0:02

All right.

0:02

Hello and welcome to the fifth of many live

0:05

stream noon conferences hosted by MRI Online.

0:08

It is just now 12 o'clock, and I see

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the number is still rising, so I wanna

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give it a few more minutes, seconds.

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Really, um, just wanted to say welcome and in

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response to the changes happening around the world.

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Right now in the shutting down of in-person

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events, we have decided to provide free daily

0:23

noon lectures to all radiologists worldwide.

0:26

Today we're joined by Dr. Harisinghani.

0:29

He's a professor of radiology at Harvard

0:31

Medical School and director of Abdominal

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MRI at the Massachusetts General

0:35

Hospital in Boston, Massachusetts.

0:38

In addition, he serves as director of the Clinical

0:40

Discovery Program, Center for Molecular Imaging

0:43

Research at Mass Gen and has been the section

0:46

editor of GU Radiology for the AJR. He has been

0:50

practicing in the field of abdominal radiology

0:52

for over 20 years, has published over a hundred

0:55

reviewed papers, and has edited five

0:57

textbooks in the field of radiology.

0:59

A reminder that there will be time at the

1:00

end of this hour for a Q and A session.

1:02

Please use the Q and A feature and

1:04

we'll get to as many of these questions

1:06

as we can before our time is up.

1:07

That being said, thank you so much

1:09

for joining us today. Dr. Harisinghani,

1:10

I'll let you take it from here.

1:12

Thank you, Ashley.

1:13

Um, and welcome, uh, everyone.

1:15

I hope everybody's staying safe and,

1:18

uh, uh, taking the due precautions, uh,

1:20

so that we can overcome this crisis

1:23

in a healthy manner.

1:25

Um, so having said that, the topic of discussion

1:27

today is gonna be, um, looking at how MR can

1:31

be helpful in patients with rectal cancer.

1:34

And if you look at the, uh, the indications

1:38

for MR specifically in the abdomen and pelvis,

1:41

uh, there are a couple of indications like

1:43

prostate and rectum where MR has certainly

1:46

uh, become front and center in terms of what

1:50

information is, is gathered prior to

1:52

therapy and, and the modality of choice.

1:54

So MR is certainly becoming the modality of choice.

1:57

And, and what we are gonna do today is, uh, talk

2:00

about these, or cover these, uh, specific points.

2:03

The first is why MR. Why do we need

2:06

to do MR in, in, uh, rectal cancer?

2:08

The second is how do we do the MR.

2:10

Talk a little bit about technique and, uh,

2:13

kind of give you some pointers in terms

2:15

of what the ideal protocol ought to be.

2:18

Uh, and then the most important thing is once you

2:21

do the MR, the question is what do you look for

2:23

and how do you put that in a comprehensive report?

2:28

Um, and while we are discussing the content

2:31

of our report, we are gonna talk about a

2:33

few iCal concepts, which are key, uh, to

2:36

remember when one is looking at rectal MR.

2:40

And talk about standardized

2:41

reporting, why that is, uh,

2:43

very important, and I'll show you, um, or, or

2:47

provide you with resources that you can use to

2:49

download, uh, free templates for, for the rectal MR.

2:54

And then talk about, uh, imaging pointers for,

2:57

um, uh, you know, that, that predict worse

3:00

prognosis in these, uh, in these patients.

3:04

So the first question is why.

3:05

And if you look at this is, you know, a

3:07

year old in 2018, um, uh, rectal cancer

3:11

gets clumped with, uh, with colonic tumors.

3:13

So if you look at colorectal, they are the

3:15

fourth most, uh, common type of cancer.

3:18

And about one third of these, uh,

3:20

patients are, uh, are rectal cancers.

3:23

Uh, so it's not a trivial number.

3:25

It certainly is a significant, uh, number

3:27

of cancer cases that we see in a year.

3:30

And if you look at this particular, um,

3:33

distribution of what the five year survival is,

3:35

it shows you that when the tumor is localized

3:38

to the lumen, um, and gets, and that patient

3:41

gets appropriate therapy, there is a very good

3:43

chance of a five year, um, disease-free survival.

3:47

But as the disease progresses and becomes regional

3:50

or distant, then the five year survival drops.

3:53

And that's the reason why we have to be very

3:55

diligent in accurately staging these patients.

3:59

So from a very simplistic perspective, uh, if

4:02

the, uh, tumor is confined to the lumen, which

4:05

means it stays inside the lumen of the rectum,

4:08

and doesn't extend out, the treatments are primary

4:10

surgical, and you know, the standard is, uh, what

4:13

we refer to as, um, trans excision or TME surgery.

4:18

Whereas if it extends beyond the confines of the wall

4:21

and extends into the surrounding fat or adjacent,

4:24

uh, pelvic, uh, parenchymal organs, and then those

4:27

patients typically get, um, neoadjuvant chemoradiation

4:31

therapy, and then they get subsequently followed up.

4:34

And if things seem to be progressing in the

4:36

right direction and looks like the tumor is,

4:39

uh, regressing and, and shrinking away, then

4:42

those patients ultimately go for surgery.

4:44

So again, this is a simplified grid.

4:48

And just to kind of highlight what some of

4:49

the, um, um, mechanisms of how the tumor,

4:53

um, is, is treated irrespective of what,

4:58

uh, or how you treat the disease, the goal.

5:02

Both for the folks that treat the patient

5:04

and for us is to prevent recurrence.

5:08

And here is a patient who had a mucinous,

5:10

uh, type of adenocarcinoma in the pelvis,

5:13

and came back after surgery with a local

5:16

pelvic recurrence, as you're seeing in this

5:18

particular instance in the presacral region.

5:21

And once the disease comes back or the

5:23

patient gets local recurrence, that is a very

5:26

difficult disease to get a, uh, handle on.

5:29

These patients typically have bad prognosis.

5:31

They have poor, very poor quality of life.

5:34

And so we have to do whatever is in our, um,

5:37

uh, you know, whatever is available to us,

5:39

use that, uh, to the best of our ability to

5:42

prevent this specific scenario from happening.

5:46

And so accurate staging and appropriate

5:48

treatment are the key things

5:50

that will end up preventing local recurrence.

5:54

And so with that said in mind, what we are trying

5:57

to do, why we are doing MR, is basically to try and

5:59

distinguish those patients into, dis, into, into

6:03

those that have early lumen-confined disease, which

6:05

means the disease is not extended beyond the wall,

6:08

and those can, you know, as I said, get surgical

6:11

modes of therapy, and distinguish those from

6:14

local spread and, and those with distant

6:16

pelvic, right?

