Interactive Transcript
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When we think about the concept of intradural
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metastases, we really have the possibility of lesions
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that are within the subarachnoid space, or so-called
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intradural extramedullary lesions, and we have
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those that are within the spinal cord,
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the intradural intramedullary lesions.
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For the pediatric age group,
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the most common primary tumors that lead to intradural
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metastases are the medulloblastoma, ependymoma,
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and pineal region tumors, and other primitive
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neuroectodermal tumors.
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These are central nervous system tumors that shed
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cells into the subarachnoid space and lead to
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metastases within the subarachnoid space
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in the intradural extramedullary compartment.
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Of these, medulloblastoma is most common.
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However, if you look at all patients who have positive
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CSF cytology for tumors, it turns out that
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the leukemia lymphoma group, again,
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which is not a primary CNS tumor,
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but a hematologic tumor,
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leukemia has the highest rate of positive CSF
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cytology for subarachnoid seeding. Unfortunately,
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these cells are small in size,
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and they usually do not demonstrate
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positive findings on MRI scans.
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So it's pretty rare that we see actual enhancing
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subarachnoid seeds of leukemia. On the other hand,
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the CSF cytology shows those cells,
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and the patient is generally treated with
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intrathecal methotrexate for leukemic subarachnoid
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seeding. Let's move to the adult age group.
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In the adult age group,
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we see both intramedullary, as well as extramedullary
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intradural metastases.
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So we do see subarachnoid seeding
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generally with primary CNS
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tumors such as glioblastomas, or some of
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the more rare adult medulloblastomas.
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We also see subarachnoid seeding
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in patients with lymphoma.
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Once again, it is more common to have a positive CSF
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cytology for cells than it is to have a positive
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enhancing MRI scan in lymphoma.
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However,
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in adults we also do see hematologic spread of
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tumors to the spinal cord from primary tumors
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such as lung, breast and gastric cancer.
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So these are actual tumor deposits in the spinal
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cord from these extra CNS primary tumors.
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So a difference between pediatric population
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and the adult age group.
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When we see intradural subarachnoid seeds,
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the lumbar region is the most common locations.
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It's felt to be due to gravity since
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we're upright most of the time,
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those cells are going to gravitate
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to the bottom of the thecal sac,
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which is where we will see subarachnoid seeding from
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things like in the children, the medulloblastomas,
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in the adults, maybe the glioblastomas.
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There are different routes of spread for
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the tumor to get to this location.
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Most people feel it's direct CSF shedding of cells
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into the CSF, so direct CSF extension.
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But occasionally, you will have lesions that
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infiltrate the choroid plexus that can therefore, from
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the choroid plexus, shed cells into the
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subarachnoid space. And rarely,
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we think it's a primary hematogenous metastasis,
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that's much more likely with non-CNS primary tumors.
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The key here is post-gadolinium-enhanced imaging,
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because very frequently, these are invisible
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on pre-gad T1-weighted or T2-weighted scans.
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And of course, when one sees them,
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you would recommend correlation or
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corroboration with CSF cytology.
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Here's a patient who had a recurrent ependymoma,
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and these are post-gadolinium-enhanced
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sagittal and axial scans.
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We see within the subarachnoid space that there are
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areas of contrast enhancement that are multiple in
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location and some of them affecting the upper
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cauda equina nerve roots. On the axial scans,
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you'll see the appearance of the seeding on the surface
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of the spinal cord within the subarachnoid space
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posteriorly located. Again, posteriorly
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located in part because we are on our
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back sleeping in many situations.
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Here we are at the cauda equina nerve roots,
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and we see avid enhancement of some of the anterior
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nerve roots of the cauda equina, which were
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verified on the sagittal scan, as well.
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This is an example of subarachnoid seeding
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to the thoracic, as well as lumbar region,
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in a patient who has recurrent ependymoma.
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This is another example of subarachnoid seeding.
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In this case, the patient had a small cell lung cancer.
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And when we look at the post-gadolinium enhanced
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scans in the center and to the right,
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we see contrast enhancement on the surface of the
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conus medullaris, as well as in
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the cauda equina nerve roots.
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So here is the enhancement on the
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surface of the spinal cord,
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this bright stuff, and then coming
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into the cauda equina nerve roots.
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And some of the cauda equina nerve roots are a little
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bit too thick and showing some contrast enhancement
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when you compare it with the pre-contrast scan.
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Now, in this situation of a patient who has a lung cancer
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that appears to be demonstrating
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subarachnoid seeding,
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I would be looking for primary parenchymal lesions,
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either in the brain that may be
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the source of the seeding,
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or in the spinal cord that are shedding
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cells into the subarachnoid space.
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So, it is worthwhile to examine the entire central
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nervous system axis in a patient who has something
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like a lung cancer, because it's unusual for it to
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just appear only in the subarachnoid space.
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Again,
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that would be one of these unusual hematogenous
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spreads from a lung cancer to
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the subarachnoid space.
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Here is a post-myelogram CT scan.
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On this post-myelogram CT scan where
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we're seeing the lumbar spine,
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you're seeing a lot of contrast accumulating
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at the C1 and C2 levels.
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Well, let me count it.
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This is S1 showing a bone metastasis,
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L5, L4, L3, L2, L1.
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So we have contrast at the L2 and L4 level,
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but we are not seeing the contrast above
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L1 and below L4.
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Why is that?
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Well, you get a sense that the reason is because
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there are masses in the subarachnoid space,
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and in the L1 level, it's massive involvement.
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Down at the L4 level,
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you'll see that this is also going to be massive tumor
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involvement in a patient who had severe subarachnoid
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shedding and seeding of cancer
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in another example of a patient who had,
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in this case, melanoma with subarachnoid seeding.
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And this is the demonstration of the lesion intrathecal.
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So, intradural extramedullary,
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particularly down in the lumbar region.
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Intradural extramedullary seeding
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from metastatic melanoma.
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Here's a patient who is an 18-year-old female
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who had a previous resection of a medulloblastoma.
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You recall that medulloblastoma is one of the
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most common of the posterior fossa masses.
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And looking at the cerebellum,
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we see that there is post-resection
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cystic cavity from the medulloblastoma resection.
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On the post-gadolinium-enhanced scans, however,
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we see that there are areas of contrast enhancement
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on the surface of the spinal cord,
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both in the cervical region, as well as
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extending to the thoracic region.
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This is subarachnoid seeding of a medulloblastoma.
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Medulloblastoma has a one third rate of
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subarachnoid seeding at presentation,
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and therefore,
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whenever we identify a medullobastoma,
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we have to scan the entire CNS axis with gadolinium
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to identify or exclude subarachnoid seeding.
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In many cases,
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this patient will again be treated with intrathecal
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chemotherapy for those seeds. Now,
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I want to just note that in some cases with
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the aggressive medulloblastoma forms,
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you may see actual intramedullary
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extension of the subarachnoid seed,
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which I believe is what is going on right here.
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