Basic Aspects of Renal and Adrenal Ultrasound

Introduction

Hello, my name is William Middleton.
I'm a professor of radiology at the Mallinckrodt Institute
of Radiology at the Washington University in St.
Louis. Today I'm going to present a lecture entitled,
basic Aspects of Renal and Adrenal Ultrasound.

Normal Characteristics of the Kidney

Okay, so let's start
with the normal characteristics of the kidney.
Normal renal size centers at about 11 centimeters plus
or minus two centimeters.
So the range is from about nine to 13 centimeters.
The echogenicity is compared to the liver on the right
and the spleen on the left,
and the right kidney should be equal
or slightly less echogenic than the liver.
The left kidney should be significantly less
echogenic than the spleen.
The renal parenchyma can be divided into the renal cortex
and the pyramids
and the pyramids are slightly less echogenic than the
cortex, although you don't always see the pyramids.
Notice on the image in the upper right hand corner,
that's a high resolution view of a renal transplant.
And you can see the location of the hypoechoic pyramids
with respect to the slightly urine distended CAEs.
The renal sinus is composed of fat
and fibrous tissue, as well as the vessels and lymphatics,
and it is hyperechoic
and is centered in the center portion of the kidney.
And then the outer margin of the kidney should be smooth.

Indications for Renal Sonography

The most common indication for renal sonography is in
patients with acute renal failure
to exclude hydronephrosis.
Now, in the general population, the yield
of finding hydronephrosis in this
clinical situation is only about 1%.
And unfortunately, false positives are
relatively frequent.
So even when patients don't have renal obstruction,
mild hydronephrosis is seen.
Now, the yield of sonography increases significantly if you
only look at high risk patients,
and those are patients that are postoperative from abdominal
surgery, have a history
or physical examination findings consistent
with a pelvic mass, have a history
of kidney stones, et cetera.

Diagnosis of Hydronephrosis

The diagnosis of hydronephrosis is made when there is
anechoic fluid separating the renal sinus.
In almost all situations, the renal
collecting system will be displayed as several
dilated infundibula that are connecting to
the renal pelvis centrally
and connecting to renal calyces
within the periphery of the kidney.
And this should be seen on both transverse
and on longitudinal planes.
If you only see it on the longitudinal plane,
but not on the transverse plane, it's probably not real.

Grading of Hydronephrosis

Hydronephrosis can be graded in
several categories.
Grade zero is considered normal.
Grade one is
where the collecting system is just barely distended
and barely abnormal, but the kidneys
otherwise within normal limits.
Grade two is a collecting system that's clearly abnormal,
but the surrounding renal cortex is well preserved.
Grade three is when the collecting system is clearly
abnormal and dilated and the cortex is thinned.

Obstruction and Hydronephrosis

Now, hydronephrosis most of the time is due
to obstruction, but that's not always the case.
You can have a patient that has hydronephrosis,
but the kidney is not obstructed.
And unfortunately, the corollary is also true.
You can have obstruction without having hydronephrosis.
And there's a couple of ways to sort this out,
or at least to help to sort this out.
One is to check arterial blood flow
by measuring resistive indices in the intrarenal arteries.
If the resistive index is unilaterally elevated on the
side of suspicion, then obstruction is likely,
and the cutoff value for an elevated resistive index is 0.7
or asymmetry between the two sides of greater than 0.1.
If the resistive indices are elevated bilaterally,
that doesn't help you in looking at the suspected side
of obstruction.
And if the resistive indices are normal,
that also doesn't help you in either excluding
or making the diagnosis of obstruction.
This is an example here that's being displayed
where the gray scale image shows clear cut hydronephrosis
and dilatation of the proximal ureter.
When you look at the resistive index of the
questionable kidney, it's 0.76
and when compared to the contralateral kidney,
which was 0.60,
so clearly there's asymmetry in the resistive indices,
and the resistive index on the right side is abnormal,
and this was a kidney that was obstructed
by a ureteral stone.
Now, another way to get indirect evidence about the presence
or absence of obstruction is to look at the flow
of urine out of the ureters and into the bladder.
If the ureteral jets are absent on one side, that means
that side is likely obstructed.
If there is a low level continuous flow of urine out
of the one side, then
that also likely indicates obstruction.
Now, the advantage that ureteral jets have
over resistive index measurements is
that they're affected immediately when obstruction occurs,
and they resolve immediately
when obstruction is relieved.
The disadvantage is that you have to scan
through the bladder for five minutes in order to make sure
that the ureteral jets are clearly absent.
And you also have to have a difference in the density
of the urine that's exiting the ureter
and the urine that's residing within the urinary bladder.
So here's another example where you can see mild
separation, very mild hydronephrosis in
that longitudinal view of the kidney.
When you look at the resistive indices,
the right kidney had a resistive index of 0.71.
The left had a RI of 0.57, so that would indicate that
that kidney, although only showing mild hydronephrosis probably is obstruction.
When we looked at the urinary bladder, we saw
that there was a detectable ureteral jet coming from the
left ureteral orifice over a span of five minutes.
We never saw a jet from the right,
and that also suspects or makes you suspicious of obstruction.
And very close analysis of
that distal ureteral orifice showed a stone in
that distal ureter.

