0:01

The following video vignette will showcase the

0:04

MR imaging appearance of normal liver anatomy.

0:07

So here we have, uh, a patient with

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an MR study covering the abdomen.

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As we scroll down, we can see over here, this is

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our T2-weighted images without fat saturation.

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Over here, this is our T1-weighted

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images with fat saturation, no contrast.

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Liver lives right over here

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in the right upper quadrant.

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We can look at its borders, and as we

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trace them, notice how smooth the borders

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are on both the T2-weighted images

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and the T1-weighted images over here.

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Because of the relatively low water

0:39

content within the liver, on the T2

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weighted images, the internal signal is

0:44

relatively low when you compare it to

0:45

other organs, such as the spleen over here.

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For the same reason, on the T1-weighted

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images, the water content is relatively

0:53

low, so the signal is relatively high

0:54

when you compare it to the spleen.

0:56

And if you look at the overall internal

0:58

architecture, it looks very homogeneous.

1:01

We can then move on to evaluating

1:03

some of the liver vascular anatomy.

1:06

So as we scroll down these images

1:08

over here, we have a T1-weighted,

1:11

fat-saturated image with contrast,

1:14

and this is done in the arterial phase.

1:17

This is a similar image, but done a little

1:18

bit later in the portal venous phase.

1:20

In the arterial phase, we can see

1:23

portions of the hepatic arteries

1:24

as we scroll through these images.

1:26

So you have a proper hepatic artery,

1:27

typically splitting off into a left

1:29

hepatic artery and a right hepatic artery.

1:31

And this supplies about 25%

1:34

of the liver vascular supply.

1:37

And again, here we can see

1:38

portions of the portal vein.

1:39

As we scroll through the images,

1:40

I'll point this out again.

1:42

But in this cut over here, we can see that

1:43

you have a main portal vein not imaged over

1:45

here, but this is the right portal vein.

1:47

Here is the left portal vein, again,

1:49

out of the plane of this, uh, image.

1:51

And the right portal vein typically splits

1:53

into an anterior branch, you can see over

1:55

here, and a posterior branch over here.

1:58

While the left portal vein, um, has branches

2:00

that go to the medial segment of the liver over

2:04

here, as well as the lateral segment over here.

2:08

And of course, the portal vein supplies about

2:10

75% of the vascular supply to the liver.

2:15

Again, as we scroll through these images, we can

2:17

see the main portal vein over here, branching

2:20

into the right portal vein over here, the

2:23

left portal vein over here, and its subsequent

2:26

segmental tributaries within the liver.

2:28

The hepatic artery is a little bit

2:29

more difficult to see, but they'll

2:31

typically come off the celiac artery.

2:33

You see the common hepatic artery over

2:35

here, and that will branch into the

2:37

proper hepatic artery and branches that

2:39

supply the right and left hepatic lobes.

2:41

In terms of the hepatic veins, there

2:43

are some variations to this, but you'll

2:45

typically have a middle hepatic vein

2:47

that we can see portions of it over here.

2:49

The right hepatic vein, portions of it

2:51

over here, as well as the left hepatic

2:53

vein, we can see a portion of it over here.

2:56

When we talk about liver anatomy, we

2:58

typically use the Cui Ngoc classification

3:00

in order to describe liver lesions and where

3:02

they're located within the liver itself.

3:04

Now it's important to know that each of these

3:06

segments that I'm going to talk about functions

3:08

independently with a unique vascular supply,

3:12

inflow, outflow, as well as biliary drainage.

3:16

And that each of these segments can

3:17

be independently resected without

3:19

affecting neighboring tissue.

3:21

So the first landmark that's important

3:23

to recognize is the middle hepatic vein.

3:25

So we can see the middle hepatic vein over here.

3:27

And if we draw a line from the IVC all

3:30

the way through the expected location of

3:32

the middle hepatic vein, this will split

3:34

the liver into the right hepatic lobe over

3:37

here, the left hepatic lobe over here.

3:40

Now this is the middle hepatic vein, and we're

3:41

going to follow it as it goes down, so that

3:43

line that we're talking about is going to be

3:44

along the plane of the middle hepatic vein.

3:47

Everything over here will be the

3:48

right hepatic vein, everything

3:50

here will be the left hepatic vein.

3:51

It's going to keep on going, and over

3:53

here it's splitting, so we can imagine

3:55

that the line now is sort of the midpoint

3:57

between these two vessels, and as you go

3:59

downward, the line sort of bisects the

4:01

mid portion of the gallbladder over here.

