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Hello and welcome to Noon Conference, presented

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by MRI Online. In response to the changes

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happening around the world right now and

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the shutting down of in-person events,

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we have decided to provide free Noon

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Conferences to all radiologists worldwide.

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Today we are joined by Dr. Ryan O'Malley.

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Dr. O'Malley is an abdominal radiologist specializing

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in oncologic and gastrointestinal imaging.

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A reminder that there will be a Q&A

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session at the end of this lecture.

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So please use the Q&A feature to ask

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your questions, and we will get to as

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many as we can before our time is up.

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That being said, thank you all for

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joining us today. Dr. O'Malley,

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I'll let you take it from here.

0:39

Thank you.

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Thank you for the introduction and the opportunity

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to be here, and thank you to everybody who

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is, uh, watching and participating today.

0:47

My topic today is, uh, MRI and CT evaluation

0:51

of perianal fistulas, and I'll talk

0:53

about what that means here in a second.

0:57

This is my disclosure, so just as a—

1:04

We'll talk first with the—about

1:06

the pathophys and the anatomy.

1:08

I think the anatomy is really the most challenging

1:09

piece, and so we'll spend a lot of time

1:11

discussing the relevant anatomical structures for

1:13

interpreting these, um, cases and these exams.

1:16

Um, we'll talk a little bit about

1:18

when and why you might use CT,

1:20

particularly in the acute presentation, and

1:22

then also spend most of the time talking

1:24

about why MRI adds value, uh, both for the

1:27

detection and the classification of fistulas.

1:29

We'll go through the classification scheme

1:31

using the St. James classification with some

1:33

selected cases, and then talk about some

1:35

cases that don't fit nicely into the St.

1:37

James classification, how you should characterize

1:39

those, and then conclude with a comparison of CT

1:42

and MRI and, uh, how they sort of complement each

1:45

other and where MR adds additional information.

1:49

So just a brief background about perianal fistulas.

1:51

The idiopathic or cryptoglandular

1:53

hypothesis is believed to account for

1:55

most of these fistulas—90% or so.

1:58

Um, the pathophysiology here is that

2:01

there is an infection of the intersphincteric

2:03

anal glands that, uh, when

2:06

normally would drain into the anal canal—

2:08

if that drainage gets blocked, um, because

2:11

the duct is blocked, then a patient might form

2:13

an abscess in the intersphincteric, uh,

2:16

glands or in the intersphincteric space.

2:18

If that abscess does not drain through the anal

2:21

canal, then it may seek an alternate means of

2:23

drainage and may develop a fistula as it drains,

2:26

uh, either through the muscles or through the

2:28

intersphincteric space extending to the skin.

2:30

These patients typically present

2:32

with acute pain or drainage.

2:34

The second big category is patients with IBD,

2:36

particularly patients with Crohn's disease.

2:38

This is really the most, uh, important or

2:40

the most commonly encountered, uh, group

2:42

that we see as imagers, and these frequently

2:45

complicate patients with Crohn's disease.

2:46

Up to a quarter of them will develop perianal disease

2:49

over their lifetime, and a significant

2:52

minority—20% or so—will present initially

2:54

with perianal disease before their diagnosis of

2:57

inflammatory bowel disease has been established.

2:59

So if you see somebody with complex perianal

3:01

fistulizing disease and it's a young patient in this

3:03

sort of, uh, category, it's something to consider.

3:07

This, uh, confers a more severe or

3:09

worse disease course and disease phenotype.

3:12

The underlying pathophysiology is a little

3:14

bit more complex and not fully understood,

3:16

but thought to be related to deep transmural

3:18

ulceration or infection of these anal glands.

3:21

There's a whole category of other diseases,

3:23

or other scenarios where you might

3:24

encounter these, particularly in the

3:25

oncologic setting—pre- or post-treatment.

3:29

So now as I mentioned, we'll spend a lot of time

3:30

talking about the anatomy because I think this

3:32

is the main stumbling block for most people.

3:34

Um, and so I want to sort of intentionally

3:37

simplify that anatomy specifically for the

3:39

purposes of characterizing perianal fistulas.

3:42

And so, just as a brief background, this is our—

3:44

our sort of feeling that this is complicated and

3:47

difficult to understand is not a new idea. As far

3:50

back as the late 1800s in the obstetric

3:53

literature, there was this written saying that

3:56

"there's no considerable muscle in the body

3:58

whose form and function are more difficult

4:00

to understand than those of the levator ani."

4:03

Part of this is because we are

4:04

not using consistent definitions.

4:06

Surgeons and anatomists use different definitions.

4:09

Uh, in 2004, uh, again, in the obstetric literature,

4:12

the group listed here, Kearney et al. sought to try to

4:15

simplify this anatomy by taking what existed in the

4:18

literature and making a more coherent description,

4:22

uh, for the different parts of this muscle.

4:23

And what they found was that it was

4:24

actually more complicated than they

4:26

expected, and they found 16 different

4:28

overlapping terms for different parts of the

4:30

muscle, the same muscle, and these are listed here.

4:34

And one of their conclusions was that the

4:35

terminology in all of the literature was so

4:37

confusing and so inconsistent that each time

4:39

they read a new article, it added more confusion

4:42

to the picture rather than adding clarity.

4:44

And often they, uh, despite studying this very

4:48

carefully and trying to reconcile these findings,

4:50

they could not reconcile what one author had

4:52

written and what another author had written,

4:54

whether they were talking about the same part of the

4:55

muscle or the same muscle or something different.

4:58

And so they offered a more sort of simplified

5:00

characterization of the different parts of the—

5:03

levator ani listed here: three main categories,

5:05

pubococcygeus, puborectalis, and iliococcygeus.

5:08

Um, the good news is I'm not going to go into

5:11

detail about all of this now, and what I'm hoping

5:14

to convince you is that for—specifically for—

5:16

the purpose of characterizing perianal fistulas,

5:18

we can intentionally simplify this anatomy.

5:21

So we'll start, um, with that—with some illustrations

5:24

and then show side-by-side image examples here.

5:27

So on the right is an illustration, and the

5:29

first structure we will, uh, describe is the

5:31

anal canal, and that's broadly defined as the

5:34

distal part of the GI tract, extending from the

5:36

levator ani or the anorectal junction to the

5:39

anal verge where it opens up to the skin surface.

5:41

And this is surrounded by the internal anal

5:43

sphincter, which is smooth muscle, and the

5:45

external anal sphincter, which is,

5:47

uh, the structure on the outer border here.

5:50

The external sphincter is striated skeletal muscle.

5:52

It's contiguous superiorly with

5:53

levator ani and the puborectalis.

5:55

And this is primarily responsible for

5:58

voluntary contractions, involuntary continence.

6:01

By contrast, the internal sphincter is smooth

6:03

muscle, and this is the continuation of the smooth

6:04

muscle that extends, uh, superiorly in the rectum.

6:08

And this is primarily responsible

6:09

for resting or involuntary continence.

6:13

Between the two, uh, is this thin fat-containing

6:16

sphincteric space between the two muscles.

6:18

And this is contiguous with the

6:20

supralevator space superiorly.

6:22

And outside of the external sphincter are

6:24

these pyramidal-shaped fat-containing spaces,

6:26

called the ischiorectal and ischioanal fat—

6:28

or ischiorectal and ischioanal, uh, spaces.

6:31

And these, uh, normally contain fat with some

6:34

small blood vessels and lymphatic structures.

