Ultrasound Evaluation of Patients s/p Carotid Endarterectomy and Stent Placement - HD

Introduction

Hello, my name is Leslie Sk and I am a professor of radiology and vascular surgery at Yale University School of Medicine in the Department of Radiology and Biomedical Imaging.

I am vice chair for education, associate program director, chief of the ultrasound section, as well as medical director of the non-invasive vascular lab.

Today I'm gonna be talking to you about the role of doppler ultrasound and the evaluation of patients following carotid intervention.

We will focus both on patients who have undergone carotid endarterectomy, as well as patients who have undergone carotid stent placement.

Disclosure and Outline

I do have one disclosure, which is that I'm an educational consultant for Phillips Healthcare.

The outline of the talk will be that we will start with carotid endarterectomy and review the normal postoperative findings, the imaging complications, the criteria for diagnosing restenosis and the evaluation of the progression of contralateral disease.

Following carotid stent placement, we will talk about the normal postoperative findings, the imaging complications and restenosis in terms of whether or the risk of complications following endarterectomy as opposed to carotid stent placement.

Risks and Comparisons Between Procedures

There are similar rates of long-term stroke and stenosis, but the durability of carotid stent placement is yet known because there has been limited follow up.

It's a very new procedure.

If you think about the risk of periprocedural myocardial infarction or mortality and cranial nerve palsy, that is clearly higher in the immediate postoperative period for patients who undergo carotid endarterectomy when you compare it to carotid stent placement.

However, the risk of periprocedural stroke in most studies has been shown to be higher for patients undergoing carotid stent placement rather than carotid endarterectomy.

However, this risk of periprocedural stroke has been decreasing in recent years as interventionalist gain experience and as the technology evolves, and in particular, the introduction of protected stents has resulted in a significant drop in the reported risk of periprocedural stroke in terms of whether or not a patient chooses to have endarterectomy as opposed to stent placement.

The recommendations for determining which of the procedures is best is somewhat controversial and also continues to evolve.

In general, most people would recommend carotid endarterectomy in a patient who has a lot of very heavily calcified plaque in vessels that are very tortuous.

The reason for this is because there is increased risk of distal embolization in such patients during stent placement.

Many people think endarterectomy is a little bit better in the older patient over 75 years of age, in addition, if for whatever reason anatomically it is going to be difficult to place the stent if the lesion is very long.

Many people think endarterectomy is a little bit safer, and if the plaque is hypoechoic and therefore more likely to be vulnerable and undergo embolization endarterectomy is likely a little bit safer than stent placement.

Another significant contraindication to stent placement is if the patient cannot receive anticoagulation or antiplatelet therapy during and following the procedure in that situation.

Endarterectomy is clearly the better option.

On the other hand, most people consider the use of a carotid stent to be preferable if the patient has high medical comorbidity.

In other words, increased surgical risk.

This is usually defined as a patient who has advanced cardiopulmonary disease.

If a patient has had a stenosis following an initial endarterectomy and intervention is required, reintervention is required.

Stent placement is better than reoperation.

Along those same lines, if for whatever reason the patient has what a surgeon would describe as a hostile neck, in other words, a patient who has a lot of fibrosis or scar tissue in the region of the carotid artery such that dissection would be difficult, this increases the risk of cranial nerve damage.

In those patients, stent placement is considered much better.

The most common things that would result in the so-called hostile neck would be a patient who has undergone radiation therapy to the neck, laryngectomy lymph node dissection, or tracheostomy.

Again, there are anatomic reasons that a stent might be better than endarterectomy.

If the lesion is inaccessible to the vascular surgeon because it's either too high or too low, again, a stent would be preferable.

Some clinicians prefer to use a stent if there's a contralateral internal or common carotid artery occlusion, although this is not a universal conclusion.

The bottom line is that both procedures do have risk.

If the patient is symptomatic with a greater than 70% internal carotid artery stenosis and at low surgical risk, the overall risk of endarterectomy when compared to stent placement is really pretty similar.

Some data suggests that the endarterectomy is a little bit better if the patient is over the age of 65.

