the SMA is 350 centimeters per second, and the best cutoff for the celiac stent is 270 centimeters per second.

Ratios are less helpful.

You have to be cautious making the diagnosis of a stenosis of a stent because ultrasound is not quite as strong once the stent has been placed.

Here's a 27-year-old with Takayasu's arteritis and there's a stent in the proximal superior mesenteric artery.

And you can see the stent on gray scale.

It looks a little bent there, but the velocity in the proximal SMA is about 300 and then it goes to, the aorta is 300.

The proximal origin of the stent is 450.

And as you go a little farther down into the stent, you get to 550 high velocities.

Lot of turbulence.

Pretty comfortable here saying there's enough narrowing in this stent to cause hemodynamic significance.

Median Arcuate Ligament Syndrome

A couple words about median arcuate ligament syndrome.

This is also sometimes called celiac artery compression syndrome.

Now this ligament, the median arcuate ligament is actually a fibrous arch and it's made up of the diaphragmatic crura on either side of the aortic hiatus and it's typically superior to the origin of the celiac artery.

If the celiac artery comes off high or the ligament inserts low, it's possible that the celiac is compressed when the patient expires or breathes out.

Now up to 24% of asymptomatic patients on CT scan, you can see this.

So the question is, or the issue is you have to only be looking for this in symptomatic patients because asymptomatic patients will have this finding 24% of the time.

There is some debate about whether this is a true syndrome.

So here's a 45-year-old patient with abdominal pain who was stented for high velocities on an expiration through the celiac axis with this median arcuate ligament.

And you can see once the stent is in there that we have low velocity, non turbulent flow through the celiac axis, and a velocity of about 250 and 240 with inspiration and expiration.

So presumably we have helped this patient who was symptomatic.

Splenic Artery Aneurysms

Let's move to the splenic artery.

So really the only thing to talk about with the splenic artery is the splenic artery aneurysm.

Interestingly, you don't think about it much, but it is the most common visceral artery aneurysm that occurs.

It's usually an incidental finding.

20% of the time these aneurysms are multiple and they're most commonly found in multiparous women, but they're also found in somewhere between seven and 20% of patients with portal hypertension, which I put a little exclamation point on there because I haven't seen them that commonly in this patient group.

And we do see a lot of portal hypertension, but it is, it can be a very hard vessel to follow.

So we probably they're probably out there and we haven't been finding them.

Patients with splenic artery aneurysms are an increased risk of rupture during pregnancy.

And when that happens, the maternal mortality is over 50% and the fetal mortality approaches 90%.

Here's a patient who came in for an abdominal ultrasound and this was an incidentally identified splenic artery aneurysm.

This is a view of the spleen and in the hilum of the spleen, we see this well-rounded structure that sort of tucks underneath the curve of the splenic vein.

And with color doppler is clearly a vascular structure.

Patient went on to have a CT and you can see this discreet, moderate sized aneurysm in the splenic artery, but she actually had three aneurysms along the course of the splenic artery.

Here's the post-op image and there's a small aneurysm here and a much larger aneurysm in the mid portion of the artery, which is what we were seeing on the ultrasound.

And on the ct.

Here's a different patient who came in, she's 36 weeks pregnant, she came into the labor floor complaining of nausea and some vague abdominal pain, sort of left-sided.

So she was sent down to have us do a biophysical profile and see if we could figure out why she was having this sort of vague left-sided abdominal pain.

So we can see the fetus is alive and we've got a great heartbeat.

And in the right lower quadrant we've got some dilated fluid filled loops of bowel.

And in the right upper quadrant there's some free fluid in Morrison's pouch.

So now I'm thinking, hmm, pregnant 36 weeks, abdominal pain vague.

Could she have ruptured her uterus?

Could she have a small rupture?

Could she be bleeding from her placenta?

Is she abrupting?

So here's a transverse image of the lateral aspect of the uterus.

Just look at the placenta and it's beautiful.

