Interactive Transcript
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Here is another patient who had a thoracic
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myelopathy. On the sagittal T1-weighted,
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sagittal T2-weighted and post-gad
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T1-weighted scans that are depicted here,
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we see deviation of the spinal cord anteriorly
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at the T6 and T7 level.
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This is best seen on the T2-weighted scan.
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Now, we're not seeing any of the border
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of an arachnoid cyst,
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but we do see that widening of the
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CSF space at the same level.
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So our differential diagnosis here includes an
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acquired arachnoid cyst, leading
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to the spinal cord deviation.
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And we want to look on the axial scans to see
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whether there is cord signal abnormality
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that might account for that myelopathy.
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Let's look at the axial scans through
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the region of interest.
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So what we see is that there is indeed
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deviation of the spinal cord anteriorly,
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and we also see a small amount
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of central high signal intensity within the spinal cord.
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So this may account for the patient's
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myelopathy. This, however,
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is not an example of an arachnoid cyst.
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This is what is known as transdural herniation
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of the spinal cord and this is best
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depicted on a CT myelogram.
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So let's go to the CT myelogram that was
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performed, as well. Here is the CT myelogram,
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which I will magnify for you and show the same
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element of deviation of the spinal cord
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anteriorly with widening of
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the subarachnoid space.
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On the axial scans, you'll see that the spinal
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cord is unusually deviated anteriorly and you
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may get the sense that there is a portion of
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the spinal cord which may even
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be outside the thecal sac.
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That is the term that is used with transdural
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herniation of the spinal cord.
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It is a cause of a thoracic myelopathy,
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or is the cause of a myelopathy, is secondary
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to a rent in the thecal sac with a spinal
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cord herniating through it.
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And that rent in the thecal sac most commonly
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is secondary to either trauma or degenerative disease.
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In this case, there is just mild degenerative changes.
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But that must have, as you can see here,
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a small osteophyte,
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which may have led to the tearing of the dura
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and allowing the spinal cord to herniate
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through the dura into the extradural space and
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leading to an appearance that
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simulated an arachnoid cyst.
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So this is what's known as TDH, transdural
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herniation of the spinal cord.
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