Conversely, some literature suggests that stent placement is better if the patient is under the age of 65 years.

Both have anatomic limitations and the elderly, those patients over the age of 80 or increased risk following either type of intervention.

As in most things, experience is key for both procedures to perform it safely with decreased complications.

Carotid Endarterectomy

Let's start by talking about carotid endarterectomy.

During this procedure, the surgeon attempts to strip off the intima and the media with a plaque.

Following that, it is really been shown with very good data that patients do better if a patch is used.

It really is unequivocal that using this patch decreases the risk and rate of stenosis.

What type of patch is used, whether it's a vein patch or synthetic patch, is less clear which of those is optimal.

Generally speaking, a patch is always used at the carotid bulb and origin of the internal carotid artery.

The result of using that patch is that the diameter, as you see here, will increase at that location following endarterectomy.

The result of that is that the peak systolic velocity in the bulb and the origin the internal carotid artery will decrease.

The other thing that happens when you use a patch is that the compliance of the vessel wall changes and typically increases, and that seems to result in some feathering of the contour of the arterial waveform and some widening or prolongation of the QRS complex.

Complications Following Carotid Endarterectomy

What about the complications following carotid endarterectomy and how can ultrasound be helpful?

In the immediate postoperative period, one type of complication is a stroke or TIA due to thrombosis, embolus or arterial dissection.

Hematoma in the soft tissues, even abscess formation happens occasionally.

Very rarely a patient will develop a postoperative arterial venous fistula or pseudoaneurysm that rarely has been reported to result in a so-called carotid blowout.

The most concerning risk is the risk of myocardial infarction or cranial nerve palsy.

These things that I've described here typically occur if they're going to occur within the first couple of weeks or days following surgery.

In terms of the risk of stroke or thrombosis, most of these patients are operated on with local anesthesia so that the surgeon and anesthesiologist can monitor their neurologic status.

If something changes, we are occasionally asked to come immediately to the OR in order to do intraoperative scanning to see if we can see some cause for the neurologic event that the surgeon can fix.

What you're looking for in that case is thrombosis or stenosis of the carotid arteries.

What you will see on your Doppler examination is an increase in peak systolic velocity at the site of the stenosis, as well as intraluminal echogenic material, which is often a dissection flap.

Sometimes if you have trouble getting access to the bulb or origin the internal carotid artery, all you see is the common carotid artery.

What you will see in that case, if there is significant obstruction up above, you will see the so-called high resistance waveform with a decrease in the amount of diastolic flow.

It's important to look not just at the origin of the internal carotid artery, but also in the common as well, because that can give you indirect information regarding the distal circulation.

Here is an example of a patient who had preoperative imaging, and you can see that at the origin of the right internal carotid artery, the velocity is 352 centimeters per second compared to 52 centimeters per second in the common carotid artery.

This was read as a greater than 70% stenosis.

The patient went on to endarterectomy and we were called to the operating room because of a significant change in the neurological exam.

You can see that the first waveform that we obtained in the common carotid artery is extremely abnormal.

There is absolutely no diastolic flow, and that ought to make you very concerned that there is distal obstruction to flow.

As we looked more superiorly, you can see on the power doppler, no flow in the distal common carotid artery and just thump flow on the spectral doppler waveform.

This patient had an acute thrombosis of the right common carotid artery, which we diagnosed and allowed them to go in and do a thrombectomy.

This was another patient who had a minor neurological event in the operating room, and we were called to the OR, and you can see here at the carotid bulb that the entire intima has actually not been stripped off.

You can see this little echogenic line here and this little tiny dissection flap with a little perhaps hematoma around it.

This is actually fairly common if you were to look at all patients following carotid endarterectomy.

Although the surgeon attempts to strip off the entire intima, they in fact often leave a little piece behind and you can see these little dissection flaps waving in the breeze.

If they're not associated with an increase in peak systolic velocity or significant thrombus around, and this really was more along the lines of slow flow than true thrombus, then generally no intervention is gonna be required in these patients.

