0:01

Fever seizure.

0:03

Here we have a patient who has a

0:05

lesion in the left occipital lobe.

0:08

It's kind of irregular on the T2-weighted scan, as

0:11

you can see, and does elicit a lot of vasogenic edema.

0:16

On the diffusion-weighted scan, we see that it's a

0:19

round lesion with high signal intensity on the DWI.

0:24

Is that from T2 shine-through, or is that

0:27

true restricted diffusion?

0:30

We go to the ADC map, we see that it is dark in

0:33

signal intensity, and when you have that rounded lesion

0:37

with restricted diffusion and mass effect in edema,

0:42

it's going to be suggestive of yet another abscess.

0:46

In this case, it is not secondary

0:47

to a patient's infection.

0:49

As far as sinusitis or

0:51

mastoiditis, we're pretty far away.

0:53

This is a primary brain abscess.

0:56

Now, a couple of features to demonstrate here include

1:00

the appearance on the T1-weighted scan, T1 scan.

1:06

You may see high signal intensity

1:09

in the wall of an abscess.

1:12

And let me just magnify this

1:14

and get this centered for you.

1:16

Why would there be bright signal

1:18

intensity in the wall of an abscess?

1:22

This is caused by the respiratory burst of the bacteria.

1:27

That respiratory burst of the bacteria converts

1:30

deoxyhemoglobin to methemoglobin.

1:34

Ah, remember about methemoglobin?

1:36

Methemoglobin has that unique characteristic of

0:01

Fever. Seizure.

0:03

Here we have a patient who has a

0:05

lesion in the left occipital lobe.

0:08

It's kind of irregular on the T2-weighted scan,

0:11

as you can see, and does elicit a lot of vasogenic edema.

0:16

On the diffusion-weighted scan, we see that it's a

0:19

round lesion with high signal intensity on the DWI.

0:24

Is that from T2 shine-through, or is that

0:27

true restricted diffusion?

0:30

We go to the ADC map, we see that it is dark in

0:33

signal intensity, and when you have that rounded lesion

0:37

with restricted diffusion and mass effect in edema,

0:42

it's going to be suggestive of yet another abscess.

0:46

In this case, it is not secondary

0:47

to a patient's infection.

0:49

As far as sinusitis or

0:51

mastoiditis, we're pretty far away.

0:53

This is a primary brain abscess.

0:56

Now, a couple of features to demonstrate here include

1:00

the appearance on the T1-weighted scan, T1 scan.

1:06

You may see high signal intensity

1:09

in the wall of an abscess.

1:12

And let me just magnify this

1:14

and get this centered for you.

1:16

Why would there be bright signal

1:18

intensity in the wall of an abscess?

1:22

This is caused by the respiratory burst of the bacteria.

1:27

That respiratory burst of the bacteria converts

1:30

deoxyhemoglobin to methemoglobin.

1:34

Ah, remember about methemoglobin?

1:36

Methemoglobin has that unique characteristic of

1:39

proton-electron dipole-dipole interaction,

1:43

which causes T1 shortening. T1

1:45

shortening on a T1-weighted scan leads to

1:48

bright signal intensity in the periphery.

1:51

This would be entirely unusual for a patient who

1:56

has a metastasis or a patient who has a high-grade

1:59

astrocytoma, which is in the differential diagnosis for

2:04

ring-enhancing lesions.

2:05

This would not be what we would see in patients who

2:08

have tumor-effective multiple sclerosis, which could

2:12

be another etiology for a ring-enhancing lesion.

2:16

In this situation, that bright signal on the T1

2:19

weighted scan, which you can also see on the FLAIR scan,

2:23

is yet additional evidence that this patient has

2:27

an abscess as the etiology for their abnormality.