Kidney Masses

Now let's move on from obstruction
and talk about kidney masses.
The most common kidney masses simple cyst,
the frequency of which increases with age.
And by the time you reach 50 years,
you have about a 50% chance of having a kidney cyst.
Ultrasound is clearly the most accurate way
of evaluating cystic lesions in the kidney.
And it's especially useful when an indeterminate mass is
seen on a CT or MR
or a urogram where a cyst is highly suspected.
The ultrasound criteria for diagnosing a simple cyst is the lumen should be anechoic.
The back wall should be well-defined.
There should be posterior acoustic enhancement,
and there should be no measurable wall,
all of which are satisfied on the image displayed.

Lesions Mimicking Simple Cysts

Now, what can look like a cyst but not actually be a cyst?
There's a number of things.
Lymphoma is a solid tumor,
but unfortunately it can look like a cyst
because it's very homogeneous and generates few reflections.
Fortunately, this doesn't happen very often,
but this is an example of hypoechoic lymphoma.
Calyceal diverticuli can mimic cyst arterial venous fistulas
can mimic cyst and aneurysms,
and pseudo aneurysms can mimic cyst.
This is a pseudo aneurysm that looks very much like a
simple cyst, but on Doppler analysis, you can see
that it has readily detectable internal blood flow.

Complex and Hemorrhagic Cysts

Now what about cyst that aren't simple,
in particular cysts that are hemorrhagic?
Well, initially when a cyst undergoes hemorrhage,
it will have a solid appearance as shown here,
often will be heterogeneous, but will appear solid.
Now, over time, that cyst
and the clot within the cyst starts to lyse
and the cyst becomes more complex, evolving into a lesion
that may be cystic with solid elements
or cystic with thick septations.
Now, eventually the cyst will,
a hemorrhagic cyst will completely liquefy
and may have diffused low level echoes
as shown in this image,
or may have a fluid cellular layer
as shown in this image.
But if you wait long enough,
and this may take a matter of several weeks or months cyst will usually convert back
to a simple appearance.
Now, in general, we think about cysts
as occurring in the cortex,
but there is a subpopulation of cysts
that occur in the peripelvic region.
These are felt to be lymphatic in origin.
They're usually solitary,
but it's not uncommon for them to be multiple
as in this example, and they can be bilateral when they become quite numerous,
they can simulate hydronephrosis as we see in these two examples.
The difference between multiple peripelvic cysts
and hydronephrosis is that with hydronephrosis,
you can almost always see a distended pelvis
extended continuously into an upper and lower pole infundibulum
and many times into a mid pole infundibulum.
And with peripelvic cyst, you see separate cystic structures
that do not communicate.

