0:03

All right, so let's go ahead and get started.

0:05

Uh, hello.

0:06

Welcome to the first of many live stream

0:08

noon conferences hosted by MRI Online.

0:11

In response to the changes happening around the

0:13

world right now and the shutting down of many

0:15

in-person events, we have decided to provide free

0:17

daily noon lectures to radiologists worldwide.

0:21

To learn more about, um, future lectures and

0:24

webinars we have coming up, please visit our website.

0:27

Uh, our software can accommodate the

0:28

first 500 attendees, so make sure,

0:31

uh, you register and show up on time.

0:33

The link is provided as a first-come,

0:34

first-serve basis, and we will be putting

0:36

them on the course after we sign off.

0:41

Today we're joined by Dr. Mahan Mathur, Associate

0:44

Professor of Radiology and Biomedical Imaging

0:46

at Yale School of Medicine, Associate Program

0:49

Director for Diagnostic Radiology Residency, and

0:51

Director of Medical Student Education in Radiology.

0:55

Awarded four times the Yale

0:57

Radiology Teacher of the Year.

0:59

Please join me in Dr. Mathur.

1:01

I'll let you take it from here.

1:05

Thank you very much, Ashley.

1:06

Let me just share my screen.

1:10

Okay.

1:11

Does everyone

1:11

hear me okay?

1:15

I am assuming that's a yes.

1:17

Um, well, welcome everyone.

1:19

Um, uh, as mentioned, uh, let's see, people said yes.

1:24

Perfect.

1:25

Thank you.

1:26

Um, my name is Mahan Mathur.

1:27

I'm a radiologist at Yale.

1:28

You can read my credentials over here.

1:30

Um, uh, I'm really, uh, honored to be here today

1:34

and, uh, I really want to thank, um, MRI Online for

1:37

putting this together and really leveraging, uh,

1:40

technology in order to bring us together in this

1:44

hopefully temporary era of, uh, social distancing.

1:48

So for the next hour or so, let's forget

1:50

about what's going on and let's, uh, sit

1:52

back and learn from each other and enjoy,

1:54

uh, learning about the retroperitoneum.

1:59

We have a couple of objectives, uh, that hopefully

2:02

you'll be able to obtain at the end of this hour.

2:04

The first is, uh, you'll be able to

2:06

review, um, and explain the normal anatomy

2:09

of the retroperitoneal compartments.

2:12

Secondly, you'll be able to describe key

2:13

imaging and clinical features of both solid

2:16

and several cystic retroperitoneal neoplasms.

2:20

And we'll finish off by talking about

2:22

imaging and clinical features of some

2:24

non-neoplastic retroperitoneal processes.

2:28

As of now, we had, uh, over a hundred

2:31

participants, 128, uh, to be exact.

2:34

And so everyone's probably gonna be

2:36

at a different stage of training.

2:37

Some people may be experts in this,

2:38

some people novices, and so we can

2:40

all get what we need out of this talk.

2:42

Um, and so hopefully, uh, within these objectives,

2:45

you can find something that you can learn from.

2:49

Let's start.

2:51

Before we get going, I wanna

2:52

show you five unknown cases.

2:54

And this is something that, uh, I just

2:56

thought about doing about 45 minutes ago.

2:58

I will show you five unknown cases,

3:00

and, uh, you know, you can jot down the

3:02

answers if you want on a piece of paper.

3:04

You can think about the answers.

3:06

And, uh, if you want, you can chat and, uh, text

3:09

us the answers as well and we'll see if we can,

3:12

uh, give bragging rights or something else to,

3:14

uh, the person or people who get all five of them.

3:17

Right.

3:17

So this is the first case.

3:19

I'm not gonna describe anything.

3:20

I'm gonna give you a couple of seconds

3:22

to look at it, see what you think.

3:24

Come up, uh, with one answer.

3:31

This is the second case over here.

3:38

Give you a couple of seconds to look at it again.

3:41

One right answer for this.

3:48

Three.

3:58

Move on to case four.

4:00

These are MRI images.

4:01

The sequences are named over here.

4:10

And last but not least,

4:15

case number five.

4:25

So,

4:25

we'll revisit these cases through the talk and I'll

4:27

give you the answers at the end of this, uh, session.

4:31

All right, so first objective

4:33

is to talk about anatomy.

4:35

And so the anatomy of the retroperitoneum is

4:37

really built around this tricompartmental model.

4:40

And this has sort of been

4:41

established at least since the 1960s.

4:44

And it's a great model to explain sort of how, um, uh,

4:47

the different components fit into the retroperitoneum.

4:50

And it's really built around what I

4:52

like to call the flagship organ of the

4:54

retroperitoneum, which is the kidney.

4:56

And you can see the kidneys

4:56

over here in this schematic.

4:58

And, uh.

5:00

Uh, around the kidneys, you have different spaces.

5:02

You have the space anterior to the kidney, the

5:04

anterior pararenal space, the space around the

5:08

perimeter of the kidney, the perirenal space.

5:11

And finally, you have this, uh, space posterior

5:13

to the kidney, the posterior pararenal space.

5:20

Now, the anterior pararenal space is

5:22

delineated anteriorly by the posterior

5:26

layer of the parietal peritoneum here.

5:28

This is highlighted in blue. Posteriorly,

5:31

it's delineated by the anterior renal fascia.

5:34

It's also known as Toldt's

5:35

fascia, highlighted in red over here. And laterally,

5:38

it's defined by the lateral conal

5:40

fascia, here highlighted in green.

5:43

And this contains several organs of

5:45

the retroperitoneum, including, uh, the

5:48

ascending colon, the descending colon,

5:51

the second, third, and fourth portions of the duodenum.

5:54

It contains the majority of the pancreas, but we're

5:57

not really gonna talk about these organs today.

5:59

We're gonna talk about the spaces in between and what

6:01

grows in the spaces in between, uh, within the fat,

6:04

within some of the vessels here, and fibrous tissue.

6:07

138 00:06:11,055 --> 00:06:13,905 The perirenal space is the space immediately

6:13

around the kidney and is delineated

6:15

anteriorly by the anterior fascia, Gerota's

6:18

fascia, posteriorly by the posterior fascia,

6:22

Zuckerkandl's fascia, here highlighted in purple,

6:25

and this of course contains the kidneys and the

6:26

adrenal glands, which are not imaged on these, uh,

6:29

on these images here, but also variable amounts of

6:31

fat, lymphatic tissue, lymph nodes, um, and other

6:35

things that we'll talk about a little bit later.

6:36

149 00:06:39,690 --> 00:06:41,400 And finally, my favorite space is

6:41

the posterior pararenal space.

6:43

It's my favorite space because

6:45

it really just contains fat.

6:46

So there's not much I have to remember about that.

6:48

And it's, uh, delineated—

6:50

lemme just go back to that last slide—

6:51

anteriorly by the posterior renal

6:53

fascia, or Zuckerkandl's fascia. Posteriorly,

6:56

it's delineated by the transversalis fascia,

6:59

this really, really thin layer that sort of,

7:01

um, surrounds some of the muscles over here

7:04

and goes out laterally. And then laterally,

7:06

this extends as the lateral conal fascia.

7:08

And this fat actually extends laterally,

7:10

and you can see it as the properitoneal

7:12

fat stripe on, uh, plain films.

7:19

And so that's the tricompartmental model.

7:21

And if that's all you kind of wanna

7:23

glean out of the anatomy portion of

7:25

the talk, I think that's sufficient.

7:26

That's sufficient to explain most processes. However—

7:31

uh, it turns out that these fascial layers that

7:33

I talked about—Gerota, Zuckerkandl, lateral conal

7:35

fascia—are not a single layer, but rather,

7:39

they're laminated, made up of multiple

7:42

layers that are fused, and as a result, they can

7:46

um, expand and form these expansile planes.

7:49

And so if we kind of wanna push our limits of

7:52

knowledge, um, to the vocabulary that we've already

7:54

established, it's important to add a few other things.