6:36

And this is bordered superiorly by the—

6:40

So, just blowing up the illustration here a little,

6:42

bit again, the internal sphincter—smooth muscle—

6:44

continuous with the smooth muscle of rectum superiorly,

6:47

responsible for resting or involuntary continence.

6:50

External sphincter is skeletal muscle.

6:52

It's continuous with the levator

6:53

ani superiorly. Between the two is a thin

6:55

fat-containing intersphincteric space, and

6:58

then outside of the external sphincter are the

7:00

ischioanal and ischiorectal fat or fossae.

7:03

So now let's look at this side

7:04

by side with the imaging anatomy.

7:06

On the top, we have coronal, uh, post-

7:08

contrast images with fat suppression.

7:10

In the middle of the image, labeled with

7:12

1, we have the internal sphincter, which

7:13

is this hyperenhancing structure, uh,

7:16

corresponding to the muscle of the anal canal.

7:19

Outside of that, uh, you have the skeletal

7:22

muscle, so slightly less enhancing, uh,

7:25

external sphincter that extends superiorly into

7:27

the levator plate, which sort of sweeps from

7:29

medial to lateral at the anorectal junction.

7:32

In between the two is a thin fat-containing

7:35

intersphincteric space—hard to see on this image.

7:37

And then outside of the external sphincter

7:39

and below the levator ani are the fat-

7:41

containing ischioanal and ischiorectal fossae.

7:43

As I mentioned earlier, the only thing

7:45

in this area should be some small blood

7:47

vessels and the fat structures. On a T2

7:50

weighted image here without fat suppression.

7:52

On the upper left-hand side, you see the

7:54

normal fat signal of the ischioanal, ischiorectal fossae.

7:57

Rectal fossae.

7:58

Now on the CT image, similarly, you

8:00

see normal fat attenuation here.

8:02

External sphincter extends

8:04

superiorly to the levator ani.

8:05

And on the CT image, you can see this nice

8:07

little thin fat-containing sphincteric space.

8:11

So now let's turn this to the axial anatomy.

8:14

Upper left, we have a fat-suppressed

8:15

T2-weighted image. Upper right, a

8:16

non-fat-suppressed T1-weighted image.

8:19

In the middle of the image, corresponding to

8:20

the anal canal, we have the internal sphincter.

8:24

Surrounding that, you have this horseshoe-shaped

8:26

structure that sweeps from front to back, or

8:28

anterior to posterior around the internal

8:29

sphincter, and that's the external sphincter.

8:32

You'll note the difference

8:32

on the T2-weighted image.

8:33

The skeletal muscle, like you see in the gluteal muscle

8:36

and other pelvic muscles, is more uniformly low signal

8:39

intensity, uh, similar to the external sphincter here.

8:41

Whereas the smooth muscle in the rectum, in the

8:44

internal sphincter, is, uh, slightly more hyperintense.

8:48

Then between the two is this thin fat-

8:50

containing intersphincteric space.

8:54

And then outside of the external sphincter, fat-

8:56

containing ischioanal and ischiorectal fossae—normal fat

8:59

signal on the non-fat-suppressed image on the upper

9:02

right, and suppressed, null, or nullified fat signal on

9:05

the image in the upper left. And on the CT, same thing.

9:08

We see normal fat attenuation in

9:10

the ischioanal and ischiorectal fossae.

9:14

So now putting it all together side by side,

9:15

coronal and axial anatomy with the illustrations

9:18

and the imaging anatomy: internal sphincter,

9:20

the smooth muscle center of the image.

9:23

Sphincter surrounds the internal sphincter, extends

9:26

superiorly and becomes the levator ani.

9:29

And the ischioanal and ischiorectal fossae

9:31

are the fat-containing spaces outside of the

9:33

external sphincter and below the levator ani.

9:38

So I wanna talk briefly about the role

9:40

of CT for these patients, uh, presenting

9:43

with a suspected perianal abscess/fistula.

9:45

Um, I think this is largely

9:47

institution- or practice-dependent.

9:49

Uh, and it's hard to establish exactly

9:51

how frequently it's used in this setting.

9:53

Um, and there's very limited published data.

9:55

And part of this is because I think in the literature,

9:57

anyway, we've sort of moved on, and there are—you

10:00

see things written like this—that fistulography and CT are

10:03

obsolete techniques for characterizing fistulas.

10:06

Similarly, the ACR Appropriateness Criteria

10:08

really doesn't directly address this, at

10:09

least in all patients—only specifically

10:12

for patients with Crohn's disease, where it

10:14

states that these are best evaluated by MR,

10:16

which is true.

10:17

And I think that in an ideal world, you

10:19

would characterize all of these by MR. But

10:21

I think there are some practical scenarios

10:23

where CT can still have, um, a role and, uh—

10:29

advantages in the CT—

10:35

readily.

10:38

In some patients, it can exclude

10:40

the so-called drainable abscess.

10:42

And I also think that if you, on CT, see no involvement

10:45

of the ischioanal or ischiorectal fat, then you

10:47

likely do not have a trans-sphincteric fistula.

10:49

And that can be helpful information.

10:50

So I think sometimes CT can be used as sort of the

10:52

first step to stratify where the patients go next.

10:55

Can they be safely discharged on, uh,

10:56

antibiotics, or do they need an MRI or an

10:59

exam under anesthesia or surgical management?

11:02

Disadvantages, of course—

11:03

um, the ionizing radiation. I think CT also

11:06

cannot readily characterize fistulas that do

11:09

not—are not—associated with abscesses, and we can't

11:11

distinguish between active inflammation and

11:13

a fluid-filled tract from fibrosis.

11:15

And so for complex, uh, tracts, particularly

11:18

in the setting of inflammatory bowel

11:19

disease, MR is really the best test.

11:22

And this is considered, uh, worldwide

11:24

to be the gold standard imaging

11:26

technique for perianal Crohn's disease.

11:30

MR can fully characterize the extent of the

11:33

fistulas, which are often complex

11:35

in patients with IBD, and characterize the—

11:38

characterize and detect the presence and

11:40

location of abscesses and secondary tracts.

11:42

And it's been shown to be superior to both clinical

11:44

exam and endorectal ultrasound for this purpose.

11:47

And this is particularly important for identifying

11:49

things that would not be seen in a, uh,

11:52

a physical exam or an exam under anesthesia or an

11:54

endorectal ultrasound, like supralevator extension,

11:56

or a pelvic fluid collection, for example.

11:59

And this is important because as surgery is being

12:01

considered, the, uh, in the surgical procedure is

12:04

balancing the, uh, minimizing the likelihood of

12:08

recurrence of the fistula as in abscesses versus

12:10

affecting the patient's, uh, underlying continence.

12:12

And so it's important upfront to fully characterize

12:15

what the extent of their disease is so that we aren't

12:19

missing some findings or missing some problems

12:22

that will need to be addressed later.

12:25

And MR has been shown to be useful in this purpose.

12:27

It more accurately predicts the clinical

12:28

outcome and frequently identifies

12:30

information that can be missed at surgery.

12:31

And this is particularly

12:32

important for secondary tracts.

12:34

These are these other branching tracts

12:36

that extend off the main tract and either

12:38

form abscesses or extend into other ser—

12:40

uh, other surfaces or structures. And if

12:42

these are not addressed surgically, then

12:44

they are likely to result in recurrence.

