0:00

For our next case, I'm gonna show you a, a case

0:03

where they already knew that there was a cancer,

0:06

uh, in this patient.

0:07

You can see here in the descending colon

0:11

and on the colon map, I'll show you the image right here

0:14

where the, um, the purple arrow is.

0:16

You can see there's an arrow of luminal narrowing on

0:19

the coronal MPR.

0:21

You can see that there's already a stent placed

0:22

through this, this colonic mass.

0:24

So we know that there is a, a mass here in the colon.

0:27

They had to put a stent in to decompress the colon

0:30

because it was an obstructing mass at

0:32

the time of presentation.

0:33

And for one reason

0:34

or other, they couldn't get the scope all around

0:36

to the remainder of the colon

0:37

to see if there were any synchronous lesions.

0:40

So this was our opportunity to complete the workup, looking

0:44

for synchronous lesions in the colon.

0:46

Similar history to the prior one, except in this case I get

0:49

to show you a, a stent.

0:52

And on the file views you can sort of see the, the mesh

0:54

of the stent here on the three D file view here.

0:56

And then we can also fly through the stent on three dbs.

1:01

So you can see the, the mesh here again.

1:04

And in this case, we're able to get through the stent

1:06

and look at the remainder of the colon.

1:09

And I believe there were findings in the remainder

1:11

of the colon in this particular case.

1:13

One thing to note is with the appearance

1:15

of motion artifact on, uh, CT colonography,

1:18

sometimes you'll see these little, uh, jagged edges.

1:21

Uh, and if you look on the coronal images in particular,

1:25

you can see they correlate, they're in the plane

1:28

of the axial, uh, slices.

1:30

And you can see there's motion artifact in this particular

1:33

scan here, and that's what the motion artifact ends up

1:35

looking like on the three D fly-throughs, these little kind

1:39

of straight cuts through the, uh, the lumen.

1:42

And it's important to just realize that

1:44

that's artifactual related to, um, respiratory motion,

1:47

usually in the proximal colon.

1:50

There are other findings here. Get to the cecum.

1:54

I think that's where the main mass was, as well

1:56

as ascending colon.

1:58

So here we're flying through the transverse colon

2:01

and you, again, you can use your colon map here to,

2:04

to show you where you are.

2:05

There's a very, very tortuous transverse colon in this case.

2:10

And again, appearance of motion artifact here,

2:17

mass fluid level.

2:20

And here we are in the ascending colon.

2:22

We can see some, uh, other abnormal findings here.

2:24

There's definitely a thickened SSL fold here

2:27

with a mass on it.

2:29

There are also other findings here,

2:32

which we can look at on the two D images

2:34

to see whether these represent real polyps.

2:37

And there's, there's multiple of these, so that,

2:39

that probably is a real polyp,

2:41

although it may not meet our size criteria.

2:44

The only time I ever mentioned polyps

2:45

that are five millimeters

2:46

or smaller in size is if I know that somebody's going

2:49

to be going on to colonoscopy or surgery.

2:52

And that area is going to be seen, going to be looked at.

2:56

If the five millimeter polyp was the only

2:58

Finding, then, uh,

3:00

gen generally it doesn't meet our size criteria

3:02

to be specific enough by CTC to call it a polyp.

3:06

And those polyps, even if they're below five millimeters,

3:10

the so-called, uh, diminutive size category,

3:12

they will get picked up if you follow a regular, um,

3:15

screening in interval.

3:17

So usually for CT colonography,

3:19

the recommendation's been every five years to get ACTC

3:22

For colonoscopies, it's every 10 years,

3:24

but usually you'll pick up a,

3:26

a tiny polyp if it grows in that interval.

3:29

Uh, it's important to note that uh,

3:31

adenomas polyps are a waxing and waning phenomenon.

3:33

Clearly not all polyps become cancer. Only a tiny subset do.

3:37

Uh, some of them will actually stay stable

3:39

or even, uh, get smaller

3:41

or completely disappear between, um, follow-up studies.

