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This is a 24-year-old woman who had an

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ankle sprain, and this is an incidentally

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discovered lesion in the neck of the talus.

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On your left is a T2 spin

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echo with fat suppression.

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In the middle is a T1 fat-weighted

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image, and on the right is a T2 spin

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echo image without fat suppression.

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The lesion is lobulated.

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It has a sharp zone of transition.

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There is a hint of a blood-fluid level within it,

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although it's not as expansile as you would expect

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an aneurysmal bone cyst to be, although note that

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aneurysmal bone cysts can be primary or secondary.

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It does tend to snuggle up along the dorsal

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cortex, and there is some irregularity of the

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cortex, so we'll focus on that a little bit.

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There's perhaps atypicality with this lesion,

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but one very important teaching point,

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that maybe has nothing to do with MRI

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at all, is that it's at the bone end.

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So when you have bone end lesions, that

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really narrows your differential diagnosis.

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You know, you gotta start thinking chondroblastoma

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in a younger person with an immature skeleton.

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And the skeleton is mature,

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the growth plates are closed.

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But had the growth plates been open,

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you might think chondroblastoma.

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Chondroblastoma is notable for its thick sclerotic

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border, which this one has a thick, dark border.

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And it exudes edema, which giant

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cell tumor is far less likely to do.

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Anytime you hear the blastoma word, edema on

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MRI is usually pretty prominent in the skeleton.

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You can get secondary ABCs,

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aneurysmal bone cysts, at bone end.

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Uh, you can get intraosseous ganglia, which

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are usually not this big, nowhere near

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this complex with fluid levels inside.

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So, that is not an acceptable

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differential diagnosis.

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You can get arthropathic lesions that

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extend from the joint into the bone

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end and there's a whole host of those.

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Telangiectatic osteogenic sarcoma would be

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another bone end lesion and the list can go

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on and on, but those are some of the main ones.

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And that can be very helpful in

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winnowing the differential diagnosis.

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Just like pure diaphyseal lesions, you know,

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you start to think about, uh, Ewing's and

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osteomyelitis and, uh, what we used to

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call reticulum cell sarcoma of bone or

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lymphoma of bone as primary diaphyseal

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lesions, eosinophilic granuloma of bone.

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So this is a bone tumor.

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It is a mass.

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It is mostly respectful of the cortex,

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although there is a little bit of

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cortical irregularity, dorsally.

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You can see it is contained on the axial T2,

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and I'll bring up the axial T1-weighted image,

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just to show you that indeed it is contained.

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There's a little bit of swelling on top of it,

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and that helps with the differential diagnosis,

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the fact that it does not break out of the bone,

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and that was unclear in the sagittal projection.

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So this is a giant cell

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tumor, as you might expect.

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Now you can get giant cells

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in a whole host of lesions.

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Giant cells are a histologic

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response to any kind of stimulus.

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The average age of onset

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is 33.5

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years of age.

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Women predominate over men.

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They usually present with pain,

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although this patient did not.

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And they involve long tubular bones

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80 percent of the time, the knee and femur

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and tibia about 55, maybe as much as 60

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percent of the time. Only 5 percent of the

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time does it involve the hands and feet.

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When you have a giant cell tumor in the hand,

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then enchondroma is in the differential diagnosis.

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Now, while we

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like to emphasize the epiphyseal

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location of these lesions,

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there has, over the last two decades,

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been increasing recognition, especially

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in the immature skeleton, that giant

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cell tumor will occur metaphyseal.

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And you can get some of these atypical giant cell

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tumors with weird internal signal characteristics,

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growth patterns that approach and even breach the

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cortex and involve the metaphyseal region, and we

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do refer to them as atypical giant cell tumors.

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If you see one in the head and neck

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region, especially around the skull,

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you should think about Paget's disease.

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Now in terms of their radiographic

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appearance, the septa are typically delicate,

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much more delicate than that seen in a

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UBC, and they are pretty delicate here.

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I have not shown you in this series UBC

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with thick septations, and those septations

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in my experience in UBC are the thickest.

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When you have the humeral UBC, you have these

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linear septa as bands of collagenous tissue.

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And the lesions are expansile.

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This one is.

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They tend to be more eccentric

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than some of their brethren.

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For instance, enchondroma, when you're

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looking around the knee, tends to be more

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towards the middle, whereas giant cell tumor

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tends to be more eccentrically positioned.

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And the degree of periosteal

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reaction is either scant or none.

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Let's take a look at this

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lesion a little bit further now.

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Let's look at this axial T2

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with fat suppression again.

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The blood fluid levels conjure up the diagnosis

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of aneurysmal bone cyst, but I just don't think

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it's expansile enough for that specific diagnosis.

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So, in total, uh, this is a

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giant cell tumor of the talus.

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It is a proven case,

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and Dr. P is out on this one next.