0:01

I'd like to thank the medical illustrators,

0:03

Paul and Lisa,

0:04

here at MRI online for some of these diagrams that are going

0:07

to nicely demonstrate the findings of brain herniation.

0:12

On this initial scan,

0:13

we see an intraparenchymal hematoma,

0:17

which is in the right frontal lobe.

0:22

This is a demonstration where we have

0:24

the falx in the coronal plane.

0:27

And what we see is a portion of the tissue,

0:32

in this case the cingulum.

0:36

The cingulate gyrus

0:40

herniating across midline under the falx.

0:44

This would be, by definition,

0:46

subfalcian herniation or transfalcian herniation,

0:51

where brain tissue, as you see,

0:53

has herniated across the midline.

0:55

So this is above and beyond just midline shift.

0:58

You actually have tissue herniating across the midline.

1:02

In this location.

1:04

We're just above the Sylvian Fissure with

1:06

this intraparenchymal hematoma.

1:08

And so you see that this mass has

1:11

impact on the medial temporal lobe.

1:17

What this illustration is demonstrating is that

1:20

the medial temporal lobe, this being the uncus,

1:25

including the amygdala,

1:27

has shifted over and caused narrowing of the adjacent

1:32

sulcus compared to the contralateral side.

1:36

So by this we would say that there is

1:37

uncal herniation or uncal deviation.

1:41

However,

1:42

because of the size of this intraparenchymal hematoma,

1:45

we note that brain tissue is herniating

1:48

downward across the tentorium.

1:52

This therefore fulfills the downward

1:59

criterion

2:02

for transtentorial uncal herniation.

2:07

So it is crossing the tentorium and going downward.

2:11

So these are all the different qualities and quantities

2:15

and degrees of herniation midline shift leading to,

2:20

in this case, some falsean herniation,

2:23

transfalcian herniation and uncal deviation

2:27

with transtentorial downward herniation.

2:31

This is with this intraparenchymal hematoma.

2:35

This is another nice diagram of the various

2:38

types of herniation. In this situation,

2:40

we have a herniation that I haven't mentioned before,

2:43

and that is the transcranial herniation.

2:46

This is an example where brain tissue is herniating outward

2:52

from the calvarium where there has been an open fracture

2:55

or wide fracture. So this would be our transcranial.

2:59

Herniation very much like a meningoencephalocele,

3:03

if you will.

3:04

For congenital basis we see this large epidural hematoma.

3:10

How do we know it's epidural?

3:12

It's lenticular

3:14

and the dura is displaced inward and we have an associated

3:18

fracture and therefore likely injury

3:21

to the middle meningeal artery.

3:23

This is leading to transtentorial herniation with a facement

3:28

of the adjacent cisterns from uncal

3:32

herniating over and downward.

3:35

And the same collection is leading to our subfalcian

3:39

herniation with a portion of the cingulum herniating

3:44

across midline from left to right.

3:47

In this diagram we see the same epidural hematoma and this

3:54

is demonstrating not just the transtentorial herniation but

3:59

a herniation that was present also in the previous

4:01

diagrams and that is tonsillar herniation.

4:05

By tonsillar herniation we refer to the degree of descent of

4:10

the tonsil through the foramen magnum

4:14

greater than four to 5 mm.

4:17

Now,

4:17

if there is asymmetry from right to left with the side

4:21

showing the hemorrhage having greater downward herniation

4:25

than the other we will describe it

4:28

even if it's less than 5 mm.

4:30

But in this situation what we see is the tonsil herniating

4:34

downward and impacting the lower medulla.

4:37

Usually this occurs with posterior fossa hemorrhages.

4:42

This is a diagram that is a little bit artificial in

4:47

claiming that this epidural hematoma by virtue of its size

4:50

had enough pressure that it led to tonsillar

4:54

herniation through the foramen magnum.

4:56

That would be unusual.

4:58

Here we have a more typical example of tonsillar herniation.

5:03

We have a collection of blood which,

5:07

as you can see is deep to the dura and therefore must be a

5:11

subdural hematoma and it's compressing the cerebellum

5:16

from right to left as well as downward.

5:20

So this is a more typical scenario where we have tonsillar

5:24

herniation downward through the foramen magnum

5:28

and right to left shift of the medulla.

5:32

In this situation, as you can see,

5:35

it may sometimes put pressure on the posterior inferior

5:41

cerebellar artery and potentially lead to its narrowing

5:46

and occlusion which could create an infarction.

5:49

This is a more typical scenario for tonsillar herniation

5:54

than that in which we see a supratentorial collection in

5:59

this. Case the epidural hematoma displacing tissue downward.

6:04

This is an old slide,

6:06

but I do want to emphasize two things

6:10

with regard to this slide.

6:11

We see that the patient has

6:16

abnormality in the midbrain from an acceleration

6:20

deceleration injury and that midbrain has banged up against

6:24

the 1000 and oral edge leading to the midbrain injury.

6:28

However,

6:29

we see findings suggestive of

6:32

an infarction in the left posterior cerebral artery.

6:38

Left and right posterior cerebral artery infarctions are a

6:43

risk factor when one has uncal or transtentorial

6:49

herniation of temporal lobe tissue.

6:51

The posterior cerebral artery may be compressed by the

6:55

downward herniating or medially herniating temporal lobe and

6:59

that can lead to an occlusion of either the right or the

7:04

left or portions of those blood vessels

7:08

and lead to infarction. Again,

7:11

these are all secondary effects of the trauma,

7:15

not the primary injury.

7:17

This is secondary to the herniation that can occur.

7:21

This is another example of a patient who had trauma

7:25

and had secondary infarction. As you can see,

7:29

the patient has left greater than right areas of infarction

7:35

involving the parietal lobe. In this case,

7:38

the abnormality was secondary to involvement of the

7:43

posterior cerebral arteries superior branches

7:47

involving the parietal lobe. However,

7:50

we can see sometimes anterior cerebral artery

7:53

infarctions from the subfalcian herniation

7:58

subfalcian herniation. Remember,

8:01

we have that diagram of the brain in coronal imaging

8:05

with subfalcine herniation of brain tissue.

8:08

This subfalcine herniation can lead to compression of

8:12

anterior cerebral artery and therefore lead to

8:16

an anterior cerebral artery infarction.

8:19

So,

8:19

usually posterior cerebral artery is due

8:22

to uncal or transtentorial herniation.

8:25

Anterior cerebral artery is usually due to subfalcine

8:29

herniation and posterior inferior cerebellar artery

8:34

infarction is usually due to the downward

8:39

tonsillar herniation.