There's no evidence of an abruption.

It had beautiful blood flow, but I was able to spot again, a little bit of free fluid down here, some bowel.

And then this hypoechoic homogeneous material along the anterior aspect of the peritoneal surface went over to the left side.

Here's the fetus.

Amniotic fluid plus uterine wall collapsed bowel.

And again this homogeneous mid-level echoes material under the peritoneal surface anteriorly.

Well, I was scratching my head, I didn't know what it was.

The patient was not comfortable, she just was not feeling good.

I sent her back up to the labor floor called the obstetrician, said, come down and look at this.

Something is wrong in here.

Something is going on on the inside of her anterior abdominal wall when I don't know what it is, but this is not a good thing.

Could it be tumor?

Could it be peritoneal carcinomatosis?

Something is wrong in there.

Be prepared.

I don't know what you're gonna find.

Obstetrician said, thank you very much.

Got on the elevator back up to the labor floor.

She was paged while she was on the elevator that the patient the fetal heart rate had dropped.

They did a stat C-section, they got in there, opened her up, her abdomen was completely full of blood.

They got the baby out, but they could not figure out where she was bleeding from.

So they called general surgery, came running over, put their finger on the splenic artery and this patient had ruptured her splenic artery aneurysm.

She had probably been leaking for the six hours of nausea and vague discomfort and finally let go, luckily on the labor floor and mom and baby did fine.

Renal Artery Evaluation

All right, we're gonna finish up with the renal artery.

So only a small number of patients with hypertension actually have renal artery stenosis as the cause.

Typically, these patients will present with abrupt onset of severe uncontrollable hypertension.

Remember that ultrasound for renal artery stenosis is a screening exam.

It is basically a division point where if you can do the renal artery stenosis ultrasound and show that everything is fine, the patient will not go on to further imaging.

But if there's anything suspicious on the renal artery ultrasound, they'll go on to have an MRA for a more definitive diagnosis.

We're looking on ultrasound for a hemodynamically significant stenosis.

In other words, a stenosis of greater than 60%.

We measure aortic velocity at the level of the superior mesenteric artery.

And then we measure the peak systolic velocity in the both renal arteries at the origin proximal mid and distal portions.

Normal velocity in the renal artery is under 1.8 centimeters a second, and normal renal aortic ratio is under 3.5.

Renal Artery Stenosis Technique

So here we are in a patient for a renal artery stenosis study measuring the velocity in the aorta and remember you're measuring a velocity, you must angle correct and keep the angle under 60.

Then we'll head out to look at the renal arteries.

Now most patients, you will not see this beautiful left renal artery and right renal artery.

This patient has retroperitoneal fibrosis outlining the arteries for us.

So that makes it incredibly easy.

Most patients will not have that.

Most patients will not be as beautiful as this where you see the right renal artery and the left renal artery filling in, in the what's termed the banana peel shot coming in coronal.

And most patients, they're gonna look like this.

It's a little tiny vessel coming off a small aorta and you've gotta find it with the right angle.

You've got to angle correct and then you can measure your peak systolic velocity.

Again, looking for a brisk upstroke and kidneys like liver get constant forward flow.

The kidneys have to work whether you're running a marathon or whether you're sound asleep, to measure renal artery stenosis.

If there's a peak systolic velocity that's elevated over 1.8, but the renal aortic ratio is under 3.5, there's stenosis, but it has not reached hemodynamic significance.

You need to have both an elevated velocity and an elevated renal aortic ratio to make the point of hemodynamic significance of over 60%.

Examples of Renal Artery Findings

Here's a patient with a high grade stenosis in the left renal artery, we can see spleen and then left kidney.

And this is a piece of the left renal artery coming off the abdominal aorta.

You can see that aliasing on color doppler and that gives you the clue of where to put your pulse Doppler.

Pulse doppler is on it right here and we see a high velocity of 400 centimeters per second markedly elevated consistent with a high grade stenosis.

