Renovascular Hypertension: Role of Ultrasound & Colour Doppler - SD

Introduction to Renal Vascular Hypertension

Hi, I'm Dr. Nathan Charbel from India Mumbai and this is a talk on renal vascular hypertension and as we'll see that it is not only renal art dys stenosis because of atherosclerosis, which can be responsible for renal vascular hypertension, but we have other causes which can also give rise to renal vascular hypertension.

So we look at the role of ultrasound and opular in evaluating renal vascular hypertension.

Definition and Prevalence

The syndrome of renal vascular hypertension may be defined as secondary elevation of blood pressure produced by variety of conditions interfering with arterial circulation of kidney tissue causing renal tissue ischemia.

This is the most common secondary form of hypertension, not easily recognized clinically.

The exact prevalence of proven renal vascular hypertension in overall hyper population is unknown, but significant renal artery disease has been found in almost about seven to 10% of hypertensive patients in various studies.

Misconceptions

There are some misconceptions.

It is commonly believed that renal artery stenosis always results in high blood pressure. This is not true. It is also commonly believed that revascularization always cures high blood pressure. This is again, not true and therefore it is very important to identify renal artery stenosis causing renal vascular hypertension and this is where doppler plays a very important role.

It is, again, wrong to believe that renal vascular hypertension means ARO or fibromuscular renal artery disease. We have so many other causes of renal vascular hypertension, which we will see in this lecture.

Role of Ultrasound and Color Doppler

Ultrasound and color doppler are most cost effective, easily available. They give us to an excellent depiction of the renal vasculature with the good accuracy. Most important is we get physiological information as compared to anatomical information in an angiography CT angiography or an angiography.

It is again, a wonderful technique to follow patients after revascularization procedure.

As we shall see, some limitations have to be kept in mind and understood.

Subgroups of Hypertensive Patients for Suspicion of Renal Artery Stenosis

Typically, the subgroup of hypertensive patients in whom renal artery stenosis should be suspected are children age of onset of hypertension, less than 30 or 50 hypertension, which is C severe, poorly controlled, rapidly worsening known peripheral vascular, cerebral vascular disease, aortic disease, either insufficiency of unknown cause abdominal debris or a unilateral small kidney picked up on ultrasound or on an IVP.

Importance of Gray Scale Evaluation

So it's very important to do a good gray scale evaluation of the kidneys. Before we start Doppler, very often we might pick up unsuspected, chronic renal disease, unsuspected, pheochromocytoma, or an unsu adult polycystic kidneys, which might be the actual cause of hypertension.

Evaluating Renal Arteries: Main and Intrarenal

When we evaluate the renal arteries, we are, we look at the main artery and the intradural arteries.

The criteria which we use in the main artery are known as direct criteria. The criteria which we use in the intrarenal arteries are known as indirect criteria.

It's very important to emphasize that when we see in, when we say intrarenal arteries, we are talking about segmental arteries and not about the smaller arteries. At the periphery, it is very important to begin the examination with the aorta.

It's very important to look at the aorta in a longitudinal plane, look at the walls of the aorta and look at the pulsations of the aorta and non pulsating abdominal aorta can be a clue towards diagnosis of things like tation or aorta arthritis as we'll see.

Then we look at the origin of the renal artery in a transverse plane and typically when I look at the origin of the renal artery, I like to switch off the color dola, but when I want to sample this renal artery at the origin, I like to tilt the patient right side up for the right main renal artery left side up for the left main renal artery.

When we are at the origin of the renal artery, very often we have this aortic wall reflection, which is a good sign that we are indeed very close to the origin of the renal artery.

For the main artery, we like to tilt the patient to one side and hit at the renal artery at angles, which are very close to zero degrees. So typically we go through the liver through the bulk of the kidney into the hilum and from the hilum to the origin of the atory at angles which are close to zero degrees.

For the left main atory, very often we might have to go little more posterior and lateral.

We can also see the origins of the renal artery in a sagittal section through the inferior renal caver.

For the intradural arteries, we like to have a posterior lateral approach. This again is a wonderful view to pick up accessory renal arteries, and the reason why we see accessory renal arteries in this view and not in other views is because in this view we are able to see the upper pole and the lower pole of the kidney simultaneously.

When we look at intraretinal arteries, it is very important to sample each and every segmental artery with a correct dopplar technique.