12:47

And this is, uh, obviously associated with poor

12:49

outcomes because if a patient undergoes this

12:51

surgery and, uh, only to recur later, this—

12:54

they've not only affected their continence but

12:56

have also not, uh, fully addressed the problem.

13:00

And for patients who are imaged at multiple

13:03

time points, MR can also, uh, distinguish

13:05

between active inflammation and fibrosis.

13:07

And this has been shown to be superior

13:08

to surgical assessments for this purpose.

13:11

And we see sort of stepwise changes on MR

13:13

that correlate with the ongoing treatment

13:16

response, starting from a fluid-filled,

13:18

actively draining tract to, uh, underlying

13:20

fibrotic tract as it responds to therapy.

13:26

So I'll talk briefly about the

13:28

technical acquisition of these exams.

13:29

Uh, these examinations, it's a combination of T

13:32

1 and T2-weighted sequences with and without fat

13:34

suppression, uh, with a multiplanar acquisition.

13:37

Um, and I've listed our technique here. Of

13:39

these, I think the two most useful sequences

13:41

that I rely most heavily on

13:43

are the fat-suppressed T2-weighted images

13:45

and the post-contrast fat-suppressed images.

13:48

So now we'll talk about

13:49

interpreting these examinations.

13:51

I think it's helpful for, um, many of these sort

13:53

of organ- or etiology-specific exams to have an

13:57

underlying set of objectives of what we're hoping to

13:59

accomplish by interpreting this exam.

14:02

So the first step is, is there a fistula? And

14:05

we need to know what a fistula looks like.

14:07

On MR, these are linear or curvilinear tracts that

14:10

are usually hypointense on T1, hyperintense on

14:12

T2, and enhance after contrast administration.

14:15

And you may see secondary signs of inflammation

14:17

surrounding the tracts, either in the, uh, in

14:19

the anal canal itself or in the surrounding fat,

14:21

with inflammation, edema, hypervascularity.

14:25

Once you identify a fistula, then we want

14:26

to assess—is it an actively draining tract?

14:29

Actively draining

14:29

tracts will have fluid within them, so they will be T

14:32

2 hyperintense and have enhancement around them.

14:34

And then if we're seeing this during,

14:36

uh, during therapy, we want to compare

14:38

it to what it looked like initially.

14:39

Has the T2 hyperintensity

14:41

or the enhancement changed?

14:43

And then the last step, uh, is

14:44

grading these from inside to out.

14:46

And that's what we'll spend a

14:47

lot of time talking about today.

14:49

And this is what surgeons rely on

14:52

to assess the relationship of the

14:53

fistula tract to the sphincter complex.

14:56

And as we're characterizing the primary

14:58

tract, we're also looking for associated

14:59

abscesses or secondary tracts anywhere along

15:01

the way, if they extend outside of the anal

15:03

canal into the pelvis or, uh, and ultimately,

15:06

where their external opening is in the skin.

15:10

So the classification scheme that we mostly

15:12

use on MR is based on the St. James University

15:15

Hospital classification, and this, uh, was

15:17

published in, uh, 2000, relating the

15:20

original Parks surgical classification to MRI.

15:23

It has been validated by surgical results and

15:25

long-term outcome, and I think it's a very helpful

15:27

scheme because it uses reproducible anatomic

15:29

landmarks that we can readily identify on MR.

15:32

We define these tracts based

15:34

on the so-called anal clock.

15:36

This is with the patient prone, as they would

15:38

be scanned on the MR scanner, and it is sort of

15:40

designed to mirror the perspective of the surgeon

15:43

with the patient in the lithotomy position.

15:45

So the anterior midline is 12 o'clock, left

15:47

lateral is three o'clock, posterior midline is

15:48

six o'clock, and right lateral is nine o'clock.

15:53

And most of these, the idiopathic

15:55

versions anyway, arise from the six

15:56

o'clock position in the posterior midline.

15:59

So now I'll talk about the St. James

16:01

University classification for fistulas.

16:03

And so there are two sort of primary

16:05

or main subtypes of the fistulas—

16:07

intersphincteric fistulas and transsphincteric fistulas.

16:09

And then we can subcategorize them after that.

16:12

The first decision is, is it an

16:13

intersphincteric fistula or a transsphincteric fistula?

16:15

Intersphincteric

16:16

fistula is one that extends, uh, through

16:18

the internal sphincter into the sphincteric space

16:21

and then heads, uh,

16:22

toward the skin surface without

16:24

crossing the external sphincter.

16:26

So this is a grade one or a

16:27

simple intersphincteric fistula.

16:29

If you have an abscess or a secondary tract

16:31

somewhere along the primary tract, then

16:33

it's a grade two intersphincteric fistula.

16:35

But it's still at its core an intersphincteric

16:36

fistula because it never crosses

16:38

the external sphincter.

16:41

As compared to a transsphincteric fistula,

16:42

these are fistulas that cross both the internal

16:45

and the external sphincter, extend into the

16:47

ischioanal and ischiorectal fossae on their way

16:49

to the skin surface, to their external opening.

16:53

Um, we can subcategorize these as transsphincteric

16:56

with abscesses or secondary tracts if you have

16:58

them anywhere along the course of the primary

17:00

tract. And the last category, grade five,

17:03

supralevator or suprasphincteric disease—

17:05

these are ones that don't fit

17:06

into the first two categories.

17:07

They either extend superiorly, uh, into the

17:09

pelvis and then cross the, uh, the levator

17:12

ani on their way back to the skin surface,

17:14

or primarily arise in the pelvis crossing

17:17

the levator ani on their way, extending to the—

17:21

So now we'll go through a series of cases illustrating

17:24

the classification of these, uh, fistulas.

17:26

Here we have a 25-year-old

17:28

man, uh, with Crohn's disease.

17:30

These are four T2-weighted fat-suppressed images.

17:33

We have an internal opening at the six o'clock

17:35

position in the posterior midline that extends

17:36

posteriorly in the intersphincteric space, but never

17:39

crosses the external sphincter. In the bottom

17:41

images here, you can see that the

17:44

internal sphincter or the external sphincter

17:46

extends like a horseshoe around the internal

17:48

sphincter and has some T2 hyperintensity,

17:50

uh, corresponding to reactive edema.

17:52

But the T2 hyperintensity is not the same as

17:54

what you see in the fluid-filled tract behind it.

17:57

And the ischioanal fat around it has normal

18:00

nullified fat-suppressed signal.

18:03

So this is a grade one simple

18:04

linear intersphincteric fistula.

18:06

Again, these are ones that just cross

18:07

the internal sphincter, course inferiorly in

18:09

the intersphincteric space, and never cross

18:11

the external sphincter and therefore never

18:13

head into the ischioanal, ischiorectal fat.

18:18

Next case, a 39-year-old woman with

18:20

Crohn's and increasing pelvic pain.

18:22

Uh, we have some T2 fat-suppressed images at

18:24

the top and post-contrast images at the bottom.

18:28

For her, we see an internal opening

18:29

at the six o'clock position in the

18:30

posterior midline, same as the prior case.

18:33

But, uh, by contrast here, we have this fluid-

18:35

filled, uh, collection in the sphincteric space

18:38

that is bowing the external sphincter

18:40

outward and the internal sphincter toward the

18:43

midline, but never crosses the external sphincter.

18:46

Again, you have the normal horseshoe-shaped

18:48

structure of the external sphincter here and

18:49

normal, uh, fat signal in the ischioanal space.