On the other hand, if you have a situation like this where you actually have what looks like an intramural hematoma or worse, perhaps even intraluminal thrombosis, you see the dissection flap up here.

With your color doppler, you can see that the residual lumen is actually quite narrowed.

With your spectral doppler, you can see that the velocity is elevated to just under 200 centimeters per second.

Clearly this is a flow reducing lesion, and there is a significant amount of intraluminal material this will not resolve on its own.

The surgeon is going to go back in, reopen the vessel and fix this in order to ensure that there is a good outcome for this patient.

This is another patient, a 73-year-old man with pain a day following carotid endarterectomy.

This is not a call to the OR this is a call to the intensive care unit.

You can see actually in this patient that there is some intraluminal material that is very hypoechoic.

You can see that it causes a color void on the color doppler image.

On the longitudinal you can see that it surrounds this hypoechoic material with an associated increase in peak systolic velocity.

This is a patient who has had acute thrombus actually in the common carotid artery.

This is a very unusual complication and people have not much experience with knowing the best way to handle such patients.

Anticoagulation obviously is important because this is really acute thrombus.

This isn't plaque, it wasn't a dissection, it was relatively central within the lumen of the vessel.

Sometimes thrombectomy is warranted under these cases as well.

This is a patient who came back two years following carotid endarterectomy.

What you can see here in this case is a little dissection flap, very similar to the first case that I showed you.

The difference is that this is two years later and this is no longer mobile.

This did not move during the cardiac cycle.

This is stiff and scarred and fibrotic, and because of that, it significantly affects the residual luminal diameter.

You can see that peak systolic velocities in that case are over 400 centimeters per second.

This little dissection flap has resulted in a high grade stenosis now two years following endarterectomy and intervention would be required.

At this point, reoperation is more difficult because of scarring from the initial carotid endarterectomy.

Typically intervention in these patients would be accomplished with a stent placement rather than an operation.

Going back to the more immediate postoperative problems that we can see with ultrasound, this patient complained of significant pain and actually visible neck swelling, which is quite atypical following endarterectomy.

In the intensive care unit, we could see that the vessel is widely patent.

However, there is blurring of the soft tissue planes.

You would probably expect that following surgical intervention, and we just thought this was initially postoperative relatively normal or within normal limits.

The swelling continued. We came back 12 hours later.

At this point you can see quite clearly on the gray scale imaging that a hematoma has developed with a fluid fluid level.

On color doppler, you can see that there's no vascularity within this collection.

It can be difficult to differentiate a hematoma from a abscess, and clinical scenario is going to be helpful.

In this case, one wouldn't expect infection 12 hours following the operation.

If you saw infection, you'd expect the overlying skin to be red and as well as swollen and the patient to be febrile and have a white blood cell count here.

Another example of a small hematoma, recognize that the gray scale appearance of a hematoma will be quite variable depending upon the time course.

Early on you might see this fluid fluid level.

Later you will see a more heterogeneous hypoechoic collection, which occasionally can be actually frankly anechoic and look cystic.

When you see little echogenic areas within a fluid fluid collection, of course you need to be concerned about air.

There are two ways you could see air within this fluid collection.

If it is packed with surgicel postoperatively, that can contain air, and this can be a benign finding.

If it's associated with erythema pain and increased white blood cell count fever, of course this is the way an abscess would look.

That was indeed what this patient had.

Late Complications Following Carotid Endarterectomy

Late complications also occur and the ones that are of most concern would be stenosis or thrombosis at the operative site.

You can also see progression of contralateral disease or disease that is distal or proximal to the operative site.

These can result in stroke or TIA and very rarely pseudoaneurysm formation at the suture line has been described as well restenosis that occurs at the operative site or was generally called the end of the operative site, and we'll refer to that as anastomosis usually occurs at the distal anastomosis in the mid to distal internal carotid artery rather than at the proximal anastomosis, so to speak, in the bulb or the distal common carotid artery.

When this occurs early though, there's some controversy as to how you define early.