When we look at intraretinal arteries, they show a quick systolic upstroke that is an early systolic peak and we have a good diastolic flow. We also look at what is known as the acceleration time and the slope of the systolic upstroke things which we'll discuss.

Again, there can be variations and one of the most common variation we see in practice is accessory renal arteries clue towards a diagnosis of renal artery sclerosis can come with a good gray scale of the renal artery origin.

For example, here we see an aro plaque at the origin of the left main renal artery.

Clues from Perfusion and Gray Scale

The other clue which can lead you to a diagnosis of renal artery stenosis, is looking at the perfusion of the kidneys.

For example, if you look at the right kidney and compare it with the left side, in this case, the left side has a, has a decreased perfusion as compared to the normal right side in this patient. Whereas in this patient, the perfusion in the left kidney is better than the perfusion in the right kidney.

This is a good clue towards a possible renal artery stenosis in the left main renal artery of this patient and in the right main renal artery of this patient.

So this is a very quick test to look at possible renal artery stenosis. Of course, the definitive diagnosis comes when we look at the renal artery.

Direct Criteria for Renal Artery Stenosis

Typically on colored obl we might see low saturated colors, we might see aliasing, and when we put our sample at that point, we typically see high velocities.

Typically if the velocities go above 180 centimeters per second, and if your technique is correct or if the TTA ratio is more than 3.5, it is considered as diagnostic for renal stenosis and that's a very good direct criteria.

Very often we might see post stenotic dilatation of the renal artery and we might see marked turbulence at the site of stenosis and beyond the site of stenosis.

Typically, the turbulence is reflected as multiple peaks and spreading up of the spectral waveform.

So it looks very simple. You look at the renal artery, pick up the point of maximum sing, put your sample and document high velocities and make a diagnosis of renal art stenosis.

But we all know that life is not so simple and in practice we have a lot of difficulties. This could come up because of patient related factors like opacity, a non-cooperative patient or this can come up because of your poor technique and because of this, we turned our attention from the manal artery to intrarenal arteries with the basic principle that whenever there is a significant stenosis in the manal artery, the intrarenal blood flow becomes dampen.

This is reflected in the waveform, which is typically described as a tardis parvis effect.

Indirect Criteria: Tardus-Parvus Effect

So typically when we look at the intrarenal waveforms, we look at the acceleration time, which is the time taken from the start of the sly to the peak systole and the acceleration, which is the slope of the systolic upstroke.

Both these measurements are given to us by the machine, so that's a classical intra inal waveform on the normal side, and that's a classical intradural waveform. On the abnormal side, we see here that the waveforms are overall dampen. The time taken to reach peak systole is almost double and the slope is also abnormal.

We can also observe that the early systolic peak, which is seen in a normal artery, is not observed in the intraoral waveform. On the abnormal side, this waveform is diagnostic of renal artery stenosis.

It has been also observed that the intrarenal ri beyond the stenosis in the intrarenal arteries is lower at the site of stenosis as compared to the opposite kidney, but will come to this point a little later.

So here's a classical example. On the right side we have a dys stenosis. Because of atherosclerosis there are very high velocities and we have dampen flow.

But when I went into the left intrarenal arteries of this patient, I had difficulty in evaluating intrarenal segmental arteries, and every time I thought that I am in an intrarenal artery, I used to get this waveform.

So in the beginning we didn't know what this pulsitile waveform represents, but now we know that whenever we have patients who have got renal artery occlusion or a critical stenosis, we get this typical intrarenal retrograde pulsatile flow.

Pulsatile Waveforms in Renal Artery Occlusion

In patients who have got renal artery occlusion, the input pressures are so low that pressures from the right side of the heart get easily transmitted into the intrarenal veins and what we see in this waveform, a prominent VA veins, intrarenal veins with the pulsitile waveform, this is now considered as diagnostic of renal artery occlusion or a very critical stenosis.

So if in a patient you see bilateral pulsatile waveform, then the first diagnosis should be congestive cardiac failure. But if the patient does not have a cardiac failure and you see bilateral intrarenal pulsatile waveform, then we should think of bilateral renal arteries occlusion or an aortic occlusion for example, in the same patient whom we saw pulsatile waveform.

If you look at the origin of the renal arteries, we see that there is a thrombus or there is a plaque like structure on color. There is no flow and an angiography, there is hardly any feeling of the renal vessels confirming a diagnosis of bilateral renal artery occlusion.