18:54

Here's a companion case on CT.

18:56

On the, uh, axial coronal images,

18:58

we see this rim-enhancing abscess within the internal

19:01

sphincter that never crosses the external sphincter.

19:04

Again, normal horseshoe-shaped structure extending

19:06

around the internal sphincter and normal fat

19:09

attenuation in the ischioanal and ischiorectal fat.

19:14

So these are examples of grade

19:15

two intersphincteric fistulas.

19:17

Again, these are intersphincteric fistulas still,

19:19

uh, never crossing the external sphincter,

19:21

but complicated either by an abscess or a

19:22

secondary tract somewhere along their course.

19:26

So the key things that we're looking for on

19:27

imaging here is, is there any part of the

19:29

tract that crosses the external sphincter?

19:31

And is there any part of the, the

19:32

fistulas or abscess that extends into

19:34

the ischioanal and ischiorectal spaces?

19:38

And on these coronal images, I think it nicely shows

19:40

that the external sphincter surrounds the outer

19:42

border of the abscess and that there's normal fat

19:45

signal and fat attenuation in the ischioanal space.

19:49

So the next case is a 49-year-old

19:51

man with a reported perianal cyst.

19:56

We have post-contrast images for axial.

19:59

We have an internal opening arising

20:02

at the four to six o'clock position.

20:04

A secondary tract that extends across

20:06

the midline toward the right, but again,

20:09

never crossing the external sphincter.

20:10

We have this nice horseshoe-shaped structure,

20:14

um, that does not have the tract crossing it, and

20:16

normal fat signal in the ischioanal space.

20:20

So this is just another

20:21

example of a grade two fistula.

20:22

This is a specific type that is commonly called a

20:24

horseshoe-type fistula because it extends on both

20:27

sides of midline within the intersphincteric space,

20:30

but again, never crossing the external sphincter.

20:34

Next case is a 31-year-old

20:36

woman with Crohn's and increasing rectal drainage.

20:40

And these are four T2 fat-suppressed.

20:43

So in her case, we have an internal opening

20:46

at the posterior midline, and you'll see

20:48

that the tract is hyperintense on the

20:51

T2-weighted images and extends through

20:52

both the internal and external sphincter.

20:54

And I've outlined the border

20:55

of the external sphincter.

20:56

In the upper left-hand image, you see that the

20:58

tract extends right through it and then courses

21:01

through the ischioanal fat on the left on its

21:03

way to its external opening in the skin surface.

21:05

So you have this hyperintense tract on the

21:07

bottom images extending through the ischioanal

21:09

fat, and there were no abscesses or

21:12

secondary tracts anywhere along the course.

21:15

So this is an example of a transsphincteric fistula.

21:17

These are tracts that extend through both the

21:18

internal and external sphincters and then extend

21:22

into the ischioanal and ischiorectal fat on their

21:24

way to their external opening at the skin surface.

21:27

So the key demarcation or delineation here is that,

21:30

if we were to draw an outline of the external

21:33

sphincter and then draw, uh, a line following

21:36

the fistula, you would see that it courses right

21:38

through the external sphincter itself.

21:43

Next case is a young man with Crohn's disease who

21:46

had multiple areas of perianal drainage and had been

21:48

noncompliant with medication for several months.

21:52

So these are— we have the primary tract here

21:59

extending in the posterior midline at six o'clock.

22:01

That extends through both the internal and

22:03

external sphincters and has, uh, Y-shaped

22:06

kind of secondary tracts that extend on both

22:09

sides of midline in the upper right-hand image.

22:12

And then extends into the left ischiorectal fossa,

22:16

where there is also this rim-enhancing abscess.

22:19

If we look on the coronal images, one of

22:22

the key distinguishers between grade

22:24

four and grade five fistulas is whether

22:26

they extend above the levator plate.

22:27

The next step is to look and see how high does

22:29

this abscess go, and we can see that it extends right

22:31

up to the levator plate, but never crosses it.

22:33

There’s no supralevator extension.

22:38

Here's a companion case on CT.

22:40

We see this, uh, large rim-enhancing perianal

22:42

fluid collection in the right ischioanal space.

22:46

We don't actually see the underlying fistula, uh,

22:48

secondary to the limitations of CT for characterizing

22:51

and detecting these, but we can see that at

22:53

least there is no extension above the levator

22:55

plate, which you see on the right-hand image.

22:58

So these are examples of grade four transsphincteric

23:00

fistulas, which are complicated by either

23:03

secondary tracts or abscesses or both.

23:06

And abscesses in this area have

23:08

similar features to anywhere else.

23:09

We see them

23:10

rim-enhancing with fluid signal or fluid attenuation.

23:14

And so once you have a grade four fistula and you're

23:16

having these complicated secondary tracts or

23:18

abscesses, the coronals I think are very useful to

23:20

see how high or how far superior does the disease go.

23:23

Does it extend superiorly across

23:24

the levator plate into the pelvis?

23:29

So the next case is a 30-year-old, uh,

23:31

woman who had had a prior J-pouch formation.

23:35

And here we have a coronal image on the

23:36

top, post-contrast images on the bottom.

23:40

We see the primary tract arising at the

23:41

10 o'clock position from the internal

23:43

sphincter that extends into the right

23:45

sphincteric space and the external sphincter.

23:48

And there were multiple secondary tracts, one

23:50

of which extended inferiorly through the right

23:53

ischioanal fat to the right gluteal cleft.

23:55

And then another one that

23:56

extended on the, uh, superiorly.

23:58

On the coronal image here, you see going

24:00

right up to, and also through the levator plate.

24:04

So this is an example of supralevator

24:05

disease or grade five fistula.

24:08

This category actually includes a variety of

24:10

other disease, uh, or other types of fistula,

24:13

but they have the common, uh, feature that they

24:15

all extend through or above the levator ani.

24:19

This includes fistulas that sometimes are known

24:21

as supralevator, extrasphincteric, translevator, etc.

24:29

Next case is a 55-year-old woman who had a history of

24:32

lymphoma and was preparing for a stem cell transplant.

24:36

She also had a history of Crohn's

24:37

disease and perirectal fullness.

24:39

So we have coronal, uh, post-contrast image

24:41

on the top, axial on the bottom left, and

24:44

T2 fat-suppress on the right-hand side.

24:47

And here we have a tract that extends from

24:49

the perianal skin towards the anal canal,

24:53

but never extends into the anal canal.

24:54

And we really only see the enhancement and

24:56

the fluid signal, in the bottom images, in

24:58

the perianal skin and in the ischial fat.

25:01

And so on the top images I've highlighted

25:04

the, uh, anal canal itself and the external

25:06

sphincter, and you see that there is normal

25:08

signal there and there's no extension of the

25:09

tracts to the anal canal or the sphincter complex.

25:12

So this is an example of a type of fistula that's

25:15

not included in the St. James classification,

25:16

this one being an example of a blind-ending sinus

25:19

tract that extended from the perianal skin in the

25:22

ischial fat, but never communicated with the lumen.

25:25

You can also have superficial fistulas that arise

25:27

from the distalmost part of the anal canal, with

25:30

their internal opening below the sphincter complex.

25:33

And so the internal and external

25:34

sphincters are intact in that case.

25:36

And then there's a variety of others, um, that we

25:40

commonly see that you may encounter in practice as

25:43

well, that don't fit into this classification.

