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Hello everyone, it's Dr. Sidney Levy here.

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3 00:00:04,950 --> 00:00:07,440 I'd like to begin this short set of

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vignettes on perineural tumor by defining

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what perineural tumor invasion is.

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The reason I am conducting this series of

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vignettes is because perineural tumor invasion

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is a feature of squamous cell malignancy as

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well as other malignancies in the head and neck,

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including adenoid cystic carcinoma, which

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is a minor salivary gland malignancy.

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Perineural tumor is malignant tumor

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spread along large nerve sheaths

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distant from the primary site of tumor.

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It's most commonly present involving the 5th

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cranial nerve, so that's the trigeminal nerve,

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or the 7th cranial nerve, the facial nerve.

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Within the trigeminal nerve, the maxillary or V2

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division is more commonly involved than the mandibular

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or V3 division, which are both much more commonly

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involved compared with the V1 or ophthalmic division.

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Perineural tumor invasion may be anterograde or

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retrograde and may involve skip lesions and may

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also cross between different cranial nerves,

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such as between the branches interconnecting

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the fifth and the seventh cranial nerves.

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So which types of malignancies apart from squamous

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cell carcinoma and adenoid cystic carcinoma

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could also present with perineural tumor spread?

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It's important to remember that lymphoma spreads

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this way and that can occur in the head and neck.

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You can also see it occasionally with melanoma as well.

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The differential diagnosis for perineural

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tumor spread is primary neurogenic tumors

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such as schwannoma or neurofibroma or a skull

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based meningioma in the appropriate site.

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You can also occasionally see infection,

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in particular invasive fungal infection,

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spreading along a nerve trajectory.

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I had like to conclude by showing you this

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42 00:02:25,025 --> 00:02:28,865 example case of perineural tumor infiltration.

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I have an axial post-contrast T1 with fat suppression

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and coronal pre- and post-contrast T1-weighted

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images in which the infraorbital branch of the

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maxillary or V2 nerve is involved with tumor.

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This patient originally had a cutaneous

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squamous cell carcinoma, but right now is

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presenting with perineural tumor spread.

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So how do we know that it's present?

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We look for abnormal enlargement of the nerve with

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abnormal intraneural enhancement and a blurred margin.

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In this case, if you're in any doubt, it's

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always important to look for asymmetry.

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In this case, the normal infraorbital nerve

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is small and can be quite difficult to see.

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Here it is on the left.

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But on the right, it is infiltrated by

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tumor and markedly enlarged by comparison.

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Once you have perineural tumor, it's necessary to

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trace it as far back or forward as is necessary.

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And in this case, this tumor spreads from the

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cutaneous layer of the cheek along the infraorbital

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nerve in the floor of the orbit to this point here.

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We can cross-reference that and

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see it on the axial projection.

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Let me draw it for you again.

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So there it is.

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Once it's reached that point, you need to look at

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where it may go next. Going back to our anatomy, the

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infraorbital nerve is a major branch of the maxillary

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nerve which passes through the pterygopalatine fossa.

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So we need to look at the

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pterygopalatine fossa in this case.

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And in this patient, the tumor does not involve

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the pterygopalatine fossa, which is here.

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So once we've established that, we know that

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we don't need to go back any further, but if

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we did need to go back further, we would be now

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looking at the cavernous sinus on the right.

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And an easy way to look for the cranial

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nerves within the cavernous sinus, including

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V2, is to find the pituitary infundibulum

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and come forward a couple of slices.

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You'll start to see the flow voids

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of the cavernous portions of internal carotid

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arteries, and you'll start to see the cranial

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nerves on the lateral wall of the cavernous sinuses.

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The V2 nerve is normal in this

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patient, but is located here.

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If this was asymmetrically enlarged and had

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intraneural enhancement that was different

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from the contralateral side, those would be

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suspicious features for perineural infiltration.

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So in summary, this patient presents with an example

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of right infraorbital nerve perineural tumor as a

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major branch of the right V2 or maxillary division

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of the trigeminal nerve on a background of a previous

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history of cutaneous squamous cell carcinoma.