Nodal Disease: Sonographic Findings - HD

Introduction

My name is Carl Redding.

I'm a radiologist in Rochester, Minnesota at the Mayo Clinic, and I'll be talking today about the appearance of lymph nodes in the neck in thyroid cancer.

Sonography is a very powerful tool that can be used in the evaluation of nodal disease in the neck, and we'll see that the sonographic findings can distinguish benign from malignant nodes with a high degree of accuracy.

I have no relevant financial relationships to disclose.

Overview of Metastatic Papillary Thyroid Cancer

What we'll be talking about today is the appearance of metastatic papillary thyroid cancer, which is by far the most common type of thyroid cancer encountered today.

And we'll see that the gray scale features of size and shape, but more importantly internal architecture with the presence of internal calcifications or internal fluid collections is very specific for metastatic disease.

Also, the color Doppler appearance of irregular increased peripheral blood flow is also very suspicious for metastatic disease as opposed to normal hilar blood flow.

We'll conclude with a look at the postoperative thyroid bed as lymph nodes can occur here as well, but this can be a difficult area to examine.

Gray Scale Features

Size

So we'll begin with the gray scale features.

Traditionally size has been used with MR and CT to distinguish benign from malignant nodes, but it's been our experience and that of many others that size is not a reliable predictor of malignancy.

The short axis measurement is somewhat helpful.

If a node is greater than five to eight millimeters in its short or smallest axis, then it's considered suspicious for malignancy or up to seven to nine millimeters at level two, higher in the neck, at the jugular digastric level.

However, this is the least specific of all sonographic features and there will be many false positive and false negative examinations if we use size alone.

Shape

In addition to size, what else can we use?

It turns out that shape is very helpful and a rounded shape often predicts malignancy, where a node that is long and thin where the short axis is less than half the length of the long axis is likely to be benign.

But a rounded node where the short axis is greater than half the length of the long axis is likely to be malignant.

And in several studies, 50 to 80% of these rounded nodes are malignant in patients with thyroid cancer.

So this is a very useful finding to use particularly during a rapid screen of the neck to look for rounded lymph nodes.

And the shape of the node likely reflects its softness or firmness where a slender shape with a soft benign node conforms to the adjacent tissue planes.

As we see here, there's no distortion of the adjacent tissue structures on real time imaging of a normal neck posterior to the sternal cla mastoid muscle.

We see multiple small normal slender lymph nodes that have no mass effect on surrounding tissues.

Malignant nodes have a different appearance.

They tend to be rounded, likely because they're firm and they have mass effect on surrounding tissues.

We wouldn't mistake this large node in the neck as being abnormal and the way it has mass effect on adjacent tissues.

But even smaller nodes, a small one, just five millimeters in size, we can see how it also distorts the adjacent tissue planes in the adjacent vessel on real time imaging.

We can see this rounded node lateral in the neck note how the muscle drapes over the surface of the node because of a distortion from the underlying firm malignant lymph node.

So again, size not as important shape more important, the nodes on the left are benign.

They're slender and tapering.

They have no distortion of adjacent tissue planes, but the node on the right, it's rounded in shape and even though it's quite small, it distorts the adjacent tissue planes.

So the nodes on the left should be malignant the node on the right benign.

Internal Architecture

Of the gray scale features, though internal architecture is perhaps the most reliable predictor of malignancy where we look inside the node and look at its features within the node, benign nodes tend to be homogeneous.

Hypoechoic have a central hilos malignant nodes heterogeneous of variable echogenicity contain can contain internal calcifications and fluid filled areas.

And we'll look at examples of these types of features.

These are two benign nodes. They're slender and tapering.

Again, as we look inside the node, they tend to be hypoechoic and homogeneous with the exception of a central internal hilus within both of the lymph nodes and that hilus is visible in more than 70% of normal nodes.

The absence however, can be normal, particularly in the smallest lymph nodes.

There's also a spectrum of appearances of the hilus.