If this is within the first six to 12 months or within the first three years, this is usually due to the development of scar tissue or fibrous tissue at the site of the operation or occasionally to neointimal hyperplasia.

When you see stenosis that is late, and again, some controversy over this, some people define it as occurring after six years, some people after three years, this is most commonly due to new plaque formation.

This can occur either in the operative site or distal or proximal to the operative site.

The incidences of restenosis following carotid endarterectomy is somewhat variable in the literature, but in most series ranges between about five and 15%.

Risk factors seem to be fairly consistent in most studies and include underlying fibrous or inflammatory plaque, older patients, females, patients who smoke or patients who have a history of diabetes.

It is somewhat controversial as to when a reoperation would be recommended, and although most people will operate on the native vessel at about 70% stenosis just because it's little bit more difficult to take care of business, once carotid endarterectomy has been performed, most clinicians wait until they think that the re-stenosis is at least 80%.

Although this depends upon whether or not the patient's symptomatic and in a symptomatic patient intervention would be appropriate at a lesser degree of stenosis.

Because of this risk of re-stenosis, patients who have undergone carotid endarterectomy are typically followed at yearly intervals with ultrasound.

Some clinicians suggest that they have an initial one month baseline study, then a repeat ultrasound at six months, and at that point start with the yearly surveillance schedule.

That's the problem, that's the way to search for the problem.

But how to diagnose the problem is difficult.

The reason for that is that the surgery, as I've mentioned, changes the vessel hemodynamics and the increase in the diameter following the placement of the patch will result in a decrease in peak systolic velocity.

As I mentioned, the vessel wall compliance will also be different and usually it increases.

The end result of these factors is that the preoperative doppler criteria really are not applicable to evaluating the patient following carotid endarterectomy.

Likely the peak systolic velocity to identify a 50 to 80% stenosis is going to be lower than the preoperative doppler criteria with which we're all familiar, but nobody is quite sure exactly what is the optimal peak systolic velocity to use.

In my experience, when you cannot confidently and accurately use a specific peak systolic velocity number, what I default to is using the peak systolic velocity ratio, putting more emphasis on that, and also putting more emphasis on a gray scale and color doppler findings.

Another thing that becomes very important in these patients when we don't have an absolute number to use, is to assess for change over time.

That is very, very common.

Here is an example of a patient a year following carotid endarterectomy, and you can see that there is clearly thickening of the carotid wall, and this is neointimal hyperplasia, if you will.

This is a fairly common appearance, and unless it is causing a significant decrease in the arterial lumen or increase in peak systolic velocity, this is generally watched and it's watched at yearly intervals.

In this particular case, you can see that there's no increase in peak systolic velocity.

Highest velocity we got was only 104 centimeters per second, and so this will just be watched and no intervention will be planned.

On the other hand, this patient was imaged at their baseline exam just one month following endarterectomy, and you can see that there is marked amount of hypoechoic material at the operative site.

One would not expect to see a neointimal hyperplasia this early.

There was concern that this was something different, perhaps thrombus, perhaps mural hematoma.

This patient was treated with anticoagulation and eventually this resolved.

You can see on the transverse view this straight line here, which again suggests that this was perhaps mural thrombus or hematoma.

Intimal hyperplasia would not give you that straight line, but again, there was no increased velocity related to that because the residual lumen is normal.

Still treatment was recommended to treat the underlying problem even though we did not feel that there was a stenosis.

This patient was anticoagulated and got continued a close follow up.

Eventually this resolved.

This is a patient that came back several years following endarterectomy and you can see that the endarterectomy site is perfectly fine and widely patent, but you can see the shelf here right at the edge of the surgical field with a significant amount of plaque in the distal native internal carotid artery.

You can see here that we've measured the residual lumen, which was only a couple of millimeters in diameter.

Although the velocity was only 200 centimeters per second, clearly by the gray scale, you can see that this is a very tight residual lumen above the endarterectomy site.

This is an example of a re-stenosis due to progression of disease in the native vessel.

Clearly intervention is warranted despite the fact that the highest peak systolic velocity we got was only 197 centimeters per second.

