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We're going to talk now about some of the congenital lesions that can

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occur in the extradural location. Some of these lesions have already been

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described in the Intradural Intramedullary and Intradural Extramedullary

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talks, because they may span from one compartment to the next,

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or may be associated with abnormalities in both compartments. Here for example,

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is a case that I've shown for the Intradural as well as the

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Intradural Extramedullary talk. And now, I'll speak to it as an extradural

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cyst. So this is a patient who has the classic findings of a

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vertebral body segmentation anomaly here at the cervical thoracic junction,

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but has a cyst, which is noted to be intramedullary. We know it's

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intramedullary because we can see the cord come up and then the cord

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widens and the CSF space narrows. However, this lesion goes from being intramedullary

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to being extramedullary in this location. How do we know it's intradural

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but extramedullary? It has widening of the CSF space in this portion.

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So here is the widening of the CSF space as this cystic lesion,

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which was initially intradural intramedullary, grows out of the spinal cord

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at this level and becomes intradural, but extramedullary. And then we can

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also use it for our extradural talk because there is the neurenteric portion

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of it anteriorly, outside of the spinal canal, which also is present.

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So this is a neurenteric cyst, which is associated with vertebral body segmentation

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anomaly as this one arm the disease. Here's another example, once again,

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showing the segmentation anomaly as well as the cyst.

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These may be associated with spinal dysraphism. The next cyst to talk about

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congenitally is the epidermoid cysts. All these are epithelial rest cysts,

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and these are typically found in the lumbar region. They may be associated

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with fat, in which case we would call them dermoid cysts. And dermoid cyst

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are more common in the thoracic region. These are usually intradural extramedullary

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lesions. However, they may have a tract which leads outside the thecal sac,

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even to the skin surface, and that would be your dermal sinus tract.

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50% of patients who have dermal sinus tracts leading to the thecal sac,

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will have within the thecal sac, an epidermoid or a dermoid. And these

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may be associated with a low lying conus.

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This is an example of a fat containing lesion in the lumbosacral region.

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However, there is an extension of this lesion through the spina bifida into

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the extradural compartment. So we note the fat containment here with a widening

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of the CSF showing that it is intradural extramedullary, and pushing the

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spinal cord, which is low lying anteriorly. However, there's a component

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that grows out into these soft tissues. You notice that the deformity here

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in the lower lumbar region, this is not the gluteus and this is

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not the gluteal fold. This is higher up than that because of the

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extension of this fat containing lesion through the spina bifida into the

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subcutaneous fat. Again, this would be a dermoid with dermal sinus tract.

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The epidermoids may be associated with osseous abnormalities, including

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hemivertebra, similar to that with neurenteric cyst or to that dermal sinus

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tract. Remember that epidermoids can be acquired in patients who have been

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instrumented either by anesthesiologists or surgeons or individuals performing

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lumbar punctures. Here, for example, is a patient who has had a previous

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puncture and had a cyst that was associated with the thecal sac and

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the facet joint. What we see is the displacement of the thecal sac anteriorly

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and to the right side. So here's the cyst, and the thecal sac is

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displaced anteriorly and to the right side. Here it is on T1 weighted scans.

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The vast majority of cysts in this location are going to be synovial

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cyst, and synovial cysts are degenerative. They occur typically at L4 5

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level, associated with degenerative changes in the adjacent facet joint.

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And they displace the thecal sac anteriorly. One of the features of a

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synovial cyst, which is very characteristic, is for it to have a dark

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rim around it of hemosiderin. So this was a fooler because even though

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the patient had had multiple lumbar punctures, this ends up being a degenerative

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synovial cyst with hemosiderin deposition in the wall,

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causing epidural compression of the thecal sac anteriorly and to the right

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side. Here is a different patient who had a marker placed on a

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skin dimple. What we see here is a defect in the posterior elements

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associated with a tract leading to that dimpling in the skin.

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So here is the marker, here's the dimpling of the skin.

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Here's the tract. Here's the gap of the spinal dysraphism, and this leads

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to the thecal sac. This is a dermal sinus tract. In this case,

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we did not see an epidermoid or dermoid cyst associated with it,

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but in an approximately 50% of dermal sinus tracts, you may find a cyst

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associated.