25:46

So, um, many of these patients with

25:47

inflammatory bowel disease are very complicated.

25:50

That involve any or many different

25:52

structures in the pelvis.

25:54

And this is particularly relevant for patients with

25:57

IBD unclassified, um, or ulcerative colitis who

26:00

have a phenotype that, uh, that changes during the

26:04

course of their disease, where the diagnosis may be

26:06

uncertain initially, but the perianal disease that

26:09

complicates their disease course may ultimately,

26:12

uh, change their disease to Crohn's disease.

26:16

Patients who've had an ileal pouch–anal

26:18

anastomosis are also prone to developing

26:20

strictures and subsequent fistulas.

26:22

Um, patients with pelvic neoplasms, either

26:25

pre- or post-treatment, can develop fistulas,

26:27

uh, uh, during their disease course.

26:29

And this is often true at the site of either

26:31

prior surgery or prior radiation therapy.

26:34

And so we'll go through a few cases

26:35

here of, uh, fistula that don't nicely

26:37

fit into the St. James classification.

26:41

This is a 59-year-old man who had a long—

26:48

So in his case, we see this fistula arising from the

26:51

distalmost part of the anal canal that extended

26:53

anteriorly into the perineum. On the upper left-hand

26:56

image, where you see this avidly enhancing tract that

26:58

continued, uh, through the ischioanal fat, through

27:00

the perineal fat, and into the left-hand scrotum.

27:03

On the coronal image on the bottom right-hand

27:05

image, I think you can see the extent

27:07

of the tract extending from the anal

27:08

canal all the way down into the scrotum.

27:10

This is an anoscrotal fistula.

27:13

Uh, next case is a 59-year-old woman who

27:15

had newly diagnosed inflammatory bowel

27:17

disease, and her diagnosis was sort of

27:20

in the IBD unclassified category, but the

27:22

features were favoring ulcerative colitis.

27:25

And so she underwent a colectomy, and in her

27:29

case we see this tiny little tract arising

27:33

from the 12 o'clock position in the anterior

27:35

midline that extended anteriorly into the vagina.

27:41

So this was an anovaginal fistula, and

27:43

because of the presence of this fistula, her

27:45

disease and subsequent management was changed

27:47

from ulcerative colitis to Crohn's disease.

27:49

And that's important to note. Many of these patients,

27:51

um, the initial diagnosis is based on the features

27:54

that are present at the time, and in some cases it's,

27:56

it's clear and in some cases it's a judgment call.

27:59

And particularly for the presence of fistulous disease,

28:02

that is often, uh, a feature that will tip the

28:05

balance toward the diagnosis of Crohn's disease.

28:08

And so this happens in about 10 to 15% of patients

28:11

where the definitive diagnosis cannot be made.

28:14

There are either, there are features of UC

28:16

and Crohn's, um, and ultimately they evolve

28:19

to one or the other during their follow-up.

28:21

But it is often, or it can be, uh,

28:24

uh, hard to classify initially.

28:26

And it's important to make this

28:28

diagnosis definitively when possible.

28:30

Um, because it has implications for treatments,

28:32

for how they're surveilled, how they're treated.

28:36

See.

28:36

Specializing disease, um, particularly upfront.

28:39

It can be very useful information to help, uh, make

28:42

that decision and usually is a feature that would,

28:45

um, tip their decision-making toward Crohn's disease.

28:49

This is the patient with ulcerative colitis

28:51

who had right buttock pain and induration.

28:54

Uh, we have fat-suppressed T2-weighted

28:55

images on the left and axial and coronal

28:57

post-contrast images on the right.

29:00

In his case, we see this very complex

29:03

branching network of fistulas.

29:04

It's hard to tell where the, uh, primary internal

29:06

opening is because there are these sort of radiating

29:08

tracts extending everywhere in the internal sphincter,

29:13

and they extended into the intersphincteric

29:14

space and gave rise to many

29:16

other secondary tracts and abscesses.

29:18

You see this avid rim enhancement, um, in

29:21

the right, uh, intersphincteric space,

29:23

and then a, a similar, a smaller area on the left.

29:28

And the secondary tracts, uh, many extended superiorly

29:31

above the levator plate on the coronal image.

29:34

And so this is an example of a patient

29:35

whose diagnosis was changed from

29:37

ulcerative colitis to Crohn's disease

29:39

following the findings of this MRI.

29:43

Here's another patient, uh, with IBD unclassified.

29:46

Um, her features were favoring Crohn's, um,

29:49

but she had had a total colectomy and an

29:51

ileal pouch–anal anastomosis initially,

29:55

which was subsequently complicated by anastomotic

29:57

strictures and required multiple dilations.

30:00

And she now was presenting

30:01

with new right labial swelling.

30:05

So in her case, we see this, uh, T2

30:07

hyperintense rim-enhancing tract that extends

30:10

from the 11 o'clock position anteriorly into

30:13

the skin and right inner labial surface.

30:17

And, uh, this is another important feature.

30:19

Sometimes we are—the findings we have on

30:22

MRI can help characterize these patients,

30:25

um, as Crohn's, or, uh, in the setting

30:28

of IBD unclassified or ulcerative colitis.

30:30

But it's also important to note that these

30:32

patients with IBD unclassified are also

30:35

associated with an increased incidence of

30:37

fistulas and pouch complications if they

30:39

are to undergo an ileal pouch anastomosis.

30:44

And so for these patients with IBD unclassified,

30:46

their natural history often more closely resembles

30:49

ulcerative colitis, and so many will undergo a

30:51

colectomy with an ileal pouch–anal anastomosis.

30:54

Um, but in this setting, they're associated

30:56

with more likely—or higher likelihood—of

30:58

fistulas and pouch-related complications.

31:00

And so you may see these patients imaged with,

31:03

uh, during the—as those complications develop.

31:07

Here's a, uh, an example of that with a 23-year-old

31:10

woman who had ulcerative colitis and had undergone

31:13

a colectomy and ileal pouch–anal anastomosis

31:15

that was complicated by recurrent pouchitis,

31:17

and now was presenting with new right pain.

31:21

So in her case, we see a fistula that's arising

31:24

at the eight o'clock position on the upper

31:26

left-hand image and upper right-hand image and

31:28

extending, um, through or, uh, at the level of

31:31

the anastomosis. It's extending to the right, into

31:33

the right ischioanal and ischiorectal fat, and

31:36

then extended, uh, through the external sphincter

31:39

and through the ischiorectal fossa on its

31:41

way to its external opening at the skin surface.

31:44

So this is a case of fistula developing

31:47

in the setting of an IPAA pouch stricture.

31:53

Next is a 60-year-old woman with perianal pain and

31:55

drainage and a longstanding history of fistulizing Crohn's.

32:02

We have axial T2-weighted images on the left,

32:04

coronal and axial post-contrast—uh, excuse me—T2

32:07

weighted on the upper left, coronal post-contrast in

32:09

the upper right, and axial post-contrast in the bottom.

32:12

And in her case, uh, we see

32:14

some T2 hyperintense tracts.

32:16

But really the predominant finding is this, uh,

32:19

intermediate signal mass arising at the anorectal

32:22

junction with abnormal mesorectal lymph nodes and

32:25

fistula that extended from the mass to the posterior

32:28

midline into the ischioanal fat.

32:33

So this is a rectal adenocarcinoma complicated by

32:35

fistulas, and there is an increased risk of rectal

32:39

and anal carcinoma for patients who, um, have

32:42

severe proctitis and chronic perianal disease.