6:17

Because those require more aggressive

6:20

modes of therapy prior to surgery.

6:23

And then this is another important point of imaging

6:25

is, you know, when you look at the primary tumor, you

6:29

have to find, uh, those specific imaging markers that

6:33

can predict that this patient is going to do worse,

6:37

are going to have adverse prognostic, uh, outcome.

6:39

And we'll be discussing what these points are.

6:42

But this is sort of more or less in a nutshell,

6:44

what the, um, uh, role of MR is in rectal cancer.

6:48

So then, then comes the question of how do we do

6:50

the MR. And, uh, you know, I think like most other

6:55

MRs in the abdomen and pelvis,

6:57

attention to detail in terms of

6:59

technique is very, uh, critical.

7:02

If you, um, use a generic protocol

7:05

that you use for all the pelvises, it's

7:06

not gonna suffice for accurate staging.

7:10

You have to spend some time in optimizing

7:12

the protocol so that you get the

7:13

necessary information that is required.

7:16

And so you use this, you know, the, again, you

7:19

can use a 1.5 or 3T, uh, use, um, uh, the

7:23

phase-array coils that are available with your

7:25

system, uh, to the best, uh, of your ability.

7:29

And so let's look at what the protocol is.

7:31

The first thing you do is you do what is referred

7:33

to as the localizers or the scout images.

7:35

And this basically gives the technologist an idea of

7:38

what is the area of anatomy that needs to be covered.

7:41

Generally, you want to be, um, covering an

7:44

anatomy that extends from the L5–S1

7:47

junction, uh, down to the, uh, level of the anal

7:50

verge, or perhaps a little bit lower than that,

7:53

uh, because that will give you an entire, uh,

7:55

coverage for, you know, where the rectum and

7:58

the anal canal lie and will give you

8:01

all the necessary information that you desire.

8:04

So that's in terms of coverage.

8:05

Then the next sequence the technologist ought to

8:07

run is the sagittal, um, T2-weighted sequence.

8:11

And typically you like it to be a fast spin

8:13

or a turbo spin, or T2, and this goes from

8:15

one pelvic side wall to the other so that

8:17

you cover the entire breadth of the viscera-

8:20

containing pelvis, and the rectum

8:23

more or less resides in the center,

8:24

as you're seeing in this, uh, instance.

8:27

The reason for doing a sagittal first is

8:30

so that you get a lay of the land of where

8:32

the, um, you know, where the rectum is, what

8:35

defines the rectum, where is the cancer.

8:37

Because based on, you know, where the tumor lies,

8:41

you are going to be prescribing some other planes.

8:44

And that's why it's important and

8:45

critical to do the sagittal sequence first.

8:49

After you do the sagittal, you do a true axial.

8:51

And again, the extent is from the level of a little

8:54

below the level of the, uh, anal verge up to the

8:58

level of L5–S1 or the aortic bifurcation.

9:01

And the reason for doing the true axial is

9:04

you're trying to look, take a look at the anatomy,

9:06

and, uh, you know, there are, um, there are

9:10

anatomical features in the, um, anal canal that

9:14

are nicely laid out on the axial images, uh,

9:16

that can help you in staging lower anal cancers.

9:19

And this is just showing you.

9:20

If you take an axial slice at the level of the

9:25

levator ani muscle, which is this U-shaped muscle, that's

9:29

where, um, uh, traditionally, you know, the, um,

9:32

the, uh, columnar epithelium of the rectum becomes

9:35

the, um, squamous epithelium of the anal canal.

9:38

And that's where, anatomically or histologically, you would,

9:40

uh, uh, locate the transition of the anal canal to

9:44

the rectum — or sorry, the rectum to the anal canal.

9:47

Now, once you're below this level in the level of the

9:49

anal canal, there are two essential sphincters.

9:53

You're looking for internal sphincter and

9:54

you're looking for external sphincter.

9:56

And so if you look here on this image, the,

9:59

the green color is the internal sphincter.

10:02

The internal sphincter is an involuntary muscle.

10:04

Um, uh, and it's the, uh, continuation of

10:07

the circular smooth muscle of the rectum.

10:09

So it is a relatively, um,

10:11

has relatively T2-bright

10:13

signal compared to the external

10:15

sphincter, which you see right here.

10:16

The external sphincter is darker.

10:18

It has similar signal intensity as the skeletal

10:21

muscle because this is a striated, uh, muscle,

10:24

which, uh, is different from the internal sphincter.

10:27

And so.

10:29

You know, uh, you need, whenever you look at a pelvis,

10:32

whether it's for rectum, prostate, you know, keep

10:34

sort of emphasizing this anatomy because it helps.

10:37

One other way that you can distinguish the internal

10:39

from the external sphincter is that the internal

10:42

sphincter will show earlier enhancement after

10:44

gadolinium compared to the external sphincter.

10:46

So that's in terms of anatomy — axial.

10:49

Now, after axial, we do what is referred to as

10:52

the, the — this is sort of the money sequence.

10:54

It is the high-resolution thin T2-weighted oblique,

10:57

axial, um, uh, images. Uh, these are the key,

11:01

um, uh, money sequences, uh, in terms of staging.

11:06

And what do you mean by that?

11:07

So remember, you acquired your sagittal, and in this

11:10

instance there is a very long, um, segment of tumor.

11:14

What you're doing is, uh, scanning perpendicular

11:17

to the plane or axis of the cancer, as you see in

11:19

this particular instance. That is the reason

11:21

why, uh, you know, that is the reason why you sort

11:24

of, uh, angle it to the, uh, axis of the tumor.

11:28

Uh, so these are the key sequences for staging. And why

11:30

do we pay such, um, close attention and, and pay a lot

11:34

of emphasis on this is basically because of this.

11:37

If you look at.

11:38

This particular case, there is a tumor

11:40

right here on the S, and here is a

11:44

true axial image without any angulation.

11:46

And when you look at the true axial image,

11:48

if you look at, um, from six o'clock to, um,

11:52

you know, about nine o'clock in position,

11:54

there appears to be relatively unharassed.

11:57

And if someone asks you, is the tumor confined

11:59

to the lumen, or do you think the tumor

12:00

is extending out, it can be very difficult

12:03

and challenging to know if that's the case.

12:05

Whereas if you look at the oblique, perpendicular,

12:08

oblique axial, you can see the tumor is confined

12:10

to the lumen and it's not extending beyond.

12:13

So it could mean, you know, a difference in accurate

12:15

staging, and that's why I cannot emphasize enough.