7:58

This is, uh, the retromesenteric plane, which is

8:00

the plane that occurs when the Gerota's fascia expands.

8:04

You have the retrorenal plane, which is the plane

8:07

of the Zuckerkandl's fascia when that expands,

8:10

and the lateral conal plane, the plane when the

8:12

lateral conal fascia expands. These meet out laterally

8:16

in something called the fascial trifurcation.

8:20

And that extends out inferiorly as something

8:24

called the combined interfacial planes.

8:26

So if you look at these sagittal images on the

8:29

CT scan, with a retroperitoneal

8:31

process—you know, I'm gonna show you a few in a

8:32

bit—you may often end up seeing a Y-shape, um,

8:37

as the combined interfacial plane, uh,

8:40

goes downwards, forming from the union of, uh,

8:43

the retromesenteric and the retrorenal planes.

8:49

If we look at axial images, this is

8:51

a CT scan with intravenous contrast.

8:54

It's very tough to see where the combined

8:55

interfacial plane is, but if I click

8:57

on the next slide, you can see that it's

8:59

gonna roughly correspond to a very thin layer,

9:01

about two to three millimeters at most.

9:03

That, uh, occurs over here, and everything

9:06

sort of behind this is gonna be part of

9:08

the retroperitoneum, and everything medial

9:10

to this over here will be intraperitoneal.

9:16

As we go down inferiorly, again,

9:18

it's very hard to see that plane.

9:20

When it's normal, you hardly see it.

9:22

But if you scroll and, uh, imagine where it

9:25

could be, you'll see that it sort of goes

9:27

along these dotted yellow lines over here.

9:30

This is where the—

9:31

combined interfacial plane goes downwards. And as

9:34

you go down even more inferiorly, very tough to

9:36

see, but it roughly follows this trajectory. And you

9:39

can see that it allows processes to go inferiorly

9:43

and communicate with the presacral space over here.

9:49

And so if we look at a few examples, we can see over

9:51

here that, uh, this person, I think, had, um, an ulcer

9:54

of the second portion of the duodenum that perforated

9:57

and had some, uh, complications related to that,

10:00

and as a result had lots of fluid that were tracking

10:02

on the retromesenteric plane in this instance.

10:04

So this is not technically

10:06

the anterior pararenal space.

10:07

It's a very

10:08

well-delineated plane that goes out

10:10

laterally, allowing processes to sort of

10:12

communicate from the right side of the

10:14

retroperitoneum to the left side over here.

10:19

This was a patient with diverticulitis

10:21

that was, sort of, of the descending colon.

10:23

And as a result, the inflammatory

10:25

change sort of, um, drained and, um—

10:29

expanded the retromesenteric plane, the retrorenal

10:32

plane over here, as well as portions of the lateral

10:34

conal plane that allowed the inflammatory process to

10:37

sort of decompress through these different planes.

10:41

This is another case of diverticulitis where the

10:44

descending colon gets inflamed, and then inflammatory

10:47

processes sort of, um, decompress through

10:50

the presence of these, uh, retromesenteric, retrorenal,

10:52

and lateral conal planes, which are expanded.

10:57

And this was that Y-shape that I showed

10:58

you over here, a sagittal CT scan.

11:00

With intravenous contrast, we can see that

11:03

the retromesenteric plane is expanded.

11:05

The retrorenal plane is expanded, and downwards,

11:08

you can sort of see that Y-shape as straining

11:10

through the combined interfacial plane.

11:18

And again, you know, the presence of these

11:20

planes allows one to perhaps appreciate and

11:23

understand how processes that sort of start off

11:26

in the abdominal retroperitoneal compartments

11:28

can communicate all the way down to the pelvis.

11:31

So this is a patient with, uh, pancreatitis,

11:33

and that advanced pancreatitis, uh,

11:35

with, uh, necrotizing collections.

11:37

And you can see that the inflammatory process

11:39

and the collections are expanding the retro

11:42

mesenteric plane over here, the retrorenal plane,

11:45

expanding the fascial trifurcation.

11:47

All this is going downwards, expanding that combined

11:51

interfacial plane on the left side. On the right

11:54

side, we hardly see that plane because it's normal.

11:57

If you follow this downwards again, you

11:59

can see that it's following the expected

12:01

location, the combined interfacial plane,

12:03

and finally going down to that presacral space.

12:05

So all of a sudden, we can appreciate

12:06

how something that started off in the

12:08

pancreas, um, is now communicating with that

12:10

presacral space.

12:16

And as we sort of finish off the anatomy portion

12:19

of this, um, the perirenal space also has, um,

12:23

ways that it sort of communicates with the other,

12:25

uh, retromesenteric and retrorenal planes.

12:28

And it turns out that the perirenal space

12:30

contains these, uh, lamellae, which are really

12:33

channels, and that allow, um, for processes

12:36

to decompress, um, within the perirenal

12:40

space, into the anterior, into the

12:43

retromesenteric and retrorenal compartments.

12:46

And so we can see that, uh, in this case

12:49

over here, uh, this person has a subcapsular

12:53

hematoma, uh, compressing the left kidney

12:56

over here and, uh, causing mass effect.

12:58

And the body itself is trying to decompress

13:01

it by opening up these different channels and

13:03

allowing some of that hematoma to communicate

13:05

with both the retromesenteric and retrorenal

13:08

planes, and that communicates inferiorly to

13:10

the pelvis via the combined interfacial planes.

13:15

This is another case that I, uh, just

13:17

saw last week that sort of demonstrates

13:19

some of these findings nicely.

13:20

This patient—um, this is an older study on the

13:23

patient—had a history of lymphoma, had, uh,

13:25

infiltrated the left kidney, has adenopathy over here.

13:28

Uh, but the processes had also sort of, um,

13:31

expanded these, uh, conduits within the

13:34

pararenal space, allowing the retrorenal plane to

13:37

be nice and lumpy, bumpy, as you can see over here.

13:40

And the retromesenteric plane to be lumpy, bumpy,

13:42

so you have soft tissue that's sort of exiting.

13:44

And, uh, the perirenal space

13:45

through these different planes.

13:47

Again, you can see on the sagittal image

13:48

that Y nicely delineated, uh, much more,

13:52

uh, thick within the retromesenteric plane.

13:55

And it goes down, and it communicates inferiorly,

13:58

uh, via the combined interfacial plane,

13:59

which is very, very thick in this instance.

14:01

So this is a case of lymphoma, um, of the left

14:04

kidney that's sort of decompressing through these

14:06

channels, um, and expanding all these different

14:08

planes.

14:14

And so we've achieved our first objective,

14:16

going through the normal anatomy of

14:18

the retroperitoneal compartments.

14:20

Remember the tricompartmental model, and if that's

14:22

all you wanna remember, that's probably sufficient.

14:24

But once you've mastered that, um, it's important

14:27

to sort of add to your vocabulary the different

14:29

planes that we've talked about—the retromesenteric,

14:31

retrorenal, et cetera—because it allows us

14:33

to understand how different compartments in the

14:36

retroperitoneum communicate with each other from

14:38

right to left and from, uh, cephalic to caudal.

14:42

So now, move on to talking about

14:44

retroperitoneal neoplasms.

14:49

And there are a lot of retroperitoneal

14:53

neoplasms, and, uh, really no talk or

14:55

paper would be exhaustive enough to cover

14:58

every single little thing that can occur.

14:59

So I'm just gonna touch upon several of them.

15:02

Um, and we're gonna talk specifically about, uh,

15:04

sarcomas—primary sarcomas of the retroperitoneum.

15:07

We'll also talk about neurogenic tumors.

15:09

Uh, we'll also touch base on metastases and

15:12

lymphoma, which are actually very commonly

15:14

seen in the retroperitoneum, and I'll finish

15:16

off with talking about a few cystic neoplasms.

15:21

So, starting with sarcomas.

15:23

Now, the good news is that sarcomas are very uncommon.