The reason for that, of course, is because velocity is low in the endarterectomy side because the diameter has increased because of the patch, and so the ratio would've been greater than four, although the absolute peak systolic velocity does not reach that benchmark that we use for grading a 70% stenosis in the native vessel.

This is another example, a 68-year-old woman who is eight years following a bilateral carotid endarterectomy who presents with a right neck bruit.

You can see here that there is now a shadowing in the origin of the right internal carotid artery.

There's some turbulent flow with some aliasing.

You can see that on the spectral waveform.

You can see in fact that velocities start to alias at over 440 centimeters per second, and the diastolic flow is over 200 centimeters per second.

No question that even though we can't see the stenosis on the gray scale because of shadowing that there's clearly a tight stenosis at the endarterectomy site on the right where the patient had a bruit.

When we moved over to the left, starting with the common carotid artery, the first thing that you'll notice is that there's no diastolic flow, and this indicates that there has to be a significant obstruction to flow more cephalad.

Looking more superiorly, you can see the shelf if you will near the endarterectomy site.

There is complete fill in of the residual lumen in the upper endarterectomy site with this very homogeneous hypoechoic material, no flow on color doppler imaging.

This blue streak here is just due to flow in the internal jugular vein.

She has a tight stenosis in the right carotid endarterectomy site and has completely thrombosed her endarterectomy site on the left.

You can see these findings on the accompanying angiogram and CTA here at the green arrow occlusion of the left internal carotid artery at the endarterectomy site and this very tight stenosis on the right.

This patient was effectively treated with stent placement on the right, as you can see in the follow-up angiogram.

Another patient who presented with TIAs five years following carotid endarterectomy.

You can see that there is a lot of hypoechoic plaque within the endarterectomy site.

You can see on the color doppler narrowing of lumen with focal color aliasing and velocities here, close to 700 centimeters per second, again, consistent with a very tight stenosis.

Note that up above the endarterectomy site in the distal internal carotid artery, you can see decreased velocities with a mild tardus parvus waveform indicating that that proximal stenosis is indeed very tight.

The appropriate recommendation here would be stent placement rather than repeat surgery.

This is an example of a very unusual delayed complication following endarterectomy.

This 67-year-old woman presented with an enlarging, hard, palpable neck mass.

She had it for about a year, and she was now three years following left carotid endarterectomy.

You can see at the proximal suture line in the distal common carotid artery, there is this outpouching from the common carotid artery.

It fills in with flow demonstrating the typical yin yang flow pattern of a pseudoaneurysm.

Notice there is some mural thrombus.

There's a very wide neck here as we don't see the true to and fro flow in the neck that we often see with a pseudoaneurysm.

This was clearly a pseudoaneurysm at the proximal suture line, kind of an unusual complication following endarterectomy.

Carotid Stent Placement

Moving on to patients who undergo stent placement.

Let's first review the normal postoperative appearance and when the stent is deployed, it should expand such that it hugs the vessel wall and that you do not see any space or blood flow between the wall of the stent and the arterial wall.

However, residual narrowing, especially in the stent center of the stent, is relatively common, and this is typically referred to as waisting.

That may happen just because of the physical principles of the stent that it's harder to expand the stent in the mid portion if particularly if it is a very long stent.

The other thing that can cause residual narrowing though, is residual plaque.

As they put the stent in, they attempt to angioplasty the plaque in the vessel and compress it, and it of course is excluded by the stent.

If it is heavily calcified, it may not be fully compressible, and therefore residual plaque may limit the full expansion of the stent and may deform the stent and narrow the lumen.

For this reason, it is very, very important to get a baseline examination.

The other thing to be aware of is that placing the stent does also change the vessel hemodynamics and the vessel becomes stiffer and the compliance decreases because you've put this rigid tube within the vessel, the stent may decrease flow in the external carotid artery resulting in increased flow through the internal carotid artery.

As I mentioned, there are a couple of reasons that you might see residual narrowing or waisting, particularly in the center of the stent.

