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<v ->So, let's start with gout.

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Gout is a clinical diagnosis.

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The clinician should know the diagnosis

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when he or she asks you to evaluate that particular patient,

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but the clinician may not share that knowledge with you

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on the request slip.

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So you have to learn some of the imaging features of gout.

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How does gout occur?

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Well, as you know,

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the crystals are carried to the synovial membrane

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via the bloodstream,

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and once they are in the synovial membrane,

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at times, they will evoke an inflammatory response,

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which leads to synovitis, synovial thickening,

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and enlarging joint fusion.

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At certain times during an attack of gout,

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the crystals will be released into the joint lumen.

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Owing to the succulence of articular cartilage,

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those crystals will penetrate the cartilage

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and reach the subchondral bone.

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Now, as you look at my drawing on the right,

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I would call your attention to the fact

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that adjacent to the area of cartilage and bone abnormality

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is relatively normal articular cartilage.

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That accounts for one of the morphologic features of gout,

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different from rheumatoid arthritis,

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joint erosions with relative preservation of joint space.

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I'm showing you such a case

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at the tarsometatarsal joint of the great toe,

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more about that localization in a minute or so.

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Subsequently, tumors may be deposited around the bone,

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and over a period of time,

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slowly lead to erosions, beginning on the bone surface.

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Because the erosions take place slowly,

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there's often a sclerotic margin around them,

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and there's a very characteristic pattern

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of bone proliferation that develops

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at the margin of that eccentric erosion

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described by a famous radiologist, Bill Martel, decades ago.

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This is called the overhanging margin or ledge of bone.

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So here's an example on your left

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of what the overhanging margin or ledge of bone looks like,

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thin, linear, or curvilinear,

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growing around the adjacent gouty deposit or tophus.

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It differs from the whiskering we spoke about yesterday,

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when we discussed the spondyl arthropathies,

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particularly, when we discussed psoriasis,

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ill defined bone proliferation, shown by the white arrows,

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related to an enthesitis

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at the site of attachment of the joint capsule.

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And indeed, the overhanging margin or ledge

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differs from the gull wing appearance,

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that indeed we can see with ordinary osteoarthrosis

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or inflammatory osteoarthritis,

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as shown in the image on your right.

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Here we can see the kind of wing-like appearance

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of the peripheral bone proliferation,

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and you can appreciate it looks like gull wings

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and note the central collapse of bone,

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characteristic of inflammatory osteoarthritis.

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Now we recognize certainly,

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that the classic target site of gout

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is the first metatarsophalangeal joint,

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and indeed, typically on conventional radiographs,

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we see erosions dominating in the metatarsal head

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and in the proximal phalanx.

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But sometimes, gout can, in fact,

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attack initially a sesamoid, and in rare cases,

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stay isolated to a sesamoid.

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Here, a case given to me by Marcelo,

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showing you involvement with gout,

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mainly of the medial sesamoid.

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There is some involvement

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of the metatarsal head and phalanx as well,

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but involvement of sesamoid certainly can occur.

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So this is a classic target site that you should remember.

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To that list of target sites that you should remember

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is the tarsometatarsal joint.

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It is interesting why and how often

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gout will localize in this particular area,

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particularly, in the great toe,

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but also in the other metatarsals as well.

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You can see that nicely here by MR and by CT,

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so always think of gout

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with involvement of the tarsometatarsal joints

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and even the intertarsal joints,

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even if the first metatarsophalangeal joint

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is not involved.

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Now, although we think of a gout as a systemic process,

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sometimes it begins by localizing within a single joint.

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And although that joint typically is somewhere in the foot,

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occasionally it's elsewhere, for example, in the knee.

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Gout of the knee has a predilection

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for certain regions of that articulation.

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One of those regions is a peri or pericruciate region.

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Here, on the three MR images,

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you can see and appreciate

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that there's extensive tophaceous deposits

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with increased radiodensity,

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some of which relates probably to secondary calcification.

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Atop those images,

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I show you two sagittal sections

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from one of the cadavers that we had

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in a person who had gout during life.

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And you can see the deposition of those crystals of gout,

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appearing as chalk-like, white-like areas

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in and around the cruciate ligaments.

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So when you see peri or pericruciate deposits,

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gout is a very good diagnosis.

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The other area, for which gout has a predilection,

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is the popliteus tendon.

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The arrows here point to, on the MR,

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point to the involvement of the popliteus tendon

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at its attachment to the distal portion of the femur.

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And this is a sagittal section

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through that same cadaver with gout.

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Here is the popliteal groove in the femur,

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and all of this is tophaceous material

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around the cruciates and about the popliteus tendon.

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So keep this location in mind as well.

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And one of the interesting things is,

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not only did you get these urate deposits,

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as in this case about the cruciates

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and in the popliteus tendon,

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but those pericruciate deposits may then involve the bone.

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And it has a very characteristic pattern,

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typically in the central aspect

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of the proximal portion of the tibia,

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kind of a lake-like appearance

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with collections of intermediate to high signal,

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as shown in this case.

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The cadaveric image on your left

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indicates intraosseous penetration of the gouty crystals.

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Gout loves the extensor mechanism,

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be it the quadriceps tendon, or as shown here,

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the patella tendon, or sometimes, the patella itself.

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So whenever you see a mass-like lesion

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in this particular area, think of gout.

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And as is typical of gout,

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even on the fluid sensitive sequences,

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low signal intensity is seen,

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either diffusely or in portions, of the gouty mass.

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Gout rarely involves the axial skeleton.

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I spoke about this yesterday.

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I showed a case just like this,

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in fact, I think it was the same case,

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to indicate involvement bilateral in the sacroiliac joint

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and involvement involving the spine,

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about the discovertebral junction,

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with well defined erosions of the vertebral bodies.