Polycystic Disease

Polycystic disease is a disease
that affects the kidneys more than any other organ,
although the liver is often affected.
The pancreas is very rarely but occasionally affected,
and you can get cystic lesions in the vasculature of the
CNS in particular, cerebral aneurysms.
Up to 10% of patients
that have end stage renal disease in North America
and Europe have this
because of polycystic disease survival is approximately 10 years on average if it's untreated.
By the time patients reach the age of 60,
they will usually have renal failure.
It's an autosomal dominant disease,
but up to 50%
of patients will not have affected family members either
because of variable expression of the gene
or due to spontaneous mutation.
So don't be surprised if you see this on a sonogram
and there's no history of family disease type one.
Polycystic disease is the most common,
and it presents earlier and is more severe than type two
and is easier to diagnose.
The signs and symptoms
of polycystic disease are listed there on the left when you're trying to make the diagnosis in a patient at risk, IEA patient who has a affected family member,
the criteria are below the age of 30.
You have to see two cysts in one kidney
or one cyst in each kidney between the age
of 30 and 60 years.
You have to see at least two cysts in each kidney.
And over the age of 60, you need
to see at least four cysts in each kidney.
Now realize these criteria will only be applicable
to patients who are at risk, patients
who have affected family members.
If you applied these criteria to the general population,
you'd be diagnosing polycystic disease much too frequently.
And these are some various examples of polycystic disease
and various stages of severity.
Because there are so many cysts in patients
with polycystic disease, it's not uncommon
to get crystalline deposits within the cyst.
And when that happens, you'll see ring down
artifacts such as this.
It's also not uncommon to have cysts that have hemorrhage,
so you'll see cysts that look solid
and will ultimately go through the evolution that I described earlier.
But polycystic disease does not have
an increased risk of cancer.
So these solid appearing lesions are almost always hemorrhagic cysts and not tumors.
Now, polycystic disease is different
from acquired cystic disease.

Acquired Cystic Disease

Acquired cystic disease occurs in dialysis patients
and generally occurs in a high percentage
that have been dialyzed for over three years.
The cysts are variably sized,
and they almost always occur in small echogenic kidneys.
And this upper right hand image shows multiple cysts in
a kidney that measures only 7.6 centimeters in size.
Now, if the cysts become very numerous,
then the kidney may actually become enlarged
as we see in this lower left hand image.
And in those situations, it can be difficult
to distinguish this condition from polycystic kidneys.
Now, unlike polycystic kidneys
acquired cystic disease does have an increased
risk of tumors.
And if you see a solid appearing mass like this, you have
to be very concerned about a renal cell carcinoma.
As was the case in this particular patient.
Another complication
that these patients get is retroperitoneal hemorrhage.

Von Hippel-Lindau Disease

Von Hippel-Lindau disease is another abnormality
that presents with abnormalities in multiple different organ systems,
but in the kidneys, it produces multiple bilateral cysts
and multiple bilateral tumors.
The tumors may be solid as is seen in this example.
They may be complex as is seen here,
or they can be predominantly cystic
with little solid nodules, as is seen in this intraoperative scan.

Renal Cell Cancer

Now, we've kind of alluded to renal cell cancer that occurs in particular conditions.
Let's just talk about renal cell cancer by itself.
It's the most common solid renal mass accounts for 90%
of all renal malignancies.
Risk factors include advanced age smoking,
and as we mentioned, Von Hippel-Lindau disease and dialysis.
It's most often detected incidentally nowadays.
And traditionally it has been treated
with radical nephrectomy,
although nowadays, there's a big increase in the number of laparoscopic procedures
that are being done and the number of partial nephrectomies
and ablative therapies that are being performed
for renal cell cancer.
Sonographically, 50%
of renal cell cancers are hyperechoic to the cortex.
About 10% are similar to renal sinus fat.
In other words, they're markedly hyperechoic to the cortex.
And this is particularly common in small renal cell cancers.
30% are isoechoic, 10% are hypoechoic,
5% are predominantly cystic,
although many renal cell cancers have
some cystic components.
And then 10% contain calcification.
And here's a collage of various renal cell cancers,
a hyperechoic cancer here that looks very similar
to an angiomyolipoma, and we'll discuss that in a minute.
A hyperechoic lesion
that's just slightly more echogenic than the renal cortex.
An isoechoic lesion, a hypoechoic lesion,
a complex cystic lesion,
and then a lesion that is contains some stippled internal calcification.
Now, one unique thing that renal cell carcinoma does is it will invade the renal
vein as we see here.
Now, renal vein tumor thrombus differs from bland
thrombus and then it has tumor vascularity to it.
And many times, although not always, you'll be able
to detect that internal vascularity on color doppler
or power doppler techniques as we see here.
Now, eventually that renal vein thrombus may extend into the
inferior vena cava as we see in this transverse view,
and it may extend well into the cava,
and sometimes even above the diaphragm and into the heart.
As we see here,

