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Dr. P here, this is a 44-year-old man who complains

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3 00:00:04,110 --> 00:00:07,170 of a knot along the medial aspect of his ankle.

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Here is the knot on the simple T1

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fat image and on the water-weighted

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proton density fat-suppressed image.

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And you can see this subtle sort

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of peppery appearance inside the

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lesion which is characteristic of it.

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And then you also notice on the T1-weighted

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image that it has this tetherball sign

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or tail sign, proximally and distally.

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Which could only mean that it's

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attached to something tubular,

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like say a tendon, or a vein, or an artery.

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But it doesn't have any signal intensity

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reminiscent of blood products,

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such as that found in a vein or an artery.

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There's no blood fluid level.

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And it's up to us to figure

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out what this structure is.

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And we will indeed do that.

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Now, this is located in the tarsal tunnel space.

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And you can see there's

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quite a few veins around it.

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which makes you think a little bit more about

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it being venous in origin, but once again

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it doesn't meet other criteria for that.

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Let's just scroll around and

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see what else we come upon.

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Some heterogeneous signal intensity,

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juxta-articular throughout the

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ankle, suggesting perhaps arthrosis.

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You can get juxta-articular signal in a number

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of conditions, rheumatoid, complex regional

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pain syndrome, and a few others, but I think

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it's time now to turn our attention away from

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the sagittal and towards another projection.

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There is quite a bit of signal

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in the lateral subtalar space.

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So let's pull down the three axials.

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I'm gonna pull down the, uh, axial T1.

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Give me a moment to do that.

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There's the axial T1.

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There's the axial proton density,

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and there's the axial T2.

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Let's get our T1 in sync

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with the rest of the scans.

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And find our mass.

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So let's scroll, let me get this one a little

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smaller so they all look nice and pretty.

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And let's get right to our mass.

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So it is clear that our mass is located

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between our friends Dick and Harry.

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We've got Tom, the tibialis posterior,

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then Dick, the flexor digitorum, and

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Harry, the flexor hallucis longus.

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So let's look at Tom for a minute.

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Tom, the posterior tibial

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tendon, has a tear in it.

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But that is not our mass.

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So I'll just point that out for you.

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Yes, there is a fair amount

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of soft tissue swelling.

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Yes, there is extensive inflammation

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in the subtalar space in the sinus

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canal and tarsi, more laterally.

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And there is a prolapsing bursal cyst

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coming out from underneath here, but that

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is not the purpose of this teaching element.

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So we go back and we see all of these blood

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vessels here, and can we hook them up to our mass?

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And the answer is, not really.

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They're right underneath the mass, but we can hook

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it up to a specific structure, and let's do that.

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So let's go to our mass, and then let's

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keep going proximally, because I think

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it's easier to figure out what structure

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it's attached to, than going more distally.

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More distally, there were just too many

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veins in the neighborhood, and I think

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that was a little bit challenging.

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As we go up, we run into the

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mass, and its attachment.

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There's the attachment right there.

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It's attached to this structure.

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Now let's go back just to prove it to you.

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And go back again.

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What is that structure?

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That is the tibial nerve,

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the posterior tibial nerve.

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So the posterior tibial nerve

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is attached to our lesion.

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Along with its signal, very bright on the water

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weighted image, it's got some peppery internal

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architecture, it's attached to a nerve, it's got

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to be a schwannoma that's located in the upper

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aspect of the tarsal tunnel area or perhaps

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just proximal to the tarsal tunnel area, which

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may in fact explain why the patient had less

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neurologic symptoms than you would expect.

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As we go a bit more distal, we're going

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to learn a little bit about anatomy.

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I'm going to put up the coronal and look

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at what happens to our tibial nerve.

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It bifurcates into two nerves,

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a medial and a lateral plantar nerve.

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There's also a very small, thin,

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calcaneal nerve that reflects posteriorly.

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I'm not going to focus on that right now,

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but let's just go down and follow these nerves.

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There's the medial plantar nerve, there's the

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lateral plantar nerve, and if we actually try

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and cross-reference them, that gives you a

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pretty good idea of where they're located in

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the coronal projection in the arch of the foot.

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See, this one is traveling very

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closely with the flexor tendons.

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It travels very closely with the flexor digitorum.

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That is the nerve right there,

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the medial plantar nerve.

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Let's follow the lateral plantar nerve.

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There's the lateral.

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Let's follow that down.

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Now that one is over here.

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It's just a little more towards the

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lateral side, more approximately.

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And now let's go down, and as we go down,

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this way, here it is, there's the nerve again.

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Let's keep going down as far as we

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can go, there's the nerve again.

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You can see it's starting to

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move towards the lateral side.

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And there's the nerve again, right there.

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And you can see it's just kind of right

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underneath the flexor digitorum brevis.

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So, the diagnosis here is a schwannoma

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of the posterior tibial nerve.

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The diagnosis was confirmed histologically along

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with numerous other findings and some key anatomy.

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Dr. P out.