As another patient where we saw bilateral intrarenal pulsitile waveform, and if you look at aorta, there's a thrombus in the aorta which is totally occluding the aorta including the origins of the renal arteries.

So a bilateral pulsitile waveform in both the kidneys of course could be because of bilateral renal artery occlusion or it could be because of an aortic occlusion.

Sensitivity and Applications of Indirect Criteria

The indirect criteria are very sensitive in picking up significant renal artery stenosis. They can also give us wonderful clues.

For example, in this patient with AOR two arthritis, there is a superior meic artery stenosis. There's a left main renal artery stenosis with very high velocities.

When you come to the right kidney, there are two arteries, one supplying the upper pole and one supplying the lower pole. If you look at the segmental artery wave form, the upper pole waveform is dampened tardis powers, whereas the lower pole waveform is normal.

If you look at only this waveform, one can postulate that this patient has a right upper pole accessory artery stenosis and rightly so. If you look at the angiogram, the upper pole is feeling up in a delayed phase suggesting that the seno there is a stenosis of the right upper pole accessory artery.

Here's another example where segmental arteries can give you a good diagnosis. If you look at the wave forms in the lower pole segmental artery and the upper pole segmental artery, we realize that the velocities in the lower pole are normal, whereas the velocities in the upper pole segmental artery are very high to the tune of almost 200 centimeters per second, which is quite unusual.

And this tells us that this patient has segmental artery stenosis that is intrarenal artery stenosis and now we know then even if one segmental artery has stenosis, the patient could have hypertension.

So this is a very important diagnosis which can be made by looking at segmental arteries very carefully.

Case Example: Young Hypertensive Patient

This is a young patient who was hypertensive very severe. He was almost on four drugs. He was in investigated earlier, but not in the correct manner.

The right main renal artery is normal. The intrarenal artery waveform on the right side is normal, but if you look at his left intrarenal arterial waveform, we have a TARDIS powers effect, and if you look at the intrarenal veins, we have a pulsatile waveform.

This suggests that this patient has left renal artery, severe critical stenosis or maybe an occlusion also. So on B mode, we were not able to look at the renal artery. We saw an rommet plaque there. The main renal artery was not seen. There were multiple collaterals, in fact, in the region of Maine renal artery and all we got on pulse doppler was a pre occlusive thumping.

We did an angiography. He had almost occluded left renal artery be able to put in a stent, and this person from four drugs went on to only two drugs and did very well after stenting.

Limitations of Indirect Criteria

We have to realize that the indirect criteria have some limitations. Typically, they're insensitive for diagnosis of renal stenosis, which is not significant like 50 or less than 60%. However, we are not much worried in this group of patient.

We have to also realize that there is a relative insensitivity in patients with elevated ri. What I mean, thereby typically in patients who have got medical renal disease, the RI is elevated with a low diastolic flow. In this group of patients, it requires a higher degree of stenosis of the main renal artery to give rise to tardive power effect and therefore this limitation of the indirect criteria has to be kept in mind.

In this group of patients stenosis, on the other hand, lowers Intrarenal RI here for example, we have right intrarenal waveform with an RI of about 0.64. This is a patient who has got left main renal art stenosis. We see TARDIS powers waveform in the intradural arteries, but along with TARDIS powers effect, we also realize that the RI is lower as compared to the right side, which is the normal side.

We now know that lower intradural RI at a site of stenosis as compared to the contralateral kidney, is not only an indication that renal stenosis the likely cause of hypertension, but is a good prognostic factor for revascularization procedure, especially if the kidney size is good.

It tells us indirectly that the patient is still in an acute phase, which is an independent or a transition phase as compared to a chronic phase where multiple factors come into picture and the RI tends to be high.

Thus, intrarenal RI is a very good tool for prognosis rather for diagnosis rather than diagnosis of renal artery stenosis and lower the intradural RI beyond stenosis, it is better for the patient

Post-Revascularization Evaluation

If You have selected your patients well and if you do a revascularization procedure, like for example, a stenting, and if there had been a TARDIS powers effect intrad ally, the wave forms come back to normal immediately after stenting.

Here, for example, before stenting, we see dampened flow or TARDIS powers effect within the intradural arteries and after stenting there's a significant improvement in the waveform.

If you see such an improvement. This group of patients do very well after revascularization procedure in future

Doppler is again very useful in evaluating stents to diagnose re-stenosis. Here for example, we see alienating happening with very high velocities suggesting stent stenosis.

