Interactive Transcript
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So let me remind you that we are dealing with our
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mnemonic of VITAMIN C and D. Vascular, Infectious,
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Traumatic, Acquired, Metabolic, Idiopathic, Neoplastic,
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Congenital and Drugs.
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And I said that the dominant diseases in the intradural
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extramedullary space are the neoplasms.
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And we've just reviewed the nerve sheath tumors,
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the meningiomas, the hemangioblastomas,
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the ependymomas,
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and we also went through subarachnoid seeding.
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We're now at the second category,
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and that is the congenital lesions,
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the C of VITAMIN C and D.
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And these congenital lesions include arachnoid cysts,
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neurenteric cysts, lipomas and epidermoid cysts.
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And we're going to deal with these cysts initially.
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There's a variety of different types of intradural
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cysts. And of these arachnoid cysts,
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whether they are congenital or acquired,
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secondary to instrumentation and adhesions, are generally
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the most common. But you can have other neuroepithelial
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neurenteric and teratogenous cysts.
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Here we have a sagittal T1 and sagittal T2-weighted scan,
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and we see the deviation of the spinal cord
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at approximately the T3 level.
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So counting down 2, 3, 4, 5, 6, 7, 1, 2, 3, 4, 5, 6, 7.
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I guess more like the T6 level,
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where we see this deviation of the spinal cord.
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We also are seeing abnormal signal intensity
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within the spinal cord. However,
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we look at the contour on the T1 and T2-weighted scan,
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and we see this unusual cystic or
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portion of the subarachnoid space,
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which is kind of widened right at the area where the
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cord is deviated posteriorly and shows
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the abnormal signal intensity.
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This is a patient who has an arachnoid cyst, secondary to
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adhesions that is leading to a myelopathy and
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causing the cord deviation posteriorly.
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So this is within the thecal sac,
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little fibrous areas that lead to encystment and
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therefore can lead to a ball valve effect, enlargement
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of the cyst with displacement of the spinal cord.
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So these arachnoid cysts can occur congenitally,
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just like we see them intracranially,
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or they may occur on the basis of trauma, inflammation,
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instrumentation, something that's going to lead to fibrous adhesions
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that will loculate these cerebrospinal fluid.
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They may be under pressure and therefore, as I said,
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in a ball valve phenomenon,
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lead to spinal cord compression.
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Most of these are thoracic and they have signal
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intensity of CSF with no evidence of enhancement.
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In these differential diagnosis would include our
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epidermoid cysts. And for that,
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diffusion weighted imaging is most helpful.
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In diffusion-weighted imaging, the arachnoid cyst
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remains with the same signal intensity as the CSF,
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whereas with epidermoid cysts, it becomes brighter
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in signal intensity on DWI imaging than CSF.
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So we're talking just now about epidermoid cysts.
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These are uncommon lesions.
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They usually are congenital lesions,
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and they are epidermal rests, if you will,
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during embryogenesis.
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They may be associated with osseous abnormalities, as well.
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And they typically occur down in the thoracolumbar
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junction or lumbosacral junction, associated with the
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cauda equina region or the lumbosacral region.
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The epidermoid cyst that can occur in an
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acquired fashion is really uncommon.
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When we think of all of the times that we do lumbar
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punctures for CSF sampling or when
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they do intrathecal anesthesia,
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we're sticking needles into the subarachnoid
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space quite frequently,
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and yet we see epidermoid cysts very uncommonly.
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The theory behind acquired epidermoid cyst is that you
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drag your epidermal cells with your needle into the
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subarachnoid space and theoretically you would have
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a cyst on that basis.
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So it's very uncommon.
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Nonetheless,
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that is another source of acquired epidermoid cysts.
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Epidermoids are more common than dermoids.
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Dermoids are distinguished from epidermoids by the
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presence of fat in association with a lesion,
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and both of them occur in the thoracolumbar region.
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However, the epidermoids are usually lower down in the lumbar,
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the dermoids are usually more at
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the thoracolumbar junction,
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and you may occasionally see a little sinus
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tract coming out to the skin surface,
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a so called dermal sinus tract with an
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intrathecal epidermoid or dermoid.
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Here is an example of an epidermoid cyst.
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We see that this lesion has signal intensity
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characteristics on the T2-weighted scan,
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which simulates subarachnoid space CSF.
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So we're looking at the signal intensity
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here and comparing it to the CSF.
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However, on the T1-weighted scan,
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this lesion is a little bit brighter
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than the subarachnoid space.
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And that might be a clue that indeed this is not
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an arachnoid cyst but an epidermoid cyst,
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because on T1-weighted scans,
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epidermoids are generally just a
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little bit brighter than CSF.
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Here on the axial T2-weighted scan, it looks purely like CSF.
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This was a really difficult case for me,
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and I sort of pondered this extensively.
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Here on the T1-weighted scan, we see a tethered cord.
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The cord is terminating at the L4-L5 level rather than at
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the L1-L2 level where we would normally expect.
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We see that there is an area of bright signal
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intensity on the T1-weighted scan.
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On the STIR image, it's brightened signal intensity.
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And on the post-gad T1-weighted scan,
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there's no real enhancement when you compare
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the signal intensity here to here.
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So my initial thought on this case was,
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this is probably a dermoid.
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It's bright on the T1-weighted scan,
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so it has some fat content with it,
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albeit not the same as the subcutaneous fat,
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so some element of fat within it.
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However, on the STIR image,
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you see that fat is suppressed.
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And if anything, this lesion actually looks brighter.
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So that didn't make sense.
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And on the post-gad fat sat, it also did not suppress.
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So I'm back to saying, all right, well,
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what is bright on T1-weighted scans other than fat?
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Well, you can have melanin,
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but this is a congenital lesion,
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so it's not a metastatic melanoma.
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It could be that there was gad enhancement there.
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That doesn't make sense.
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We know that the gad did not enhance. Hemorrhage,
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could this be a hemorrhagic lesion?
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But, look, there's no evidence of blood products on the
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T2-weighted scan with being so bright.
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The final thing that can cause high signal intensity on
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T1- weighted scan is hyper proteinaceous
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secretions, high protein content.
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And this is what is known as a white dermoid.
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By white, we mean it's white on the T1-weighted scan.
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Most epidermoids are like the case I showed previously,
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where they're dark, almost like CSF.
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This is a white epidermoid secondary
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to the high protein content,
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and that's why it's bright in
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signal intensity on T1.
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It's bright on T2 because of cystic and protein
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content, and it does not show contrast enhacement.
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So an epidermoid, but a white epidermoid,
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an unusual variety of the epidermoids that is bright
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in signal intensity on T1-weighted imaging.
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