12:18

You have to spend some time in terms of making

12:21

sure that these, uh, sequences are adequately

12:24

performed and they are more, uh, they are higher

12:26

in resolution than the conventional axial, uh,

12:29

T2-weighted sequence, so they have more detail

12:32

that you can look for in terms of

12:34

delineation and staging of the tumor.

12:37

After you do the, uh, uh, the, uh, oblique

12:40

axial, you do the coronal T2-weighted,

12:42

and again, the coronal sequence

12:44

is, um, to emphasize the anatomy — particularly

12:48

for the low rectal cancers, where you're looking

12:50

for, um, involvement of the sphincter complex.

12:53

And so this is what the coronal, uh, looks like.

12:56

Um, and just to kind of blow it up a little bit,

12:59

you see the, um, the levator ani muscle on either side.

13:02

The levator muscles, um, that form the pelvic

13:05

floor are like hammocks on either side.

13:08

These levator muscles come down and insert into

13:11

the puborectalis, which is this muscle that

13:14

is, um, uh, shown by the turquoise, uh, arrows.

13:19

And then below the puborectalis,

13:20

you have the external sphincter.

13:21

The external sphincter typically has three

13:23

fascicles, which you're seeing right here.

13:25

We have the upper, the me and the lower fascicle.

13:28

Then you have the green arrows, which

13:31

are pointing to the internal sphincter.

13:32

That's this between the internal and the external

13:35

sphincter is this bright, uh, fat-containing space,

13:38

and that is referred to as intersphincteric space.

13:41

Again, you know, you need to kind of keep looking at

13:43

this and reinforcing the anatomy when you're looking

13:46

at, uh, you know, images where patients don't have

13:50

cancers and other pelvic, so that you know, when

13:52

you do have a patient with, uh, low rectal cancer.

13:56

Accurately depicting the anatomy and, and trying

13:58

to figure out what's, uh, involved or not.

14:01

So pay attention to the anatomy in

14:03

terms of, um, in the coronal images.

14:06

Uh, then we do DWI.

14:08

Now the money sequence is truly, in terms

14:10

of staging, are the T2-weighted sequence.

14:12

There is a school of thought that the

14:14

diffusions and the gadolinium-enhanced

14:16

images are really not required.

14:19

I can tell you in our practice, they can be extremely

14:22

helpful and beneficial, and they can complement the

14:25

information that you get from the T2-weighted sequence.

14:28

So typically you do a low B value, a

14:30

high B value around 800 to a thousand,

14:32

and then calculate an ADC from that.

14:35

And then, uh, we also do gadolinium-enhanced

14:38

images, and more so than the primary staging,

14:42

these can be very critical when you're

14:43

looking at post-treatment scans.

14:46

And so here is an example of a patient who has a

14:48

tumor in the, um, in the, uh, on the right wall.

14:53

Uh, and you can see that there is restricted

14:55

diffusion and abnormal enhancement, and after

14:58

therapy on the T2, it's very difficult to

15:00

know whether there is any residual cancer.

15:02

But on the ADC of the DWI, and based on

15:05

the enhancement, you can see that there

15:07

is some residual cancer in that location.

15:09

So.

15:11

Certainly of, of benefit in terms of follow-up.

15:14

Um, and like I said, it's, it doesn't

15:18

hurt to do that in the regular, um, uh,

15:21

staging protocol as well because you

15:23

certainly end up getting useful information.

15:26

So that is the, uh, how we do it.

15:28

Now we come to, what do we look for? Now before we

15:31

talk about, um, uh, looking at the specific features

15:35

for the rectal cancer, we need to reemphasize.

15:38

Uh, some, um, anatomy facts and also, uh,

15:41

go through some of the terms, uh, that are

15:43

critical for you to know before you actually

15:46

start looking at rectal cancer patients.

15:49

So the first is anatomy.

15:50

And the question is, how do we define the

15:52

rectum on MR? And, and what, what are

15:56

the boundaries that we use, uh, on MR

15:58

to truly say, you know, where the

16:01

rectum begins and ends and so on?

16:03

MR. Excuse me.

16:05

We follow the, um,

16:07

the, uh, the perspective of the endoscopists, and

16:10

from an endoscopist's perspective, the, the rectum

16:13

is the most distal part of the, um, GI tract

16:17

that extends 15 centimeters from the anal verge.

16:20

So this is what the endoscopist looks for

16:23

and, and, and characterizes as the rectum.

16:26

So here is the anal verge, and they

16:27

go 15 centimeters from there, and then

16:30

they, they break it up into upper,

16:33

rectum, which is upper five centimeters, mid

16:35

rectum, mid five centimeters, and lower rectum,

16:37

that is the lower, uh, five centimeters.

16:40

And this is what we follow.

16:42

And here is a sagittal T2-weighted MR,

16:45

showing you how you go along the, uh, the

16:48

lumen of the rectum and draw 15 centimeters.

16:51

And that's what, um, is, uh, is

16:54

classified as the, um, as the rectum.

16:56

Now you will see here that,

16:59

based on this definition, you are actually

17:02

including the most distal part, which

17:04

is the anal canal within the rectum.

17:08

You know, that's what the endoscopists

17:09

do and that's what we follow.

17:11

So that's something for you to

17:12

keep in the back of your mind.

17:14

Now, uh, the question is, what defines the anal verge?

17:19

Typically, it's where the external sphincter ends.

17:22

So the external sphincter is a little bit, uh, extends

17:24

a little bit lower than the internal sphincter.

17:27

There are some institutions that take the most distal

17:29

part of the internal sphincter as the anal verge.

17:33

There are some institutions that take the most,

17:35

uh, distal part of the anal canal, which is where

17:38

the external sphincter is, as the anal verge.

17:40

I mean, the difference between

17:41

those two is about 0.5 centimeters.

17:43

So you really are not.

17:46

You know, uh, accounting for a lot of difference.

17:48

But the key is to talk to the surgical colleagues

17:51

and oncologists in your respective institutions

17:53

and see, you know, which, which definition

17:55

of the anal verge they would like to use.

17:58

But irrespective of that, make sure that, you

18:00

know, it's, it's the 15-centimeter counting

18:02

from the, uh, the anal verge as the, as the, uh,

18:06

definition of the rectum. Now, because, uh, this

18:11

definition of the rectum includes the anal canal.

18:14

It means that if there are tumors primarily arising

18:18

in the anal canal, which are primarily squamous

18:20

cell carcinomas, you know, are also included in

18:23

this, uh, in this, uh, supposed, uh, definition.

