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Hi, this is Dave Yousem from Johns Hopkins University School of Medicine,

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talking to you today about extradural non degenerative spine lesions.

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We've discussed in the past, intradural intramedullary and intradural extramedullary

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lesions. Now we're going to be talking about those things that compress

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the dura or are outside the dura, and manifest

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pathology in the spinal canal. This is our diagram of the various types

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of spinal lesions. As you recall, the intradural intramedullary lesions

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are characterized by being within the spinal cord, seen as the pink fleshy

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tumor here on the left hand side. And in addition, one identifies narrowing

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of the subarachnoid space at the level of the tumor, which is one

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of the manifestations that we see of intradural intramedullary lesions.

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Contrast that with the intradural extramedullary lesions, a separate topic

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that we've discussed. In intradural extramedullary lesions, you see expansion

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of the subarachnoid space at the level of the tumor, and the cord is

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displaced over. The cord itself is not enlarged, which is what happens with

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intradural intramedullary lesions. We're now on the topic of extradural

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lesions. Extradural lesions, as you can see, lead to narrowing of the subarachnoid

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space as well. So in that case, they are very similar to those

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patients who have intradural intramedullary lesions. The difference is that

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this is usually eccentrically located compared to centrally located within

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the spinal cord. And in general, these lesions are associated, not with

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enlargement of the spinal cord as opposed to intradural intramedullary lesions,

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which expand the spinal cord. I say, "In general", because sometimes,

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extradural lesions cause cord edema by virtue of their compression.

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Once again, we characterize the extradural lesions using the mnemonic that

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I use frequently of vitamin C and D. That being, Vascular,

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Infectious, Traumatic, Acquired, Metabolic, Idiopathic, Neoplastic, Congenital

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and Drugs. Far and away, the most common extradural process that affects

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the spinal canal is degenerative disease, be it osteophytes or disc disease.

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We will have a separate talk on degenerative disease of the spinal canal.

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When we think of non degenerative disease extradural processes, we're usually

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dealing with tumors that affect the bone, infectious etiologies, and traumatic

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etiologies. So let's start with that. Here is an example of a patient

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who has a herniated disc. This is a

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patient whose disc would be characterized as a protrusion. Protrusions are

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separated from extrusions by virtue of their shape. And with a protrusion,

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the base with the parent disc, is wider than any portion of the

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peripheral portion of the disc. So by that I mean that at the

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base with the parent disc, it's wider for the protrusion than it is

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for an extrusion. An extrusion will have a narrow base and then a

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wider peripheral portion. Here, for example, is an extrusion in which one

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sees, particularly on the sagittal scan, that there is a narrow base,

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but the more peripheral portion of the disc is wider. So if we

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look at the base here, and then we look at the width here, it's

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wider in the more distal portion, this would be termed an extrusion.

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In the cervical spine, the most common abnormality that we see are discs

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and osteophytes, and uncovertebral joint degenerative spurs. Here is a cervical

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spine examination, in which the patient has high signal intensity disc material

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as well as dark signal intensity osteophyte, contributing to indentation

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on the fecal sac. The beauty of the gradient echo scan is that

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disc material is bright, whereas bone material is dark, and therefore we

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can say that this entity has a component that is both disc and

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osteophyte. Here is a patient who has ossification of the posterior longitudinal

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ligament. This is another degenerative manifestation and can lead to a myelopathy.

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On the CT scan, you see that there is diffuse hyperdensity along the

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posterior aspect of the vertebral bodies, and this is at multiple levels.

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It may be slightly eccentric. In this case, it's going into the lateral

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recess on the left side. And it's kind of a diffuse process.

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This leads to spinal canal narrowing, spinal stenosis, myelopathy, and requires

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decompressive laminectomies. Here is it demonstrated on MRI scan. So because

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it's bone, it's actually harder to see on the MRI than on the

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CT scan. So it would be manifested as the darker signal intensity tissue.

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So perhaps best seen on the T2 weighted scan, you see this dark

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signal intensity tissue, which is posterior to the vertebral bodies, and

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it represents the ossification of the posterior longitudinal ligament. In

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this example, you do see that the patient is showing high signal intensity

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in the spinal cord from the cord edema and the spinal stenosis.

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Here is a patient in the thoracic spine who has ossification of the

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ligamentum flavum. So OPLL, Ossification of the Posterior Longitudinal Ligament,

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is part of an overall entity where you can have ossification of other

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ligaments, including, posteriorly, the ligamentum flavum. In this situation,

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you have the cord being compressed from posteriorly by those dark signal

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intensity ossified ligamentum flavum.