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I'd like to talk briefly about TDL,

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Tumefactive Demyelinating Lesion.

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These are large demyelinating lesions that may or

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may not be associated with multiple sclerosis.

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These are often single lesions,

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although they may be paired.

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Or sometimes you will see

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multiple lesions that are that large.

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They usually do not show very much mass effect,

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but they will have surrounding edema

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and usually open ring enhancement.

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The differential diagnosis when seeing this,

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often, is a neoplasm.

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And if the patient does not have a preexisting

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diagnosis of multiple sclerosis,

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it can indeed be quite confusing.

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What we generally do in this situation is perform

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cerebral blood perfusion scanning sequences.

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The reason is that most neoplasms that have a

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peripheral rim of enhancement are going to be high

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grade astrocytomas and therefore demonstrate

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increased cerebral blood volume

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and cerebral blood flow.

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Contrast that with tumefactive

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demyelinating lesions or TDLs.

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They usually show low cerebral blood

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volume as opposed to the tumors.

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If you perform magnetic resonance spectroscopy on

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these lesions, you may show high choline,

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but that could be present in both multiple sclerosis,

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as well as in neoplasms.

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The NAA depression is greater in tumors

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than it is in multiple sclerosis,

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but there is a fair amount of overlap.

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So, let's see an example in slides of what we're

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talking about with tumefactive demyelinating lesion

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or tumefactive sclerosis.

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So here, we have a patient who has a very large

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lesion in the right hemisphere

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I'm sorry,

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in the left hemisphere,

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and it does seem to be causing some midline shift.

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So there is an element of mass

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effect from left to right.

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However,

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when we look at the post-gadolinium

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axial and coronal scans,

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this is somewhat bizarre because although

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we have a rim of enhancement,

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it is an incomplete rim of enhancement along the

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medial and inferior border.

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That would be very unusual for a neoplasm.

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So, this would be one indicator that you're dealing

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with a tumefactive demyelinating lesion

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as opposed to a high-grade neoplasm.

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The other thing that we would do, obviously,

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is said we would do perfusion-weighted

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imaging and look at CBV or CBF

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and determine that these are decreased in

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tumefactive demyelinating lesion,

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as opposed to GBMs

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or plastic astrocytomas

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where you have increased cerebral blood volume.

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So if you are confused,

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perform that perfusion-weighted sequence

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in order to make this distinction.