0:01

Here we have another teenager with knee pain.

0:05

I think you can see already that the

0:08

abnormality is centered around the patella.

0:11

Here is our fat-suppressed, fluid-sensitive

0:13

sequence on the left, T1 sequence on the right,

0:17

and you can notice that the entire patella

0:20

is edematous and it's actually irregular.

0:23

There's an area of central well-defined

0:27

bright signals surrounded by low signal.

0:30

It is actually destruction of the anterior

0:34

cortex, such that fluid is present between

0:37

the soft tissues and the bone itself, or the

0:41

patellar tendon as it drapes across the patella.

0:45

And this is likely in a prepatellar bursa.

0:48

So, a bursitis has developed in this patient.

0:51

Not only that, but the edema has

0:54

also extended into Hoffa's fat pad over here.

0:57

Here's the lateral aspect of Hoffa's fat

0:58

pad, and you notice that it's very edematous.

1:01

So this tells us that this is probably

1:03

going to be very painful because it's

1:05

eliciting an inflammatory reaction.

1:08

On the T1-weighted sequence, we can see

1:10

that, in fact, yes, there is an abnormality

1:12

here extending into the patellar tendon.

1:15

There is indistinctness and blurriness of

1:19

the cortical margin of the anterior patella.

1:22

And yes, there is.

1:23

There is Hoffa's fat pad edema as seen by the

1:27

linear and smudgy low signal in the fat.

1:31

Is there a joint effusion?

1:33

Remarkably, there actually isn't

1:34

a very lot of joint effusion.

1:36

So this patient was treated for a long time

1:39

as psoriatic arthritis because the patient

1:41

had a history of joint problems and such,

1:44

but this lesion actually never got better.

1:46

And finally it was biopsied

1:48

because they thought, well maybe

1:50

this isn't psoriatic arthritis.

1:51

And this came out to be osteoblastoma,

1:55

which is a benign bone tumor.

1:57

You may or may not know, osteoblastomas

2:00

are the smaller cousins, or actually, sorry,

2:03

they're the bigger cousins of osteoid osteomas.

2:06

There are slight differences, however.

2:09

For example, typically, osteoid osteomas

2:13

do better with NSAID treatments, but

2:16

osteoblastomas don't, and frequently

2:20

these lesions have to be excised and

2:23

removed for symptoms to go away.

2:26

And so, there's no pathognomonic finding

2:29

here that says this is osteoblastoma, but if

2:32

you see a lesion in the patella, there are a

2:36

couple of things you should be thinking of.

2:37

Remember the patella is what we call

2:40

an epiphyseal-type bone.

2:43

So, such as the tarsal bones,

2:46

carpal bones, and the patella.

2:49

So what does that mean to

2:50

be an epiphyseal equivalent?

2:52

It means that lesions that occur in

2:54

the epiphysis also have a propensity

2:57

to occur in these epiphyseal

2:59

equivalent bones such as the patella.

3:01

And so when you see something like

3:03

this, osteoblastoma is something you

3:05

should think about and chondroblastoma.

3:09

If you remember from one of the prior

3:10

vignettes, we know that chondroblastoma

3:12

typically occurs in the epiphysis.

3:14

So if I see a lesion here, chondroblastoma

3:17

is another thing to consider.

3:18

Infection is also on the differential.

3:20

You know, when something is this

3:21

aggressive, with cortical destruction,

3:24

always think about infection.

3:25

Eosinophilic granuloma is another

3:27

possibility because it can affect anywhere.

3:30

But the trick is to know that

3:33

there are not a lot of malignant

3:35

processes that arise in the patella.

3:38

Could this be an early manifestation

3:40

of Ewing's or osteosarcoma?

3:42

Sure, it could be.

3:43

But the likelihood is low.

3:45

Uh, ultimately it requires biopsy and this ended

3:48

up being an osteoblastoma, a benign bone lesion.