Transitional Cell Carcinoma

Transitional cell carcinoma
is much less common than renal cell carcinoma,
but it is the most common urothelial cancer.
The rest of urothelial based cancers are squamous cells.
10% of transitional cell cancers are synchronous
and occurs much more frequently in the bladder than the
renal pelvis and more often in the renal pelvis
than in the ureter.
Now, ultrasound is not sensitive in detecting transitional cell carcinoma in the kidney ureter
or renal pelvis, better in the bladder.
When it is seen, it's often seen
as a solid mass centered in the renal sinus
or as shown in this image focal eccentric,
urothelial thickening seen here in the upper pole of this kidney
or thickening of the renal pelvis as seen in this transverse view.

Metastasis to the Kidney

Now, metastasis also occur in the kidneys
and in fact, an autopsy series.
They're seen in up to 20% of patients dying from cancer,
but most of the time they're small
and they're not imageable when they can be seen.
They're often infiltrative and they're frequently
and almost always solid.
They can be single, multiple unilateral or bilateral.
So the appearance unfortunately overlaps with that of primary renal cell cancer.
So in a cancer, in a patient that has an extra renal cancer,
when you see a renal mass, you have to consider metastasis.
And since metastasis will not require nephrectomy
and renal cell cancer will require nephrectomy biopsies
are appropriate in this situation.
These are examples of renal cell a small lesion
with a hyperechoic halo on the left
and an isoechoic lesion that was seen really only on Doppler techniques as an area of decreased vascularity in the kidney.

Lymphoma of the Kidney

Lymphoma also affects the kidney usually in the setting
of widespread disease elsewhere in the body.
Non-Hodgkin's disease is much more common in the kidney
than Hodgkin's disease.
It's very rarely symptomatic on sonography.
It typically appears as a solid hypoechoic
multifocal bilateral process.
Less often it's unifocal and unilateral or diffuse
and infiltrative, as we mentioned earlier,
it rarely is anechoic and can simulate a cyst.
And one unique thing about lymphoma is
that can infiltrate the perinephric region.
And in those situations it also looks very hypoechoic
and can simulate perinephric fluid.
Again, since lymphoma does not require a nephrectomy,
and it overlaps in its appearance with renal cell cancer,
if you are faced with that differential diagnosis,
it is appropriate to do a biopsy to distinguish those.
These are different examples of lymphoma.
This is an enlarged kidney that is just slightly lumpy,
bumpy, although it's hard to discern discreet lesions.
This is a lesion with multiple hypoechoic masses.
This is a lesion with a solitary unilateral
isoechoic mass.
And then here's another patient that has several lesions that are hypoechoic
and look at least somewhat like renal cysts.
And these are four different examples of perinephric infiltration of lymphoma that look very similar
to perinephric fluid collections.
So just keep that in mind when you're faced with that appearance.

Angiomyolipoma

Angiomyolipoma is a benign renal tumor that's composed
of vessels, muscle and fat.
It's the most common benign tumor.
It tends to occur in middle aged women.
And in patients with tuberous sclerosis,
it has no malignant potential.
So if the diagnosis can be made reliably,
the patient does not have to have surgery
unless the tumor gets to be big
and beyond the four centimeters in diameter,
these tumors tend to bleed
and sometimes they'll be removed just prophylactically
to avoid the bleeding complications.
80% of angiomyolipomas are homogeneous
and very echogenic, 20 to 30% will attenuate the sound beam.
And that's another thing that's unique to
or almost unique to angiomyolipomas Our approach to suspected angiomyolipomas is to do periodic ultrasound follow up if they're
less than a centimeter and to do CT
or MRI if they're larger.
CT and MRI are pretty reliable in confirming the presence
of fat in small or in larger angiomyolipomas.
It's more difficult with the smaller lesions.
And here's the typical angiomyolipoma.
You can see a very echogenic solid mass in
the cortex of the kidney.
Now, in this conventional view,
we don't see any sound attenuation from that lesion,
but when you look with a high resolution linear array,
as shown on the right, you can see some attenuation
of the sound deep to that lesion.

