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Dr. P here.

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3 00:00:01,569 --> 00:00:03,630 This 14-year-old individual I'm going to

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present to you fell down about a year ago

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and now feels a palpable lump on the shin.

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We have before you a heavily water-weighted,

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fat-suppressed image on the left,

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a so-called STIR sequence, a T1 coronal.

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Both show this curious oblong area of signal

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change, and then the sagittal or lateral view

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of the lower extremity in which there is a mass

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located within the cortex deep to the periosteum.

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Now if we look at the pulsing

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sequence here, this is a standard T2

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spin echo without fat suppression.

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And we see this gray area that resides

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outside the medullary cavity and in the

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cortical space deep to the periosteal space.

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There really isn't a tremendous differential

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diagnosis here as you might expect.

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This is an osteoid osteoma,

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and this is a spectrum of disease.

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For the osteoid osteoma, when it

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gets to a certain size, say 1.5

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to 2 centimeters in size,

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is considered an osteoblastoma.

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And when they get to 3 centimeters

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in size, they're usually expansile.

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Now these are more common in males, and they

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do like tubular bones, especially long bones.

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The lower extremity more than the upper extremity.

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When they occur in the upper extremity,

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then they tend to involve the elbow.

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And sometimes in the long

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bones, they can be diaphyseal.

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Sometimes they can be at the bone end,

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and this could be particularly tricky.

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A couple of pearls.

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They're very rare in flat bones.

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And they're also very rare in the fibula.

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And when they occur in the spine,

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almost exclusively in the posterior

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column from the pedicle on back.

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Now, one thing they're famous for is producing

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exuberant cortical thickening and/or periostitis.

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And that has occurred here.

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It could be so severe that it can

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result in a saber shin-like appearance,

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or even create an angular

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deformity of the extremity.

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Fortunately, that's not too common.

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Now, when they're purely located in the

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medullary cavity, they produce less reaction,

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and so the amount of edema that you're

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going to see is variable and slim to none.

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This has also been my experience when

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they occur in the intra-articular space.

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They can produce almost no soft tissue reaction,

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or they can produce a horrendous soft

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tissue reaction that even includes synovitis

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and changes in the overlying cartilage.

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The main differential diagnosis

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here is really Brodie's abscess.

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And here are a couple tip-offs to

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the differentiation between the two.

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While osteoid osteoma can have exuberant marrow

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edema, it doesn't have nearly the extent of

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soft tissue edema that a Brodie's abscess

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would have and frequently a Brodie's abscess

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is accompanied by other changes in the bone.

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Whereas the osteoid osteoma kind of sits

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there all by itself with or without edema.

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People with Brodie's abscess usually

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have a reason for having them.

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Whereas osteoid osteoma is just

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kind of a spontaneous lesion.

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The course of osteoid osteoma is different.

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Brodie's abscess patients are sicker.

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They present in a shorter period of time.

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Osteoid osteoma may take as long as a year

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to present, as occurred with this individual.

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Let's look at the axial projection

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and you can see how exuberant the

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periostitis is that has occurred.

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I mean, look at what it's done to the

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cortex and the periosteum. It's made them

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quite thick from anterior to posterior.

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Now, another tip-off, when it's present,

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that's helpful in differentiating Brodie's abscess,

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is on the water-weighted image, the T2,

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and especially the proton density fat suppression,

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the Brodie's abscess is hyperintense.

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Very hyperintense.

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It's liquefacted.

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You know, occasionally you'll get a lot

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of neutrophils aggregating in there,

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and you get a lot of phagocytosis.

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And peroxidase is made that may

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bring the signal down in the middle.

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But that is the exception rather than the rule.

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And the Brodie's abscesses tend to be brighter.

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The edema is more consistent.

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The edema is more extensive.

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The soft tissue edema is more extensive.

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And the history is also quite different.

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Diagnosis, Brodie's abscess of

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the tibia in a young individual.

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Dr. P out.