18:27

And so the question that begs the question is if

18:31

you are looking at a pelvic MR, are you trying

18:33

to distinguish an anal cancer from rectal cancer?

18:37

And so if I show you these two coronal images,

18:40

One of them is a rectal cancer,

18:42

and one of them is an anal cancer.

18:43

And ask you, uh, what is the,

18:47

um, uh, which one is which?

18:50

It's very difficult to predict.

18:52

If you look on histopathology, it's

18:54

the one on the left was rectal and one

18:56

on the right was anal cancer.

18:57

So as radiologists, we are not in the business

19:01

of distinguishing anal from rectal cancer.

19:04

So even before you sit down and open the

19:06

MR and apply everything I tell you today,

19:10

it is very, very, very important.

19:11

I can't emphasize that enough, that you look

19:13

and make sure that from a histopathologic

19:16

perspective, what you're looking at has been,

19:19

uh, biopsy-proven to be a rectal cancer.

19:22

Because if what you are doing or what you're looking

19:25

at is a biopsy-proven anal cancer, then none of what

19:28

I tell you is going to apply to anal cancer, because

19:31

the staging and the treatment is totally different.

19:34

And so.

19:35

You know, again, the, the take-home

19:38

point here is do not try and distinguish

19:40

rectum from anal based on imaging.

19:43

You need to know that a priori before you

19:45

look at the exam to apply whatever I tell you.

19:48

You need to be sure that what you're looking for

19:50

is rectal cancer and not anal cancer before you,

19:53

uh, uh, before you, um, um, uh, you know, start

19:58

applying the, the rules that we, we talk about today.

20:02

One more anatomy, um, fact that you need to

20:05

keep in mind is that not the entire part of the

20:08

rectum is extraperitoneal. Uh, the peritoneum

20:12

inserts in the upper part of the mid rectum.

20:15

And so in men, it's typically, here you

20:17

can see the tip of the seminal vesicle.

20:19

This black line that you see going towards

20:22

the rectum is a peritoneal reflection.

20:24

And in women who have their uterus, it's typically

20:27

at the junction of the uterus and cervix.

20:29

You see this thin black line extending

20:32

onto the anterior part of the,

20:33

um, uh, anterior part of the rectum.

20:36

So that is the peritoneal insertion. Above this level,

20:40

the anterior part of the

20:41

rectum is lined by peritoneum.

20:43

And why is that an important point?

20:45

It becomes important from a staging perspective,

20:47

and it also becomes important from, uh, a few of

20:51

the imaging features that we will be talking on.

20:54

On axial, if you take an axial slice at

20:56

this level, this is what it looks like.

20:58

It has this sort of a gulling pattern

20:59

of, uh, thin black line that is

21:02

inserted anteriorly onto the rectum.

21:04

So when you're looking at your MRs, please

21:06

make sure that you identify this landmark,

21:09

because this is going to be a key landmark

21:11

for, uh, not only for staging, but also

21:14

for assessing, um, um, assessing some of the

21:18

other features that we'll be talking about.

21:21

This is what the specimen looks like.

21:22

So here is the anterior part of the,

21:25

uh, TME specimen where you can see

21:27

this glistening surface of the rectum.

21:29

That's what is lined by peritoneum.

21:32

Whereas posteriorly, there is no peritoneal, um, line.

21:35

So.

21:36

You know, just, uh, keep in mind that.

21:39

Now the next point is, um, the appearance of the,

21:44

um, the rectal wall on T2-weighted sequence.

21:47

'Cause that's what governs a lot of the

21:50

staging information that we will be talking about.

21:53

So here is an anatomy depiction of the wall of

21:55

the rectum, and this is what we see on an axial

21:59

T2-weighted sequence.

22:00

So we look at two bands, essentially.

22:03

Uh, the inner bright or hyperintense

22:05

ring comprises the mucosa and

22:07

submucosa that you're seeing right here.

22:10

And then the outer ring, which is a dark

22:12

ring, which is the most important part that

22:14

we look for, is the muscularis propria.

22:16

So you see this dark line that extends all along.

22:19

That's the, um, uh, the muscularis propria.

22:22

And that is one very important

22:24

structure that we pay attention to.

22:26

We are looking at the MR. So here is

22:29

a coronal, um, and an oblique image.

22:32

You can see this is the dark line of

22:34

the muscularis going all the way around.

22:36

And this is sort of the relatively

22:37

brighter mucosa, submucosa.

22:40

Now there is another structure that you see

22:42

on this T2-weighted sequence. That's this

22:44

black line that extends all along in a

22:48

circumferential manner surrounding the rectum.

22:51

And that's the other important landmark

22:52

that we need to pay attention to.

22:54

And that is the mesorectal fascia.

22:57

Uh, it's a connective tissue sheet that encloses

23:00

the, um, uh, the rectum. Also encloses the

23:03

perirectal, uh, uh, fat, perirectal vessels, and

23:07

small nodes that are in that, uh, location.

23:10

And so, uh, the reason why this is an

23:13

important landmark is because, uh, as we will

23:16

see from a T staging perspective as well

23:19

as, um, from a surgical, uh, perspective.

23:24

Because typically when the surgeon does their

23:26

surgery and does the mesorectal excision, they try and,

23:31

um, go along the plane of this mesorectal fascia.

23:35

Now, it may not be very precise.

23:37

It could be a little bit to the inside, a

23:39

little bit to the outside, but this is more

23:41

or less the, they define surgical plane, if

23:44

you will, laterally for the TME. And when the

23:47

specimen does come out, this is the plane of

23:50

resection that is, um, you know,

23:53

that is defined by the mesorectal fascia.

23:55

Now there are two, um, points to

23:58

remember about the mesorectal fascia.

24:00

One is, it is most, uh, generous or

24:03

capacious in the mid part of the rectum.

24:06

As you come to the lower part of the

24:07

rectum, it becomes very closely applied

24:10

to the, uh, to the wall of the rectum.

24:14

In fact, below the level of the

24:15

levator muscle, the mesorectal fascia

24:19

practically encloses, um, uh,

24:22

attachment to the wall of the rectum.

24:24

And so that's important because, you

24:26

know, if you have lower rectal cancers, then

24:31

there is a chance that it's

24:33

directly involving fascia.

24:34

We'll be talking about that.

24:36

But this is an important anatomy, uh,

24:38

uh, point to, uh, to keep in mind.

24:41

And so, uh, that brings us to the next point.

24:43

What is total mesorectal excision we have been talking about?