Oncocytoma

Oncocytomas are another benign renal neoplasm
that account for about 5% of all renal tumors.
The appearance overlaps that with renal cell carcinoma.
And as you can see in the two images on the right,
those are very non-specific solid renal masses
that look for all the world like renal cell carcinomas.
But when these were resected, they were found
to be oncocytoma.
Now, occasionally you'll see a central scar on a contrast
enhanced CT or MRI,
or if you do contrast ultrasound,
you can see it on a contrast ultrasound as well.
But in general, these lesions can't be distinguished from
renal cell carcinoma.
So they're treated surgically just like renal cells are.

Multilocular Cystic Nephroma

The last tumor that I'll discuss is a
multilocular cystic nephroma.
This also is a benign tumor that tends
to occur in young boys and older women.
They appear as masses with multiple variable size
non communicating cystic elements as shown on the two examples on the right.
Unfortunately, the appearance of multilocular cystic nephroma overlaps with the appearance
of cystic renal cell carcinoma and Wilms tumors.
So these lesions are also treated surgically just like renal
cells because we can't tell the difference.

Non-Neoplastic Mass-Like Lesions

Now, there are a few things that are non neoplastic
that can appear mass like on sonography,
and one is pyelonephritis pyelonephritis, typically if it
doesn't have a normal ultrasound appearance,
will appear as renal enlargement
with focal cortical changes.
Now, these are often wedge shaped. Not always.
They can be either hyperechoic or hypoechoic.
And unlike other organs
where inflammatory lesions are hypervascular in the kidney,
infection causes decreased vascularity,
Urothelial thickening can also be a sign
of pyelonephritis.
But occasionally you'll get focal masses
as we see on the two images on the right that will look
for all the world like a renal neoplasm,
but will turn out to be inflammatory in nature.
And those often have to be correlated clinically
and sometimes need to be biopsied to prove that they
truly are inflammatory.
Renal abscesses are another inflammatory condition
that can simulate the appearance of a cystic renal cell carcinoma.
They like renal cell carcinoma, can appear
as complex cystic masses.
And to make the diagnosis, you really need to correlate
with the clinical history and again, aspirate the lesion
and see what you get for further evaluation.

Summary on Renal Masses

So just in summary, renal masses often have characteristic ultrasound features,
but like all modalities, there's a fair amount
of overlap in the ultrasound appearance of both benign
and malignant and non neoplastic renal masses.
So ultrasound should be viewed as complimentary to CT
and MR when evaluating renal masses.
And it's especially valuable in evaluating
cystic lesions.

Renal Stones

Now, I also need to discuss renal stones.
We no longer do ultrasound as often for evaluating patients with suspected stones,
but you can see stones with sonography
and you should become familiar with the appearance.
They really appear similar regardless of the type of stone,
whether or not you see them depends on how
large they are.
And stones that are five millimeters
or smaller get progressively harder to see.
On the other hand, stones that are five millimeters
or larger are seen fairly reliably
and they all appear as hyperechoic lesions most
of the time with an associated shadow.
And oftentimes with a twinkle artifact.
So this is your hyperechoic lesion with a shadow.
This is a large staghorn calculus that appears hyperechoic with shadowing.
And here's a twinkle artifact on color doppler seen from a very small stone that was difficult to detect
with gray scale.
Now realize that renal stones are more difficult
to detect than gallstones.
Gallstones ultrasound is fantastic.
Renal stones ultrasound is much more limited,
and that's reason that we do non-contrast CT to identify renal stones nowadays.

