0:01

This was a patient who presented with fever and

0:04

seizure and headache. On the sagittal T1-weighted

0:07

scan, we see the opacification of the paranasal sinuses,

0:11

including the frontal sinus,

0:12

as well as diffused edema in the frontal lobe on the left side.

0:18

You notice that there is a low density,

0:21

low intensity collection here with a peripheral rim of

0:25

hyperintensity. On a T1-weighted scan, that is very

0:29

suspicious for the presence of a potential abscess.

0:32

We can verify the abscess on our DWY and ADC map.

0:37

Here is the ADC map showing dark signal intensity restricted

0:41

diffusion, low ADC surrounded by vasogenic edema.

0:46

This is going to be purulent material in the frontal sinus, in an

0:50

abscess showing marked mass effect on the frontal horns

0:54

of the lateral ventricles and a little

0:56

bit of left to right shift.

0:59

We also see the frontal sinuses here,

1:02

which also show low signal intensity tissue.

1:05

That, again, is going to represent pus.

1:07

It's going to be purulent material from

1:10

infection in the frontal sinuses.

1:12

So let's look at the post-gadolinium enhanced scan.

1:16

We see the peripheral opacification

1:19

of the frontal sinuses.

1:20

We see the peripheral enhancement

1:23

of the frontal lobe abscess.

1:26

We see the meningeal enhancement in close association with

1:32

the frontal sinus, contrast enhancement and osteitis.

1:37

And we see secondary inflammatory change

1:40

in the dura overlying the abscess.

1:44

So this is clearly an emergency for which we would call the

1:50

referring physician and let them know that

1:53

we suspect an abscess in the frontal lobe.

1:56

Why is this not a glioblastoma or a lymphoma?

2:00

That dark signal intensity on the ADC map is pretty

2:03

convincing. And we have the etiology on the films.

2:08

That is the sinusitis affecting the

2:11

frontal and ethmoidal region.

2:13

As you can see here,

2:15

that bright signal intensity that we saw on the T1

2:19

weighted scan, in the periphery of this mass, usually represents

2:24

methemoglobin that has occurred during the

2:26

respiratory burst of the aerobic bacteria.

2:31

So the respiratory burst converts the oxyhemoglobin

2:35

and deoxyhemoglobin to met hemoglobin

2:37

accounting for the bright signal intensity periphery.

2:41

You can see that this is dark in signal

2:42

intensity on the T2-weighted scan.

2:45

So it's likely intracellular methemoglobin, bright on T1,

2:50

dark on T2 in this abscess.

Case: Sinusitis with Frontal Lobe Abscess

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