The end result of all of these things is that peak systolic velocity is very often increased in the stent in comparison to the native vessel.

Here are some examples of the normal postoperative appearance of a carotid stent.

You can see the stent is very echogenic and linear.

It's often flared a little bit at each end.

Depending how you're angled, you may see these little parallel lines representing the struts of the stent if you image a little bit obliquely, but you can see that this is expanded so that the stent is directly opposed to the vessel wall and there is no space between them.

This stent looks completely normal.

However, you can see that the velocity is a little bit elevated over a hundred centimeters per second compared to what we would normally see in the distal common carotid artery.

Here's an example where there is clearly waisting within the stent, but this was immediately postoperative or post-placement.

There are no intraluminal echoes to suggest that there is neointimal hyperplasia or there is thrombus.

This is likely due to the fact that the plaque could not be completely compressed.

Where this stent is narrowed, notice that the velocities are very high, they're 300 centimeters per second, and if you saw a velocity like that in the native internal carotid artery, you would say clearly there's greater than a 70% stenosis.

Looking at this, you can say, yes, it is narrowed.

There is a focal area of waisting velocities go up, but this is not a re-stenosis, this is just the way this stent is going to be.

It's very, very important therefore that you get a baseline exam so that if you saw this patient in follow up a year later for the first time, saw these very high velocities, you might be concerned that something bad had happened to this stent that you just couldn't see very well.

In fact, this velocity is gonna stay like this for the lifetime of this stent.

Here is an example where you can see this very heavily calcified plaque with shadowing, and you can see how that plaque actually deforms the near wall of the stent at the yellow arrows.

Notice the velocities are quite high at that point, at close to 150 centimeters per second.

In fact, the stent is narrowed, the velocities are elevated, but there is no stenosis, and so no intervention would be warranted.

Here is another example of a patient who has had a stent placed.

Notice that you can see that the velocities here are about 200 centimeters per second waveforms look relatively normal.

But again, you can see that the stent is deformed by the presence of this plaque.

Here you can see the struts of the stent on the near wall, and this plaque was not fully compressible as they put in the procedure.

Residual plaque is there and it deforms the stent causing this increase in velocity.

It's very important to know this so that you compare your velocities to the baseline exam and not to the velocities you would expect to see in a normal vessel.

Here is an example where actually there were overlapping stents and there is a step off, and this is not a good outcome.

The upper stent is not opposed to the vessel wall, nor is the top of the lower stent.

You can clearly see that between these two stents, there's a passageway and blood will get out of the stent into the space between the upper stent and vessel wall, and this is not considered a good outcome.

Here's another example where heavily calcified plaque actually lifts off the posterior wall of the stent from the vessel wall, and you can see on the color doppler that some blood flow gets around or goes between the stent and the vessel wall.

This again, is not a great outcome.

The stent will prevent anything from immediately going well.

It's sort of a blind ending area here, and so the stent does still exclude this material or anything that might develop here from the residual lumen, but it's easy to appreciate that one could get slow flow in this area and eventually it might fill in with thrombus.

If it does, that thrombus might extend beyond the distal end of the stent and therefore be at risk for embolizing.

What actually would've been best in this case would have been had they extended the stent, put another stent in so that down below it was completely opposed to the vessel wall and then that would've provided a little bit better protection.

Experience is evolving in terms of stent placement.

Complications Following Carotid Stent Placement

Going now to the complications following stent placement in the immediate periprocedural time.

The thing of most concern, of course, is the possibility of a stroke and that risk is higher following stent placement than following endarterectomy.

The other thing that can happen is complications related to the puncture of the groin or the arm for placement of the catheters to introduce a stent.

These are things with which I'm sure you're familiar, the development of pseudoaneurysm, arterial venous fistula, dissection of the artery, and even thrombosis of the artery or the adjacent vein.

As I mentioned, the periprocedural stroke risk is higher for stent placement than for endarterectomy.

The actual specific risk of distal embolization thrombosis clearly related to two things, the degree of stenosis and the amount of experience.