Medullary Nephrocalcinosis

Now, another type of calcification in the kidney
is medullary nephrocalcinosis.
This occurs most frequently in patients with
hyperparathyroidism, renal tubular acidosis
and medullary sponge disease.
This causes increased echogenicity to the renal pyramids,
as you see in the first two images below.
And it tends to start in the periphery of the pyramids
and then progress into the central aspects of the pyramids.
As the calcification becomes more progressive, you'll start
to see shadowing associated with these hyperechoic pyramids,
as you see on the third image.
Now, ultrasound is very sensitive in detecting medullary nephrocalcinosis,
which is a little strange given
that it's got limitations in detecting renal stones.
But medullary nephrocalcinosis is seen very easily
with sonography probably as well
or perhaps even a little bit better than seen on ct.

Renal Doppler

Okay, now I wanna shift gears a little bit
and talk about renal doppler
and first talk about renal arterial doppler.
Specifically, renal arterial doppler
for the detection of renal artery stenosis,
there's a variety of criteria that have been established.
These are the ones that I rely on
most heavily.
One is on color doppler imaging detection
of focal flow abnormalities that include focal aliasing
of the doppler signal and focal vibration
of the perivascular tissues around the stenotic site.
Measurement of the waveform
of velocities is also very helpful.
And the cutoff value
for renal artery stenosis is a peak systolic velocity in the
main renal artery greater than 200 centimeters per second,
or an elevation of the ratio between the renal artery
and the aorta, the renal to aortic ratio
or RAR greater than 3.5.
And here's some examples.
An upper left is an example of focal aliasing
where you see this abrupt color conversion in the proximal left renal artery.
Upper right you see this focal tissue vibration manifest as extravascular color dots
equally distributed between red
and blue in the areas around the right renal artery.
The lower left is a patient with elevated peak systolic velocity of 327
centimeters per second secondary to stenosis.
And in the lower right is the patient
that has a borderline elevated peak systolic velocity in the
proximal right renal artery of 213
centimeters per second.
But when you compare that to the velocity in the aorta,
you see that the renal to aortic ratio,
it's slightly greater than five.
Meaning that this is very likely
to be a significant renal artery stenosis.

Limitations of Renal Arterial Doppler

Now there are limitations in renal arterial doppler.
And these include poor visibility
of the artery secondary to a variety of causes,
but most frequently obesity, bowel gas,
and shortness of breath.
Sometimes the doppler angle is very limited
and you can't measure velocities at a doppler angle greater than 60 degrees.
Extensive arterial calcification can cause enough shadowing
that you just can't evaluate certain
segments of the renal artery.
Cardiac arrhythmias can affect your doppler wave form.
Fibromuscular dysplasia
and distal atherosclerotic lesions are more difficult
to detect because they're not in the proximal renal artery accessory.
Renal arteries are common and difficult to detect
with sonography even in the best patients.
Examination times are relatively lengthy
and it's important to remember that even at the best
that we can do.
We don't detect stenosis less than 60% diameter narrowing.
We don't even try to,
we're really focusing on detecting stenosis
that are significant and those are the ones
that are greater than 60 to 70% narrowing.

Intrarenal Arteries for Detecting Stenosis

So how do we get around some
of these limitations in looking at the main renal arteries?
Well, one is to look at the intrarenal arteries.
Significant stenosis in the proximal main renal artery will
cause parvus tardus effects in the distal renal arteries in the
arteries within the kidney themselves.
And parvus tardus refers to decreased systolic amplitude
and slowed systolic acceleration.
And there's a variety of ways that we can identify parvus tardus effects.
The schematic that's showing in the upper right hand
corner shows a normal renal arterial doppler
with a very rapid systolic upstroke
and a sharp early systolic peak with proximal stenosis.
The distal wave form start to look like this.
You lose that early systolic peak
and the early systolic acceleration starts to decrease.
And then with progressive stenosis,
the systolic peak gets progressively blunted,
the acceleration diminishes
and that early systolic peak gets very rounded.
So what do we use to quantify this well,
in addition to looking for loss of that early sharp systolic peak, we can quantify it
by measuring the early systolic acceleration.
And that's done by looking at the up slope of early systole.
Now in the image in the upper right hand corner from the
left kidney, you can see that the slope, which is the early systolic acceleration is 92
centimeters per second square.
And that's extremely low compared to the right kidney
where it's 1,806 centimeters per second
squared, which is much faster.
Now you don't really need to measure the slope in this case 'cause you can just look at the waveforms
and see how different the systolic acceleration is in the
left kidney compared to the right kidney.
But in borderline cases, measurement of
that early systolic acceleration can be handy.

