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49-year-old male with

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"osteoarthritis and knee pain."

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Let's take a look at how

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the T2 weighted image can hurt you.

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Let's begin in the center

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with a proton density fat suppression.

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Now, a mistake was made here.

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If you look in the upper left hand corner at the TE,

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the TE is 15.

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That is too short a TE for a proton density

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fat suppression, spurse bearer special.

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The TE should hover around 30 to 50.

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That's going to give you your maximum intensity

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for water signal intensity.

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So you're actually,

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in some ways,

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dulling the contrast resolution

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by making the TE too short.

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Okay, let's set that aside.

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That being said,

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what is all this dark stuff in the joint?

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I mean, it's everywhere.

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Let's scroll it.

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And some of it is tumefactive.

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In other words, it exhibits mass effect.

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And unlike, say, synovial chondromatosis,

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where the abnormalities,

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kind of round and repetitive,

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they all have about the same size.

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It's almost like pebbles or stones.

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This is more mass like,

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more ill-defined,

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more random shapes, bulkier.

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And it happens to be diffused

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in multiple compartments.

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This is what pigmented

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villonodular synovitis looks like.

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And the knee is the most common joint to have it.

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Now, when it gets really big in joints

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with smaller capsules,

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like the hip, the elbow, the ankle,

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the ones with the three smallest capsules,

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you're going to see pressure erosions.

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The knee happens to have a nice floppy capsule,

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so not too many pressure erosions.

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But after all that being said,

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that's not why I'm showing the case.

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It just happens to be a crazy good case.

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Look at the T1 weighted image,

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the siderotic character of the abnormality,

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not really easy to appreciate.

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What might you look for?

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A little bit of methemoglobin staining,

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a lot of mass effect.

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The bulk of the PVNS is so great

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that even on the T1,

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some dark signal is present and abides.

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So even on the T1,

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if you just got showed this,

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you would be suspicious of the diagnosis.

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Now we flop over to the T2

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and, wow,

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everything is just black.

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All the structures,

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all the internal structures are buried in a

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morass of villonodular siderotic tissue.

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So, what's a mother to do?

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Well, you could go to a T2 fast spin echo,

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and this has less of a susceptibility distortion effect

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with metal and iron and siderosis,

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but unfortunately, we don't have one.

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So, what's the next best choice?

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T1.

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Let's go over to the T1 and check out some

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of our internal structures.

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We've got a posterior cruciate ligament,

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and we have an anterior cruciate ligament,

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except that the anterior cruciate ligament

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is not coursing in the right direction.

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It should be going a little bit higher

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following blumensaat line.

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It should insert over here.

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It's going more towards, say,

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North Carolina than Maine,

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more towards Brisbane than Cairns.

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In other words, it's not headed northeast enough.

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The axis is off,

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and we don't see it connect to bone.

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There's a gap. We never,

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ever see it connect to bone.

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What does it connect to?

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The PCL.

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Now, if you tried to make that diagnosis

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on the T2

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with all the siderosis and the dark ligament,

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it's impossible.

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Your confidence level would be extremely low.

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How about on the PD?

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Maybe on the PD.

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You know,

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because there's some siderotic material

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that's stringing along the ACL.

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And you can appreciate that the axis is too low.

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It's too mid.

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Should be higher,

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coming right up to this point.

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So this is an example where the T2,

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while assisting you with the diagnosis of PVNS,

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is not your friend in this scarred siderotic ACL tear.

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Just for giggles,

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let's put up some coronals

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and see what else we have,

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because that's the essence of the case.

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Let's look at these two coronals right here

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in the middle and the right,

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PD spur.

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This time,

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they did choose the correct TE,

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TE 50.

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So that gives you some heavy water weighting,

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showing you an effusion and some chondromalacia

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a large pseudocyst,

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or penetrating erosion at the base of the PCL,

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really not adding a lot to the character

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and the diagnosis of the case.

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The meniscus on the lateral side is pseudo-extruded.

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It's hypofunctioning.

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It's not really adding to the patient's support

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because the patient's lying on their back.

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So, it isn't really supporting

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the femur and the tibia.

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It also has a tear in it.

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That's not really extremely relevant to the case.

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And then,

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let's just look at the bulk of the

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PVNS on the axial T2 weighted image,

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and it is tremendous.

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So the take-home message,

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and by the way, there's a bursal cyst in the back.

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The take home message is,

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when you have chronicity, siderotic change,

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fibrotic change, scarring in an ACL,

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or any ligamentous injury in the body,

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you cannot rely on the T2 spin echo

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or fast spin echo for a diagnosis.

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Let's move on, shall we?