24:46

This is, you know, this is the surgery

24:48

that, uh, really, um, uh, revolutionized

24:52

the, uh, the treatment of rectal cancer.

24:55

And what was found is instead of just taking out

24:57

the rectum, uh, along with the, uh, cancer, if you

25:01

dissect along the plane of the mesorectal fascia,

25:04

and not only remove the, uh, the rectum, but also the

25:07

fat and the, and the lymph nodes and, and structures

25:11

that are present in the mesorectal fascia, the outcome

25:14

in patients is much better in terms of

25:16

reduced chance of local recurrence.

25:18

So these are diagrams showing you

25:20

what essentially you are doing.

25:22

When you're doing a TME. You are dissecting

25:25

along the plane of the mesorectal fascia, and

25:29

that's what, um, defines the lateral extent.

25:33

So then you'll ask me if TME excision is defined

25:37

laterally by the mesorectal fascia, how high does

25:40

the surgeon go and how low does the surgeon go?

25:44

So in terms of, so this is

25:45

what the specimen looks like.

25:46

Here is the, um, uh, you know, the, the,

25:49

the rectum, rectal lumen with the cancer.

25:52

You can see right here. You can

25:54

see all the fat that comes out.

25:55

And this is the plane of dissection

25:57

laterally along the mesorectal fascia.

26:00

Now, superiorly, they go up to the

26:02

takeoff of the inferior mesenteric artery.

26:04

So you can see this is a CT scan

26:06

of a patient who has undergone

26:08

TME surgery, and this is where the surgeon

26:11

has left clips of how superiorly they were.

26:15

Now, inferiorly depends on whether the cancer involves

26:19

the sphincter muscle in the anal canal or not.

26:22

If the cancer does not involve the anal canal,

26:25

then the surgeon does what is referred to as LAR,

26:29

where they basically, um, uh, uh, the inferior

26:33

margin is at the level of the, uh, the levator or the,

26:37

the pubis, and, and they spare the sphincter muscle.

26:43

Whereas if the tumor involves the, uh, the,

26:45

uh, uh, the, uh, sphincter mechanism, then

26:49

they do what is referred to as an APR, or

26:52

abdominal perineal resection.

26:55

Where they have to sacrifice the, um, the

26:57

sphincter mechanism, and these patients

26:59

get left with a permanent colostomy.

27:02

So that's sort of in a nutshell

27:04

at the, what we are looking for.

27:07

The couple of anatomy facts.

27:09

Now in terms of standardized reporting, I

27:12

am not going to go through the template,

27:14

but I'll point you to this website.

27:16

Uh, it's, uh.

27:18

The Society of Abdominal Radiology website, and anybody

27:21

can go to this website. It's www.abdominalradiology.org.

27:26

When you go to the website, there is a tab for

27:29

DFPs, which stands for Disease-focused, uh, panels.

27:32

And if you click on the rectal and anal

27:34

cancer panel, it brings you to the,

27:37

uh, various templates that are there.

27:39

So you don't have to kind of create these on your own.

27:42

You can just take the templates.

27:44

You know, if you click on any, any one of these,

27:47

for instance, if you click on the, um, uh, rectal

27:50

cancer staging — oops, rectal cancer staging

27:52

template — it brings the, um, for some reason the

27:56

link is not active, but it'll bring the, uh, the

27:59

template that is available in a PDF format that

28:02

you can then import into your respective reporting.

28:05

Um.

28:06

Uh, reporting, um, uh, you know, software,

28:10

so you don't have to sort of, uh,

28:12

reinvent the, uh, the, the template.

28:14

So keep an eye.

28:16

I mean, you, you know, use this as a

28:17

resource, and it gets continuously updated.

28:20

And, and, and the, um, the DFP panel and SAR's done

28:24

an excellent job at, um, at providing the, um,

28:28

the most up-to-date, uh, recommendations, as well

28:31

as, um, a lot of other resources that one can use.

28:35

When looking at these, uh, templates.

28:37

So having said that, um, let's talk about now

28:42

on the imaging side of things. Yes, you will

28:45

use a template, but you have to pay particular

28:47

attention to those, um, imaging features that

28:52

predict that the rectal cancer is going to behave

28:55

in, in a, in a, uh, adverse prognostic way.

28:58

In other words, the, the, the

29:00

prognosis of the tumor is worse.

29:02

Then when these factors are not present,

29:04

and the key factors that we are looking

29:06

for, uh, in terms of adverse prognostic,

29:09

um, indicators are mucinous pathology.

29:13

And when you do have mucinous pathology,

29:15

you have very specific imaging appearance.

29:19

We talk about the T stage and the CRM, which

29:22

stands for the circumferential resection margin

29:24

positivity, and we'll go into what that means.

29:28

Uh, you need to know the presence or absence

29:30

of EMVI, or extramural venous, um, invasion.

29:35

This is, um, again, relatively, um, a new addition —

29:39

I mean, it's, it's been around, but you know,

29:42

particular emphasis is being paid to this because this

29:45

is considered to be a harbinger for worse prognosis.

29:48

Patients who have EMVI typically behave,

29:51

uh, in a, in a worse manner with.

29:54

Having large number of nodal mets and also

29:56

being, um, predisposed to distant metastases.

30:00

And then looking at close proximity

30:03

to the anal sphincter complex.

30:04

Obviously the anal sphincter complex is involved,

30:06

and as I said, the surgeon has to do an APR,

30:09

and these patients are also difficult to get a,

30:12

uh, get a, um, uh, you know, get a surgically

30:16

clear margin, especially if the tumor is, um.

30:19

Is well beyond the confines

30:21

of the, uh, sphincter complex.

30:23

So let's look at each one of these, uh,

30:26

five, uh, adverse prognostic indicators.

30:29

Um, and the reason I'm doing this is so that,

30:31

you know, I'm showing you the worst thing

30:33

that you need to pay attention to when you're

30:34

looking at that standardized reporting format.

30:38

And so if you look at the mucinous

30:40

pathology, as the name implies, if you have

30:42

mucinous adenocarcinoma, uh, mucin in the

30:45

adenocarcinoma can be extremely bright on T2.

30:48

And that's what it looks like.

30:49

So here is an example of a large, uh, mucinous,

30:52

uh, tumor in the, uh, you know, in the, uh, pelvis.

30:56

And you can see it's extremely bright, uh,

30:58

when you do have this kind of signature

31:01

of, uh, the tumor on the T2 images.

31:04

It usually, uh, means the tumors

31:06

have a higher pathologic grade.

