Mesenteric Ischemia US, CT and CTA - HD

Introduction

Good morning.
I'm Dennis Foley from the Medical College of Wisconsin in Milwaukee.
I'm going to speak today about mesenteric ischemia and the role of Doppler ultrasound and the diagnosis of this particular entity.
We're going to speak today about mesenteric ischemia.
The role of ultrasound, particularly Doppler ultrasound and the diagnosis and its association clinically relevant with ultrasound, with CT and CT angiography.
I have no disclosures to report.

Clinical Presentation

The issues relate to clinical presentation of this entity, whether acute or chronic, and the role of CT and particularly spectral Doppler in the diagnosis and its correlation with intravenous arteriography.
We are not going to spend very much time in technique or utility, but simply correlation of intravenous arteriography, the Hiselod diagram that demonstrates the mesenteric vascular system and our efforts will be concentrated on the proximal superior mesenteric artery and celiac artery.
Not to say that disease that affects mesenteric blood flow does not occur in more distal vessels as it does and also can involve the inferior mesenteric artery.
We're not going to be touching on issues that relate to focal intestinal ischemia as may occur in patients with intestinal obstruction and volvulus.

So the clinical presentation of mesenteric arterial insufficiency classically is progressive weight loss food fear in a patient with a vascular comorbidity.
These usually are middle aged patients, usually female, and the food fear relates to the mesenteric angina that patients experience sometime in the nature of 15 to 45 minutes after taking food that's predictable and leads the patient to concentrate on frequent small meals if possible.

Anatomic Basis and Prevalence

The anatomic basis of mesenteric arterial insufficiency is high grade stenosis that is greater than 50 and particularly greater than 70% stenosis or occlusion of the celiac mesenteric arteries, which is combined with inadequate collateral flow.
The issue here is that quite a high proportion of the population have atherosclerotic disease of the celiac or mesenteric arteries, but because they have adequate collateral flow did not manifest any of the clinical symptoms of mesenteric ischemia.

Now, the prevalence of mesenteric arterial stenosis occlusion affecting the celiac or superior mesenteric arteries in the Medicare age population is actually quite high up to 18%, 11% of those single vessel and 7% dual vessel.
So these patients in very large part, compensate for their disease by the development of collateral flow.

Normal Doppler Studies

Here's an example of a Doppler study, a color Doppler to begin with of the aorta and celiac and superior mesenteric arteries.
You'll notice that there is color aliasing, particularly involving the SMA, but that reflects more the angle of insonation rather than the presence of an underlying stenosis.
And here we are obtaining a spectral waveform from the celiac artery that has a peak systolic velocity of about 160 and a normal spectral waveform with good diastolic flow.
And the systolic interval is characterized by sharp systolic upstroke.

Here is the SMA artery.
Again, it has a focal zone of aliasing, which reflects increased velocity around the curvature of the vessel as well as the angle of insonation.
And then we are obtaining a spectral waveform from the proximal SMA, which is normal in terms of peak velocity.
There's also normal in terms of waveform characteristics with a relative decrease in diastolic flow at the beginning of diastole, characteristic of a high resistant circuit, which is the mesenteric arterial system at rest.
Here we are further inferior, with the appropriate angle correction and again, a normal spectral waveform and a normal peak systolic velocity.

Diagnostic Cutoff Points

Having said that, at normal spectral velocities, the latest information in terms of cutoff points for the diagnosis of greater than 50 or 70% stenosis is labeled in this particular slide.
Notice in general, we could say 250 to 300 would cover the spectrum of 50 to 70% stenosis in the celiac artery and 300 to 400 in the superior mesenteric artery.
So here in general are the figures that we use for PSVs, systolic flow velocities in the celiac or superior mesenteric arteries for a 50 at the lower end to a 70% at the higher end of the velocity scale.

Here's a superior mesenteric artery evaluated approximately with a normal velocity and a normal spectral waveform.
Here's a celiac artery evaluated again approximately with a normal peak velocity at the top left and a normal spectral waveform.
And then here is the same celiac artery evaluated during expiration when the PSV systolic flow velocity increases quite significantly, but still within the normal range.
And this is something to be expected, you'll notice that there is not only an increase in the peak systolic velocity, but also an increase in the diastolic flow velocity as well.

Effects of Respiration

So it's also been found that the characteristics of flow in inspiration and expiration do vary between these two vessels.
In that inspiration results in a lesser systolic flow velocity then does expiration both for the celiac and the superior mesenteric arteries.