It can range from a very thin structure to a more thickened structure that nearly replaces the central portion of a lymph node.

It can be indistinct a sort of cloud-like pattern within the central portion of a node, and also it's generally central within the broad surface of the node, but sometimes can be centric as in this node where it lies in the superior aspect.

Malignant nodes, this one is rounded.

We often do not see the hilos because the node is completely infiltrated with malignancy.

These may be hypoechoic as many types of metastases are.

But one type of particular occur or appearance of papillary cancer is that it is frequently hyper coic relative to the adjacent musculature in the neck.

We're also starting to see another finding within the central portion of this node.

Small areas of increased echogenicity and what these represent are calcifications within lymph nodes.

In these two examples, we see posterior acoustic shadowing from the calcifications.

And this is the same as we see in the primary thyroid cancer within the thyroid gland.

As seen on the right, the same type of appearance, these calcifications are seen in 50 to 70% of metastatic nodes.

So it's a very helpful and very common sort of appearance to look for when we're examining lymph nodes in the neck.

On this longitudinal view, we see multiple enlarged nodes adjacent to one another on a real time transverse clip.

As we go transversely through these nodes, we see multiple enlarged masses with mass effect on adjacent tissues, lots of calcifications within them, very specific for papillary cancer.

There are a few other causes of calcification in cervical lymph nodes occasionally in granulomatous disease or treated lymphoma.

But rarely do these actually cause difficulty in distinguishing them from papillary cancer, which is much more common as a cause of calcification.

This node also shows a small amount of fluid within its lateral portion, which is another important feature to look for.

This particular node has a large amount of internal fluid within it, the corresponding bivalve specimen, we see that large amount of clear fluid within the node.

These may have a thickened wall, some internal nodularity, which we nicely see on the pathologic specimen and on the ultrasound image they may have internal septations and these are seen in 20 to 70% these fluid filled areas of metastatic node.

So again, a very helpful feature to look for in metastatic disease.

There can also be a spectrum of the appearance of the fluid component.

It can range from a very small amount in this node to larger areas within this midsize node to nearly completely replacing the node here on the right within the solid components on the right, we also do start to see small micro calcification.

So both of those features of fluid and calcification are seen here.

Sometimes the node is virtually completely replaced by fluid and this often occurs in the younger patients.

And this can cause difficulty in differentiating it from one other pathologic process, which is a brachial cleft cyst that often occurs in younger patients as well.

The second brachial cleft cysts lie in a very typical location, though they lie adjacent to the anterior aspect of the sternal cla mastoid muscle at the level of the angle of the jaw.

So if we were to do ultrasound and CT imaging of a brachial cleft cyst, what we would see is a cystic mass sono graphically, often with some internal debris.

And on ct the cyst is located in a very typical spot between the sternal clotted mastoid muscle laterally, submandibular gland anteriorly, and the internal jugular vein and carotid artery medially.

So it's high at level two in the neck.

Metastatic papillary cancer tends to have a somewhat different appearance.

It's generally more of an admixture of solid and cystic components, and it lies at a lower level in the neck, generally level three or four.

It can extend more superiorly into level two, but usually the lower levels are involved first.

So it would be rare to find a single cystic papillary cancer node at level two.

And if we see something there, we should think more of a brachial cleft cyst.

Another cystic mass that you may encounter in the neck, which is not a malignancy, but we need to be aware of is this cystic structure here adjacent to the internal jugular vein in the low left neck with gentle pressure with the transducer, we see that there's actually flow between these two structures and what this represents is the distal end of the normal thoracic duct.

The large structure that extends superiorly through the chest to then circle around the internal jugular vein and have its confluence with the vein on the lateral side, there's a similar smaller right thoracic duct in the right side of the chest.

And sometimes though we don't see the communication as clearly.

We'll just see a cystic structure low in the left neck near the jugular vein.

We think it might be a cystic metastasis, but if we're aware of this normal structure, it can be helpful.

If you do place a needle into the distal duct, it won't damage the duct, but you just won't get any diagnostic cells from that aspiration.