Limitations of Intrarenal Arterial Analysis

Now, what are the limitations of
intrarenal arterial analysis?
Well, many people, including myself, feel
that it's less sensitive
to borderline stenosis than main renal artery analysis.
It does not distinguish occlusion
with collaterals from a high grade stenosis.
It doesn't localize the stenosis to proximal mid
or distal renal artery.
And in fact, you can get changes if the stenosis is in the
aorta or in the aortic valve.
Sometimes the cursor location
for measuring the early systolic acceleration is questionable and all of it is dependent on having compliant vessels, which is not always the case,
especially in elderly patients
with the significant intrarenal atherosclerosis.

Renal Vein Thrombosis

Okay, now let's change gears
and talk about renal vein thrombosis.
This is something else that we sometimes try to detect
with renal doppler.
Realize that this requires a combination
of both gray scale findings and doppler findings.
You can miss it on gray scale if you just rely on that,
you can miss it on color doppler if you just rely on that.
Now, in the right renal vein,
we have a fairly high sensitivity
because it's a short vessel
and you've got that nice big liver to scan through.
The left renal vein sensitivity is lower
because the vein is longer.
There's more of it to evaluate
and you don't have as good acoustic window.
It's important to realize that
with even total renal vein thrombosis,
it still is not uncommon
to have venous flow in the hilum of the kidney.
So you can't just take views of the kidney,
see venous flow in the kidney and exclude the diagnosis.
You really need to see the entire renal vein to get a full examination.
And also realize that arterial flow
into the kidney is usually not affected
or only minimally affected in native kidneys
that have renal vein thrombosis.
Now on the other hand, in renal transplants,
the arterial flow is affected to a much larger degree,
and you get that to and fro pattern.
So here's an example where you can see renal vein thrombosis
in the left renal vein of the native left kidney,
both on gray scale and doppler.
And this image on the right is an example
of a renal transplant with renal vein thrombosis,
where you can see that to
and fro waveform pattern within the supplying renal artery.

Pseudoaneurysms

We used Doppler to diagnose pseudo aneurysms.
Those occur secondary to trauma from biopsies,
trauma from penetrating trauma from gunshot wounds or knife wounds.
And occasionally from infection.
They occur most commonly in renal transplants.
'cause renal transplants get biopsied more
frequently than native kidneys.
They can be a source of hematuria.
As we mentioned earlier, they can appear
as a simple cyst as we see here,
but they'll have internal blood flow.
As you see on the Doppler image, the to
and fro pattern in the neck of a pseudo aneurysm
that you commonly see in pseudo aneurysm in the groin.
It's much more difficult to diagnose in renal pseudo aneurysms.
But occasionally you can see it as we see here.
And remember that they can coexist
with arterial venous fistulas, which brings us
to arterial venous fistulas.

Arteriovenous Fistulas

The etiology is similar to pseudo aneurysm.
They typically are self-limiting,
but they can cause persistent hematuria.
Now, generally there's no gray scale findings for AV fistulas, but on Doppler analysis you'll see a prominent
artery with high velocity in a low resistive index.
So on this image obtained in diastole,
you see one vessel heading into the lower pole
and no vessels any place else.
That's because there was some underlying renal parenchymal
disease in this transplant kidney.
In systole, you continue to see
that one prominent artery heading to the lower pole.
Now you see another artery heading to the mid pole here.
But look at the difference in color saturation.
You can tell that that artery that's heading
to the lower pole has a lot more blood flow in it,
and that's confirmed when you do
doppler analysis to the artery.
That's supplying the fistula gangbusters arterial flow
and a lot of diastolic flow compared to the artery going
to the rest of the renal cortex, which has much less flow.
Now in addition to differences in the arterial flow,
you can see arterial
and disordered flow in the draining vein
and typically you'll see fairly extensive
and dramatic tissue vibration around the area
of the fistula.