32:45

And so it's important to, particularly for these

32:46

patients with Crohn's who have a longstanding

32:48

history of the disease and a longstanding history of—

32:51

disease in particular—that these are high risk for

32:54

developing, uh, subsequent carcinoma in that region.

32:57

This is thought to probably represent a

32:59

dysplasia–carcinoma sequence, um, from the

33:01

repetitive, uh, episodes of inflammation,

33:04

although it's not as, uh, direct a

33:06

correlation as with ulcerative colitis.

33:11

Uh, next case is a 71-year-old man with perirectal

33:13

pain and drainage, and he had a history

33:15

of prostate cancer. And post-contrast images

33:19

are at the top, T2 fat-suppressed in the

33:21

bottom left, and fat post-contrast in the bottom

33:23

right. Here we see another enhancing mass,

33:26

this time arising in the prostate bed.

33:29

Um, you can see a susceptibility artifact

33:31

corresponding to the resection bed along the midline.

33:36

This mass extended posteriorly into the

33:39

anal canal from the prostate bed and

33:40

was invading the, uh, sphincter complex.

33:43

And so this is an example of recurrent

33:45

prostate cancer, uh, arising in the prostate

33:48

bed and extending into the anal canal.

33:50

And, uh, the anatomic landmarks I showed you

33:52

at the beginning, with the internal sphincter

33:54

in the center of the image, the horseshoe-

33:56

shaped, uh, external sphincter surrounding it—

33:58

you see that the mass extends and, uh,

34:00

involves the internal sphincter from

34:02

about, uh, nine o'clock to three o'clock.

34:08

Next case is a 48-year-old woman with

34:11

unresectable rectal cancer, um, who'd had

34:13

prior chemotherapy and radiation therapy,

34:16

and was noting enteric material on her tampon.

34:21

So on the, uh, T2-weighted images on the left, we

34:23

see this necrotic rectal mass with, uh, surrounding

34:26

post-treatment changes and post-treatment edema.

34:29

And then extending from the mass, we see

34:31

this, uh, T2 hyperintense tract, uh,

34:34

with peripheral enhancement that extended

34:35

anteriorly from the mass into the vagina.

34:38

And you see that on the sagittal

34:39

image on the bottom right as well.

34:40

This, uh, peripherally enhancing tract

34:42

extending from the mass into the vagina.

34:44

So this is a rectovaginal fistula,

34:46

arising in the setting of a treated rectal—

34:50

um.

34:51

Specifically, vaginal fistulas commonly arise in the setting

34:54

of treatment, uh, for underlying mass or cancer.

34:59

Um, and the radiation therapy is cytotoxic to

35:04

the targeted cells, of course, but this also

35:06

results in chronic inflammation and ischemia in

35:08

the surrounding structures, including the tumor,

35:10

which can result in a fistula.

35:15

Before starting this series of these

35:17

other types of fistulas that don't fit into the

35:19

St. James classification, there's not a neat

35:21

classification system, but rectovaginal fistulas—

35:24

it is usually helpful for surgeons to

35:27

know whether these are high or low.

35:30

Um, the high ones are those proximal to the

35:33

sphincter complex, and the low ones are those that

35:34

are involving the complex. And that can be useful

35:37

information when considering operative intervention.

35:41

Other causes of rectovaginal fistulas: IBD, of

35:43

course, which we've mentioned, obstetric trauma,

35:46

prior pelvic infection, and inflammation as well.

35:51

Um, this is a patient with Crohn's disease,

35:53

a history of multiple complex fistulas.

35:56

Uh, we have side-by-side MR and CT images here.

36:00

In this case, this is just an example

36:02

of a cone, which you commonly see, uh,

36:04

as an intervention for these patients.

36:06

And it's this thin, flat or ribbon-like structure

36:08

that is low signal intensity on MR and high

36:11

intensity—uh, high attenuation—on CT for, like, a

36:14

thin purse-string sort of appearance that's

36:16

used to, um—is placed in the tract and connects

36:20

into the internal opening and is subsequently

36:22

tightened, um, over time to obliterate that tract.

36:25

And so this is just an example of what

36:27

these look like both on CT and MRI.

36:31

Um, so

36:35

that concludes the classification.

36:39

I think that the St. James classification structure

36:41

is useful and is often helpful for characterizing

36:44

these fistulas, but we often see patients with

36:46

either very complex disease or treated types

36:49

of, um, cancer or neoplasms that don't nicely

36:52

fit into the classification scheme.

36:55

So I think it's useful to use when you can.

36:57

And for those where you can't, then you

36:59

just describe what the fistulas are.

37:05

Move on to the next section, comparing,

37:07

uh, how you might use CT and MRI.

37:09

This is a 36-year-old woman with Crohn's and left

37:12

perianal pain, so side-by-side CT images on the

37:16

left with the images on the right. In her case, on

37:20

the CT, we see this rim-enhancing abscess in the

37:22

left ischioanal space with some surrounding fat

37:24

stranding and inflammation in the ischioanal space.

37:28

We don't see an underlying fistulous tract.

37:31

Uh, by comparison on the MR, we see

37:32

the same rim-enhancing, uh, in this,

37:34

in her case, fluid-filled tract

37:37

in the left ischioanal space.

37:39

And in addition, on MR, we see these branching

37:41

tracts that extend from the posterior midline at

37:44

six o'clock through the, uh, external sphincter

37:46

and a secondary tract that was extending to the

37:49

right of midline, um, on the, uh, top axial images.

37:55

Here's a different patient, um, with

37:56

side-by-side CT images on the left, post-

37:58

contrast MR images on the right. On the CT,

38:02

you see this ill-defined sort of soft tissue

38:04

thickening and some fat stranding in the, uh,

38:06

left ischioanal fat, but we don't really see a

38:08

discrete fistula or underlying fluid collection.

38:12

Uh, by contrast, on the MR, you can see an, uh,

38:14

rim-enhancing sphincteric abscess between the

38:17

internal sphincter and the external sphincter,

38:20

and these branching transsphincteric tracts that extended,

38:23

uh, anteriorly and posteriorly in the left

38:26

ischioanal fat with all of this surrounding

38:28

enhancing edema in the ischioanal fat.

38:35

And so for this patient, um, her history

38:37

was such that she had had a longstanding

38:39

history of an anal canal and was now

38:41

developing recurrent perianal pain and drainage.

38:47

The added features that we can see on MR that

38:51

are not ever really going to be occult on CT.

39:00

So that brings us to the summary here.

39:02

Um, I know this has been a whirlwind tour,

39:04

but hopefully I've, um, illustrated some of

39:07

the uses, um, for MR for perianal fistulas.

39:10

Um, starting with the anatomy. I think the anatomy

39:12

is often a stumbling block for many people, and

39:16

it's because it can be and is exceedingly complex,

39:18

particularly if you use existing literature to try to

39:21

help, um, sort it out. That

39:24

can actually add to the confusion.

39:25

And so what I would say for these exams anyway,

39:27

is we can intentionally simplify the anatomy to

39:30

only the key structures that we need to know—

39:32

the internal sphincter, external

39:33

sphincter, intersphincteric space, and the

39:36

ischioanal and ischiorectal fossae.

39:40

CT, uh, is often or can be useful as a

39:42

first-line modality, but we should have

39:43

a low threshold for recommending MRI.