So we've looked at a number of features, gray scale features of lymph nodes, and if we were to compare two nodes that initially look very similar, the one on the left is slender and tapering.

We look inside, there's it's homogeneous, perhaps a indistinct internal hilos, whereas the node on the right has a slightly more rounded configuration.

It wouldn't meet the criteria of its small axis being greater than half the length of the long axis, but it does have mass effect on the adjacent tissues where we see the adjacent muscle distorted by the node itself.

Also within the node we see microcalcifications, we see a small amount of fluid within the superior aspect of the node.

So we could say that the node on the left is very likely going to be mal benign.

The node on the right is very likely going to be malignant.

So just with grayscale features, we can do a very good job of separating these two types of nodes.

Color Doppler Features

Another method to employ though that can give one even a higher degree of confidence is to use color doppler when evaluating the lymph nodes.

And to understand their color doppler appearance, we need to understand the structure of a lymph node.

It generally has entering afferent lymphatics from the periphery of the node exiting larger efferent lymphatics centrally in the hili and entering and exiting vessels through the hilos of the node.

So when we look at this with gray scale imaging, we get the indistinct appearance of the hilas in this node.

It's increased reflection from the central vessels, the larger caliber lymphatics, perhaps some adipose tissue giving the brighter structure centrally.

And if we look with color or power doppler here, we see flow within the hili of the node that is branching in a regular arbor rising pattern, it doesn't quite reach the periphery of the lymph node.

So the central hilar type of flow or even no flow is what we would see in normal types of lymph nodes.

In malignant nodes, they have a different appearance.

They have large amounts of internal malignancy.

And when we look with colored doppler imaging, we often see this irregular increased peripheral type of flow.

No evidence of a central hilar pattern.

It's likely that there's some recruitment of neovascular through the capsule of the node, giving it this type of appearance.

And with side by side imaging of examples of a benign node.

Here we see that hypo coic node, a faint central hilus.

With doppler imaging, we see flow in a irregular branching pattern, not quite reaching the periphery of the node as opposed to a malignant node on the right it's rounded.

We see a very irregular type of pattern, lots of flow within the periphery of the node and a much different appearance than the highler flow.

And in one study, the accuracy of just the color doppler appearance alone approach 90% in distinguishing benign for malignant nodes.

So this is a very useful method to employ.

So if we were to apply all of these features, the gray scale and the color in this case, this node is slender and tapering, it doesn't really have much mass effect on surrounding tissue planes, but when we look inside it, the upper half is more echogenic.

There might be some microcalcifications.

When we place color doppler flow here, we see lots of abnormal flow within the superior aspect of this node, very little within the coddle portion or none really.

And at surgery the upper half is infiltrated with tumor, the lower half was benign.

Another similar example, a normal appearing node in its superior part hypoechoic a hili within it, but within the inferior portion we see a five millimeter echogenic area, a similar finding on the corresponding pathologic specimen.

We look at that in real time.

It's more clear that it its presence.

We also see more increased flow within that hyper coic portion than the smaller amounts of flow within the normal remainder of the node.

Fine Needle Aspiration and Thyroglobulin Assay

Once we find an abnormal node sono graphically, if it's going to change the management of a patient, then one would do an FNA of the node by placing a needle into that under ultrasound guidance using a similar process that one would use for thyroid nodule FNA.

In addition, however, to sending this for cytologic analysis, it's becoming the standard practice to send this as well for thyroid gly bone assay to distinguish if the node is a differentiated type of thyroid cancer such as papillary cancer.

And to do that, there are a number of methods in our practice.

We simply wash the needle biopsy with a small amount of saline solution.

And after several passes in the node one and washing the needle, after we had placed the material on a slide for cytologic analysis, we place that washed fluid into a standard type of test tube.

You'll have about a cc of blood tinged fluid.

And in this one study of FNA of suspected papillary cancer in 122 cases, many of the results were clearly positive.

Some were clearly negative.