Adrenal Glands

Well, that does it for the kidneys.
I wanna just briefly review the adrenal gland.
We often ignore the adrenal gland when we're doing
sonography of the abdomen
and that's probably appropriate
'cause ultrasound is certainly not a mainline test
for looking at the adrenal glands.
The normal adrenal glands are difficult to evaluate,
easier on the right side than the left side,
but even on the right side it can be tough.
These are some examples
of normal adrenals on the right side.
Typically you'll see them
as just little linear hypoechoic bands of tissue
between the liver
and the crus of the diaphragm near the vena cava.
And occasionally, if you're lucky,
you'll see the Y shaped appearance of the adrenal gland.

Adrenal Masses

Now, adrenal masses are also more difficult
to detect than on ct.
But in the right adrenal masses, you know,
if you pay attention can be seen with the fair sensitivity,
much more difficult on the left side.
Unfortunately, the sonographic appearance
of masses is usually very non-specific,
and you have to rely on a combination of detection
of mass on sonography and clinical history.
Clinical history can be very helpful,
but many times you need to get follow up laboratory values
and often we'll need to further evaluate these patients
with CT or MRI.
So just a few adrenal lesions that you can see with sonography.
One is the adrenal cyst.
Simple adrenal cysts are very uncommon,
but they do get encountered occasionally.
And you see this one here in the liver,
which is a low attenuation lesion.
Looks a lot like a cyst,
could potentially be a low attenuation adrenal adenoma,
but on sonography it clearly has appearance of a cyst.
So those are usually pretty easy to diagnose.
Adrenal adenomas on the other hand, are very common tumors.
They're usually non-functional. They're usually small.
Three centimeters is a reasonable number to remember
and they typically are solid and homogeneous.
And these are three different examples of adrenal adenomas that have been seen on sonography.
And they all have a fairly typical,
although non-specific appearance,
Adrenal metastases are also relatively common.
It's the fourth most common organ that develops metastatic disease.
And on ultrasound, again, the appearance is nonspecific,
but they're usually larger than adenomas
and they're often heterogeneous in appearance as we see in this transverse and longitudinal view of a patient with metastasis from lung cancer.
Adrenal pheochromocytomas are the 10% tumor.
That's because 10% are malignant, 10% are extra adrenal,
10% are bilateral,
and 10% occur in patients with multiple endocrine neoplasia syndromes.
They typically present with hypertension, headaches,
tachycardia, anxiety, palpitations,
they can be seen with sonography.
But again, they have a non-specific appearance.
They're usually solid, usually large heterogeneous
and hypervascular as we see in this example
of a left adrenal adenoma in the left
para aortic region.
Myelolipomas are a benign tumor that's usually asymptomatic.
They contain hematopoietic elements and fatty elements.
They're variable in size,
but they usually contain some hyperechoic component
because of the fatty elements within the lesion.
And that's what we're seeing on these two examples
of a patient with a relatively typical myelolipoma.
So when you encounter a lesion like this, a CT scan
or an MRI should be obtained to confirm the presence of fat.
And then the final adrenal lesion is the adrenal
cortical carcinoma.
These are rare. They usually occur in the elderly.
They're usually large,
and they usually present with symptoms of some sort.
10% will be hyper functioning
and usually that's produces Cushing syndrome.
On imaging, they often will have necrotic areas,
we'll have hemorrhagic areas
and calcification is not uncommon.
And like renal cell cancers,
they can invade the adrenal vein
and then go on into the inferior vena cava.
Here's an example of a large mass
that has invaded the inferior vena cava consistent
with an adrenal cortical carcinoma.

Conclusion

So that concludes this whirlwind tour
of the kidneys in the adrenal glands.
Please recognize that this is a very basic introductory
review of the topic.
If you really want to start doing renal
and adrenal sonography
and do it well, I'd advise you to go
and review some chapters that are specifically focused on these two areas.
Thank you very much.