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Chondroblastoma in the Knee

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I want to end my discussion of cartilage and

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cartilage-based lesions by showing you a couple

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of classic benign-appearing cartilage tumors.

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This is probably the most

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common that you're going to see.

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We're looking at a frontal and lateral view of

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the knee in an 11-year-old boy with knee pain.

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What can we see?

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We can see, first of all, that

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the physes are still open.

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So that's one of the things I want

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to drive home, is always look to

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see what the physes are doing.

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That's very important in

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the pediatric population.

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Is it very wide?

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Is it about to fuse?

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Has it fused?

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And it's important to include

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that in your dictation.

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It tells the clinician where in the

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maturation process this person is, and it

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may affect the way they provide treatment.

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So, growth plates are widely open.

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And what we notice is this lucent lesion here,

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centered in the epiphysis, may be extending

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down a little bit into the metaphysis.

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So, I want to show you, if I can, with a pen,

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what the margins of this lesion look like.

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Let's do it on the lateral view first,

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because I think it's the most difficult area.

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Here is the top margin, and

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it goes something like this.

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It's going to go through your physis,

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and here, it's a little difficult

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to see, but I think this is good.

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where we're looking at the lesion.

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And I'm not sure what's happening

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at the periphery, so I'm going

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to go from here, like this.

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So I believe the lesion

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looks something like this.

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And of course on the frontal,

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it's a little easier to draw.

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I'm just going to go like this, and it comes up

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all the way up to the surface, comes here, goes

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down like this, and looks something like that.

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That's what I think the lesion looks like.

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Some keywords you want to use, you

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want to say it's relatively well

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marginated in most of what I can see.

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It's centered in the epiphysis with maybe slight

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extension into the metaphysis, and it approaches

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or abuts the chondral or the articular surface.

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And it's eccentric, meaning that it's

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not completely centered; it's slightly

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eccentric towards the medial side.

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So, what the margins are doing is involving

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the growth plate, where it's located.

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And if it abuts the articular surface,

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and is it centered or eccentric?

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So those are the things that you want

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to talk about when you describe a lucent

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lesion in, um, any part of the bone.

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Lateral view, it's a little bit

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more difficult to see, but I think

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you can appreciate it right here.

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It's like this.

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You also want to mention if

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there's any periosteal reaction

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or pathological fractures.

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I don't think this person has it,

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although I'm unsure here at the surface.

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Uh, but.

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I don't think this person has a fracture, but we

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have a well-demarcated, lucent lesion, uh, which

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tells me that it's probably something benign.

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So with that in mind, MR was obtained to

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further characterize what this lesion is.

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We're going to show you a couple of

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MRs, a couple of sequences: first a

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coronal fat-suppressed fluid-sensitive

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sequence, and then a sagittal.

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We have several other sequences: T1,

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post-contrast images available to you

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through your PAC system, but these

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are illustrative of what this lesion is.

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First of all, we see that it's actually

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multiple rounded areas of fluid signal.

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Here, here, here.

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Uh, there's even perhaps a

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little air-fluid level, right?

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So, some people may think, oh, air-fluid

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levels, rounded lucency, aneurysmal bone cyst.

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And you wouldn't be wrong in considering that.

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But other factors have to be considered.

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Its location.

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In the epiphysis mainly, with some, there

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really is some extension into the metaphysis.

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Again, there is no periosteal reaction,

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and there is quite a bit of edema, if you

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look over here in the epiphysis, right?

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So, if you see a well-defined lesion

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in the epiphysis with marrow edema,

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the first three things on your

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differential should be chondroblastoma,

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chondroblastoma, chondroblastoma.

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This is chondroblastoma until proven otherwise.

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Yes, there are some features of aneurysmal

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bone cyst, the fact that you have a couple

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of fluid-fluid levels, and that should be

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on your differential, maybe a little lower,

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but if you see an epiphyseal lesion in a

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skeletally immature person, and it's well

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defined, and there is surrounding edema, it's

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going to be chondroblastoma most of the time.

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This is very, very unlikely to be malignant.

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So, edema, that's the key thing.

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You want to look for edema.

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I have not seen a single case of

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chondroblastoma without surrounding bony edema.

Report

Faculty

Mahesh Thapa, MD, MEd, FAAP

Division Chief of Musculoskeletal Imaging, and Director of Diagnostic Imaging Professor

Seattle Children's & University of Washington

Tags

X-Ray (Plain Films)

Pediatrics

Non-infectious Inflammatory

Neoplastic

Musculoskeletal (MSK)

MRI

Idiopathic

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