In 19 cases, though the cytology was indeterminate, but in those 19 cases, 18 of the 19 were diagnostic on the thyroglobulin assay.

Either the result was markedly elevated in the hundreds or thousands of nanograms per milliliter in the positive cases or near zero in the negative cases.

So a very helpful type of test and it's relatively inexpensive and rapidly performed.

So it would be very helpful in the biopsy of these peripheral lymph nodes to also send this for thyroid globulin assay.

Postoperative Thyroid Bed

In the last few minutes, we'll focus on the postoperative thyroid bed as this can be an area that is difficult to examine sonographic and understand what we're seeing.

But there are several types of things that we can see within the bed, and we'll look at examples of these.

One thing that you may see, one finding is this triangular type of mid-level echogenicity material within the bed between the trachea and carotid artery.

When we place color doppler flow on this, we get small amounts of flow within it.

This is the typical appearance of some residual thyroid tissue in the bed.

The surgeon often leaves a small amount of tissue they're trying to avoid damaging the recurrent laryngeal nerve or the parathyroid glands within the bed.

They may list that within the operative note, but it may not be listed there.

But if we see tissue with this triangular type of mid-level echogenicity appearance, we say this has the appearance of residual thyroid tissue in the bed.

If they're treated with radio iodine, this will slowly shrink over time.

If there's a recurrence in the bed, as we see here in the right neck between the carotid artery and trachea, it's often a large mass and irregular lobulated mass.

We would clearly say this is an abnormal mass within the bed and place a needle into that to obtain material show confirming its malignant nature.

Other times though, if the mass is smaller, it can be more difficult to define.

Here between the carotid and a trachea, we see a small nodule.

We look within the nodule.

We see small areas of increased echogenicity seen better on real time as tiny flex of echogenicity within the small recurrence.

And these are microcalcifications within this soft tissue nodule.

In a separate patient in another nodule in the left thyroid bed, it's rounded about six millimeters in size.

We look at that with real time.

We don't see these microcalcifications, but when we place color doppler a flow on that, we see lots of irregular flow, a lot of flow in the periphery of the node, and that's an abnormal finding.

And indeed this was also a recurrence in the thyroid bed.

So microcalcifications abnormal color flow, very important to look for in these nodules within the bed.

Most of these tiny nodules you're going to see within the bed though, are going to be benign.

This one is very small, just measuring two by three by four millimeters.

We look carefully with and we don't see microcalcifications within it.

We use colored doppler imaging with very high sensitive technique.

We don't see any abnormal flow within this.

So in our practice, I say these are tiny nodules in the thyroid bed of doubtful significance.

And unless you see those calcifications, unless you see the abnormal blood flow, you will be right the vast majority of the time that this is a benign process in the bed.

Perhaps tiny nodes, perhaps a bit of postoperative tissue or scar tissue, but not malignancy.

There is one other finding to be aware of in the thyroid bed.

Here we see two hypoechoic nodules, both with increased echoes centrally within them.

So a little bit of a worrisome appearance are these microcalcifications.

We place color doppler on this. There's very little flow.

There's a little flow at the periphery, but nothing really to speak of within this nodule.

But if we look very carefully at that central echogenic material, we see that it's composed of parallel lines.

And here in a different patient, a specimen, this is a suture granuloma with a granulomas reaction developing around the suture material centrally.

Sometimes you won't always see the suture material.

You might see a little bit of echogenic material centrally or sometimes even not that.

But if we do see the parallel lines, we can very comfortably say This is a benign suture granuloma.

If you're not sure and you do place a needle into this, you will just get inflammatory cells, but no malignant cells.

Summary

So in summary, we've looked at a number of features of cervical lymph nodes, their gray scale features of size and shape, but more importantly, internal architecture.

Also importantly, the color Doppler appearance, and also looked at the postoperative thyroid bed where recurrence can also occur.

And I hope that there's been information here that will help you in your practice in distinguishing benign from malignant nodes with a high degree of confidence.

Thank you very much.