39:45

And so I'd like to think of it as sort

39:47

of the screening tool for this case.

39:48

If you don't see any involvement of the ischioanal,

39:50

ischiorectal fat, and you don't see

39:53

anything in the pelvis, you likely do not have

39:55

a transsphincteric fistula or supralevator fistula.

39:58

And so those patients, it may be appropriate to just

40:00

send them home with antibiotics, with outpatient

40:03

follow-up. If you do see a fluid collection in the is—

40:07

or a pelvic fluid collection, or there is concern

40:10

for, uh, IBD and the potential for more complex

40:14

underlying tracts, then we should have a low threshold

40:16

for recommending follow-up MRI, because for those

40:18

patients, it is very likely that they have more

40:20

complex disease that we're just not seeing on CT.

40:24

And MR is really the gold standard for

40:27

guiding management, particularly for patients

40:28

with IBD, and it's the best tool that we

40:30

have for identifying the entirety of the—

40:34

perianal disease—both the primary tract

40:36

and its internal opening, and any secondary

40:39

tracts or abscesses that may complicate it,

40:41

and where it, uh, extends to the external—

40:43

uh, opening over the, at the skin surface.

40:46

And it's been shown to be the best modality

40:47

for complete characterization of the

40:49

underlying disease at any given time.

40:51

It's also—

40:52

useful for imaging these patients longitudinally.

40:55

We can watch as the tract starts as a tract

40:58

that is T2 hyperintense with associated

41:01

enhancement at the beginning when it's an actively

41:03

draining tract, and as it responds to therapy,

41:06

starts to lose the T2 hyperintensity and

41:08

ultimately may become low signal on both T1

41:10

and T2-weighted images, indicating fibrosis.

41:15

St. James classification is a nice scheme, um,

41:18

subdividing these fistulas into intersphincteric

41:20

tracts or sphincteric tracts, and I think

41:23

many surgeons are looking for that information.

41:25

So it's useful to describe them as such

41:28

and characterize them in the one through

41:30

five, uh, classification when you can.

41:33

But you may see patients that have

41:34

more complicated disease that don't

41:35

nicely fit into that characterization.

41:37

So I think it's useful just to describe

41:39

what structures are involved and

41:41

what the complexity of disease is.

41:44

And with that, I will conclude the formal part of the

41:46

presentation and we can take time, uh, for questions.

41:51

Great.

41:52

It does look like we have a decent

41:54

amount of questions in the Q and A field.

41:56

All right.

42:03

Um.

42:05

First question is about case one, which

42:07

I get this question on every, pretty much

42:09

every time, and I need to be better about

42:11

demonstrating this when I talk about it.

42:13

The question is, how does it get, um, from

42:16

the internal opening here to the intergluteal

42:18

cleft without crossing the external sphincter?

42:20

And in fact, the upper left-hand image here

42:22

appears to show that it's crossing right

42:24

through the, um, uh, the external sphincter.

42:27

And I think this is a hard thing to demonstrate

42:30

on static images without being able to scroll.

42:33

But when you have tracts that are arising,

42:36

particularly at low in the anal canal, the

42:38

path of least resistance is to go below the

42:40

external sphincter rather than to cross it.

42:42

At least for patients who just have

42:43

the idiopathic types of fistula, rather

42:45

than patients with Crohn's disease.

42:47

So if you're at the distal,

42:48

most part of the anal canal.

42:50

The key thing or the more likely scenario is that

42:53

it's going below the fibers of the external sphincter

42:56

as it extends toward the, um, toward the anal verge.

42:59

The fibers of the external sphincter start to fan

43:01

out, um, toward the, uh, toward the skin surface.

43:04

And so these tracts usually go

43:06

under them rather than through them.

43:07

And that's—

43:08

often a distinction you can only make by

43:11

scrolling through the images and seeing them live.

43:12

And so the example here is you see how there's

43:15

this little area below the, um, below the external

43:18

sphincter where these tracts can head through it.

43:24

Um, next question.

43:26

What's—

43:29

The fistula dissects the external sphincter

43:31

without reaching the ischioanal fossa. Intrans—

43:33

that would be intersphincteric. It has to

43:35

cross through the external sphincter to

43:38

be considered a transsphincteric fistula.

43:42

Um, is the external sphincter deficient anteriorly

43:45

considering that it is horseshoe shaped?

43:47

Um, let me get that.

43:50

Yeah, so you have, um, depending on whether

43:53

it's a male or a female, you have the

43:54

sphincter extending anteriorly.

43:57

And so there is, uh, a space, um, immediately

44:00

anterior to the internal sphincter,

44:02

at least where the external sphincter is not present,

44:05

and where it's heading more, uh, more anterior.

44:11

Can we diagnose abscess based

44:13

on T2 without gadolinium?

44:14

I think you can.

44:16

Um, based on the configuration. These— the

44:17

fistulas themselves or the tracts tend to

44:19

be more linear or curvilinear, whereas the

44:22

abscesses tend to be more rounded or ovoid. Um—

44:26

So like this, for example, you see this

44:28

sort of bulging T2 hyperintense structure

44:31

that's more likely an abscess or a fluid

44:32

collection as opposed to these kind of nicely

44:34

linear, branching, fluid-filled tracts.

44:36

Although sometimes it can be hard to tell whether you

44:38

just have a tract that sort of bulges a little bit and

44:41

then continues on, or whether it's a distinct abscess.

44:46

Um, distinguishing vessels from secondary tract—

44:48

the T2-weighted images are helpful for that.

44:50

The, uh, vessels usually have signal voids, and

44:53

the, uh— are not as large, um, whereas the—

44:57

should be these large, hyper—

44:59

hyperintense structures.

45:04

Um, how are you branding—

45:05

which tract is primary or secondary?

45:07

Um, that's a good question.

45:08

Sometimes it's just the radiologist

45:10

arbitrarily making that judgment.

45:11

My approach is usually just to go kind of inside out.

45:15

So start in the anal canal, find where you think

45:18

the, the tract is arising, and designate that as the

45:20

primary tract based on where the internal opening is.

45:23

So I sort of start at the inside, find the

45:25

internal opening, and then just follow it on

45:27

its way out, ultimately to the skin surface.

45:29

And—

45:31

designating anything that sort of branches

45:33

off the main path as secondary tracts.

45:38

Um, how to differentiate a tract from an abscess,

45:41

um, that I think is the same question as before.

45:44

The abscesses usually have a more

45:45

bulging or a rounded configuration.

45:49

Um, how to differentiate a

45:50

Seton from a fibrotic tract.

45:52

Um, they both will have low signal, um, but the

45:55

Seton should look more like a, a foreign body

45:58

or a structure as opposed to just the tract.

46:00

Um,

46:03

so it should have this kind of flat ribbon

46:05

like appearance, and so it looks like it's

46:07

something that's, um, human-made as opposed

46:09

to, uh, underlying tract. Grade five, um...

46:14

Um.

46:18

Let's see, go back.

46:19

These are tough because these are often the most

46:22

complicated disease, but the common feature is that

46:24

there is involvement of the levator plate, whether

46:27

it's something extending from above, going through

46:29

it, um, or starting from below, going up above the

46:33

levator plate, and then coming back down through it.

46:35

The common feature is that there is a tract

46:37

that crosses the levator plate at some point.

46:42

Um.

46:45

I have only CT.

46:45

Yeah.

