Mesenteric Ischemia - HD

Approach to the Evaluation of Mesenteric Ischemia

Good morning everybody. Continuing in the theme of how I do it, I'm gonna talk about my approach to the evaluation of mesenteric ischemia.

For the next few minutes, I'm gonna describe the techniques we use for the examination of the mesenteric vessels. Discuss methods to optimize the examination, review current protocols and criteria. And I'm gonna finish off with my seven keys to success.

Patient Presentation

For the evaluation of mesenteric ischemia, we typically consider if the patient is presenting with acute symptoms or chronic pain.

Obviously we know when patients present acutely because they come into the emergency room with severe abdominal pain, nausea, vomiting, diarrhea, and usually those patients are wis off for a CT angiogram if there's a concern for vascular compromise.

The patients that we typically see in ultrasound have chronic abdominal pain, fairly nonspecific, they have pain after eating. Sometimes they may give you a history of fear of food and that when they eat they have abdominal pain, may complain of weight loss and not enjoying food so that they take in small meals.

Causes of Mesenteric Ischemia

The causes of this type of pain, mesenteric ischemia can be related to arterial stenosis or occlusion can be due to venous thrombosis or less commonly may be related to a non occlusive process such as patients have low flow, related to shock or hypertension.

Classically, patients with chronic mesenteric ischemia, as I mentioned, may have what they call mesenteric angina. Pain after eating the pain is typically nonspecific and these patients usually have other atherosclerotic syndromes give you a history of lower extremity arterial occlusive disease history of MI or CVA.

Role of Ultrasound in Evaluation

If you look at the A CR appropriateness criteria, you'll see that ultrasound is listed right below CT angiography through the evaluation of chronic mesenteric ischemia right there with conventional arteriography. And of course the advantage is there's no radiation associated with our ultrasound exam.

Now for the ultrasound examination, the findings typically are nonspecific with gray scale. We'll see some bowel wall thickening and distention, and typically there may be some ascites. So of course we're going to perform the doppler evaluation to look for patency of the abdominal vessels.

Evaluation of Mesenteric Arteries

For the evaluation of the mesenteric arteries, we are gonna be looking for evidence of vascular compromise in the celiac, superior mesenteric and inferior mesenteric near the origin from the abdominal art and into the proximal segments.

For the diagnosis of chronic mesenteric ischemia, we typically need to see stenosis or occlusion of at least two of those three vessels. And as I mentioned, it's not really recommended for an acute presentation. Those patients with acute thrombosis typically should go for CT angiography.

Protocol

As part of our protocol, we'll start out with an evaluation of the abdominal aorta looking for aneurysm plaque stenosis, and then we're going to take samples from the celiac, superior mesenteric and inferior mesenteric arteries.

Of course, for all of our examinations, we want to optimize both the gray scale and the color doppler.

Taking a look first at the abdominal aorta, nice sagittal view, looking for evidence of plaque. And we're gonna turn the color on to look for vessel patency and evidence of stenosis or thrombosis.

We want to adjust the color gain pulse, repetition, frequency, and wall filter so that we normalize to laminar flow.

In a normal vessel we see a nice homogeneous color flow pattern, no evidence of disturbed flow or aliasing to suggest an abnormality. This allows us to screen the vessel very quickly.

Normal Flow Patterns

Normal flow patterns in the mesenteric circulation typically run into flavors, right? We can get the low resistance pattern typically in the proximal aorta that feeds the celiac and the renal arteries and we can have a high resistance pattern in the distal aorta that feeds the lower extremities as it becomes a high resistance phasic pattern.

It's also interesting to note that the flow in the mesenteric arteries is typically very high resistance in the fasting state and we use that as a check to know if patients are fasting because if they don't have a high resistance pattern in the mesenteric arteries that we know they're cheating and they probably had breakfast.

Here's some examples of normal flow patterns and you can see in the abdominal aortic approximately near the origin of the celiac has continuous forward flow throughout diastole as we would expect in the celiac artery because the celiac again is feeding the low resistance organs of the liver and the spleen.