Now you'll also note that we are getting close to the cutoff points for the diagnosis of 50% stenosis in the celiac and superior mesenteric arteries, but we actually use inspiration or quiet respiration as the method of obtaining the velocities that we use for the diagnosis of stenosis.
It is just simply taken as a matter of normal flow that there will be this difference between inspiration and expiration that we do expect, but we use the inspiration or quiet respiration as the method of obtaining velocities that we use to determine the presence of underlying stenosis.

So here is a celiac artery approximately that is 241 centimeter per second with a normal waveform characteristic.
Here it is on expiration where it is increased to 365 and that would be considered abnormal, but here it is on inspiration and it drops to a much lower level.
And so again, expiration is a stress as it were, where the median arcuate ligament will compress the celiac artery and maybe even the celiac enteric, but we do not use that for the diagnosis of stenosis.

Here's the SMA at rest on inspiration and postprandially also on inspiration with no significant change in the peak systolic flow velocity between those two, we don't use a provocative test meal to evaluate the mesenteric arterial flow velocities.

Provocative Testing

In the past, this has been done somewhat effectively in looking at the response of total blood flow as reflecting in the superior mesenteric vein volume flow.
And it has been shown that normal individuals with a provocative test meal increase the volume flow in the superior mesenteric vein by up to four times, and those with mesenteric ischemia are unable to do this and increase it by less than two.

Additional Imaging Views

Coming back to diagnostic imaging, here we are with the sagittal view of the superior mesenteric artery, which is a curved vessel.
We are looking at approximately appropriate angle corrected and with a normal PSV flow velocity, we are looking at it in its mid segment where it is still normal with a normal spectral waveform and we're looking at it distally.
Again, it is normal with a normal spectral waveform.
So we look not only at the origin of the vessel, but also we look around the curve and distally if it is possible to obtain these velocities.

Here is the superior mesenteric artery approximately again with a normal flow velocity.

Here we are with the inferior mesenteric artery with a normal velocity and a normal spectral waveform for the inferior mesenteric artery.
We don't have the normative standards that we do have in the SMA and the celiac artery.

This is showing us in a lateral CT arteriogram the view of the celiac and superior arteries, and giving us a view of the sonographic window that we have for evaluating these vessels.
And you'll notice that we see these vessels with a narrow angle of insonation until we get to the curvature of the proximal superior mesenteric artery.
The inferior mesenteric artery is seen more inferiorly anteriorly and is usually only imaged when the patient is relatively thin without intervening bowel gas for the celiac and superior mesenteric arteries, we're using the acoustic window provided by the left hepatic lobe.

Here is the celiac artery evaluated during inspiration and subsequently during expiration, again, showing you the increase in flow velocity with expiration as compared to inspiration.
But again, that is not used diagnostically.

Here is the sagittal view of the superior mesenteric artery.
Here is the bend in the superior mesenteric artery.
Here we are more distally in the superior mesenteric artery, again with normal waveforms both approximately and distally.

Here is the inferior mesenteric artery evaluated in this patient.
And again, we see a normal waveform characteristic with a relatively high PSV flow velocity, but one which in this particular circumstance combined with normal patency of the celiac and superior mesenteric arteries.

Summary of Doppler Technique

So to summarize, celiac and mesenteric Doppler studies are performed in the fasting state.
We do use inspiration and expiration imaging but rely upon inspiration or quiet respiration for determining peak systolic flow velocities.
And we do not employ a pre or post provocative test meal because its only value is in looking at superior mesenteric venous flow.
And that is not routine clinical practice.

Abnormal Findings and Examples

Here is an example taken some years ago of a patient who had a flow jet, which was not angle dependent in the superior mesenteric artery and had a very high systolic flow velocity of almost 500 with a ratio of SMA to aorta greater than 3.5 to one.

The same patient celiac artery, again, had color aliasing perivascular tissue bruitery in this particular case with a peak systolic flow velocity, again, which was 357, which was abnormal and a high celiac to aortic systolic flow velocity ratio.
And in this patient, the collateral blood supply came from the inferior mesenteric artery where we had both an increase in systolic flow, but particularly a more robust diastolic flow in this particular instance indicating that the collateral flow was supplying a relatively low resistance, more distal circuit as occurs in patients who have proximal SMA stenosis.