15:27

You can see that, um, incidence of cases

15:30

is, uh, one to three cases per million.

15:33

Um, but the bad news is that when they do

15:36

occur, they almost always are malignant.

15:38

About 80% of them will be malignant.

15:40

They tend to present in patients around

15:42

the fifth or sixth decades of life, and they're

15:45

rather large on presentation, oftentimes

15:47

more than 10 centimeters on presentation.

15:50

The five-year survival is not great.

15:53

A lot of this depends on the histologic

15:55

grade of the individual neoplasm—

15:57

that is, the degree of de-differentiation.

16:00

It also depends on the type of sarcoma that you

16:03

have—the histologic subtype. But also, even

16:06

if it's something that's relatively, uh, benign or

16:09

indolent, um, the survival rate may not be great,

16:12

because as I said, they tend to grow very large,

16:15

and it is very difficult for surgeons to get

16:18

tumor-free resection margins.

16:20

So the mainstay of treating these

16:21

retroperitoneal sarcomas is surgery—

16:23

have to try to take it out if possible.

16:25

But because they get so large and because they can

16:27

grow in this, um, space in the retroperitoneum for

16:30

a long time before they come to presentation, it's

16:33

very tough to get tumor-free resection margins.

16:35

And so that also plays into the overall prognosis.

16:42

We're gonna talk about sarcomas again.

16:44

There are many different types of sarcomas, but

16:45

I'm only gonna touch base on the three most common ones.

16:49

Liposarcoma is the most common.

16:51

It'll account for about 40% of all primary

16:54

retroperitoneal sarcomas, and it also

16:57

consists of different histologic subtypes.

17:00

Now, to be honest, I don't typically like

17:02

committing these things to memory. But I,

17:04

the only times I do commit it to memory is

17:06

because if there are some, um, uh, imaging

17:09

findings of them or some clinical significance.

17:12

So within liposarcoma, you have different groups.

17:14

The first group consists of an atypical lipomatous

17:17

tumor (ALT), well-differentiated liposarcoma,

17:21

and de-differentiated liposarcoma.

17:24

The second group often includes

17:26

myxoid and round cell tumors,

17:27

while the third is pleomorphic.

17:29

And so one thing you need to know is as you go

17:31

from one to three, the prognosis gets worse.

17:34

And the other thing I'll point out is that

17:36

these two entities—atypical lipomatous tumor

17:40

and well-differentiated liposarcoma—are

17:42

essentially the same histologic entity.

17:45

So why do we have two different names for them?

17:48

Well, it turns out this is more a pathology, um,

17:51

differentiation—or pathologist differentiation, I

17:54

should say—in that when they see tumors that look

17:57

the same, but when they occur within the extremity,

18:00

um, they'll call it an atypical lipomatous tumor.

18:03

When it occurs in the retroperitoneum, they're

18:05

prone to calling it a well-differentiated

18:07

liposarcoma.

18:08

And that simply is because the same tumor occurring

18:10

in the extremity will have a much better prognosis.

18:13

It's much easier for the surgeons to take it out.

18:16

The, um, the, uh, likelihood of, uh,

18:18

recurrence at that site is very, very low.

18:20

And so they chose to give a different name to it.

18:23

Um, and also—

18:25

some pathologists, uh, you know, have, um, their own

18:29

preference, thinking that, uh, you know, something

18:31

like a well-differentiated liposarcoma, as we'll

18:33

talk about, is a tumor that does not metastasize.

18:36

And so, because it does not metastasize, it

18:38

doesn't warrant, uh, the name sarcoma. So,

18:40

they like to call it an atypical lipomatous tumor.

18:43

All that you need to know is that if you see

18:45

this in your reports—ALT or well-differentiated

18:47

liposarcoma—it's essentially the same entity.

18:52

Leiomyosarcoma is the second most common primary

18:54

retroperitoneal sarcoma, an incidence of about 30%.

18:58

The third most common is what we used

19:01

to call malignant fibrous histiocytoma.

19:04

Now, the updated terminology is actually

19:07

undifferentiated pleomorphic sarcoma.

19:10

I'm sure many of, uh, you people

19:12

on the call will, will know that.

19:13

Um, but I do find that, um, when I

19:15

was training, it was called an MFH.

19:17

And so just, I'll use both in this instance,

19:20

just to sort of make that connection

19:21

with anybody who's used to hearing it as

19:23

a malignant fibrous histiocytoma.

19:28

So liposarcomas, well-

19:30

differentiated, are the most common.

19:32

And as you can imagine, on imaging, they

19:34

contain fat—uh, mostly composed of fat.

19:38

They may have a few septations, but if

19:40

they're present, they'll be very thin.

19:43

Uh, you know, we're talking about

19:44

a millimeter—hairline thin.

19:46

They may have a few nodular components, but

19:48

again, the nodular components are gonna be small,

19:50

typically less than a centimeter, and it'll

19:52

exert mass effect upon the organs around it.

19:56

I mentioned it's a very low-grade

19:58

tumor, and it does not metastasize.

20:01

The only problem is if you don't get

20:02

tumor-free resection margins, there

20:04

is a good chance of local recurrence.

20:06

You do need to monitor these patients,

20:08

um, periodically, even once resected.

20:12

Now, some of you on the call may think,

20:14

well, you know, you have a mass like

20:16

this, looks, um, uh, like it contains fat.

20:18

Why don't we just call it a lipoma?

20:21

And that would be a very good question, or very

20:23

good consideration, except it turns out that pure

20:26

lipomas are exceedingly rare in the retroperitoneum.

20:30

So this is a case of a lipoma, and

20:32

the reason I know it's a lipoma is

20:33

because they actually resected this out.

20:36

The point here is that when you see a fat-

20:38

containing lesion in the retroperitoneum, even if

20:40

it's simply containing fat, no other complexity

20:44

within it, it needs to be evaluated as a well-

20:47

differentiated liposarcoma until proven otherwise.

20:50

Uh, because lipomas are very, very rare.

20:52

And if you biopsy these lipomas, um, you could

20:55

miss out on the small component that would

20:58

make this a well-differentiated liposarcoma.

21:00

Therefore, biopsy is often not encouraged.

21:02

If you can take it out, it

21:03

suggests that you do take it out.

21:08

This is opposed to de-differentiated liposarcoma.

21:12

Now, this can occur de novo, but can also occur

21:15

in up to 15% of well-differentiated tumors

21:18

over the course of about seven to 10 years.

21:20

A well-differentiated tumor could potentially

21:23

become de-differentiated in up to 15% of patients.

21:26

As you can imagine, these just look more complex.

21:29

They will contain somatic components.

21:31

As you can see over here, they're

21:32

gonna have much more soft tissue.

21:34

They're gonna have some calcifications.

21:35

They're gonna have nodular components that

21:37

are greater than a centimeter in size.

21:40

Why does de-differentiation matter?

21:42

Because these tumors can metastasize. Well-

21:46

differentiated tumors won't, but

21:48

de-differentiated tumors can.

21:54

And so this is an example of a patient who, over a

21:56

decade, uh, was unable to get resected for their lipos-

21:59

arcoma, but was followed to make sure it didn't

22:02

um, uh, metastasize or get too, uh, large in size.

22:06

Um, and over 2005 you can see the tumor

22:09

over here mainly composed of fat, a few

22:11

imperceptibly thin septations, and just over time,

22:15

the tumor gets larger, but more concerning.

22:18

Um, certainly in 2008 you start to get soft tissue

22:21

components form, and these soft tissue components

22:23

start to get larger and larger and larger.

22:26

There are new and enlarging calcifications that

22:29

also form during this period of time, and so this

22:32

is an example of a well-differentiated liposarcoma

22:35

that, over a decade, has undergone de-differentiation.

22:43

Another example over here, coronal CT scan.

22:45

This is over a course of three years,

22:47

mainly fat-containing tumor with some

22:49

soft tissue and, uh, calcified component.