The superior mesenteric artery on the other hand, typically has little to no flow in diastole in the fasting state here, in normal fasting measurements typically around a hundred centimeters per second.

Keep in mind that the flow velocities in the celiac and mesenteric artery should closely resemble the velocities in the abdominal aorta should be a close to a one-to-one ratio.

We think about velocities around a hundred centimeters per second for the celiac in the SMA, maybe a little bit higher in the IMA.

Diagnostic Criteria

This chart just shows that there are lots of different articles that were published to describe diagnostic criteria by multiple authors looking at different criteria with different sensitivity specificities and cutoffs.

What I'm gonna do is I'm gonna boil this down. So what a number of proposed diagnostic criteria there are and we look at three specific areas to evaluate the peak systolic velocity, the aortic mesenteric ratio, and the end diastolic velocity. And here all publish criteria.

What I did some years ago is we looked at these different criteria in a subset of 205 patients that were referred for the evaluation of the mesenteric arteries. And in this group we had angiographic correlation on all of them.

I pulled the data from the mesenteric studies and I found that of these three different criteria, the most sensitive and the most accurate is the peak systolic velocity. The mesenteric aortic ratio is neither as sensitive or as specific as the peak systolic velocity, but is useful to have as a check very much like we do with the carotid studies. We use that I-C-A-C-C ratio as a check on the peak systolic velocity and the end diastolic velocity I found wasn't very sensitive, but it adds some specificity and again, like the end diastolic velocity in the ICI sort of reserve that to the back.

These are the criteria we use. This is what I recommend to look first at the peak systolic velocity and those velocities are 200 centimeters per second for a cutoff for stenosis in the celiac and IMA and the tic criterion of 275 centimeters per second for a cutoff in the SMA.

To augment that by looking at the mesenteric aortic ratio, typically if it's greater than three to one, is certainly abnormal and looking for post stenotic turbulence.

Examples of Abnormal Findings

Here in this example, the celiac artery has an elevated velocity over 300 centimeters per second. And as you continue to drag your sample volume, you can see a classic post stenotic turbulence with decreased velocity bidirectional flow in this very shaggy picket fence type post stenotic waveform.

When you look at your image with color DOPP look for evidence of color alias, you can see the change in the color in the area of the stenosis and color brewery that flash that occurs over the stenosis in real time.

When we do the pulse doppler sampling, obviously all el elevated peak systolic velocities in the stenosis. And as you move downstream you'll see the post stenotic turbulence and frequently TARDIS parvis waveforms.

Now here's an example, a 68-year-old with abdominal pain and with sampling the peak systolic velocity. Velocity is 131 within the normal range under 200. But as we look at the superior mesenteric artery, we see there's aliasing and a little bit of color brewery artifact at the origin of the SMA.

When we place the sample volume angle corrected direction of flow in the SMA, the velocity is 400 centimeters per second, so clearly a high grade stenosis.

Next we're gonna check the inferior mesenteric artery and that is also irregular with aliasing. And when we take the P systolic velocity from the I am a C, it's also elevated at 360 8 and we compare it to the velocity in the aorta, which is 72. So we have two vessel disease consistent with chronic mesenteric ischemia.

Postprandial Studies

People always ask, what about postprandial studies? That's very old school. Years ago we would challenge a patient with a meal and we'd look at the mesenteric vessels before and after eating and we stopped doing that years ago because it's really not necessary.

This study shows that you can identify high grade stenosis whether you do fasting or postprandial studies.

Mesenteric Veins

One thing I don't want you to forget is looking at the mesenteric veins as a cause of mesenteric ischemia. Venous thrombosis occurs in about 10% of cases, with up to 50% mortality. And it's typically seen in a younger population.

Again, the presentation may be non-specific, it's variable. And the typical course is thrombosis of the superior mesenteric vein with involvement of the ileum angio genum.

Here's an example of thrombosis of the splenic vein into the portal confluence. Here's another example of a patient that presented with abdominal pain and elevated liver function tests. And we can see that there's thrombus in the splenic vein extending into the portal vein and also in the superior mesenteric vein confirmed on the CT angiogram.