The tighter this stenosis, the higher the risk, however, the reported incidence is falling as the technique matures and as clinicians gain experience, there's also risk of microembolic cerebral injury.

We're now finding following any of these procedures, and that seems to be a little higher for stent placement than following endarterectomy as well.

The long-term risk of stroke though seems similar to patients who have undergone carotid endarterectomy.

In this patient, a stent was placed for a stenosis and notice that you can see a little bulge here in the stent.

If you image obliquely, it almost looks like it's fractured.

You have to be very careful if you think it's stent is deformed or fractured to make sure your imaging in the midline.

In fact, this stent was completely intact.

It just had this little bulge.

You can see in fact following stent placement they could see the bulge on the angiogram.

That was just what happened is they tried to open the stent during placement, but this patient did have a stroke 24 hours later.

You can see now that there is a lot of hypoechoic plaque at the origin of the internal carotid artery.

With diffusion weighted imaging, you can see these tiny little microembolic events.

This is a little bit more common following stent placement than it is following endarterectomy.

This patient presented with arm pain following stent placement, and the stent had been placed through the brachial artery.

You can see on the color Doppler image that what has happened here is that the brachial artery unfortunately has thrombosis, and this is just a complication of having put a relatively large catheter in order to introduce the stent into a relatively small vessel.

This is an example of a patient who presented with groin pain following stent placement through the right common femoral artery.

You can see this large fluid collection immediately above the vessel on color doppler.

You can see the yin yang appearance.

You can see the neck and you can see that classic to and fro pattern within the neck of the pseudoaneurysm at the site of the groin puncture.

Delayed Complications Following Carotid Stent Placement

Moving on to complications that are delayed complications.

Again, the things that happen here are restenosis, occlusion and rarely fracture.

The rate of stenosis following stent placement is in most series reported to be fairly similar to carotid endarterectomy.

In general, the risk of neointimal hyperplasia seems a little bit less than what has been reported in stents that are placed in either the coronary or iliac arteries.

I must tell you that follow up of carotid stents has been shorter.

The answer to this has not yet been fully determined.

In general, I want to reiterate that the durability of stents has not been well established.

Most people think one ought to consider stent placement in the carotid arteries very carefully in a young patient with a long life expectancy.

When patients develop restenosis, they're typically asymptomatic.

Most of these begin after six months, and the mean time of onset is about 14 months.

An interesting thing about the intimal thickening that occurs following stent placement is that it very often stabilizes after 12 months.

Interventionalists are loathed to go in and intervene the first time they see neointimal thickening unless the patient is symptomatic or unless the lumen is drastically reduced in size.

They will typically watch it, watch it carefully, maybe every six months, but they won't intervene unless it progresses or the patient is symptomatic.

Because of this risk, surveillance is recommended to assess for patency of the stent, the development of stenosis, as well as the progression of distal native or contralateral disease.

The schedule is a little bit different than for carotid endarterectomy for most clinicians, and they almost always will get a baseline examination at one month because again, people have less experience with this procedure.

Then they will get a six month follow up than a 12 month follow up.

At that point they typically move to annual evaluation.

Other centers are a little more conservative and will get imaging every six months and only move to yearly follow up if the patient's stable after 18 months.

If any degree of stenosis is seen and intervention is not planned, they will continue the six month follow up schedule.

Once again, when one intervenes with a stenosis following stent placement is somewhat controversial and people usually wait till the stenosis is a little bit tighter following stent placement than they do for the native vessel.

Somewhere typically between 75 and 80% stenosis, though, again, it depends whether or not the patient is symptomatic.

The risk factors for re-stenosis are very similar to the risk factors following endarterectomy.

If you still have a stenosis following stent placement, if there's a history of cervical radiation therapy, if the stent was placed because of restenosis at a prior carotid endarterectomy site, older age diabetic patient, or a patient with a smoking history.

Placing that stent changes the vessel hemodynamics in the anatomy resulting in most patients in an increase in peak systolic velocity for the reasons that we've already described.

There have been many, many studies looking at exactly what doppler numbers should be used to identify a re stenosis in a patient following stent placement.