22:52

Probably that component was differentiating at this

22:54

time, but certainly, over a period of three years,

22:57

it grew much larger, with the calcium also growing larger.

23:00

So typically, when I'm looking at well-differentiated

23:02

liposarcomas on the surveillance imaging,

23:05

I'm not so much looking at the fat as looking

23:08

at the soft tissue components and seeing

23:09

how they're doing over a period of time.

23:16

Myxoid liposarcoma is another category

23:18

of liposarcoma, and this is an interesting

23:21

tumor in that it contains an abundance

23:23

of myxoid, gelatinous components.

23:25

We can see this tumor over here

23:27

in the pelvis, um, on the CT scan.

23:30

Has low density, certainly looks like fluid

23:32

density, has some interspersed areas of fat, so we

23:35

should be suspicious that this is a liposarcoma.

23:38

If we were to just look at the, uh, T2

23:40

imaging, it looks quite bright, and so you would

23:43

think that this is, uh, maybe a cystic neoplasm.

23:46

Unlike any cystic neoplasm, when

23:48

you give contrast, this enhances.

23:50

There's heterogeneous enhancement.

23:52

It doesn't have to be hypervascular.

23:53

Even low-level enhancement is fine.

23:55

When you see, uh, a tumor in the retroperitoneum

23:58

with T2 hyperintense components which

24:00

enhance and have a sliver of fat in it, you

24:02

gotta think of a myxoid liposarcoma.

24:09

So this here is a patient with liposarcoma.

24:11

You may be familiar with this.

24:12

This was our, uh, unknown case number one.

24:15

You can see a large liposarcoma

24:16

centered in the pararenal space, pushing

24:18

the kidney, um, cephalad to the right.

24:21

Um, and this here, uh, is also a fat-containing mass.

24:24

Looks very complex.

24:27

You could be, uh, mistaken in calling

24:29

this a liposarcoma, but of course,

24:31

this is a renal angiomyolipoma.

24:33

You can see a claw sign in this little knuckle

24:35

of tissue that's emanating from the kidney.

24:37

And so these two are vastly different

24:39

tumors that are treated differently.

24:41

So it's important to sort of recognize and see if

24:43

you can see whether it's coming from the kidney,

24:45

in which case it's gonna be an angiomyolipoma.

24:49

Another potential mimic—on this axial CT

24:51

scan, a fat-containing mass in the retroperitoneum.

24:54

You may be tempted to call liposarcoma, but

24:56

always look at, uh, every available plane.

24:59

Uh, when you're evaluating

25:01

these cases. This is a coronal mass.

25:03

You don't see the right adrenal gland.

25:04

This is a myelolipoma of the right adrenal gland.

25:08

Again, uh, a benign lesion that is treated

25:12

and evaluated very differently than a liposarcoma.

25:13

575 00:25:19,350 --> 00:25:22,080 Leiomyosarcoma, as you recall, the second most

25:22

common primary retroperitoneal sarcoma.

25:24

And what you're gonna look for in leiomyosarcomas

25:26

is contiguous involvement of vessels.

25:30

So you can see this lesion over here,

25:32

heterogeneous mass that's inseparable

25:34

and expanding the inferior vena cava.

25:37

Um, you gotta think that, could this be a leiomyosarcoma?

25:41

Cystic changes and internal necrosis have

25:43

been described within these lesions, uh,

25:45

but calcifications are quite uncommon.

25:47

So if you see involvement of the vessel with areas

25:50

of necrosis in the mass, think of a leiomyosarcoma.

25:57

This is a case—this is our second unknown

25:58

case—which is a leiomyosarcoma.

26:00

You can see that in this instance there's actually

26:03

quite a large component that's extravascular,

26:05

but it is contiguous and involves the IVC.

26:08

So an intra- and extravascular component.

26:10

In this instance of a leiomyosarcoma, it can

26:15

be completely intravascular, as seen in

26:17

this case over here where it's, um, uh,

26:19

involving the, uh, renal vein and IVC.

26:24

And they've also described them as extravascular.

26:27

In this instance, there's probably

26:28

some vascular involvement that, uh,

26:30

of some vessels that we're not seeing.

26:32

But when you look at them on imaging,

26:33

um, it's hard to find that component.

26:35

And so this was a patient who had a history of

26:37

breast cancer and had these nodes, sort of, or

26:39

this mass, sort of, pop up in the retroperitoneum.

26:41

And we thought that was unusual because—

26:45

there was no disease elsewhere. For nodes

26:46

to pop up here in the retroperitoneum

26:48

from a breast cancer, it'd be unusual.

26:50

And over time, you can actually see that

26:51

it grew, and this was actually resected

26:54

and turned out to be a leiomyosarcoma.

27:00

This is another interesting case, uh, to

27:01

show how subtle these findings can be.

27:03

This patient had a, uh, renal cell cancer and

27:06

it was being monitored over a period of time.

27:08

There was an exophytic mass arising from the

27:10

right adrenal gland, or at least we thought it

27:11

was an exophytic mass arising from the right

27:13

adrenal gland over here, very close to the IVC.

27:16

Uh, we presumed it was an adenoma, and we just

27:18

followed over a period of time, but you can see—

27:21

see that, over a period of time, you have a knuckle

27:23

of tissue that starts to invade the IVC here.

27:26

That knuckle becomes more nodular and more invasive.

27:29

This was resected, and this turned

27:30

out to be a leiomyosarcoma separate

27:33

from the adrenal gland.

27:39

And this turns out to be a leiomyosarcoma

27:41

that arose in an adrenal vein.

27:43

So the point here is that sometimes,

27:45

uh, these sarcomas, as you know, can

27:46

grow quite large when they present.

27:49

And it may be just very difficult

27:50

to know where this is coming from.

27:52

So we thought this could be a primary adrenal

27:54

cancer, like an adrenocortical carcinoma.

27:56

Turns out the adrenal gland was okay

27:58

over here, and this was a tumor that

27:59

was arising in one of the adrenal veins.

28:01

So sometimes, uh, you know, when it gets quite

28:04

large, these things can be quite challenging.

28:10

And the last sarcoma that I'll talk about is the

28:12

undifferentiated pleomorphic sarcoma, formerly

28:15

known as malignant fibrous histiocytoma, or MFH.

28:19

And, uh, the imaging features

28:21

here are really non-specific.

28:23

Um, calcifications have been described as being more

28:26

common in these tumors—up to 20% of these tumors.

28:29

But overall, this just appears very heterogeneous.

28:32

Cystic changes, possibly due to some necrosis.

28:34

There's often hemorrhage in it.

28:36

So we'll see bright signal on T1-weighted images.

28:38

The enhancement will be quite irregular.

28:40

And, uh, somewhere in the literature someone saw

28:42

this and thought this looked like a bowl of fruit.

28:44

And so that's also been described.

28:45

But the point here is that, uh, you're not gonna be

28:48

able to make a specific diagnosis, and this often is a

28:50

diagnosis of exclusion, uh, at least based on imaging.

28:57

And so if we review the sarcoma clues, and

28:59

just to break it down very simply, if you see a

29:01

retroperitoneal mass—a primary retroperitoneal

29:03

mass—that contains fat, it'll be a liposarcoma,

29:06

and then you can look for other

29:07

clues to see if you can kind of place it

29:09

within one of those histologic categories.

29:12

If you see a tumor that has involvement of

29:14

vessels and/or with extensive cystic changes

29:18

and necrosis, you're gonna think of leiomyosarcoma.

29:21

And undifferentiated pleomorphic sarcoma

29:23

is gonna be very tough to call on imaging.

29:26

Um, if you don't see fat, if you don't see involvement

29:28

of vessels, a mass, uh, has some calcifications—

29:32

perhaps it's an undifferentiated pleomorphic sarcoma.

29:34

But again, very tough to make that call on imaging.

29:40

So that covers our sarcomas.

29:42

Let's move on to neurogenic tumors.