Here's an example of a sagittal view of the proximal SMA, which is normal in terms of velocity, somewhat more distally.
In the mid segment of the SMA, we have a significant increase in systolic flow velocity to 392 and more distally.
It decreases.
So in this particular case, we made a diagnosis of not an SMA stenosis, but a more distal downstream SMA stenosis.
And this was confirmed by the intravenous CT arteriogram showing you both a focal area of dissection and aneurysm and then a stenosis at the distal extent of that disease.

Here's an example of a celiac artery study during inspiration and expiration with an increase in expiration as expected, but the peak systolic flow velocity greater than 450 obviously abnormal and combined with the evaluation of the hepatic artery on inspiration and expiration in both respiratory phases demonstrating tardus parvus waveform.

So here we have downstream tardus parvus waveforms being used to substantiate the presence of a proximal celiac artery stenosis with an elevated systolic flow velocity.

Here's another example of a hepatic artery tardus parvus waveform in a patient who had a stenosis of the artery that you see detailed with that particular arrow and a very short segment of aliasing.

Here's another example where we have the aorta with a normal systolic flow velocity with the SMA being recorded as also normal just at its origin, but more distally.
We have a very high systolic flow velocity.

This is an example of a patient in which we have a spectral waveform obtained adjacent to the orifice of the superior mesenteric artery where the velocity is normal within the superior mesenteric artery where we have a markedly increased peak systolic flow velocity.

And in this particular circumstance, the hepatic artery demonstrated a very abnormal waveform where systole is on the up slope of the spectral waveform.
And at the end of diastole, we have a total cutoff in blood flow.
So that was expiration.
And here the comparison with inspiration showed a more characteristic tardus parvus waveform.

So this is an interesting demonstration of a very abnormal spectral waveform obtained during expiration extending tardus parvus waveform flow characteristics to showing absence of flow in end diastole, again, a significant increase in peak systolic flow velocity in the celiac artery with a prominent increase in diastolic flow and the hepatic artery demonstrating a tardus parvus waveform to again corroborate the hemodynamic significance of the celiac artery stenosis.

Another example of a patient in this particular case, the peak systolic flow velocity in the celiac artery was at the cutoff point suggest of a significant stenosis and confirmed by the presence of the hepatic artery expiration image demonstrating tardus parvus waveform.
And then this was confirmed by the intravenous arteriography demonstrating the typical appearance of a celiac artery compression of the proximal celiac artery by the median arcuate ligament.

Aneurysms

Aneurysms can also be demonstrated by imaging techniques.
Here's an example of a celiac artery aneurysm on a CT arteriogram involving the more distal aspect of the celiac artery.
And here is the Doppler study that demonstrates the aneurysm in its dimension.
These aneurysms can be associated with proximal celiac artery stenosis due to median arcuate ligament compression, or they can be associated with segmental arterial mediolysis, a condition in which the wall of the celiac artery degenerates and the pathology approximates that what one would expect to see in fibrodysplastic disease of the renal artery.

Stents and Endovascular Therapy

We are now turning our attention to stents in a patient who's got a stent in the celiac artery, the superior mesenteric artery, and the inferior mesenteric artery.
Again, looking at the celiac artery, the superior mesenteric, and the inferior mesenteric artery.
In this particular circumstance, the curved plane reformations with CT demonstrated normal patency of the celiac, the superior mesenteric, and the inferior mesenteric arteries.

The Doppler study demonstrated aliasing involving the celiac artery with a PSV flow velocity still within the range of normal, but getting close to 250 in the proximal SMA, still within the range of normal, again with aliasing in the lumen, but getting close to the 50% cutoff and more distally extending beyond that particular level, which would in a native vessel suggest a 50% or close to 70% stenosis.

The issue with these vessels in stents is that the vessel has lost its compliance and a vessel that loses compliance.
The peak systolic flow velocity will compensate by increasing.
So studies have shown that in patients with stents involving the celiac artery in the superior mesenteric artery, the peak systolic flow velocity for a greater than 50% stenosis is elevated above what we would expect in patients with a un-stented celiac or superior mesenteric artery.

Here's an example of a patient who's got a stent in the celiac artery on a CT study transverse image whose SMA is occluded and whose curved plane reformation through the celiac to the hepatic artery demonstrates normal patency.
And in this particular case, the celiac artery evaluated an expiration instant, demonstrates a normal velocity at 200 centimeter per second, and we substantiate the fact that it's normal by also looking at the hepatic artery in the decubitus position showing a normal spectral waveform and no tardus parvus characteristics.

