0:01

So this is another patient with biopsy-proven

0:03

rectal cancer and comes to us for staging purposes.

0:06

So in this instance, um, you know, there are two

0:10

or three findings on the MR that are critical to

0:14

make and also in terms of take-home messages.

0:19

Uh, there are two sort of key take-home messages here.

0:22

So the first thing that is obvious is, you

0:24

know, when you look at this tumor, the bulk

0:26

of the tumor has a very bright T2 signal.

0:30

When you have a lesion or a rectal cancer

0:33

that demonstrates high signal intensity and

0:36

by high, I mean similar signal intensity to

0:39

that of fluid in greater than 50 percent of

0:42

the tumor, we call those tumors mucinous.

0:45

Subtypes.

0:46

Why is it important to make that

0:48

morphologic distinction and why is it

0:50

important to call attention to that?

0:52

It's important because these mucinous

0:54

tumors typically, they are bad actors.

0:58

They typically, when they present, are more

1:01

advanced in their, uh, local staging, uh, they

1:04

have a higher propensity to cause nodal mets

1:07

and they have a higher propensity to spread.

1:10

And so typically these patients have worse

1:13

prognosis than those that do not have the

1:15

mucinous, uh, subtype of the adenocarcinoma.

1:19

And so, uh, this particular cancer, as you can

1:22

see, you know, the bulk of the tumor is T2 bright

1:25

signal, so clearly is, uh, is a mucinous subtype.

1:31

The second interesting part here is that the lesion is

1:36

in the inferior aspect of the lesion is in the lower rectum

1:39

because, as you know, this is only four centimeters.

1:42

So clearly it is involving the mid to low rectum.

1:45

And so here is one example where

1:48

you have a tumor low-lying.

1:50

And when you have a low rectal cancer, you have

1:52

to tweak the template in terms of reporting.

1:56

And so let's look at this, uh, tumor in

1:58

the different planes so that, there you go.

2:02

So as I'm scrolling on the sagittal, you can

2:04

clearly see that there is a large tumor that

2:07

is going well beyond the, um, lumen into

2:11

the surrounding fat and it's very bright

2:13

and more than 50 bright in signal intensity.

2:16

So this is mucinous. It's low-lying.

2:19

Now these patients typically, as I said, they are

2:22

advanced in terms of rectal staging.

2:26

Now if you pay close attention on the true axial

2:32

you can see that there is a lymph node right here

2:35

posteriorly, which is sitting right on the mesorectal

2:37

fascia, and this node is bright in signal intensity.

2:40

So remember, as I mentioned earlier, when you

2:43

have a positive node that contains mucin in

2:47

a patient who has a primary mucinous cancer,

2:50

you do not use any of the size criteria.

2:52

You just call this node positive because

2:54

it clearly has mucin within it, which

2:56

reflects what you see in the primary tumor.

2:58

So this is a positive lymph node.

2:59

The patient does have additional nodes that are not

3:02

mucin-containing.

3:03

There is also an obturator node right

3:05

here, which is not mucin-containing.

3:10

And in those instances, you will follow

3:12

the same criteria that we talked about.

3:15

So in this case, so this is

3:18

between 5 and 8 millimeters.

3:20

You have to look at any two.

3:22

So is it rounded?

3:23

It looks sort of rounded.

3:25

It has ill-defined margins, has no heterogeneous

3:28

signals, so it meets two of the criteria.

3:31

So that clearly means that it would be a positive

3:34

node and the obturator node that we see right here.

3:38

So remember, the reason it's obturator

3:40

is because if you draw the line like

3:43

so it's not medial, it's lateral to it.

3:45

So that's along the obturator antenna.

3:47

So this is an obturator node.

3:49

And if I okay.

3:50

Again, measure the short axis.

3:52

Remember, for the pelvic side, well,

3:53

it has to be more than 7 millimeters.

3:55

This does not meet the criteria.

3:58

And so that's, um, it's not positive.

4:01

So again, you can see the outline of

4:03

the mesorectal fascia and clearly here,

4:06

posteriorly the tumor is reaching it.

4:08

So the MRF is involved in this case, has

4:12

positive nodes and it has mucinous pathology.

4:15

Now the other thing is, when you're looking at

4:19

the lower extent of

4:21

the cancer, in terms of lower rectal cancer.

4:24

So remember when we talked about anatomy, I told

4:26

you the mesorectal fascia, as you come down into the

4:29

pelvis, it is closely approximated to the rectal lumen.

4:34

And in the pelvis, the mesorectal fascia basically

4:37

inserts on the puborectalis and on the levator muscle.

4:40

So, when you are talking about low rectal cancers in

4:44

your template, in terms of looking at MRF extent, you

4:49

measure the shortest distance to the levator muscle.

4:52

Rather than, you know, looking at mesorectal

4:55

fascia because you really cannot identify the

4:56

mesorectal fascia lower down in this region.

4:59

So when in this particular instance, you

5:01

can see on the coronal, I can see the

5:03

iliopsoas muscle on the right side.

5:06

And as I'm scrolling through, and here it is on the

5:08

right side, on the left side, it clearly is involved.

5:10

So the iliopsoas muscle is involved and there is perhaps

5:13

a bright signal extending, as you can see right here,

5:17

beyond the iliopsoas or the part of the levator ani.

5:21

And so when you have levator muscle involvement, in this

5:25

instance, it indicates that this is T4 disease.

5:29

So the two take-home points in this

5:31

case are if you have more than 50%

5:33

involvement of the tumor with T2 bright signal.

5:37

It's a mucinous subtype of adenocarcinoma,

5:41

and you have to call attention to that in

5:43

your report in terms of morphologic evaluation

5:46

because these tumors typically are bad actors.

5:48

They have worse prognosis and they

5:50

are higher in grade and staging.

5:52

And if there is accompanying adenopathy,

5:54

which is bright in a T2 signal, you do not

5:57

use the conventional size criteria for adenocarcinoma.

5:59

Instead, you call that node positive.

6:02

If you have a tumor that is in the lower

6:04

rectum, in that instance, for the status of

6:09

the mesorectal fascia, there is no shortest

6:11

distance to measure because the mesorectal

6:14

fascia is closely applied to the levator ani muscle.

6:17

So for low rectal cancer, the take-home

6:19

message is to give the shortest distance to the

6:22

levator ani or the shortest distance to the

6:25

puborectalis, depending on where the cancer is.

6:29

Because if there is involvement of the levator

6:31

ani, as is the case in this particular

6:34

patient, that indicates it's T4 disease.