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I'd like to show two cases to emphasize the

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innervation of the parotid gland and the

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potential for perineural spread.

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As you can see on this slide set,

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we have a mass that is infiltrating

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the parotid gland,

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both the superficial and deep

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portions on the left side.

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Here is the superficial portion.

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We'd imagine the styromandibular tunnel

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here and here is the deep portion.

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You notice that the signal intensity of the parotid

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gland is abnormal compared to the left side,

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which has the normal bright signal intensity.

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On T1-weighted scans.

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Why is it bright?

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Largely from the content of fat within

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the parotid tissue. In fact,

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in order to identify parotid masses,

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I usually go first to the T1-weighted sequences

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because you have a nice bright background in which

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to see the lesions on the T1-weighted images.

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Because of the parotid fat.

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This patient presented with pain in the mandibular

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region and we identified that the patient had

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perineural spread via the foramen ovale from the

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third division of the fifth cranial nerve,

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the mandibular nerve.

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Here it is seen on the coronal MRI scan.

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So on the coronal MRI scan, we see an enlarged

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foramen ovale compared to the more normal side.

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Over here we see soft tissue which is entering the foramen

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ovale and then going into

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an enlarged Meckel's cave.

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Here's the normal Meckel's cave on the left side.

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The method by which this tumor was able to

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infiltrate the third division of the fifth cranial

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nerve is the auriculotemporal nerve.

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This is a branch of the mandibular nerve,

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the third division of the trigeminal nerve that

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courses through the parotid gland and therefore

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perineural spread with parotid masses can occur up

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the third division of the fifth cranial nerve and

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through the foramen ovale to

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get to Meckel's cave region.

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This is where

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the trigeminal ganglion, the Gasserian ganglion, resides.

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Let's look at a second case.

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This is a patient who has a parotid

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mass also on the right side.

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The lesion is predominantly in the deep portion

2:46

of the parotid gland but infiltrates

2:51

into the superficial portion.

2:52

So here is our mastoid styloid area.

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Here's our mandible.

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So if we did our styromandibular tunnel.

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We would identify this as the superficial,

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and this is the deep portion.

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More importantly in this case,

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is that we see intermediate signal intensity tissue

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right at the stylomastoid foramen.

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And we know that the stylomastoid foramen is

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the exit zone for the 7th cranial nerve.

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This patient, therefore,

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is at high risk for the potential for perineural

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spread up the 7th cranial nerve via infiltration

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of the stylomastoid foramen.

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If we look on the sagittal scan of this individual,

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we actually see quite nicely the second genu

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of the course of the 7th cranial

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nerve in the temporal bone,

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this being the tympanic portion and this being the

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descending intramastoid portion

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of the 7th cranial nerve.

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So we have nicely outlined the 7th cranial nerve,

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and at its exit,

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we see that there is tumor growing into the

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stylomastoid foramen and the distal portion of the

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descending intramastoid portion

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of the 7th cranial nerve.

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So this patient had a malignancy that was traveling

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up the temporal bone via perineural

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spread of the 7th cranial nerve.

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And the patient presented with facial nerve palsy.

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The facial nerve, as is clear,

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is one of the nerves that innervates

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the parotid gland.