The criteria which are currently used diagnose stent stenosis are similar to those which are used for diagnosis of native kidney in stenosis. But typically when we are evaluating patients with stents, we focus again on intrarenal wave forms.

Here for example, this is a patient who a stent on the left side, his intrarenal waveforms had come back to normal. This patient unfortunately had some problems and because of dehydration, he came to us with hypertensive crisis and what we realized is that we had difficulty in looking at his stent, but when we look at his intrarenal waveforms, what was normal has come back to TARDIS power effect.

This is a very good clue towards a diagnosis of stent stenosis or a stent occlusion. In fact, in this patient we managed to do a stent angioplasty and we realized that after angioplasty, the intradural wave forms have come back to almost normal.

So intradural wave forms give us a very good idea about stent patency.

Other Causes of Renal Vascular Hypertension

We have to realize that renal vascular hypertension can be caused not only ROS sclerosis of fibromuscular dysplasia, but we have other causes of renal vascular hypertension. Also, needless to say that the most common causes atherosclerosis, we often see fibromuscular dysplasia typically in young females where we see a beed appearance of the renal artery.

Typically, as we know this involves the mid or the distal portion of the renal arteries. And again, other modalities like Mr. NO can be very useful, but very often we can have aorta arthritis, giving RA to renal vascular tation aorta.

Arthritis can affect the aorta and give rise to renal vascular application where we see intrarenal dampen flow in both kidneys or it can affect the aorta and it can also affect the renal arteries directly.

Here, for example, there's a direct stenosis of the right main renal artery. Here we have a case with severe aorta, arthritis aorta shows marked thickening of the walls, some areas of focal dilatation and both the renal arteries are involved by oto arthritis with marked narrowing of the lumen.

Another patient with aorta arthritis called with renal vascular tation. Not only is the aorta affected, but the right and the left mean renal arteries are also affected by aorta arthritis.

Whenever you suspect aorta arthritis, the best thing is to put your probe on the carotid artery or the subcon artery. Typically what we see is marked thickening of the carotid or the subcon artery, which is diagnostic of aorta. Arthritis, aorta, artery can all not only involve the abdominal aorta, but it can also involve the arch of the aorta or the descending aorta.

This is difficult to evaluate on ultrasound and we might have to take help of CT or even a conventional angiography to look at the arch and the descending aorta as well.

Case: Coarctation of the Aorta

This is a patient who came with hypertension, young patient. If you look at the upper abdominal aorta, we realize that we have dampen flow with tardive power effect. This tells us that something is gone wrong approximately, but the walls of the aorta look quite okay and therefore the next vessel lab would do to evaluate this patient, patient is to look at the subc artery.

The subc artery walls are again normal and we have beautiful waveform with these two findings. The only diagnosis one can consider in this patient would be a coarctation of the aorta, which it was in this case undoubtedly, CT NO and a conventional NO are diagnostic for coarctation of the aota, as in this case, we not only confirmed it, but we also put in a stent and expanded that segment.

Case: Polyarteritis Nodosa

This is a 10-year-old boy who presented with hypertension, and if you look at the renal arteries, typically wherever there's a bifurcation of the renal arteries, we see small aneurysms at the bifurcations. This was confirmed on angiography and this was a case of polyarthritis, no doza.

Case: Mycotic Aneurysm

This is a patient who was very sick but also hypertensive and the cause of this hypertension was a mycotic aneurysm of the renal artery. So that's an aneurysm of the renal artery.

If you look at the waveform of the veins, we see a pulsitile flow. There's hardly any flow seen in the renal arteries. On follow-up, this patient did well and as things resolved we started seeing flow within the intra arteries and the vein, which was sile earlier, also showed normal waveform.

Unfortunately, this patient succumb to fungal infection in the brain.

Case: Post-Traumatic Renal Artery Occlusion

This is a patient who again, had history of trauma and presented with hypertension. What we see is that the left, the left renal vein is seen very well. However, the renal artery was not seen.

If you look at intradural wave forms, again, we have tardis promise effect, and if you look at the wave form within the veins, we see a pulsitile flow.

So here again, non visualization of the renal artery or occlusion of the renal artery because of trauma gave rise to renal vascular hypertension. But this is a post-traumatic case.

Acknowledgment

I have to acknowledge several references, which we have used, in preparation of this talk.