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<v ->We're going to finish up in the last few minutes,

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showing you a few other lesions near joints

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that may affect joints.

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So osteoid osteoma,

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every radiologist knows about osteoid osteomas.

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We think of them as cortical lesions

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associated with cortical thickening,

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but a number them, in fact,

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begin in the periosteum and appear to be later

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in within the cortex because the periosteum

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has laid down bone.

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In addition, osteoid osteomas can occur within joints.

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And if they do, as in this example I show you here,

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with involvement of the femoral neck,

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classic appearance of an osteoid osteoma,

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with initis that's lucid with areas of calcification,

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that when they occur within a joint,

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they elicit a synovial inflammatory response,

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producing a synovitus that's said to be lymphofollicular

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in type.

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This is described most commonly in the hip,

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as you're seeing in this case,

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with synovial proliferation in the knee,

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but can be seen in other locations as well.

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Later on, not so common,

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you may see involvement of cartilage

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and bone erosions that relate

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to the abnormal synovitis that has occurred.

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I'm going to show you just a few examples.

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Here's another one.

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And again, I'm going to use the word "favorite".

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This is one of my favorite osteoroid osteomas

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because it is so typical.

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If you see a lesion involving the dorsal aspect

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of the talus right here,

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okay, it is an osteoroid osteoma,

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that's my first diagnosis until I prove it isn't.

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And those can produce a synovitis.

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Here you can see the joint effusion.

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Such a classic location for an osteoroid osteoma.

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Here's another one.

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This one a small osteoid osteoma is associated

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with a small ankle effusion.

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And as you look at these images,

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it points out that although MR is good for osteoid osteoma,

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hopefully showing you the lesion

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but certainly showing you the marrow edema

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CT shows you prettier images.

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And so I think when you're not sure, get the CT.

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Look how nicely you can see the calcified

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or partially calcified initis in this case

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better than on the MR examination.

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Another one, this one in the elbow,

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we can see here with CT and with MR

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the synovitis and joint a fusion within the elbow.