There is very little agreement on the numbers, which may be laboratory and stent type specific.

The bottom line is that all studies agree that both peak systolic velocity and ratio should be higher following stent placement for a given percent stenosis than for the native vessel.

I am just giving you a summary of many studies that I've looked at.

I'm not going to reiterate them all here, but I will point out what they have found in these last two studies, which is namely that the absolute peak systolic velocity is not as important as change over time and that the ratio, again is probably more important than peak systolic velocity.

Since there is not a strong agreement between labs and studies as to exactly what numbers that you should use, the color doppler and gray scale imaging features are going to be more important.

My recommendation is that you assess for change over time and the peak systolic velocity ratio and look very carefully at the gray scale and color doppler images.

Here you can see an example of a patient who has had a stent placed.

You can see this hypoechoic material within the stent.

This has not significantly reduced the arterial lumen, and this is neointimal hyperplasia.

Because the lumen is not reduced and the velocity doesn't increase along the length of this, this is just going to be continued to be watched at six month intervals.

If the patient is asymptomatic and this does not progress, the interventionalist will not do anything.

In this particular patient, the stent was placed because of a stenosis following endarterectomy, and you can see both on the angiogram and on the doppler that there is residual waisting and narrowing of the lumen of that stent.

You can see that the velocity is increased up to as high as 250 centimeters per second, but there are no intraluminal echoes and there's no change in the peak systolic velocity and the narrowing at the six month interval follow up.

This is just the way the stent is gonna be, and we're going to relax about these elevated peak systolic velocities.

Here again, six years after the one I just showed you, velocity's still about the same.

There is no reason to intervene in this patient.

This patient came for ultrasound follow up several years following carotid stent placement.

You can see on the gray scale image that there are intraluminal echoes and there is significant decrease in the caliber of the residual lumen.

On the color doppler. You can see how narrow that residual lumen is and the color doppler aliasing with increased velocities of over 400 centimeters per second at that site.

This would be of course, consistent with a tight in-stent stenosis as is confirmed on the angiogram here.

Here's another example where there has been just progression of the native disease here, velocities over 327 centimeters per second.

Yet another case where you can actually see the intraluminal echoes within the stent.

You can see the narrowing of the residual lumen, the elevation in peak systolic velocity.

This is stenosis with progression of distal native disease as well as the neointimal hyperplasia within the stent itself.

Stent fracture is extremely uncommon.

I've only seen a couple of cases, and you can detect this on the gray scale here.

The lower part of the stent appears to be in a longitudinal plane, but the upper part of the stent appears to be in a transverse plane.

You can see the fracture to even better advantage on this plain film of the neck.

Here is an example where you can see actually there has been complete thrombosis or occlusion of the stent within the internal carotid artery.

This is a very unusual complication and most cases have been reported fairly acutely.

Conclusion

In conclusion, the referral of patients for endarterectomy or stent placement does decrease the incidence of stroke in patients with carotid stenosis greater than 70%.

There is less risk of perioperative stroke in patients who undergo carotid endarterectomy, but there is less risk of perioperative myocardial infarction or cranial nerve damage in patients who undergo stent placement.

The incidence of re-stenosis following endarterectomy and stent placement seems to be similar, but the durability of stent placement is as yet unproven.

The doppler criteria for the diagnosis of stenosis following endarterectomy or stent placement are yet to be accurately and reproducibly determined.

The peak systolic velocity for a greater than 70% stenosis in a patient undergoing endarterectomy is probably lower than it is for the native vessel, but it's probably higher in the patient who has undergone stent placement.

Since there aren't specific numbers that I can give you that you can use in all of your patients reproducibly and accurately to predict a greater than 70 or 80% stenosis, my recommendation is that you look carefully at the gray scale and color Doppler images.

Look for the intraluminal echoes.

Look for a change in peak systolic velocity over time, and remember that you probably will not be quite as accurate and as specific in evaluating these patients as you are in the native vessel.

You can consider referral to CTA or Angio in those cases, which are problematic.

Thank you.