46:46

So that's why I used to give this without

46:48

any discussion of CT because what you

46:50

find in the literature is that CT is

46:51

basically not used for this purpose.

46:53

But the reality is that it often is, and

46:54

in particular, our, um, our institution,

46:56

we have residents and fellows on call.

46:58

They often see these first on CT.

47:00

And so one of their questions is always,

47:02

how do I clearly do my best on CT?

47:04

And when should I request more?

47:06

Request an MR. And so I think that the, the

47:09

things that I've highlighted here are, if you have—

47:12

If you don't have any involvement of the ischio-

47:14

anal or ischiorectal fossa, in other words, you

47:17

have normal fat attenuation there with no edema

47:20

or no tracts extending into it, you can be

47:21

pretty confident that you, you're at worst

47:24

dealing with a simple intersphincteric tract.

47:27

Um, and if you have no pelvic

47:29

inflammation, same thing.

47:30

There's no supralevator disease.

47:31

So I think you can at least use it as a nice screening

47:33

tool and then you just do your best from there.

47:38

Um, let's see.

47:45

Complications in fistula?

47:46

Do we classify them as Crohn's?

47:47

Ultimately, that is their gastroenterologist's—

47:50

is the gastroenterologist's decision.

47:53

But I think if you encounter that scenario,

47:55

then you should have that conversation

47:57

and say, this looks very complicated.

47:58

It looks more like Crohn's.

47:59

Then they can take that information

48:02

and make the final decision.

48:03

And often it will be the, the feature

48:05

that, um, tips it from IBD unclassified

48:08

to Crohn's or from UC to Crohn's.

48:10

Um, but I think it's useful to have—

48:12

a conversation about that if you see it.

48:17

Um, how to measure the tract from the anal—

48:19

uh, from the anal verge. Um, the anal verge.

48:25

Let's see, where do I have—

48:29

Where’s a good image of it?

48:32

This is pretty good here on the

48:34

CT actually, and the MR here.

48:35

So it's where you see the lowest part of the anal

48:37

canal, usually on the coronal or the sagittal images.

48:39

And so if you just connect it back upwards,

48:42

um, that's how I would usually measure it.

48:45

Either the coronal or sagittal where you see

48:46

kind of the muscle ending and you extending

48:49

either to an opening at the skin surface

48:50

or the fibers are starting to fan outward.

48:55

Um, template reporting.

48:57

Uh, yes.

48:57

I, in general, am a fan of templated reporting.

49:00

There's not a great template out there for this,

49:01

although I was just asked by one of our surgeons

49:04

about this recently, and I found one published.

49:08

Um, hold on.

49:10

If you give me a second, I can find

49:11

it and I can put it in the chat.

49:14

Um, so I'll hold that question for a

49:16

second, and I'll come back to it.

49:20

Uh, let’s see.

49:20

Next question.

49:23

Experience with pediatric fistulas.

49:24

I don’t have a lot of experience with this, although

49:26

there is some overlap as you get into like the 15–

49:30

to 18-year category. Do we characterize these as—

49:34

Uh, are these pediatric patients or adult patients?

49:36

And many of them, you know, go from being pediatric

49:39

patients to adult patients while we’re following them.

49:42

Uh, I don't have a ton of experience with that.

49:43

I would say that, um, there's a lot of published

49:46

literature about that, uh, particularly from

49:47

Jonathan Gilman at the University of Cincinnati.

49:50

Um, if you have a pediatric population,

49:52

I would, uh, look specifically for that.

49:56

Um, can we assess the fistula alone

49:58

on fat-suppressed, uh, sequences?

50:00

I assume you mean T2.

50:01

Do we need contrast enhancement?

50:03

You don't need it, but I think it's helpful.

50:05

I think it often, um, is putting them together best

50:09

demonstrates, uh, the entirety of the disease, and

50:12

it is, um, a way, uh, just sort of an added way that

50:15

you can ensure that you're fully characterizing it.

50:17

Although if you had a patient who could not

50:19

get gadolinium, you could just use the T

50:21

2 weighted sequences, um, to characterize.

50:26

Um, which extends lower, the

50:28

internal or external sphincter?

50:30

Um, they're about the same, but the internal

50:32

sphincter I think actually comes to the skin surface.

50:36

Uh, examples of chronic fistulas, um, I mean

50:42

all of these are chronic to some degree.

50:44

Uh, I assume you mean chronic

50:45

as in an inactive tract.

50:48

I don't think I do in here, and

50:50

I don't know that I have one

50:52

offhand, but they, um, classically are

50:55

low signal intensity on all sequences,

50:58

same as fibrosis kind of everywhere.

51:01

Um, let me look for that template now real quick.

51:05

So I think this kind of follows the same

51:07

mental checklist that I would use when I'm

51:10

reporting these, but I think if you, if

51:11

you like templated reporting or you like

51:13

having checklists, I think this is an example.

51:16

There's balance in and checklist.

51:20

Be comprehensive but not overwhelm the reader.

51:27

Um, so I'll leave that up for a second while

51:28

answering the last couple questions here.

51:30

What if you, I think that must be, what

51:32

if you can't see the internal opening?

51:34

I would just describe what you see.

51:36

Then there are some where you can't see

51:37

the internal opening either because,

51:39

um, because of the resolution or—

51:42

the internal opening may be fibrosed, or

51:44

maybe there's no internal—maybe the fistula

51:46

is entirely outside of the, um, anal canal.

51:49

I think I would just describe what you

51:51

do see and where it is involving it.

51:54

And then the last question is, does DWI have

51:56

a place? It's not part of our protocol, but

51:59

there is a lot of published data about that,

52:01

particularly imaging these, um, longitudinally

52:05

over time and how it correlates to response.

52:07

Um, and—

52:11

Uh, if you had it or if I was using it, I think

52:14

it is a supplementary feature in sort of adding

52:16

to your confidence or helping your detection.

52:19

Um, similar to, um, how we use

52:21

it in some other applications.

52:23

As far as the quantitative part of DWI, not really

52:27

routinely part of it, but there is a lot of interest

52:29

in that, and so it may eventually make it to that.

52:32

Um, it looks like—it also looks like we have,

52:34

um, one more question, um, that came in.

52:38

Uh, can fistulas be strictured or stricture—

52:42

stricted?

52:42

I think that is, um—

52:46

They can be. I would, uh—I think when they

52:49

tend to respond or become fibrotic, it tends to be

52:52

the entire part of the tract as opposed to just, uh—

52:57

specific areas, like we think about strictures

52:59

in the bowel or the urinary tract.

53:01

They don't tend to stricture like that.

53:03

Um, they tend to become kind of

53:05

fibrotic as a, uh, as an entirety.

53:11

Alright, well that looks like

53:12

it's it for the questions.

53:13

Um, and as we bring this to a close, I wanna thank Dr.

53:16

Dr. O'Malley for this lecture.

53:18

And thanks to all of you for

53:19

participating in our noon conference.

53:21

Just a reminder that this conference

53:23

will be available on demand

53:25

on mrionline.com in addition to

53:28

all previous noon conferences.

53:30

And, um, just to finish up, uh, be sure

53:33

to join us on Friday for a lecture from

53:35

Dr. Nanda Thimmappa on imaging of renal masses.

53:38

You can register for that at mrionline.com and follow

53:41

us on social media at MRIonline for updates

53:45

and reminders on upcoming noon conferences.

53:48

Thanks again and have a great day.

53:50

Thank you everyone.