29:46

And one of the reasons I wanted to talk about

29:48

neurogenic tumors is it's often, uh, something that I

29:50

still just forget to put on a differential diagnosis,

29:54

and then it comes back as a neurogenic tumor.

29:55

And I think, oh, yes, that's—

29:56

that's what it could have been.

29:57

I always forget it.

29:58

And so I like to sort of make a point

30:00

to, uh, include it and talk a little bit

30:02

about it in this retroperitoneum talk.

30:05

And so these neurogenic tumors

30:06

can arise from the nerve sheath.

30:07

It could be schwannomas, neurofibromas.

30:10

You have malignant nerve sheath tumors as well.

30:12

We'll talk a little bit about those.

30:14

They can arise from the sympathetic ganglionic cells.

30:17

You have a family of tumors there:

30:18

neuroblastoma, ganglioneuroblastoma.

30:21

These are seen in, uh, pediatrics and, uh,

30:23

an adolescent population. We'll touch base on

30:26

ganglioneuromas that are seen in adults.

30:28

And finally, the parasympathetic

30:30

ganglionic cells, which give rise to

30:32

Paragangliomas, we'll talk a

30:34

little bit about that as well.

30:39

We will start off with schwannoma, and unfortunately,

30:43

schwannoma does have a non-specific appearance,

30:45

but I think it's something good to sort of just

30:47

think about, and whether you include it or not, your

30:49

differential is really based on the lesion itself.

30:52

But it's important to think about when you see

30:54

a paravertebral mass, um, it can have a

30:56

variable amount of calcification and necrosis.

30:59

This lesion here, none of us could

31:01

have thought it was a schwannoma.

31:02

Um—

31:03

in fact, we may think it's a leiomyosarcoma

31:05

'cause you don't see the IVC.

31:06

Perhaps it's invaded.

31:07

This turned out to be a schwannoma.

31:09

So a paravertebral mass, possibly when you

31:12

have expanded, uh, neuroforaminal canal as well,

31:15

I think schwannoma is a good thing to think about.

31:17

Neurofibromas, uh, can be isolated or they

31:22

can be seen in the context of Neurofibromatosis

31:24

Type 1, in which case you'll see multiple or

31:26

a plexiform neurofibroma, seen in this case.

31:29

And one of the clues you can see with

31:30

neurofibromas, and you can also sometimes see

31:33

them with schwannomas, is this target sign on MR

31:36

imaging where the central nerve is relatively

31:38

T2 hypointense and the periphery

31:41

has a myxoid matrix. And we talked about myxoid

31:44

matrix in the, uh, myxoid liposarcoma, so the

31:46

periphery bright on T2-weighted imaging.

31:49

So when you see that sort of target sign, that's also

31:51

been described on ultrasound and other modalities,

31:54

um, gotta think about could this be, uh, a nerve

31:57

sheath tumor. Compared to schwannomas, uh,

32:01

neurofibromas and certainly plexiform neurofibromas

32:04

have an increased risk for malignant degeneration.

32:12

Speaking of malignant degeneration, this is an

32:14

example of a malignant peripheral nerve sheath tumor.

32:16

You can see on the plain film a bunch of

32:19

distended loops, then an opacity of gas

32:21

in the left side of the abdomen. Looks like

32:22

these loops may be even being pushed away.

32:24

Maybe there's a mass effect.

32:26

If you look at the imaging on the

32:28

CT scan, looks a predominantly low-

32:29

density mass, quite complex on the MR

32:32

images.

32:33

Um, has T2 hyperintense component,

32:35

lots of thick septations within it.

32:38

This turned out to be a malignant

32:40

peripheral nerve sheath tumor.

32:43

These can arise de novo.

32:44

They can also be associated with NF1,

32:46

and they can also be seen occasionally

32:48

status post-radiation treatment.

32:50

So particularly if you have young patients

32:52

who got radiation in the belly, perhaps for

32:54

a tumor like lymphoma when they were young,

32:56

um, over the course of, uh, a decade or so,

32:58

they can potentially develop these peripheral,

33:01

uh, malignant peripheral nerve sheath tumors.

33:05

Unfortunately, based on imaging, it's very difficult

33:07

to differentiate, um, this, uh, as a benign

33:11

or a malignant, uh, nerve sheath tumor mass.

33:14

But you know, you can kind of use, um, common

33:17

sense to suggest that it may be more malignant,

33:20

particularly if it's rapidly increasing in size,

33:23

if clinically the patient has new neurological

33:25

symptoms, or just in general, the larger it

33:27

is—certainly greater than five centimeters.

33:29

And if the margins are ill-defined, if internally

33:31

it looks more complex, you're gonna suggest

33:33

that potentially it could be a malignant

33:36

peripheral nerve sheath tumor.

33:37

Um—

33:41

Ganglioneuroma comes from

33:43

the sympathetic nerve cells.

33:45

Um, again, a very difficult tumor

33:47

to call prospectively on imaging.

33:49

It's been described as having sometimes lobulated

33:51

margins, tends to be low density in its appearance.

33:54

Uh, a whorled appearance has been described

33:57

on, uh, T2-weighted imaging on MR. We

33:59

have concentric circles within this lesion.

34:02

They may occasionally have some calcifications.

34:04

Uh, this, uh, has a—

34:06

relatively good prognosis.

34:07

You can see this mass over here adjacent to the IVC.

34:11

Tough to call that prospectively as a ganglioneuroma,

34:13

but potentially given its paravertebral

34:15

location and potentially given its somewhat

34:18

whorled appearance internally, we could consider

34:20

that this may be of neurogenic origin.

34:22

As I mentioned, ganglioneuroblastoma,

34:24

neuroblastoma.

34:25

Well, these are seen in the pediatric and young,

34:27

uh, adolescent population, and, uh, unfortunately,

34:30

they tend to be more aggressive neoplasms.

34:32

This tends to have a relatively good prognosis.

34:37

This was an unusual case of a ganglioneuroma that I'll

34:39

just share with you, but has quite atypical features.

34:43

Uh, a large mass looks actually

34:44

quite low in its density.

34:46

It's displacing the right, uh,

34:48

uh, iliac vasculature anteriorly.

34:50

It's squeezing the left internal iliac vein over here.

34:53

If you look at on the coronals, we can see

34:55

the right, uh, external iliac vein looks

34:57

patent, and the left one is actually thrombotic.

34:59

So this was a large ganglioneuroma

35:01

with mass effect causing a thrombus.

35:04

In the left lower extremity.

35:09

Paraganglioma, uh, these are for the

35:11

parasympathetic ganglionic cells.

35:13

When they arise in the, uh, adrenal

35:15

gland, we call them pheochromocytomas.

35:17

Elsewhere, we call them paragangliomas.

35:20

And it turns out that extra-adrenal paragangliomas are

35:23

more aggressive than pheochromocytomas, and only about

35:26

40% of them may have elevated catecholamine levels.

35:30

On imaging, they tend to be very hypervascular.

35:33

So you can see this lesion over

35:34

here is quite hypervascular.

35:37

And, uh, if they do appear heterogeneous,

35:39

it may be because they sometimes

35:40

have internal hemorrhage within them.

35:43

And so these, uh, sometimes have been

35:44

described at least in the adrenal gland

35:46

as, uh, having light bulb, uh, signal.

35:48

And I don't know how accurate that always

35:50

is, but one thing that we do see somewhat

35:52

consistently is their hypervascularity.

35:58

This is a case.

35:59

Uh, I show my trainees from time to time and

36:02

they look at it and, um, it's quite a large tumor

36:05

here, but on the axial, sometimes it can be tough.

36:08

You know, this is the aorta you may be tricked into.

36:10

Think this is the IVC and that this is

36:12

just something else adjacent to it, or

36:14

you don't notice. This turns out that this

36:16

tumor is between the aorta and IVC on the

36:18

coronals, and this is a paraganglioma.

