0:01

And so having said that, let's look at

0:02

these two cases with those points in mind.

0:04

So, and if I'm looking at the sagittal

0:06

image, here is the anal verge, which is the

0:09

most distal part of the external sphincter.

0:11

And you can see the lowest part is, you know,

0:16

about a centimeter from the, um, which means

0:19

it is extending way into the anal canal now.

0:23

When it goes so far down into the anal canal,

0:26

remember it can cause inguinal nodes, which is not

0:29

present in this case, but just keep that in mind.

0:32

And it can also spread to the mesorectal nodes above.

0:36

So we'll look at that.

0:37

But let's first focus on the primary tumor itself.

0:40

So it's a fairly large tumor that sort of spans the

0:45

entire extent of the lower rectum into the mid rectum.

0:49

It has frown-like sort of features.

0:51

Polypoid pattern.

0:53

And if you look at the true

0:54

axial, so here's the fascia.

0:57

You still see in the mid rectum that the tumor, there's

1:00

a fair amount of inflammation that you're seeing.

1:02

And as we come down, you can start seeing the

1:05

tumors of the polypoid nature of the puborectalis

1:09

muscle and we are extending further down into these.

1:14

So here we are at the anal verge.

1:16

And so clearly it's going way

1:19

low down into the anal canal.

1:21

And as I said, it.

1:22

You need to see if this is involving the internal

1:25

sphincter, is it involving the intrasphincteric

1:28

space, or is it involving the external sphincter?

1:31

And so again, it's important, it's very

1:33

imperative that you kind of look at all the

1:35

planes together because that gives you a

1:36

good idea as to what the tumor is doing.

1:39

So, the puborectalis is nicely identified.

1:42

Once you get below the level of the puborectalis,

1:44

you get into the anal canal.

1:48

So here is the coronal image.

1:51

And you can see that on the coronal image,

1:53

the bright intrasphincteric space on either

1:56

side is well maintained in the proximal half.

2:01

So the entire extent is seen here on the right

2:04

side, but on the left side, it looks like the

2:06

tumor is going beyond the internal sphincter

2:10

and is obliterating the intrasphincteric space.

2:12

Remember, it should be like this, where you have

2:14

fat that extends throughout the entire extent.

2:16

Whereas here, intrasphincteric, you can see

2:18

that the fat is obliterated and there is

2:20

clearly extension beyond the internal

2:24

sphincter into the intrasphincteric space.

2:26

It does not involve the external sphincter.

2:29

As you can see, it's sort of maintained on either side.

2:31

There's a little bit of push, but there is no clear

2:34

extension into the external sphincter that we see.

2:38

So this is again, highlighting or emphasizing the

2:40

importance of looking at the various planes in

2:43

terms of low rectal cancer so that you get a good

2:46

And remember, as I mentioned early on in the anatomy,

2:48

this has to be an oblique coronal to look at the

2:52

anatomy of the anal canal so that you can look for

2:55

involvement of the structures in a better way.

2:59

The take-home message is for low rectal cancers,

3:03

if they end at the level of the liver or the

3:07

puborectalis, measure the shortest distance to those.

3:10

If they extend below the level into the anal canal,

3:13

you're looking for extension into three structures.

3:15

You're looking for extension into the

3:17

internal sphincter, looking for extension

3:19

into the intrasphincteric space, looking

3:20

for extension into the external sphincter.

3:23

In this case, it is involving the external

3:24

sphincter and, you know, likely we'll

3:26

have to have the sphincter compromised.

3:28

Again, it'll depend once neoadjuvant chemoradiation

3:31

is given, what the tumor appears like.

3:34

But that sort of would be the initial

3:37

planning when they think about it.

3:40

So here's another example.

3:41

And again, this patient actually has a nice

3:43

depiction of the anatomy of the anal verge.

3:48

You can see here is the external, the U-shaped external

3:51

sphincter, and that ends right here, whereas the

3:54

internal sphincter ends a little bit more proximally.

3:57

So clearly there is, the most lowest aspect

4:01

of the, and on the axial, it's, it's actually

4:02

this U-shaped area, which is the external sphincter.

4:05

There is no internal sphincter at this level.

4:08

And if I measure the distance

4:11

to the lowest part of the tumor.

4:14

It's about 2.4 centimeters.

4:14

95 00:04:15,935 --> 00:04:18,115 So it's still, you remember that there's

4:18

still five centimeters is the lower rectum.

4:19

So this clearly is involving the lowest part

4:22

of the rectum, which includes the anal canal.

4:25

And then as you can see, on the axial

4:28

image, and this is again, highlighting the

4:31

importance of looking at all the three planes

4:33

closely to look for the extent of the tumor.

4:37

So here is the bright fat in the intrasphincteric space.

4:41

This is the dark external sphincter, which is

4:44

similar in signal intensity to the skeletal muscle,

4:47

and inside is a bright internal sphincter.

4:50

So on the left side, you can

4:52

see the three planes nicely.

4:53

On the right side, you can clearly see the tumor

4:56

involves the internal sphincter, extends into the

4:58

intrasphincteric space, and you can see that the

5:00

external sphincter is also involved with tumor

5:03

extent beyond the level of the external sphincter.

5:07

So clearly this is another sort of aspect that you need

5:10

to evaluate and mention in your report because that is

5:13

going to have implications for the patient's treatment.

5:16

And the take-home message here is in terms of

5:19

looking at low tumors is to kind of pay attention

5:22

to the anatomy of the sphincter complex.

5:24

Make sure that you have all three planes that

5:27

you can closely pay attention to in terms of looking

5:30

at those three structures for involvement and also

5:34

in terms of, you know, looking at the template

5:37

and commenting on the involvement of those three

5:39

because that is going to affect how the surgical

5:42

approach is ultimately going to be performed.