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Case 45 - Frontal Lobe Abscess, Sinusitis

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This was a patient who presented with fever and

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seizure and headache. On the sagittal T1-weighted

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scan, we see the opacification of the paranasal sinuses,

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including the frontal sinus,

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

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You notice that there is a low density,

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low intensity collection here with a peripheral rim of

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

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suspicious for the presence of a potential abscess.

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

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Here is the ADC map showing dark signal intensity restricted

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diffusion, low ADC surrounded by vasogenic edema.

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

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abscess showing marked mass effect on the frontal horns

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of the lateral ventricles and a little

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bit of left to right shift.

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We also see the frontal sinuses here,

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which also show low signal intensity tissue.

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That, again, is going to represent pus.

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It's going to be purulent material from

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infection in the frontal sinuses.

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

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We see the peripheral opacification

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of the frontal sinuses.

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We see the peripheral enhancement

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of the frontal lobe abscess.

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We see the meningeal enhancement in close association with

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the frontal sinus, contrast enhancement and osteitis.

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And we see secondary inflammatory change

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in the dura overlying the abscess.

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

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referring physician and let them know that

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we suspect an abscess in the frontal lobe.

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Why is this not a glioblastoma or a lymphoma?

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That dark signal intensity on the ADC map is pretty

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convincing. And we have the etiology on the films.

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That is the sinusitis affecting the

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frontal and ethmoidal region.

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As you can see here,

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that bright signal intensity that we saw on the T1

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

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methemoglobin that has occurred during the

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respiratory burst of the aerobic bacteria.

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So the respiratory burst converts the oxyhemoglobin

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and deoxyhemoglobin to met hemoglobin

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accounting for the bright signal intensity periphery.

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You can see that this is dark in signal

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intensity on the T2-weighted scan.

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

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dark on T2 in this abscess.

Report

Faculty

David M Yousem, MD, MBA

Professor of Radiology, Vice Chairman and Associate Dean

Johns Hopkins University

Tags

Neuroradiology

Head and Neck

Emergency

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