Pitfalls

There's a number of pitfalls to keep in mind. You can have anatomic variance, the median AR ligament sig syndrome, which I'll talk about in a second. There's vessel tortuosity, which makes it difficult to angle correct aneurysmal dilatation of the abdominal aorta, which you'll cause decreased velocities, aortic stenosis, which may cause increased velocities and TARDIS waveforms, cardiac arrhythmia, which can cause marked variability in the peak systolic velocity measurements.

Of course postprandial states which will cause increased velocities even if you think the patient may be fasting.

Seven Keys to Success

Here I'm gonna finish up with my seven keys to success.

Number one patient should be fasting prior to the study. Check on that, tell in advance, scan all three arteries and check the veins. Take velocity samples from the sagittal views. Don't forget to sample the aorta. Check angle correction carefully sample through presumed stenosis to assist the post stenotic turbulence and evaluate from median arcuate ligament syndrome.

Patients should be fasting. I like to do it the night before and I schedule my patients in the morning. It reduces the scatter and attenuation from bowel gas as you see on this image, which can make it a non-diagnostic study. We don't give any medication prior to the exam.

Number two, scan all three arteries. Again, in order to make the diagnosis of chronic mesenteric ischemia, you have to find diseases in at least two of the three vessels. So look for the IMA. Studies have shown, you can see the IMA in most of your patients, particularly when they're fasting. We use a velocity cutoff of 200 centimeters per sec.

Take velocity samples from the sagal views. This is probably the most common mistake I see in studies that are done. You can see a longer course of the vessel, you can improve your angle correction and you can get accurate velocity measurements.

Don't forget the aorta again, the velocity should be similar in the mesenteric vessels to the abdominal aorta. So think about the mesenteric AOR aortic ratio as your check. And this avoids multiple pitfalls from aortic stenosis, which again could increase velocities and cause TARDIS waveforms, aortic aneurysms, which can decrease the normal velocities and can cause aberrations in your evaluation.

Number three, threat. Check your angle correction carefully. Many errors are related to poor angle correction. The doppler angle should be in the direction of blood flow. You need to see the vessel well and drag the sample volume through the origin into the vessel lumen.

Avoid multiple measurements at different angles. I think this is another very common mistake. People take 5, 6, 7 measurements from the same vessel and then you have this array of velocities. You don't know what to do with it. Take few measurements and carefully angle correct.

Here in this example you can see when the SMA is not well seen, the one is 1 36, but when you extend the vessel, see the longer course, the velocity is really two 19 sample through the stenosis.

Very important for all of our arterial studies, always sample through the stenosis to look for the post stenotic turbulence. Here you could see in this example the celiac velocity's obviously elevated, but as you move through it, you get that post stenotic signal, velocity drops, bidirectional flow, very shaggy waveform. It confirms it's a flow reducing lesion.

And finally, check for the median arcuate ligament. Now the median arcuate ligament, as most of you know, is this leaflet of the diaphragm that crosses the celiac artery. You can see nicely here in this illustration.

Here on this sagittal MRI, you could see the indentation on the celiac artery that occurs with rest or expiration. And that causes increased velocities during that phase of respiration.

The pain that the patients experience can be related to the vascular or nerve compression, really not sure. But we do know in some patients they do get relief when you cut the ligament.

We may see elevated velocities at rest, but they go away. When you have the patient take in a deep breath.

Here in this example you could see this patient is an expiration. You get to sort of fish hook appearance as the ligament is tugging on the celiac artery causing narrowing aliasing and increased velocities up to 450 centimeters per second.

But then when you have the patient taking a big inspiration, you can see velocities come right back down into the normal range.

This is a very common pitfall, particularly in thin patients and we see it especially in young women.

Conclusion

Here I'm gonna conclude there are multiple non-invasive techniques that we can use for the evaluation of mesenteric vascular disease. We've had a very high success rate using doppler ultrasound. Again, there's no radiation. We evaluate for peak systolic velocity and post zoonotic treadmills as our primary parameters. And don't forget the veins. Thank you very much.