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All right.

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So, um, in the next, uh, 45 minutes

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or so, I will, uh, discuss the, uh, anatomy

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and the most common entrapment neuropathies of, uh,

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the nerve of the lower extremity.

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So, uh, entrapment neuropathy can occur anywhere on the path

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of the nerve, but it tends to occur at specific locations,

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usually at a narrow passageway, like a fibro osseous tunnel,

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where even a slight divergence in the normal anatomy can

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cause compression of the nerve.

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And this can be caused by a variety of, um,

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etiologies like osteophytes, scar tissue,

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hematomas tumor, or ganglion cyst to name a few.

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So the symptoms can be, uh, confusing clinically

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because they're often vague and poorly, uh, localized.

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So it's important for the radiologist to be aware

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of these entrapment neuropathies nerves, uh,

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that are located superficially,

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like the common peral nerve are also at risk of injury.

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Like in this example, uh,

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the patient had a postal lateral coronary injury,

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and you can see that the common perennial nerve

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is markedly enlarged.

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Now this is a drawing showing the normal anatomy of a nerve.

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So nerves are composed of multiple fales.

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The fales that we can actually see on MRI.

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Uh, between the fassal we have, uh, some fat,

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and within the fat there are some arteries and veins.

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So these arteries can be affected by systemic diseases such

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as diabetes, which will cause microangiopathy.

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Now each SLE is surrounded by a layer of perineurium,

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a connective, some connective tissue,

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and the, uh, sles are compo composed

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of multiple axons bundled together.

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Each axon is, uh, surrounded by a myelin sheath,

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and the myelin sheath is surrounded by the endoneurium.

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And finally, the nerves are surrounded by a layer

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of connective tissue, the epineurium.

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So we have three layers of connective tissue, the epineurium

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perineurium around the fascicle

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and the endoneurium around the axon.

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This is a cross-section of a normal nerve

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with magnification on the bottom right

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and the dark dots correspond to the axons.

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And then the white, the myelin sheath around the axon.

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And then we have the endoneurium.

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And this endur, uh, endoneurium contains fluid,

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which is similar to the, uh, cerebral spinal fluid

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of the central nervous system,

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and that's why normal nerves have a slightly increased T

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two single intensity.

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When a nerve is injured, there's a non-specific response

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with a increase in the single intensity of that

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Thatum on T two weighted images.

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So normal nerves like, um, this example

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of the sciatic nerve, uh,

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will show an intermediate single intensity

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on T one weighted images.

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And normally, like for the sciatic nerve,

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because it's the largest nerve of the body, we can see the

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sles and we can see the fat in between the sles.

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The, the normal nerves will be slightly hyperintense

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to a muscle on two, two weighted images

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because of the ural fluid.

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And if the blood nerve barrier is intact,

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there will be no enhancement of normal nerves.

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This is an axle image, uh, of the thigh showing the, uh,

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sciatic nerve, a normal sciatic nerve.

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So you can see the sles

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and you can see the fat between the sles

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and surrounding the nerve.

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So it's important when assessing the nerve to have, uh, uh,

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T one weighted image, which is not fat saturated.

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So you can appreciate if there is, uh, some abnormality, uh,

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within the sles

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or the fat surrounding the fas, the, the nerve, like

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for example, if there's scar tissue.

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Notice also the proximity of the hamstring tendons,

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which can, uh, cause, uh,

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some sciatic neuropathy if there's injury to the, um,

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to the, uh, hamstring tendons

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or if there's a hematoma, scar tissue or surgery.

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When assessing the nerves, we also need a robust

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T two weighted, uh, uh, fluid sensitive sequence to be able

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to appreciate any difference in, uh,

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single intensity of the nerve.

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So this is an example of the s normal sciatic nerve

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that is slightly hyperintense to the age adjacent muscle

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on the, this situated image.