31:08

They have a greater tendency for metastasis

31:11

both in the lymph nodes and beyond, and they

31:14

typically have an unfavorable prognosis.

31:16

And so here's another example.

31:18

You can see this is a bright lesion inside the lumen.

31:21

It seems to be confined to the wall, but there

31:24

is a, uh, a lymph node that has, uh, near total

31:29

replacement by the mucinous deposit within it.

31:31

So, you know, despite being a small lesion, it does

31:34

have a large nodal metastasis in the mesorectal space.

31:38

So if you do see, um, features suggestive of

31:41

mucinous, uh, um, composition of the adenocarcinoma,

31:46

you make sure you put that in the report.

31:49

Then the next point is looking at the T

31:51

stage and looking at the circumferential

31:53

resection margin positivity.

31:55

And so let's look at what this means.

31:57

So if you look at, um, the local

32:00

staging, the T staging, basically

32:02

the T1 is confined to the mucosa.

32:05

T2 disease is confined to the, by the muscularis.

32:09

It doesn't extend beyond the muscularis. T3

32:12

disease is when the disease has spread beyond

32:14

the muscularis into the surrounding mesofat.

32:18

And then T4 is when the disease

32:20

invades adjacent pelvic organs or it

32:23

invades into the peritoneal cavity.

32:25

So that's sort of in a nutshell, uh, the T

32:28

staging of, um, you know, of rectal cancer. Now

32:32

detection of locally advanced, which means T3.

32:36

That is, you know, the tumor has gone beyond

32:38

the muscularis and extends into the mesofat.

32:42

Um, typically those patients are treated with

32:45

pre-surgical chemoradiation therapy, so that is the

32:48

first point to remember that essentially, you know,

32:51

our goal is to identify the T3 and above.

32:55

With MR. We don't do a good job of distinguishing

32:58

T1 from T2 and you shouldn't even make an

33:01

attempt to because you'll be wrong most of the time.

33:03

And so, you know, one way would be is just to sort of.

33:07

Say that the, the tumor appears to be confined to the

33:10

wall by or by the muscularis, not extending beyond.

33:13

And once it does, then you call it a T3.

33:16

Now let's look at T3 disease

33:17

in a little bit more, um, detail.

33:20

So, as I said, T3 disease is when

33:22

the, when the tumor extends beyond the

33:24

muscularis into the adjacent mesofat.

33:27

So here is an anatomical depiction where you

33:29

see the outline of the mesorectal fascia.

33:31

These are small, normal-sized nodes.

33:34

Here is the rectum and this is the tumor.

33:37

That is extending through the

33:38

muscularis into the adjacent mesofat.

33:41

Now, T3 is divided into four distinct categories.

33:45

The first is T3a where the tumor is extending

33:49

beyond, uh, the, uh, the muscularis into the fat,

33:53

but that extension is less than one millimeter.

33:56

And in this case, you can see the dark line here.

33:59

But as you come to this part, you can see that there

34:01

is relative lack of that black line of the muscularis.

34:05

There is a very subtle, less than a millimeter, or

34:08

practically, um, uh, you know, the tumor is, is sort

34:12

of invading the muscularis and just stops right there.

34:16

And it's less than a millimeter of

34:17

extension into the, um, into the mesofat.

34:21

Now T3b is when it is between one and five

34:24

millimeters, and in this case, you can see here is

34:26

a deposit right here, uh, that is going to less than

34:30

five millimeters into the adjacent, um, mesofat.

34:35

T3c is when the tumor is greater

34:37

than five, but less than 15 millimeters.

34:41

And then finally, T3d is when the tumor is greater

34:44

than 15 millimeters extending into the mesofat.

34:48

And so the question is, why are we taking the

34:51

T3 and breaking it up into A, B, C, and D?

34:55

The first fundamental reason why we do that is

34:59

the five millimeter cutoff, which means that,

35:02

tumors once they extend beyond the muscularis into

35:06

the adjacent fat, if they are five millimeters

35:09

or less, their overall survival is pretty good.

35:13

But it drops precipitously if it is,

35:15

if it extends beyond five millimeters.

35:18

And so you can see that, you know, essentially

35:21

the goal of the A, B, C, D is to try and find those

35:24

that are less than five millimeters, where

35:26

there is a good five-year survival versus

35:28

those that are greater than five millimeters.

35:31

Then the survival drops, uh, 250%.

35:36

So then you'll ask me, well, if it's, if it's five

35:39

millimeters, why don't you just have A and B, where

35:41

it's less than five and greater than five millimeters?

35:45

The whole purpose of having A and B, that is less

35:48

than a millimeter or between one and five millimeters,

35:51

is because there are certain, uh, institutions

35:54

that still treat early T3 disease as T2,

35:58

which means they go for surgical resection.

36:00

And that's the reason why you have that subtle

36:03

distinction of T3a and T3b. But

36:06

the take-home point for you guys, you know,

36:08

in terms of T3 disease is remember, if it

36:10

is less than five millimeter extension beyond

36:13

into the fat, it usually is good prognosis,

36:16

whereas if it is beyond five millimeters into the

36:19

um, uh, mesorectal fat, prognosis is very bad.

36:24

Then comes the next point, which is

36:25

the circumferential resection margin.

36:27

Now, this is a, uh, CRM, uh, in, in, in short is

36:32

a, actually a pathologic term, which means once

36:35

the surgeon dissects along the plane of the, um, mesorectal

36:39

fascia, gives the specimen over to the pathologist.

36:43

The pathologist then looks at, uh, the, um,

36:47

the extent of the tumor in terms of,

36:50

uh, involvement of this resection margin

36:52

or circumferential resection margin.

36:54

So it's essentially a pathologic term.

36:56

The other important point to remember is, although

36:59

it is referred to as a circumferential resection

37:02

margin, it's not circumferential in the sense

37:05

that it portrays. Circumferential resection

37:09

only below the level of the peritoneal reflection.

37:12

Above the level of the peritoneal reflection,

37:14

it is non-circumferential because you cannot

37:17

assign a CRM status to that part of the rectum

37:21

that is anteriorly covered by peritoneum.

37:24

So please keep those two points in mind when

37:26

you are, uh, reading and staging these tumors.

37:30

So let's look at the equivalent of CRM

37:33

that we need to put in our reports.

37:35

And the equivalent is you measure

37:38

the shortest distance from the tumor

37:41

to the non-invaded part of the mesorectal fascia.