4:04

So at this level, the line will be

4:05

approximately over here, where this will be

4:08

the right hepatic lobe, and over here,

4:11

and over here will be the left hepatic lobe.

4:14

The other landmarks that we need to use

4:16

are the right hepatic vein, so we can

4:18

draw a line right through it over here to

4:19

the IVC, which splits the liver into an

4:22

anterior segment and a posterior segment.

4:25

So if we look at this, this

4:26

is the middle hepatic vein.

4:28

All this is the right side, and the right

4:30

hepatic vein splits that right lobe into an

4:32

anterior segment and a posterior segment.

4:35

And the third landmark that's important

4:36

is the intersegmental fissure.

4:38

You can see the intersegmental

4:39

fissure over here, this little black

4:41

structure over here that I'm shading in.

4:43

And as we scroll upwards from this, it's going

4:46

to go up, up, up, and for the most part,

4:49

as it comes up to the liver dome, join with

4:52

the plane where the left hepatic vein runs.

4:55

And that splits the liver or the left

4:57

hepatic lobe into a medial segment over

5:01

here and a lateral segment over here.

5:04

So again, we can follow the intersegmental

5:06

fissure all the way. Again, this is the plane

5:09

of the intersegmental fissure, so it's

5:10

going to be extrapolated all the way to the

5:12

liver surface over here.

5:15

And it's going to be approximately

5:16

in this location, that same plane.

5:19

As we go upwards, at this level,

5:22

the plane is going to lie over here.

5:24

This is where the middle hepatic vein is,

5:26

so this portion is going to be the lateral

5:28

segment of the liver up high over here, and

5:30

a portion of the liver over here is going to

5:32

be the medial segment, and this here is the

5:34

heart that's sort of getting in the way.

5:37

The final landmark that we need to

5:38

look at is the main portal vein.

5:41

So over here is the main portal vein.

5:43

And the main portal vein will split the liver

5:45

into a superior segment and an inferior segment.

5:49

So everything above the main portal

5:51

vein will be considered superior.

5:53

So all this above over here is superior to it.

5:56

And everything below the main

5:57

portal vein will be inferior.

5:59

So once we have those landmarks

6:01

in place, it allows us to describe

6:03

eight segments of the liver.

6:06

The first segment is the caudate lobe,

6:07

and we can see the caudate lobe over

6:09

here just hugging a portion of the IVC.

6:11

So we call that segment

6:12

1, it's the caudate lobe.

6:14

And this often has direct connections to

6:16

the IVC through the hepatic veins that are

6:18

separate from the main hepatic veins.

6:21

And this becomes important in the setting

6:23

of cirrhosis, as there can be morphological

6:25

changes to this particular lobe.

6:28

Then, again, we see a portion of the middle

6:30

hepatic vein over here, and the intersegmental

6:33

fissure. If we extrapolate it upwards,

6:35

we'll be approximately in this location.

6:38

The right hepatic vein will be over here.

6:40

If we look at the left liver, that

6:42

intersegmental fissure will split it into a

6:44

medial segment over here and a lateral segment.

6:47

At this cut, we are above the portal vein, and

6:49

so this will be known as segment number two,

6:51

and this will be known as segment number four A.

6:54

At this level, within the right hepatic

6:57

lobe, anteriorly, so anterior to the right

7:00

hepatic vein, we are above the portal vein.

7:01

And this will be known as segment eight.

7:03

And this will be known as segment 7.

7:06

We're now going to cut to a level that's

7:07

below the level of the main portal vein.

7:10

We can imagine that the middle hepatic

7:12

vein splitting the liver into the right

7:14

and left hepatic lobe runs across a

7:15

plane approximately in this location.

7:17

This is the intersegmental fissure

7:19

that splits the left lobe into a

7:20

medial segment and a lateral segment.

7:23

Below the level of the main portal vein, the

7:25

medial segment becomes known as segment 4B.

7:28

Below the main portal vein, the

7:30

lateral segment becomes segment 3.

7:32

Over here is the right hepatic vein plane.

7:35

Below the main portal vein, the anterior

7:37

aspect of it becomes segment 5, and the

7:39

posterior aspect of it becomes segment 6.

7:43

And we'll revisit this nomenclature as we

7:45

go through a variety of liver lesions that

7:48

we'll see on subsequent case vignettes.