Interactive Transcript
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Fat within the thecal sac and associated with the
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spinal cord can be due to a variety of etiologies.
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We can have lipomas of the spinal cord generally
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affecting the thoracic region
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or the filum terminale.
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We can also have lipomyelomeningoceles, in which case
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there is fat associated with
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a spinal dysraphic state.
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When we have selected lipomas,
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they're usually intradural
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in location at 60%, 40% may be extradural, and that
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might occur generally down at the lumbosacral
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junction. As we look at this example to the right,
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we see that there is bright signal intensity on
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the T1-weighted scan, which is the same as the
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subcutaneous fat, and on the T2-weighted scan,
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again, the signal intensity of the lesion is the same
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as the subcutaneous fat. Not only that,
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but on this example, we have something called
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the chemical shift artifact. That's
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this bright area at the edge of the lesion in the
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frequency encoded direction, secondary to the
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presence of the fat and the shift that
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that can occur with the frequency.
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So, this is often seen as a bright area in one
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dimension or a darker area in another dimension,
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which is an artifact, which identifies the
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presence of fat. In this situation,
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we we also appear to have an area
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where there is spinal dysraphism.
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So this is more likely to be
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a lipomyelomeningoceles,
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especially since we see that
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the patient has a low cord.
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We also identify that there is a
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meniscus sign of widened CSF,
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identifying that this is indeed in the intradural
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extramedullary compartment.
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Here is another example.
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In this case, we have a patient who has an
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abnormality at the termination of the spinal cord,
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and clearly, there is an area where there
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is high signal in the cord itself.
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So we see bright signal intensity at the termination
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of the spinal cord followed by this large mass.
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Now, this large mass has areas in which
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there is bright signal intensity on T1-weighted scan
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that is showing suppression on the STIR image, and remains
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bright signal intensity on the T2-weighted fast
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spin echo sequence. So this is fat-containing lesion.
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However, there is an additional area here where there is
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intermediate signal intensity on T1-weighted
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scan, which would not be what we would expect for
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fat, and it's bright also on the STIR image,
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so it's not suppressing like fat.
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This is associated with the tethering of the
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cord, which you see at the L4 level.
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So this is more likely to represent
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a dermoid lesion.
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Dermoids are, again, congenital rests
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that are associated with fat and/or soft tissue
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associated, you know, potentially even hair follicles.
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And this lesion is in the congenital category,
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and it may have a sinus tract which leads outside to
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the skin surface, the so-called dermal sinus tract.
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In this case, we don't see the actual tract.
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You'd want to have the clinicians evaluate the
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patient for any abnormalities
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seen on the skin surface.
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So, this is another of the fat-containing
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lesions of the intraspinal canal.
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