Case: Abscess on MRI (Case 1)
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So we're still in scenario number five,
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where we have a patient who has a fever and
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a new seizure disorder, and therefore we're
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still worried about infectious etiologies.
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Here we have a patient that, as we scroll up the FLAIR
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scan, we see immediately a large lesion that is
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present in the left frontal lobe with surrounding edema.
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It has sort of a rim of darker signal
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intensity on the FLAIR images that
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is worrisome.
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We note that the patient has adjacent sinusitis
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of the frontal sinus associated with this mass.
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On the diffusion-weighted imaging, we see bright signal
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intensity on the DWI that is also associated with
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bright signal intensity in the medial frontal sinuses.
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Is this T2 shine-through?
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Well, if we go to the ADC map, what we find is
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dark signal intensity, not bright signal intensity,
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suggesting that this does indeed show restricted diffusion.
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This is a pattern that is highly
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suggestive of a brain abscess.
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In this case, what we're seeing as
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the dark signal intensity is not from
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cytotoxic edema and cellular death.
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What we're seeing is the dark
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signal intensity from purulent material.
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Pus in the center of this abscess that is being
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demonstrated on the FLAIR and the diffusion-weighted
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imaging. There's a lot of mass effect in this case.
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Now, when we look at patients who have abscesses
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in the brain, we are usually worried about things
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like septic emboli leading to an abscess.
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But when it's in the periphery of
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the brain, we also worry about.
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Spread from adjacent infections in the
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perinasal sinuses, mastoid air cells,
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middle ear cavity, or a puncture wound into
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the brain—an open fracture, for example.
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So this presence of sinus opacification of the frontal
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sinuses that we're seeing on the FLAIR scan and the
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presence of bright signal intensity in the sinus,
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suggesting purulent material in the medial
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frontal sinuses, is worrisome that this is a spread
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from the sinuses to the brain with an abscess.
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Let's look at the post-gadolinium enhanced scan.
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In fact, we will magnify this.
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So here on the post-gadolinium enhanced scan, as
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we proceed upward immediately, we see that there
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is thickening and abnormal enhancement of the dura.
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So this is inflamed dura.
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We're suggesting that there is a
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meningeal inflammatory process going on.
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We see that the patient has an abscess cavity with
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a nice surrounding enhancing rim, and as we go
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further inferiorly, we again see that inflammation
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of the frontal sinus with subdural enhancement.
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Why is this important?
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Well, we can still treat the abscess and drain
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the abscess 'cause it's got so much mass effect.
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But the underlying condition, which led to
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the abscess, is the frontal sinus, which also
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probably should be addressed at the same
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time, either with functional endoscopic sinus
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surgery or aggressive intravenous antibiotics.
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This—
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Ring-enhancing lesion by itself would lead
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to a differential diagnosis of a high-grade
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astrocytoma or a metastasis, but the presence
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of the restricted diffusion on the ADC map
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is what gives this away as being an abscess.
David M Yousem, MD, MBA
Professor of Radiology, Vice Chairman and Associate Dean
Johns Hopkins University
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