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<v ->So here's my chart of differential diagnosis

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and distribution of abnormalities

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that involve the sacroiliac joint.

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Typically, bilateral symmetrical,

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but can be slightly asymmetrical in ankylosing spondylitis.

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In psoriasis, bilateral in my experience,

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asymmetrical more common than symmetrical,

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rarely unilateral.

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In reactive arthritis,

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what we used to call Reiter's syndrome,

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asymmetrical is the dominant pattern.

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I have one or two cases

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where the sacroiliitis was unilateral

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and osteoarthrosis or osteoarthritis bilateral, symmetrical,

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asymmetrical or unilateral disease, so any distribution.

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In gout, rare in the sacroiliac joints,

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bilateral involvement symmetrical or asymmetrical.

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In rheumatoid sacroiliac joint involvement is rare.

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It occurs in late stages of the disease.

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If you see it in my experience

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more often bilateral than unilateral

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but there are other abnormalities that occur

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in that area, producing pain.

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I'll talk about that.

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In hyperparathyroidism bilateral symmetrical related

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to subchondral bone resorption, I'll show you an example

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and in infection, unilateral involvement dominates.

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So that's the key distribution

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of the sacroiliatic joint abnormalities.

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Now, a few words about the diagnostic methods.

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conventional radiography, I always liked, but I gotta agree.

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It's certainly relatively insensitive.

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If you use conventional radiography

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consider AP radiographs with angulation about 20 or 30

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degrees toward the head that can help you.

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It elongates the sacroiliac space.

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My experience CT

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is most sensitive to morphologic abnormalities.

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And by that, I mean, bone sclerosis, bone erosions,

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how wide the joint is how narrow the joint is.

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Is there interarticular bone fusion?

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I think CT is best for that.

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The major value of MR is picking up

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the inflammatory findings associated with sacroiliitis,

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the detection of inflammation.

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Initially marrow edema, secondary fatty deposition.

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I'll show you what that looks like.

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There is a differential diagnosis for that.

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I'll show you a few examples.

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The typical planes that are used

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is a Coronal plane along the long axis

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of the sacrum and then a transverse plane obliquely

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oriented at right angles to this line.

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The Coronal plane shows you pretty nicely

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and elongated view of the sacrum and the ilium.

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And typically we get a T1 rated image

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and then some form of fluid sensitive sequence.

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Again, I'm gonna show you a few cases.

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Many of these come from Marcelo De Abreu

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who was doing a lot of imaging of sacroiliitis.

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But you can see here, I mean, fairly good images.

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I don't feel as comfortable judging the width of the joints.

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I can see some erosive disease here.

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I see some here, but the inflammatory reaction

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the high signal clearly well shown with MR Imaging.

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Here's another example.

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So we can see the marrow edema on the stir sequences.

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We can see areas of low signal reflecting bone sclerosis.

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We see what looks to be some areas

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of joint space narrowing, but again, not well seen.

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I think CT shows that better.

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And the point that has been made

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is that following the active stage,

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following the inflammation

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there is fatty metaplaisia,

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and there is something called backfill.

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And the backfill fills the erosive areas with fat,

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bright on T1, dark on the stir sequence

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and will even include fat extending

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across areas of bone ankylosis of the joint.

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So this is something you can see in the later stages

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of sacroiliitis.

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In this patient with active enthesitis

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going on at the same time.

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With regard to the immature skeleton,

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there are articles that have pointed out

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that there are slivers of fluid that can be seen

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in one or both sacroiliac joints in the child or adolescent.

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And that is not diagnostic of sacroiliitis but here

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at the bottom is a case

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we recently had of proven sacroiliitis.

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All right.

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And you can see that in this

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there are some is a fluid within the sacroiliac joint

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maybe a little bit more fluid than in the normal case

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but this sort of finding creates diagnostic difficulty

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of telling normal from abnormal.

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The differential diagnosis of the sacroiliitis

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that we see in the spondyloarthropathies includes

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the sacroiliac changes that we see following pregnancy.

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And these can probably last three or six months

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you will get edema, you will get bone sclerosis

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you'll get widening initially of the sacroiliac joints.

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So this can certainly simulate sacroiliitis.

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Another condition as you know,

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that involves this area is known as osteitis condensans ilii

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most common in multiparous women, occasionally in women

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who've had no pregnancy, rarely in men.

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The changes are almost isolated to the Ilio side

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of the joint with rare involvement of the sacrum.

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The changes are dominated

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by bone sclerosis and hence the MR

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dominated by low signal.

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So in most cases

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you're not gonna see a dominant signal when you're dealing

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with osteitis condensans ilii.

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And with dealing

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with septic arthritis in the vast majority of cases

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a unilateral distribution is seen.

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And in some cases you're gonna see nearby abscess formation.

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Now, one of the interesting diseases that we deal

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with is hyperparathyroidism.

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So let me just say a couple words about this disease.

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When I was a first year resident, I learned

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about primary and secondary hyperparathyroidism.

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I learned that secondary occurred

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with chronic renal disease.

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And what I needed to look for radiographically

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was on the views of the hands,

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looking for subperiosteal bone resorption

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on the radial aspect of the proximal, middle phalanges.

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and tuftal resorption at the tips of the distal phalanges.

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That's what I learned.

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If that's what you learned, it's inadequate.

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There's a lot more going on

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because hyperparathyroidism produces far more

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than subperiosteal bone resorption.

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It produces subligamentous bone resorption,

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subtendinous bone resorption, subcapsular bone resorption

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and it produces subchondral bone resorption.

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So it's the subchondral bone resorption that leads

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to the widening

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and ill Definition of the sacroiliac joints shown here.

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It leads to the widening of the synthesis pubis shown here.

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It leads to widening of the acromialclavicular

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and sternalclavicular joints it's everywhere.

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So you can get bilateral symmetrical involvement

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of the sacroiliac joints

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with primary and secondary hyperthyroidism.