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<v ->Okay, we're gonna finish up with some interesting topics,

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things we haven't yet covered.

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And I'm gonna talk a little bit about the next tumor

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or tumor-like lesion

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that may involve the synovium-lined joints,

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and that's an intracapsular chondroma.

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And this is an entity that has a variety

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of names because it's not clearly,

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it's not clear exactly what the pathogenesis is.

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So you will see intracapsular osteochondroma,

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you'll see Hoffa's disease,

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because one of the characteristic locations

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of an intracapsular chondroma is in Hoffa's fat pad.

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You'll see giant solitary synovial chondromatosis

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but the tumor appears to represent a metaplasia

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of the synovial lining into cartilage.

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All right?

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Seen it, in fact,

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most of the cases with the exception, I think,

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of two have occurred in the knee

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and particularly in one particular region of the knee

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which I will show you.

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It's a mass.

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We see it on MR.

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It has inhomogeneous signal intensity.

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So this is the classic appearance and location.

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And I've seen about 10 or 12 of these through my career.

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And at least 9 or 10 of the 12 were exactly

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in this location.

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It looks like a poorly organized second patella

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located beneath the main patella.

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And it is usually located posterior to the patellar tendon,

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but it will in fact,

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displace the patellar tendon in an anterior direction.

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It is calcified and ossified.

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You know, we always try by plain films to say,

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"Is this calcified or is it ossified?"

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Because if we can prove it's ossified,

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the list of differential is much shorter

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than if you think it is calcified.

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And the way you would do that is try to decide,

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"Does this look like trabeculae?

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Is it organized like bone?"

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And I would say in this case,

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this looks more like ossification

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than it does calcification.

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That limits down the differential diagnosis

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and explains why some people call this

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an intracapsular osteochondroma.

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It can erode the patella.

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I don't think we see that in this case.

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It looks inhomogeneous,

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but has areas of fat with MR imaging.

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This is absolutely characteristic.

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And as I show you in the next case you see

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somewhat similar findings, same location,

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displacement of the patellar tendon.

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Note the marrow fat.

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This is related to ossification within this lesion.

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So, this location is really very, very typical.

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This is one of the two cases, in fact,

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that I have seen not involving the knee joint.

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And here the diagnosis is extremely difficult.

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So difficult, this is one of the choices I made

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to include it on the film panel

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of the International Skeletal Society a number of years ago.

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And frankly, as I remember, they didn't do too well

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in trying to diagnose this particular lesion.

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But it looks like the thing we had just saw in the knee.

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It looks ossified, maybe areas of calcification,

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but it looks like a shell of ossification here.

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The main differential would be myositis ossificans

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if we were dealing with a patient

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who had a history of an injury,

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which was not the history in this particular case.

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So, we called this, and histologically was said to be,

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an intracapsular chondroma.