0:01

The following case, we'll go over some

0:03

normal anatomy, as seen on MR imaging.

0:06

I'll withhold the history for just a few minutes.

0:10

As we start going through this case, you know,

0:13

usually for most imaging of the abdomen, MR

0:15

imaging of the abdomen, we start off with our

0:17

T2-weighted sequences, as you can see over here.

0:20

And that's already a workhorse sequence that

0:22

you can sort of evaluate all the organs on.

0:24

Now, it's important to realize that to see,

0:28

sort of the normal bile ducts on T2

0:30

weighted sequences, it's often very challenging.

0:32

You can see a little bit over here,

0:34

maybe a little bit over here, and a

0:37

little bit of the extrahepatic biliary

0:39

tree you can see right over there.

0:40

But oftentimes, and a little bit over here as

0:42

well, it's very challenging to see these ducts.

0:44

And that's a good thing.

0:45

If they're not dilated, if they don't

0:46

have any pathology, you're really not

0:49

supposed to notice them that much.

0:51

Oftentimes, I would say we use our

0:53

referring providers to ask for MRCP

0:54

sequences to evaluate the bile ducts.

0:57

And we're going to go through

0:58

a whole bunch of those today.

1:00

In our own experience, our institution,

1:02

oftentimes there's lots of artifacts

1:04

associated with MRCP sequences.

1:06

So even those sometimes I find

1:07

are not the greatest sequences.

1:09

So the point is, if you do want to

1:10

evaluate the bile ducts, it's good

1:12

to look at a whole bunch of sequences

1:13

in order to visualize them.

1:16

This particular case is of a young patient

1:18

who's being evaluated as a liver donor.

1:20

That is,

1:21

that they may potentially give up a portion

1:23

of their liver to a friend, family member, or a

1:25

colleague who's in need of a liver transplant.

1:27

Before we do that, we perform MR imaging

1:29

and CT imaging to evaluate anatomy.

1:32

A big part of the MR imaging is

1:34

done to evaluate the biliary tree.

1:36

For that, we use a whole bunch

1:38

of sequences, as you can see over

1:39

here, and use T2-weighted sequences.

1:43

We also use post-contrast sequences

1:46

after administering an intravenous contrast agent with

1:49

partial hepatobiliary excretion, that is Eovist.

1:52

We image at different time points,

1:54

15 minutes, 20 minutes, 25 minutes, and

1:56

sort of these five-minute increments.

1:58

We find that excretion of that

2:00

contrast agent through the bile ducts

2:02

helps us evaluate the biliary tree nicely.

2:05

And so that's what we're seeing over here.

2:07

This particular T1 post-contrast image is done

2:09

about 20 minutes, and we can see the bile ducts

2:12

manifesting as these linear hyperintense foci

2:16

within the liver.

2:17

Here, we can see the

2:18

left hepatic duct very nicely.

2:21

This small twig over here is going

2:22

to be the right hepatic duct.

2:24

They join together to form

2:25

the common hepatic duct.

2:28

The common hepatic duct goes downwards,

2:31

is joined by the cystic duct, which you

2:33

can see right over here at that junction.

2:36

After that junction, this becomes

2:38

the common bile duct as it goes all

2:40

the way downwards to the ampulla.

2:42

You can also visualize this

2:45

anatomy on coronal T1 post-contrast

2:47

images in a very similar manner.

2:49

Here, you can see the left hepatic duct.

2:52

This portion here is the right hepatic duct.

2:55

This tiny portion here, as it goes

2:57

downwards, is going to be the common

2:59

hepatic duct coming down here as well.

3:03

That's joined by the cystic duct over here,

3:05

and as it goes downwards, this longer segment

3:08

right here is going to be the common bile duct.

3:12

Now, the normal caliber of the intrahepatic ducts

3:14

is about two millimeters in size.

3:17

The extrahepatic biliary tree is

3:18

about six millimeters.

3:20

As one gets older, we allow for a little

3:22

bit more laxity in the intrahepatic duct,

3:24

with upper limits of the extrahepatic

3:25

biliary tree, adding a millimeter

3:27

per decade above the age of 60.

3:29

So at 60, it will be six

3:31

millimeters; at 70 years of age,

3:33

we can allow for seven millimeters, top normal

3:35

size; at 80 years of age, eight millimeters,

3:38

and oftentimes post-cholecystectomy,

3:40

the extrahepatic biliary tree can also get

3:43

a little bit larger, and we allow up to

3:45

about 10 millimeters for that caliber.

3:49

The last thing I'll mention about the

3:50

anatomy is just for the right hepatic

3:53

duct. There are two specific branches

3:55

that we should always try to evaluate.

3:58

This small twig over here is the right hepatic

3:59

duct, but there's an anterior branch over here

4:03

and a posterior branch over here. These two

4:06

small branches join together to form that right

4:08

hepatic duct, and oftentimes the variations

4:11

that we're going to see in the next few cases

4:14

will involve some variations of where these two

4:17

ducts insert with respect to the right hepatic

4:19

duct and the left hepatic duct.