36:20

Again, notice the hypervascularity within

36:23

it, a key feature of paragangliomas.

36:28

And they can be single.

36:29

They could be multiple.

36:30

You can see in this instance, in the retroperitoneum,

36:32

another hypervascular mass. There are areas

36:34

of heterogeneity, but by and large, quite

36:36

hypervascular. Hypervascular, another mass

36:38

seen more posteriorly over here.

36:45

And this one, of course, we look at it and, uh,

36:48

oftentimes, uh, we consider this one a, not many.

36:51

We see a large mass over here.

36:53

At the bifurcation of the aorta, you

36:55

can see it on the coronals as well.

36:58

Peripherally hypervascular.

36:59

Internally, not so much.

37:00

This turns out to be another paraganglioma

37:03

at the famed organ of Zuckerkandl,

37:05

right at the aortic bifurcation.

37:06

Just beneath the inferior mesenteric, uh,

37:09

mesenteric artery, we see something like this.

37:11

You gotta think of the paraganglioma.

37:14

Uh, an extra-adrenal paraganglioma.

37:16

If you want nuclear medicine confirmation,

37:19

in this case, MIBG is the best test to get.

37:22

You can see over here uptake of this

37:24

paraganglioma on the MIBG images.

37:31

So that covers neurogenic tumors, the nerve sheath

37:34

tumors, uh, sympathetic and parasympathetic tumors.

37:38

Move on to lymphoma.

37:42

We look at lymphoma, it's the

37:43

most common retroperitoneal tumor.

37:46

We can maybe recognize this case

37:48

as one of our unknown cases.

37:49

Case of lymphoma.

37:51

Uh, there are two categories, Hodgkin's

37:53

and non-Hodgkin's, and there are certain

37:54

imaging clues that we look for to make

37:56

a prospective diagnosis of lymphoma.

37:58

Uh, we notice that lymphoma often when it

38:01

involves, when it's involved in the retro-

38:02

peritoneum, will lift the aorta off the spine.

38:04

We call it the floating aorta sign.

38:07

Sandwich sign has also been described where you

38:09

have masses of, uh, lymphoid tissue that are

38:13

essentially surrounding vessels, um, with the vessels

38:17

appearing as the condiments or the contents of a

38:19

sandwich, and the lymphoma masses as the, uh, bread.

38:22

Another key feature, of course, is

38:24

that it tends to encase vasculature

38:26

without causing any, uh, organ damage.

38:29

So if you see over here.

38:30

The aorta completely encased, but this

38:32

is perfused perfectly over here.

38:35

The arteries completely encased, but again,

38:37

the, uh, kidneys perfused, uh, perfectly.

38:44

This is lymphoma.

38:46

And, um, we can see in the perirenal space has,

38:49

uh, a reasonably distinctive appearance.

38:51

It can appear as one mass.

38:52

It appears multiple masses surrounding the kidney.

38:55

Can also have this very

38:56

ill-defined sheetlike appearance.

38:58

And when you see that sort of soft tissue surrounding

39:00

it, um, you can think of, uh, potentially lymphoma.

39:07

I always like to look at the occasional

39:09

plain film to see, uh, what I'm missing.

39:11

Uh, retrospectively.

39:13

So this was a plain film here.

39:15

And, uh, this is the left kidney.

39:16

You can see kind of the outline of it.

39:17

The right kidney looks a little bit more dense.

39:20

If we look at it on the, um, CT scan, we can

39:22

see that there's a mass in the perirenal fat.

39:25

This is, uh, turns out to be mets from melanoma.

39:27

So melanoma can certainly metastasize anywhere,

39:30

and, uh, certainly the retroperitoneum,

39:32

uh, will not be spared in this instance.

39:38

And this is an important cancer to remember in terms

39:40

of, uh, metastasis, and that's testicular cancer.

39:44

And so this is a patient who had

39:46

a known choriocarcinoma and, um,

39:49

testicular cancers, uh, like to.

39:52

Uh, metastasize, have nodal metastasis

39:54

to the retroperitoneum, typically at

39:56

the entry point of the gonadal veins.

39:59

Um, this was a little bit lower down, very

40:01

aggressive tumor actually that invaded some

40:03

of the vessels, causing some, uh, collaterals

40:05

to form and, in fact, invaded the bowel as well.

40:07

This was choriocarcinoma mets, and this was an

40:11

interesting case of a young, uh, gentleman who had

40:14

been doing a lot of sit-ups, had some pain, got

40:16

an ultrasound, uh, they saw a hematoma, what they

40:19

thought was a hematoma, told him to go back home.

40:23

He came back a few days later with more pain.

40:25

This time they got a CAT scan.

40:26

It turns out that, uh, there's actually a, a

40:29

thick-rimmed mass in the retroperitoneum.

40:32

And, uh, you know, if you were considering

40:34

primary retroperitoneal tumors, maybe

40:35

leiomyosarcoma may, uh, a good possibility.

40:38

But it's a young gentleman, uh, with

40:41

retroperitoneal mass and no other history.

40:43

You gotta think about testicular

40:45

tumor as a primary neoplasm.

40:46

And so when we did the ultrasound,

40:48

we actually see that there's a, uh,

40:50

coarse calcification in the person's—

40:52

in the patient's right testicle.

40:54

This was all removed and this turned

40:56

out to be a burned out testicular tumor.

40:59

Quite an uncommon entity where the thought process

41:02

is that the patient had a testicular tumor.

41:04

It did metastasize, but for a variety

41:07

of reasons, the primary tumor regressed,

41:09

uh, but the metastases persisted, and so

41:11

this was a burned out testicular tumor.

41:18

We'll move on to cystic neoplasms now.

41:20

And you know, just like solid neoplasms, there

41:22

are lots of different varieties, cystic neoplasms.

41:26

Um, I'm only gonna go through these three, um,

41:29

'cause they're, uh, relatively common, I would say.

41:32

But, uh, again, the list is exhaustive.

41:35

So lymphatic malformation, we

41:37

do see these from time to time.

41:38

It's a developmental abnormality where the lymphatic

41:41

tissue fails to communicate, um, and it results

41:44

in these low-density masses that are cystic.

41:48

They may have some variable signal in

41:50

MR imaging due to the chyle content.

41:52

It can have fluid-fluid levels within them.

41:54

One of the key features is that it

41:56

sort of insinuates between multiple

41:58

structures and multiple, uh, compartments.

42:01

Um, and so when you see a lesion that sort of

42:03

insinuates, is low in density, maybe fluid-fluid

42:06

levels, gotta think of lymphatic malformation.

42:09

Patients are often asymptomatic.

42:10

However, if it gets very large, it

42:12

can result in pain and distension.

42:17

And this is an example of lymphangiomatosis,

42:19

where you have a very large lymphatic malformation

42:22

and really multi-system lymphatic malformations

42:25

involving, again, multiple compartments.

42:27

And so, um, it can be more infiltrative in appearance,

42:30

can occasionally have foci of calcium, but again, we

42:33

have a large mass involving multiple compartments.

42:35

Gotta think of the, um, sort of

42:37

spectrum of lymphatic malformations.

42:43

And this is the answer to one of, uh, I think

42:44

it's the fourth unknown case, a tailgut cyst.

42:47

Um.

42:48

And this is something that, uh, you know, we see

42:51

not uncommonly, and the literature would suggest.

42:53

It's not very common.

42:54

We do see it from time to time, and it's almost

42:57

always an incidentally found, uh, lesion.

42:59

And the key finding here is that

43:01

it's in the presacral location.

43:03

Uh, again, you look at the literature, they'll

43:05

describe it more often in middle-aged women, but

43:07

we've seen it in males and females. It's from, uh, an

43:10

embryonic hint. The key is the location, which is

43:14

presacral, the fact that it looks multiloculated.

43:17

So on the T2-weighted images, I was trying to show

43:19

you that there's, you know, one cystic component

43:21

here, one here, one here, one here, one here.

