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Hello everyone.

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Dr. Sidney Levy here, continuing our discussion of

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perineural tumor as part of our series on the diagnosis

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and staging of head and neck squamous cell malignancy.

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In our previous vignette, we introduced an

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example case of right infraorbital nerve

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perineural infiltration on a background of

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previous cutaneous squamous cell carcinoma.

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I would like to return to this case.

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So I have here the axial projection and the coronal

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pre- and post-contrast T1-weighted sequences.

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Just going to quickly draw the

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abnormal nerve for you again.

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Reinforcing three of the cardinal features which

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are demonstrated in this particular lesion.

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There is abnormal tubular nerve enlargement.

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There is abnormal intraneural enhancement

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on the post-contrast sequences, and the

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normal margin of the nerve is blurred.

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It has an irregular infiltrative margin.

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Other features that you can look for,

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depending on the site, are loss of the

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normal fat plane surrounding nerves.

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So, for the V2 nerve, or maxillary nerve, one of

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the things you can look for is loss of normal fat

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in the pterygopalatine fossa or premaxillary fat.

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So for example, here in our case, we have the

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abnormal infiltration of the right infraorbital

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nerve, which we can trace out to the left

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premaxillary soft tissues.

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And you can see here that the normal fat plane

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beneath the superficial muscles of facial expression

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is effaced here, compared with the normal side.

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You need to have pre-contrast, non-fat-suppressed T1

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weighted imaging in order to assess this accurately.

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If you trace the nerve back along here as

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far as the inferior orbital fissure where it

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appears to disappear, it hasn't disappeared,

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it's just that the perineural infiltration

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hasn't extended more proximally to this level.

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We can look at the pterygopalatine fossa, which is

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in this area here, let me draw it for you, abnormal

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infraorbital nerve, traceable here,

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continues out to the premaxillary soft tissue.

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Then we have the pterygopalatine fossa here.

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You can see that the normal pterygopalatine

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fossa contains fat, which is T1 hyperintense

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and which suppresses on fat-suppressed imaging.

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You can also see that it is

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the same as the opposite side.

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So it has not been effaced.

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So, therefore, we can say with confidence that this

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perineural tumor, whilst it involves the entirety of

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the right infraorbital nerve, has not infiltrated the

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maxillary nerve within the pterygopalatine fossa.

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And therefore, we can be somewhat

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reassured that it is more confined.

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However, you must always check the entire course

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of the nerve, so once you go more proximal to

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the pterygopalatine fossa, you need to check

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the cavernous sinus on the same side, and indeed

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the cerebellopontine angle and brainstem.

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You need to go all the way back to the brainstem

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to ensure that there are no skipped

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lesions, because that can occasionally occur.

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For the other cranial nerves, the places where

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you may see loss of the normal fat plane are

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beneath foramen ovale for the mandibular division.

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In this case, I have loaded up some coronal pre- and

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post-contrast T1-weighted images at the level of

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foramen ovale in order to show you the fat which

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normally surrounds the mandibular nerve at this site.

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When there's perineural infiltration

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around the mandibular nerve,

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These fat planes may become effaced.

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So that's a helpful thing to look for as well.

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The ophthalmic division, or V1, is much

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less commonly involved, but you may see

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loss of fat in the superomedial orbit.

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And in the case of the facial nerves, you may

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see loss of fat planes beneath the stylomastoid

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foramen, particularly on the axial projection.

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If you have access to CT imaging, you may

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see foraminal or canal widening on CT.

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And this can be particularly relevant in the vicinity

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of the hard palate, where you can have enlargement of

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the palatine foramina, which the greater and lesser

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palatine nerves are branches of the maxillary nerve.

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The last thing you can look out for on fluid

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sensitive sequences is muscular denervation,

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which may present with edema or T2

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hyperintensity in the acute phase and fatty

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atrophy or T1 hyperintensity in the chronic phase.

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This is more likely to occur with the third division

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of the trigeminal nerve and involve the masticator

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muscles, which are supplied by the mandibular nerve.

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It can also occur with the

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facial nerve but less commonly.

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In our last vignette, we will discuss some common

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pathways of spread of perineural tumor infiltration.