3:44

So, so some polyps can be safely watched.

3:49

Many of them can be. The smaller they are,

3:50

the more safe they are to, to watch.

3:52

But in this case, we have a synchronous mass

3:55

in the ascending colon.

3:57

On the two D images, you can confirm that it's soft tissue

4:01

and attenuation here.

4:03

A lot of it is, is mostly soft tissue.

4:06

There's some contrast outlining the submerged portions

4:08

here on the two D images.

4:10

You can see how grainy our images are here

4:12

because we're using a very low radiation dose study

4:16

analogous to lung cancer screening, right,

4:18

and lung nodule screening.

4:21

So in this case, this is important to note that there were,

4:23

um, both polyps

4:25

and masses seen in the right colon, um, much more,

4:30

uh, proximal to the known anular constricting mass

4:34

in the descending colon.

4:35

And we were able to get this patient set up for a,

4:39

a subtotal colectomy rather than just a left hemi colectomy.

4:43

So this is very important for the surgical planning.

4:46

Uh, other things that I should point out here,

4:49

the low dose images, um, they can look a little grainy

4:53

because you don't need much radiation to render a,

4:55

a polyp in a gas filled loop of bowel,

4:58

just like you don't need much radiation to,

5:00

to render a pulmonary nodule in the lung.

5:03

Uh, we aim with our radiation doses to be lower than that

5:07

of a barium enema.

5:08

So even with both supine

5:10

and prone images combined together, our,

5:12

usually our radiation dose ends up being less than

5:15

five milli seaberts.

5:16

Sometimes, um, even two or three milli seaberts.

5:19

And I've seen some groups get it to even closer, close

5:22

to one milli seabert depending on, uh, what kind

5:24

of iterative reconstruction

5:25

or deep learning image reconstruction, uh,

5:28

algorithms you use to, to aggressively get that uh,

5:31

radiation dose down.

5:33

When you are reading extra chronic findings,

5:35

sometimes the image noise can really get in the way.

5:37

Um, but uh, one thing that you can do to reduce

5:41

that appearance is you can read with, uh, a thicker cuts.

5:44

So you can, instead of looking at the thin cuts here,

5:46

the 1.25 millimeter cuts, you can

5:50

set the slice thickness a little bit thicker.

5:53

That will reduce your image noise quite a

5:55

bit. And then this way

5:56

You can look for any adjacent adenopathy next

5:59

to these masses as well as, uh, any incidental liver mets

6:03

that you might be able to pick up on a, um,

6:06

non-contrast study.

6:08

And then you can get a sneak peek at the lung basis as well.

6:11

So you can do some of the, um, m staging,

6:16

although this is not a, uh, contrast enhanced study.

6:19

One other thing I would probably bring up here in this case,

6:21

the one thing that could have made this study even better

6:24

than it was and even more helpful than this was,

6:27

is performing it with IV contrast.

6:30

So if you know that the reason that patient is coming to you

6:33

is for a known obstructing colon cancer

6:36

and it hasn't been fully staged yet with a, um, CT abdomen,

6:40

pelvis or CT chest, abdomen, pelvis,

6:42

you can combine the staging CT with IV contrast

6:47

with the CT colonography at the same time.

6:49

So what we would usually do then is what we would,

6:51

we would inflate the colon

6:53

and probably scan a non-contrast in the prone position

6:56

and then flip the patient's supine

6:58

and set them up with a higher radiation dose, uh, routine

7:02

contrast enhanced CT with the colon still distended.

7:06

And then we would scan through the, uh,

7:08

the relevant body parts with the IV contrast onboard

7:10

with the usual routine, uh, contrast timing

7:13

and be able to stage all the solid organs, uh,

7:16

at the same time as doing the, um, the CT colonography

7:20

to look at the rest of the colon.

7:22

So keep in mind that that is an option,

7:24

but that you don't want to use low radiation dose

7:26

for the IV contrast portion of that study.