43:24

And they may have variable signal

43:25

because of the variety of, uh,

43:27

internal hemorrhage or protein content.

43:30

Um, and they won't enhance internally. The

43:32

peripheral aspect of the cystic lesion will enhance.

43:35

Um, and so what do you do

43:36

with these when you see these?

43:39

You know, you, you call it as such. It's a tailgut

43:41

cyst.

43:41

The other name for this is a retrorectal hamartoma.

43:44

So some people gave that answer.

43:45

You'd also be correct.

43:46

You do need to actually take this out because

43:49

there's a small risk of malignant degeneration.

43:52

One series that I read, uh, was up to 14%,

43:55

and that, that seems quite large to me, but

43:57

that's what's out there in the literature.

43:59

Um, and oftentimes it's quoted that squamous

44:02

cell cancer is what it, uh, degenerates to, but

44:04

I've seen it degenerate to all sorts of tumors.

44:07

And so I suppose it's not as important

44:09

to know the exact histology that it

44:10

differentiates to, but know that it can.

44:13

And so when you see this and someone

44:15

asks you, what should I do with it?

44:16

Well, they should see a surgeon, see if they

44:18

can take this out safely.

44:23

So that covers our neoplasms.

44:26

And one—

44:26

last objective, to get through some non-

44:28

neoplastic retroperitoneal processes.

44:33

And these are the four that I'm gonna talk about.

44:36

Most of these here are gonna be very,

44:38

very, very uncommon, but you may see it

44:41

in your practice occasionally, rarely.

44:44

And hopefully I can give you some

44:45

clues to, to make the right diagnosis.

44:49

So I'll start with retroperitoneal fibrosis.

44:51

And it's actually a, uh, a disease that

44:53

encompasses, um, you know, a range of findings

44:56

and diseases and, and ultimately what happens is

44:58

you have proliferation of a fibroinflammatory

45:03

tissue, the epicenter of which

45:07

is around the infrarenal abdominal aorta.

45:10

It can also involve the IVC and iliac

45:12

vessels, and it likes to envelop the ureters.

45:15

Now there's a laundry list of things that

45:17

can cause retroperitoneal fibrosis, but most

45:20

commonly it's idiopathic in up to 60% of cases.

45:26

And this is really rare.

45:29

All right?

45:29

Some studies suggest that it's probably maybe

45:31

a little bit more common than we thought,

45:32

but ultimately this is a rare diagnosis.

45:34

We don't see this every day,

45:36

maybe once or twice a year.

45:38

It's seen more often in males and it's seen, um,

45:41

often in the fifth to seventh decades of life.

45:43

What I want you to remember about this disease and

45:46

something I didn't appreciate till a little bit

45:47

later on, is that it's actually a dynamic disease,

45:50

um, in that, you know, it's called fibrosis, but

45:54

in the early stage of the disease, it actually

45:56

consists of very edematous tissue that's highly vascular.

46:00

And that fibrotic component really becomes, uh,

46:03

more manifested in the late stage of the disease.

46:06

We have a reduced inflammatory infiltrate,

46:08

more, uh, avascular, hyalinized collagen content.

46:12

And so why is that important?

46:13

Well, the reason is that if we can detect

46:15

the stage, the early stage, perhaps this

46:18

is more amenable to medical therapy.

46:20

Or if it's in the late fibrotic stage,

46:22

medical therapy doesn't work as well.

46:24

And you may have to, um, do some surgery to

46:26

sort of free up the ureter from the disease,

46:29

um, and free up vessels from the disease.

46:35

So this is what it looks like on, uh, on imaging.

46:37

On CT imaging.

46:38

It's an ill-defined sheetlike mass,

46:40

the borders of which are irregular.

46:43

Now, this is not always true, but I like

46:45

to remember that it involves typically the

46:47

anterolateral borders of the aorta and that

46:50

it likes to spare the posterior border.

46:52

You can see this mass over here,

46:55

sheetlike mass forming the epicenter,

46:57

which is around the anterolateral aorta.

46:58

Aspects of the aorta going down the iliacs,

47:00

posteriorly looks pretty okay over here.

47:05

And it can involve the ureters 'cause

47:08

they go right in this location, and you'll

47:09

often see medial deviation of the ureters.

47:12

That's a characteristic finding when it involves,

47:15

when it wraps around the ureters, and, um, quite a

47:18

large number of patients can actually present with

47:21

obstructive nephropathy because of that obstruction.

47:25

This is another case of retroperitoneal fibrosis.

47:27

On a reformatted coronal image, how you can see

47:29

that the ureter is being pulled in medially.

47:31

This one's also being pulled in medially,

47:33

but this kidney's not working as well, so

47:34

we don't see the excreted contrast here.

47:40

So it likes to pull in the ureters, and occasionally

47:42

it'll also, uh, encase vessels, resulting

47:45

in collaterals and deep vein thrombosis.

47:46

So this was another, uh, case

47:48

of retroperitoneal fibrosis.

47:50

You can see the soft tissue over here.

47:52

You can see that somewhere more inferiorly.

47:54

It's obstructing the ureter.

47:55

We can see a lot of collaterals that are

47:57

developing 'cause it's also enveloping

47:59

the IVC and some of the venous vessels.

48:01

And you can see that there's a DVT

48:03

as a result of that as well.

48:08

And we talked

48:08

about the early stage and the late stage, and so how

48:12

does one go about potentially differentiating that?

48:16

It's quite hard on, uh, CT imaging.

48:18

PET imaging may be a little bit more

48:19

promising in that, um, early stage

48:21

will have a little bit more

48:22

FDG avidity. On MR imaging,

48:25

um, chronic disease tends to be

48:27

T1 and T2 hypointense.

48:29

As you can see over here, I'm gonna give contrast.

48:31

There'll be minimal enhancement.

48:33

And I want you to sort of compare that to what

48:35

active disease looks like, where, you know, it looks

48:38

sort of, on a non-contrast CT, like soft tissue. On

48:41

T1-weighted images, relatively hypointense.

48:44

On T2-weighted images, does look quite markedly hyper-

48:48

intense compared to the other case, and noticeably

48:52

hypervascular, um, on post-contrast imaging.

48:55

So if we can catch it in the early stage and

48:58

let our referring providers know about it,

49:00

potentially this is amenable to some of the

49:02

medical therapies that they have out there.

49:07

This is always, uh, a nice, uh, thing to remember.

49:10

How do you differentiate this term of common

49:12

retroperitoneal tumor that's lymphoma?

49:14

Well, retroperitoneal fibrosis, as

49:16

I said, spares the posterior border.

49:18

As I mentioned with lymphoma, it lifts

49:20

the aorta off the spine typically.

49:24

And retroperitoneal fibrosis obstructs ureters,

49:27

can obstruct vessels. Lymphoma, as seen in these

49:30

two cases, while lymphoma does not tend to do that.

49:34

Lymphoma will envelop vessels

49:35

without causing obstruction.

49:37

Um, potentially can cause that if

49:39

it gets very, very large and bulky.

49:41

But for the most part, it doesn't, uh, cause any

49:43

sort of, um, obstruction to vessels or the ureters.

49:50

So that's RP fibrosis.

49:52

So we can start to get to some of the more

49:53

exotic diseases as we finish up this session.

49:56

This is a case of Erdheim-Chester Disease.

49:59

It's a non-Langerhans cell histiocytosis.

50:02

Clinical presentation is variable.

50:05

Uh, patients can be asymptomatic.

50:07

They can have bone pain, weight loss, malaise,

50:09

fever, and on imaging, you get characteristic

50:12

bony lesions, which are bilateral, symmetric,

50:15

and, uh, they're sclerotic, involving the

50:17

metaphyseal and diaphyseal areas of long bone.

50:19

This is taken from the literature.

50:21

Um, extraskeletal manifestations are seen in about

50:24

50% of cases, and the most common extraskeletal

50:26

manifestation is in the retroperitoneum.

50:29

And, uh, it likes to form this

50:31

perinephric rind of tissue.