Ancillary findings for renal artery stenosis would be a small renal size.

A kidney that has had longstanding renal artery stenosis and has not gotten enough blood will eventually start to shrink.

We can look for the TARDIS parvus, that slow and late delayed up stroke wave form in the kidney that's not getting enough blood.

And interestingly, remember that the resistive index drops in renal artery stenosis and if it's over 5% different or lower from the opposite side, that suggests that there may be true renal artery stenosis.

An elevated RI suggests that there's end stage medical renal disease and treatment of the stenosis is unlikely to reverse the hypertension according to one author.

Some do not feel that that is true.

So here's an example of a patient where we're looking at an intrarenal doppler on the right kidney in the upper pole.

And we can see we have an RI of 0.7, which is normal.

There's a brisk upstroke and a reasonable amount of diastolic flow.

Again, we're measuring the ri, it is systole minus diastole divided by systole.

If you look at the left kidney, we can see that the intrarenal wave form is slow, doesn't have that straight upstroke that we like and it's late.

It takes a long time to get to its peak and it's low.

So the peak systolic velocity is down compared to the normal right side and the ratio of diastolic flow is up compared to the systolic flow.

This is almost 50%.

This is maybe 30 or even a little bit less.

So that will cause a decrease in s and an increase in D will cause the RI to go down in renal artery stenosis.

Once the renal artery stenosis is found, sometimes we'll get patients who've had stents placed.

So here's a transverse view of the abdominal aorta and here's the right renal artery stent and we can see that it has normal blood flow in it coming out of the aorta and heading down towards the right kidney with a beautiful upstroke and a great velocity of 1.24.

Here's the left, here's the aorta with the left renal artery stent here and then the normal directed flow down towards the left kidney.

And I find that these stents are best seen with gray scale, not with color doppler.

The issues with renal artery stenosis are that it's time consuming.

It requires a high skill level on the part of the sonographer or sonologist bowel gas can get in the way particularly to try and find the origins.

Patients who are unable to breath hold are gonna be extremely difficult to get good flow through those kidneys.

Accessory renal arteries are gonna be a bugaboo for everybody and the most important thing is it's unclear which patients will benefit from the diagnosis and treatment of a renal artery stenosis.

Here's a patient who came in and we saw, here's the abdominal aorta and we saw this beautiful right renal artery, the whole right renal artery origin, proximal mid.

Look at the turns, we can do all those measurements and we're thinking, aren't we great?

We've got all the velocities.

But then when you look, sadly you realize that the patient actually has two renal arteries and you gotta go back and do this for the other artery as well.

A 38-year-old patient who came in for a renal artery stenosis study and we noticed that in the upper pole of the right kidney are multiple koic tubular structures.

And then on transverse we can see an enormous dilated renal vein.

With color doppler.

We can see that these are all vascular structures in the upper pole of the kidney.

And again, vascular structures with an enormous renal vein and an enormous renal artery.

Put pulse doppler on and we can see that it's a high velocity, incredibly turbulent structure.

And the CT on this patient shows this multiple tubular structures, big renal artery, immense draining renal vein in this AV malformation which was successfully coiled.

A little bit of a different problem in this 75 year old who came in with flank pain and there's a big hypoechoic mass right in the region of the hilum of the kidney transversely.

We could see that there was an anechoic portion and a hypoechoic portion.

So of course you turn on, a video clip here, we can see that it's sitting right in the hilum of the kidney and probably causing some hydronephrosis on the in the kidney itself.

And we turn on the color doppler and realize it looks just like our aortic aneurysm.

This is a partially thrombosed large renal artery aneurysm.

You can see the artery coming through.

And then this large aneurysm, which is partially thrombosed, probably saving his life.

But unfortunately, it was we were not able to save his kidney.

Conclusion

So that brings us to the end of our talk on abdominal doppler and branches of the aorta.

Remember to do abdominal doppler work.

You need optimal technique, you need a lot of patients and you need a lot of practice.

Thank you very much.