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I mentioned previously, Horner syndrome,

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and I think it's important for me to define it.

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And this is due to damage to the sympathetic

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nervous system plexus,

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which is often associated with carotid dissection.

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Remember that the sympathetic nervous system plexus

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is just behind the carotid artery within the

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carotid sheath, so it's located posteriorly.

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The classic triad for Horner syndrome is meiosis,

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a small pupil, ptosis,

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a little bit of a lid drop, and facial

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anhidrosis, which is absence of sweating.

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So I've taken this well-known individual and

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identified for you the lid lag and the drop

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in the eyelid over the iris of the globe.

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And you see that it's covering a portion of the pupil.

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So that's the ptosis,

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the pupil itself is smaller in caliber on the side

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with the Horner syndrome versus the normal side.

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And then you have facial anhidrosis.

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So this is showing that this side is sweating,

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this side does not sweat.

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And that's anhidrosis, facial anhidrosis.

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Here's another example of Horner syndrome.

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The lid is down. It's covering part of the iris,

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more of the iris than the normal side.

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The pupil is smaller in size than the normal size.

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Miosis, ptosis, and facial anhidrosis.

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When you have Horner syndrome,

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most people would likely evaluate

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the patient with a CT angiogram (CTA).

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And the reason for that is because you really have

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to extend from intracranially to the cervical region

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down to the mediastinum and maybe

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even into the upper chest.

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And we just don't get that coverage very well with

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the various surface coils associated with MRI.

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So CTA to look also at the blood vessels and the MRI

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is good for looking at hypothalamic lesions,

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brainstem lesions, and cervical spinal cord lesions.

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But the initial diagnosis is

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usually made with CT angiogram (CTA).

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Sometimes you'll need a chest CT to look at the lung

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apex to see where there's a lesion at the lung apex

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which is pooching up and affecting the

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stellate ganglion at the C7-T1 level.

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Here we have a diagram looking at the neurons that

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are associated with Horner syndrome.

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We start off with the hypothalamus,

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and we see the first-order neuron is the one that

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goes down into the cervical spinal cord

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to the C6, C7, T1 level.

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So anywhere along the brainstem

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and the cervical spinal cord,

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you could affect the first-order neurons.

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You then have the ganglion here,

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which leads to the second-order neurons.

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These second-order neurons are the ones that transfer

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over the top of the lungs and therefore.

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A Pancoast tumor of the upper lung will affect the

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second-order neuron or the superior cervical

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ganglion that is associated with that.

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After the second-order neuron,

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you then have the crossing over

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into the carotid sheath.

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And these carotid sheath branches are part of the

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distal second-order neuron and the third-order

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neuron associated with the carotid artery.

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So here's our carotid artery,

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here's the carotid bifurcation,

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here's the superior cervical ganglion,

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usually at the C4 level and then the third-order

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neuron which goes up from the carotid sheath into

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the intracranial compartment once again and goes

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into the orbit and along the ophthalmic artery

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to lead to the pupillary dilator fibers.

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So the sympathetic nervous system plexus descends

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from the hypothalamus down to

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the thoracic spine T1,

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T2 level and then ascends via the carotid sheath

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up into the orbit to lead to the

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findings of miosis and ptosis.