37:44

So in this case, you are below the level of the

37:48

peritoneal insertion, and you're going to measure

37:50

this distance, um, which is the shortest distance.

37:54

Now, the earlier descriptors actually included

37:57

not only the shortest distance from the

37:59

primary tumor, but also to positive nodes.

38:02

But in, in the current consensus, and you know,

38:05

going forward, it's recommended that you only put

38:08

the shortest distance to the primary tumor.

38:11

If you do have nodes and, and, and you

38:14

are, you are pretty sure the nodes are positive,

38:17

you can mention it in the, in the, in the

38:20

report and let the, uh, you know, let the

38:22

oncologist and the surgeon decide what they

38:24

would like to, to do with that information.

38:28

And so, uh, what are the criteria? If the tumor

38:33

reaches and touches the mesorectal fascia or

38:36

within one millimeter of the mesorectal fascia,

38:39

the CRM is considered to be positive. If it is very

38:43

close, but between one and two millimeters, CRM is

38:47

considered threatened, and if it is more than two

38:50

millimeters, CRM is considered to be negative. Again,

38:54

why are we doing this exercise?

38:55

We are doing this exercise because if there is

38:59

involvement of the circumferential resection margin,

39:02

that usually means there is a higher likelihood

39:05

that patient is going to locally recur and do worse.

39:08

And that is the whole reason why we are trying,

39:10

uh, you know, we are, um, uh, we are taking an

39:13

extra effort to do and measure this distance.

39:16

So in this, in this particular example, you are

39:18

seeing, I have outlined the mesorectal fascia and you can

39:22

see that there's a large tumor, uh, extension that

39:25

is, uh, involving, it's less than a millimeter.

39:28

So in this case, it is

39:31

reaching, uh, and in this case, the CRM is positive,

39:35

and so that's what you'll put in your, in your report.

39:40

Um, now, uh, in terms of CRM positivity,

39:43

as I mentioned, we do not consider the

39:47

involvement of the peritoneal lining.

39:50

That is a separate, uh, category

39:52

in terms of descriptor and

39:58

prognosis.

39:59

So remember, um, it was a thin black line that

40:02

we saw extending, um, from the, uh, utero-

40:06

cervical junction posteriorly into the rectum.

40:09

In these two different patients, you can

40:10

see that the tumor is clearly extending

40:13

to involve that peritoneal reflection.

40:15

And when you see that, you need to put that in

40:17

the report, and that indicates T4a disease.

40:21

So it's no longer T3, it's T4a disease.

40:24

And, you know, again, it requires

40:26

presurgical radiation therapy.

40:29

And also, um, it indicates worse prognosis because

40:33

what it tells the, uh, referring oncologist is

40:36

that the, uh, tumor has involved the peritoneum and

40:39

has shed cells into the peritoneal space, and thus

40:43

there is a higher risk of local, um, uh, recurrence.

40:46

So make sure that you, you mention that.

40:49

Again, the pitfall alert is the peritoneum

40:51

involvement is not equivalent to the CRM involvement.

40:55

Remember, the, um, the CRM corresponds to the

41:00

cut surgical resection margin, and does not

41:03

cover the anterior aspect of the upper rectum.

41:06

The surgeon cannot influence

41:08

the free peritoneal surface.

41:10

Surgical resection margin will be negative

41:13

since the whole rectum will be excised.

41:15

So that's an important point to distinguish.

41:18

When you do have peritoneum involvement, it is T4

41:20

a and it is reported as CRM negative, but you will

41:24

mention that there is, uh, peritoneal involvement.

41:27

I hope that point is clear so that, you know, that's

41:29

one, um, potential source of confusion and error.

41:33

And when, when reading these, uh, cases.

41:37

Moving on to the next adverse prognostic indicator,

41:40

and that is the extramural, um, uh, venous invasion.

41:44

And what essentially means is, you know, you

41:47

have these perirectal veins that arise from the

41:50

rectal wall and extend into the adjacent fat.

41:53

If you have tumor that extends into these veins,

41:56

then that is considered to be, um, an

41:59

independent predictor of, uh, worse prognosis.

42:02

These patients typically have local

42:04

and distant recurrences, nodal disease,

42:06

and the overall survival is worse.

42:09

MR is extremely good at detecting

42:10

EMVI and also stratifying patients.

42:12

So here are two examples.

42:14

You can clearly see that there is a bifurcating

42:16

vessel where there is sim, similar signal

42:19

intensity as a tumor extending into the vein.

42:22

Here is another example where you can clearly

42:24

see that there is tumor extension into the,

42:26

um, into the, uh, venous radical, uh, similar

42:30

in signal intensity as the primary cancer.

42:33

One word of, um, uh, of, uh, caution and also to

42:37

look for is, you know, sometimes the, um, extent

42:41

of involvement in the vein may not be similar.

42:44

Um, in terms of, uh, size. In other words,

42:47

you can have a vein take off from the wall

42:50

and you can have a larger tumor deposit

42:53

distally, uh, compared to proximally.

42:55

And just to show you the example, here

42:57

is a patient where you can see this

42:58

is, uh, the rectal wall right here.

43:01

And here is a vein that is emanating

43:03

from the posterior wall of the rectum.

43:04

And as we scroll, you can see that

43:07

there is clearly tumor involvement here.

43:09

But as you go further, there is a larger deposit

43:12

somewhere in the mid portion of the, um, of the lumen.

43:15

So keep in mind that, you know, you can have

43:18

this, um, uh, these nodular deposits along the

43:23

course of the vessel, and that's something

43:25

you need to pay attention to and call,

43:27

um, you know, call, call it appropriately.

43:29

EMVI.

43:32

So the lastly is looking at, um, close

43:34

proximity to the anal sphincter complex.

43:36

And as I mentioned, you have to

43:38

pay close attention to the anatomy.

43:41

The anatomy is what, um, is going to help you

43:45

in terms of, um, uh, you know, in terms of,

43:49

uh, defining whether there is extension into

43:51

the, um, into the sphincter complex or not.

43:55

And so if you have involvement of the

43:57

verge, that is considered T4 disease,

44:01

and again, it is treated as such.

44:03

And then once it extends lower down into the anal

44:06

canal, what you're doing is you are trying to

44:08

look for involvement of three distinct structures.

44:11

The first is the internal sphincter.

44:14

The second is the intersphincteric space, and

44:16

third is the external sphincter.

44:18

And so you have to be descriptive in your outline and

44:21

need to let the, know, need to let the surgeons know

44:24

if the intersphincteric space or the external sphincter is involved.