In looking at the endovascular therapy for mesenteric ischemia, this was a small study published a number of years ago, and the main point is that most patients with mesenteric ischemia who have transvascular intervention require more than one stent, that these patients may have secondary interventions.
And it's important role for Doppler ultrasound in evaluating patients with stents to determine whether or not an in-stent stenosis has occurred so that appropriate management can be instituted.

Surgical Management

Patients may instead of having stents, and this is more common, and 10 to 20 years ago, have had surgical bypasses.
This is an example of a superior celiac to mesenteric artery surgical bypass.
Again, an AP view of the same bypass if there's appropriate acoustic access by the left hepatic lobe.
This particular type of bypass can be imaged by sonography.
And again, the flow characteristics criteria should be similar to those of native vessels.

This is not a standard vessel with the loss of compliance, is another example of a prosthetic graft from the infrarenal aorta to the superior mesenteric artery, which potentially could be evaluated by Doppler ultrasound, but depends upon the degree of overlaying bowel gas.
These are now more of historical rather than practical interest because most patients with disease these days are treated by endovascular techniques rather than by surgical bypass.

In terms of the surgical management of intestinal ischemia, its major role is in the treatment of patients with acute mesenteric ischemia.
In those patients who may require acute thromboendarterectomy or thromboembolectomy, notice that the perioperative mortality in patients with acute mesenteric ischemia can be quite high, that the five-year patency rate is quite good.

So to summarize, for endovascular and surgical management, endovascular techniques are favored for treatment of proximal arterial disease in both acute and chronic intestinal ischemia.
That surgical bypass or thrombectomy is utilized for acute mesenteric occlusive disease but not for stenotic disease.

Overall Summary

So in summary, mesenteric vascular insufficiency, we have looked at the diagnostic criteria utilizing both the clinical presentation, the vascular imaging studies, and basically utilizing these to determine a therapeutic approach and if the patient has intervention, the therapeutic response that is the cure of the patient's mesenteric angina is the ultimate diagnostic arbiter.

We've looked at patients with chronic mesenteric ischemia predominantly, and those patients presenting with typical clinical symptoms.
The imaging role of ultrasound is critical, and ultrasound is also used in the post intervention evaluation of these patients.

Patients with acute mesenteric ischemia usually have CT imaging for their evaluation, and that may be combined with CT angiography.
A diagnosis is based upon that imaging appearance as well as clinical presentation and imaging usually is reserved for the follow-up of those patients following their surgical management.

Liver Transplants: Application of Principles

Just to finish this particular presentation on mesenteric and celiac artery disease, I'll just demonstrate to you some patients with liver transplants where the same principles and the same vascular field apply.

This is a patient with a liver transplant who has a normal portal vein flow velocity and flow characteristics, who has also a normal appearance of the celiac artery.
This will be proximal to the anastomosis for the transplant hepatic artery.
Again, here's a celiac artery, which is normal, and when we look at the hepatic artery though at the hepatic hilum, we notice there's a tardus parvus waveform and we look at the intrahepatic arterial flow waveforms to both the right and the left hepatic artery.
It is abnormal tardus parvus.

So we can therefore presume that between the native celiac artery and the transplant hepatic artery at the hilum, the patient has an arterial stenosis, almost certainly at the surgical anastomosis.
And in fact, that was confirmed in this particular case.
Where we have on the top left the intravenous arteriogram, we have the Doppler studies that demonstrate the critical information of a normal celiac artery trunk PSV systolic flow velocity and waveform characteristics with the tardus parvus at the hepatic hilum, and then the confirmation during intervention where the catheter is being placed in the celiac artery and we see a stenosis at the anastomosis.

This is another example of a patient with a liver transplant.
In this particular case, there is a very high flow velocity in hepatic artery at the hilum with a tardus parvus waveform intrahepatic in the right hepatic artery and also the left hepatic artery.
So what this patient has again, is a stenosis and the surgical anastomosis, in this case, closer to the hilum than we had in the first particular case.
And that is now demonstrated in this collage where we again have the Doppler waveform characteristics, the first diagnostic test, and then the confirmation by intravenous arteriography showing you an anastomotic stenosis in this case very close to the hepatic hilum.

So that is the finish of this presentation.
I hope that you have enjoyed listening to this and have picked up some pointers that are going to be useful in the diagnosis of celiac and mesenteric arterial disease in patients who are presenting with mesenteric angina, who progress through the process of evaluation, have corrections, and have post surgical or post intervention follow up.
Thank you.