50:33

You can see in this case over here, um,

50:36

around the left kidney on the coronals,

50:38

you can see it over here as well.

50:39

And this was our last unknown case where you can

50:41

see that rind of tissue that's surrounding both

50:44

kidneys in a patient, uh, who also had bony lesions.

50:48

Um, this was Erdheim-Chester Disease.

50:53

Amyloidosis is very, very, very uncommon.

50:56

It may be primary or secondary.

50:58

It's due to extracellular deposition of amyloid, and

51:01

the imaging findings are going to be nonspecific.

51:05

It can be localized where you see a soft

51:06

tissue mass with calcifications, but that's

51:08

not really gonna help you systemically.

51:10

It can involve the retroperitoneum,

51:12

or again, you see a retroperitoneal

51:13

soft tissue that over time will calcify.

51:16

Uh, but again, a very, very tough

51:18

diagnosis to make prospectively.

51:23

I will finish off with extramedullary hematopoiesis.

51:25

Now this we see, uh, not uncommonly.

51:28

Um, and this is due to ectopic deposition of, uh,

51:31

hematopoietic tissue outside of the bone marrow.

51:34

You often see it in context of patients who

51:37

have, um, hemoglobinopathies, perhaps

51:40

myelofibrosis, and things like leukemia, where

51:43

you have the need for, um, developing, uh, bone

51:46

marrow that's outside of the, uh, bone marrow,

51:48

uh, normal places of bone marrow development.

51:51

It can occur in the liver, spleen, lymph nodes.

51:54

When it occurs in the retroperitoneum,

51:55

it often looks like paravertebral masses.

51:58

But this presacral space is a common location.

52:02

And it can look soft tissue-like. This, in

52:04

2007, didn't change over three years in the

52:06

patient who I believe had myelofibrosis.

52:09

Um, it can also contain a variable amount

52:11

of fat, as you can see in this case.

52:13

Um, a patient with soft tissue and fatty components.

52:15

Now, there's a differential for this,

52:17

but in the context of this patient, this

52:19

was deemed to be extramedullary hematopoiesis.

52:22

The key things that you're gonna look for are

52:24

any skeletal changes, um, that can be seen with,

52:28

uh, things like myelofibrosis, perhaps signs

52:30

of iron overload that can be seen in patients

52:32

with leukemia, and of course the presacral mass.

52:35

If you see stability over time, think that

52:37

it could be extramedullary hematopoiesis.

52:39

1238 00:52:43,455 --> 00:52:45,105 So that's our last non-neoplastic

52:45

entity that I wanted to discuss.

52:47

And let's sort of circle back to the

52:49

objectives before getting to the unknown cases.

52:51

So over the last, uh, 50 minutes or so, these

52:54

are the objectives that we went through.

52:55

We talked about the tricompartmental model of the

52:58

retroperitoneum that's built around the kidney.

53:00

And to that we sort of added this

53:02

concept of interfascial planes that allow

53:04

communication between different compartments.

53:07

We then went through some imaging features

53:08

of retroperitoneal neoplasms, um, the three

53:11

sarcomas: liposarcoma, leiomyosarcoma, and

53:14

undifferentiated, uh, pleomorphic sarcomas.

53:18

We talked about a few neurogenic tumors.

53:20

Remember the target sign with neurofibromas?

53:23

And remember the hypervascularity of

53:25

parasympathetic tumors, metastasis, lymphomas.

53:28

Well, remember lymphoma lifts the aorta.

53:31

We talked about the sandwich sign.

53:32

We talked about lymphoma enveloping

53:34

structures, not causing damage or obstruction.

53:37

Then we talked about a few cystic neoplasms,

53:39

namely lymphatic malformations and tailgut cysts.

53:43

We finished off with these non-

53:45

neoplastic retroperitoneal processes.

53:48

What I want you to remember for retroperitoneal

53:50

fibrosis is that it's, um, anterolateral infrarenal aorta.

53:54

Okay.

53:55

And it's a dynamic disease, has an active stage

53:57

or an early stage or a late stage, and we can

54:00

use imaging potentially to differentiate that.

54:03

Erdheim-Chester is always a fun, uh, thing to think

54:05

about when you see these perinephric soft tissue

54:08

surrounding the kidneys, making it look like a

54:09

hairy kidney with these characteristic bony lesions.

54:12

You gotta think of Erdheim-Chester, and amyloidosis,

54:15

I mentioned here, but it is quite nonspecific

54:17

and a very tough diagnosis to make prospectively.

54:23

So let's cycle back to our objectives.

54:25

First case, uh, everyone who got

54:27

this right can pat themselves on the back.

54:28

Liposarcoma, large fat-containing mass, the

54:31

perirenal space, pushing the right kidney anteriorly.

54:36

Our second case was leiomyosarcoma, a mass in

54:39

the retroperitoneum, majority of which is

54:41

outside of the vessel, but you certainly see

54:42

a component that's invading the IVC here.

54:44

So that's a leiomyosarcoma.

54:47

This was lymphoma. Lymphoma's lifting

54:49

the aorta off the spine, enveloping, uh, the,

54:52

uh, vessels, not causing any degree of, uh,

54:55

obstruction within this left kidney over here.

55:00

This is a tailgut cyst.

55:02

Uh, pardon the spelling over there.

55:04

Uh, also retrorectal hamartoma.

55:06

Uh, and so if you got that, uh,

55:08

as an answer, you'd be correct.

55:10

This multiloculated cystic mass in the presacral

55:12

space, uh, enhancement of the septations in the

55:15

periphery, you gotta think of tailgut cyst.

55:17

Remember, these can

55:19

degenerate into malignancy.

55:20

So you gotta take them out if possible.

55:24

And last but not least was, uh,

55:26

Erdheim-Chester Disease, hairy kidney.

55:28

This perinephric soft tissue surrounding the

55:30

kidneys with sclerotic lesions surrounding

55:32

the metaphyseal regions of, uh, of long bones.

55:38

So that, that's a little tour of the retroperitoneum.

55:41

Uh, thank you everyone for your attention.

55:43

There's been a bunch of comments and, uh,

55:47

uh, I'll open it up for some questions

55:49

that people have, and we'll see if I can

55:52

get through them.

56:01

All right, so we have a few people with

56:04

that, with, uh, answering the cases.

56:06

So thank you so much for your participation there.

56:07

I'll certainly, uh, we'll certainly have

56:09

a look at that, um, and see if we can

56:12

announce, uh, some winners over here.

56:16

So we will just, uh, put that aside for the moment.

56:19

Let's see, in the Q—

56:19

and A, nothing right now.

56:38

So everyone—

56:38

writing in.

56:39

Um, thank you so much.

56:40

You're so kind to take a

56:42

moment to, to, uh, to thank me.

56:47

I'm so happy to be able to do this.

56:49

They—

56:49

have, uh, one person raise their hand.

56:51

Let's see if I'm gonna allow him to talk

56:52

and we'll see if they have a question.

56:54

Yeah,

56:54

absolutely.

57:21

Roman, are you here?

57:21

Do you have a question?

57:30

No, that's working.

57:31

Uh, if anyone has a question, they can

57:32

add it into this Q and A section or put

57:34

it in the question or the live chat.

57:40

And also, there's my email here, so if anyone

57:42

has a question, uh, later on, feel free—

57:45

you can get in touch with me and I'll.

57:49

I have some free time nowadays,

57:50

so I'm happy to answer them.

57:53

All right, perfect.

57:54

Uh, as we bring this to a close, I wanna

57:56

thank you, Dr. Mathur, for your time today.

57:59

Thanks to all you guys for participating in our

58:01

noon conference. A reminder that this presentation

58:03

will be available on demand on our website.

58:06

Please find it at mrionline.com and

58:09

sign up for future, uh, conferences.

58:11

We have one again tomorrow and the rest

58:13

of the week also available on our website.

58:15

Thanks so much for joining.