44:27

Because these two factors are what, uh, sway them

44:30

towards doing a, um, APR versus, uh, doing an LAR.

44:35

And so here is an example of a, um, uh, lower

44:39

rectal tumor with the involvement of the intersphincteric space.

44:42

So you can see,

44:44

here is a circumferential lesion on the left.

44:46

The fat in the, um, uh, is maintained in the, uh,

44:51

in the, um, in the, uh, uh, left intersphincteric space as we go.

44:55

As you scan through the coronal, on the right side,

44:58

there is clearly tumor involving the intersphincteric space,

45:01

and it kind of abuts the external sphincter, which

45:04

appears to be relatively well maintained in this case.

45:07

So here there is involvement of the internal

45:09

sphincter and extending into the intersphincteric space with

45:12

relative sparing of the external sphincter.

45:14

And again, one useful caveat is when the

45:17

contralateral anatomy is spared, it's good to, you

45:19

know, compare and, and, and show what's going on.

45:23

And here is another example of a patient

45:25

where there is external sphincter involvement.

45:27

Two different patients.

45:28

So here is a mucinous lesion.

45:30

Clearly there is extension into the, um,

45:32

external sphincter on the left side and beyond.

45:35

And here is another patient where you can

45:37

clearly see there is involvement of the external

45:39

sphincter on the left and extending beyond the,

45:42

uh, the, uh, the external sphincter complex.

45:44

And in this case, these, these patients

45:46

clearly will have to undergo, um,

45:49

depending on what the features are.

45:51

Um, after neoadjuvant, they may still

45:54

have to get their sphincter sacrificed

45:57

and get a permanent, uh, colostomy.

46:01

So I think that was, in a nutshell, you

46:03

know, covering, um, more or less, uh,

46:05

the pertinent points for rectal cancer.

46:08

Mr. A couple of take-home messages that

46:10

I would like to reemphasize. Uh, do

46:13

not, uh, skimp on the oblique axial plane.

46:16

Please pay attention to, uh, you know,

46:19

to your technique to ensure that the oblique

46:21

axial plane is performed, uh, properly.

46:25

If your techs, uh, don't, uh, have the ability to

46:28

identify, which in most cases, you know, it's very

46:30

difficult for them to know where the cancer is. It

46:32

requires active participation from the radiologist

46:36

to ensure that the plane is correctly selected.

46:39

Then you have to pay close attention to those

46:41

factors that contribute to local recurrence.

46:44

Follow the template, but within the template

46:46

framework, these are the, you know, key elements

46:49

that you need to pay particular attention to.

46:51

Looking for the T stage, presence or

46:54

absence of peritoneum involvement.

46:56

And then also looking at the CRM status.

46:58

In terms of extension to the mesorectal fascial, uh, margin,

47:03

you are looking for the presence or absence of EMVI.

47:06

And with low rectal cancers, you're looking

47:08

for extension into the sphincter complex.

47:11

Vis, you know, going into the internal sphincter,

47:14

intersphincteric space, or involving the external sphincter.

47:17

And then, you know, standardized reporting. I can

47:20

emphasize how important it is to have a standardized

47:22

template so that everybody in our practice follows

47:26

the same, um, uh, reporting guidelines and follows the

47:29

same, um, same, uh, uh, pattern of, uh, of dictation.

47:34

With that, uh, I'm gonna stop and say,

47:36

thanks again for listening, and, um...

47:39

I will, uh, see if there are any questions

47:42

that the audience would like to, uh, to post.

47:48

So there are a couple of questions

47:49

that have already popped up.

47:50

Um, I'm gonna read through them and see, uh, about

47:54

the rectum being divided into three portions.

47:56

Each one measures about five centimeters.

47:58

A low rectum extension, the anal

48:00

words, or from the anorectal junction?

48:02

I think we have, uh, gone through that.

48:04

It's, uh, extension from the anal words,

48:07

um, not, um, you know, not from

48:10

the, uh, level of the puborectalis.

48:13

Can we please see the reporting template?

48:15

I think, uh, I have given—if you go to the Society of

48:18

Abdominal Radiology website—you don't need a login.

48:21

You know, you can pull it up without

48:23

login information, and it should be pretty

48:25

straightforward to, to, to look at that.

48:28

What if the tumor involves

48:30

the anterior peritoneal root?

48:32

Again, it's T4a disease. That

48:36

does not count as CRM involvement.

48:39

Next question is, uh, for T3 disease, when

48:42

measuring the distance from the tumor to mesorectal fascia,

48:46

and if the mass has spiculation, does one measure from

48:48

the tip of the longest spicule or from the mass itself?

48:52

And the answer is, um, you know, I didn't cover

48:55

this, but one source of error between, uh, T2

48:59

and early T3 disease can be these spicules,

49:02

which are, uh, related to, uh, inflammation and...

49:06

What has been described in the literature is unless

49:09

you see frank nodular extension of the tumor into

49:12

the mesorectal fat, you do not call it T3 disease.

49:16

Subtle spicules can be, uh, seen with inflammation.

49:19

And I know rectal cancer can be

49:21

a fairly inflammatory, uh, disease.

49:24

Uh, and so if you have linear lines, those

49:27

don't, uh, classify as, uh, T3 disease.

49:30

Again, there is a difference of opinion between

49:33

that because, you know, there are some groups

49:35

which will call, call it a T3 disease or

49:37

early T3 disease, even if there are spicules.

49:40

And this is a dialogue that you need to have with

49:42

your surgeon, uh, to, um, you know, to, uh, to

49:46

figure out what's the best way to, um, to do that.

49:50

Uh, can you, can you please give us

49:52

an example where contrast is helpful?

49:54

Again, I think, um, you know, like I said, in

49:56

our practice, it's a useful complement.

49:59

Uh, sometimes when tumors are, uh, you know,

50:03

are fairly large or when tumors are fairly

50:06

small, uh, looking at the differential

50:08

degree of enhancement between the wall

50:10

and the, uh, and the tumor can be useful.

50:13

I'm not saying that that is

50:14

the primary means for staging.

50:16

It can serve as a useful complement

50:18

to actual detection and staging.

50:22

Should we be reporting on CRM given

50:24

that this is the pathologic term?

50:26

I, I don't think you are reporting on the CRM.

50:29

What you're giving them is an indication of

50:31

what they can perceive the status of the CRM

50:34

to be, should they operate on the patient.

50:36

So that is why you give the distance. You don't call

50:39

it CRM. You give them the shortest distance between

50:42

the tumor and the outline of the mesorectal fascia.

50:44

Is this...