0:01

In my introduction to this topic, I talked about

0:04

the clinical scenario of fever and seizures.

0:08

And said that you want to look for findings of

0:11

meningitis, or encephalitis, or meningoencephalitis.

0:15

The truth is that for most patients with meningitis,

0:18

the CT scan and the MRI scans are stone-cold normal.

0:23

You might occasionally see a case where you do see,

0:27

on gadolinium-enhanced imaging, high signal intensity

0:31

of the meninges in a patient who has meningitis.

0:35

And sometimes you may also see high signal intensity

0:38

in the subarachnoid space on the FLAIR scan, where

0:41

you would expect to have suppression of CSF signal.

0:46

Those would be the findings of

0:48

meningitis, but they are rare.

0:50

This is less than 25% of cases.

0:53

So, really, what we're looking for is the brain

0:57

tissue manifestation of the infection—

1:00

that is, the encephalitis of meningoencephalitis.

1:06

Although AIDS is probably the most common thing that

1:09

we see in the brain with respect to infections of the

1:13

brain that may cause a meningoencephalitis, at this

1:17

juncture, that has become a readily treatable disease,

1:21

and you don't see that coming in through the emergency

1:23

department very often as an acute presentation.

1:27

That's in contrast to this case.

1:29

So, here we have a patient who presented with

1:32

fever and seizures and was not immunocompromised.

1:36

And as we look at this patient's scan, what we see is

1:41

high signal intensity that is localized to the peri-

1:45

insular region and lateral temporal lobe, extending

1:49

to involve the cingulum as well as the hippocampus.

1:54

And we notice that this abnormality is a

1:57

bilateral process where the uncus in the

2:00

medial temporal lobe on the left side is also involved.

2:05

When you look at the diffusion-weighted imaging,

2:08

the patient has some abnormalities here,

2:10

which represent hemorrhages, but there is

2:13

very slight high signal intensity on the DWI

2:16

in the subinsular region on the right side.

2:20

Is that T2 shine-through from this

2:24

abnormality, or is this cytotoxic edema?

2:27

Remember, T2 shine-through is vasogenic edema.

2:30

For that, we need to look at the ADC map.

2:33

We look on the ADC map, and what we see is that

2:36

this signal intensity is actually bright here.

2:40

So this is not infarcted tissue or cytotoxic edema.

2:44

This is T2 shine-through of vasogenic edema in this

2:48

patient who has a bilateral temporal lobe process.

2:53

I would also point out that the

2:56

subarachnoid space of this patient shows

3:00

high signal intensity in the sulci.

3:03

You can see this pretty nicely right here.

3:06

Bright signal intensity over

3:08

the right inferior frontal lobe.

3:10

Contrast that with the normal CSF over this way,

3:14

and going into the subarachnoid space here.

3:16

Here's normal, dark signal on FLAIR.

3:19

Here's bright signal on FLAIR.

3:20

That means that there's an

3:21

abnormality in the subarachnoid space.

3:24

This is indeed an example of a

3:27

patient who had meningoencephalitis.

3:30

Of the cases of meningoencephalitis that favor the

3:35

temporal lobe, the peri-insular region, and the

3:37

cingulum, herpes encephalitis—and we're talking

3:41

about herpes type 1 encephalitis—is the most common.

3:46

Hemorrhage may occur in herpes meningoencephalitis

3:50

in approximately 30% of individuals.

3:54

It may or may not show cytotoxic

3:57

edema on the diffusion-weighted imaging.

3:59

If you look at the patient's post-gadolinium

4:01

enhanced scan, you may or may not see enhancement.

4:05

If you do see enhancement, as in this case, it usually

4:09

means a more fulminant variety or more fulminant

4:12

case of herpes encephalitis because enhancement

4:16

is only in about 30% of cases as well.

4:20

In this case, you see enhancement along the

4:23

walls of the Sylvian fissure and into this

4:26

periinsular region, as well as the diffuse

4:31

enhancement of the meninges bilaterally.

4:34

The patient has already had a shunt catheter placed here.

4:38

So this is a patient who has pretty

4:41

fulminant herpes encephalitis.

4:43

What are the features?

4:45

Bilateral involvement,

4:47

peri-insular, medial, hippocampal.

4:50

Temporal lobe involvement, hemorrhage in 30%,

4:54

enhancement in about 30%, cingulum involvement—

4:58

these are all part of the limbic system.

5:00

Remember, the cingulum is this tissue

5:03

that is on either side of the genu of the

5:06

corpus callosum, extending upward, and then

5:09

the posterior cingulum coming backwards.

5:11

So, herpes encephalitis.