Cranial Nerves 3-6

Cranial Nerves III-VI

Now for the next 25 minutes we'll be talking about cranial nerves three through six.

I have no financial or commercial things to disclose.

Cranial Nerve III: Oculomotor Nerve

The oculomotor nerve and its nucleus is in the midbrain at the level of the superior colliculus.

It exits at the interpeduncular cistern between the posterior cerebral and superior cerebellar arteries.

And it goes into the cavernous sinus, the superior orbital fissure and through the annulus of Zinn.

And if we look, it has two major divisions.

The upper division innervates the levator palpebrae superioris and superior rectus muscles while the inferior division gets the medial and inferior rectus muscles as well as the inferior oblique muscle.

So if we look at the normal anatomy on three planes, here is a nice example of the third cranial nerve exiting the brainstem at the interpeduncular cistern.

Here you see the cross-sectional flow voids of the posterior cerebral and superior cerebellar arteries.

If we look at this on a T1 axial, we can see the nerve coming out of the interpeduncular cistern crossing the cistern to go into the posterior superior aspect of the cavernous sinus.

And on this T2 coronal, we see the third cranial nerves in the cistern between the posterior cerebral and superior cerebellar artery vessels.

Now the third cranial nerve within the cavernous sinus runs in the high posterior lateral aspect, usually above the cavernous carotid, at least on this image.

Brainstem Pathologies

So here is a patient with an oculomotor nucleus infarct and we can see that there is a hole in the midbrain at the level of the superior colliculus and the oculomotor nucleus lies in the periaqueductal gray.

And you can see the aqueduct is just this big thing and there's really nothing around it.

Notice here that both of the medial rectus muscles are extremely atrophic.

All right, so this is from a brainstem insult.

Here is another brainstem insult.

This patient has an obvious cavernoma also at the superior colliculus, right at the level of the aqueduct.

Cisternal Segment Pathologies

If we go on to the cisternal segment, what else can affect the third cranial nerves?

Well this patient has HSV ophthalmicus, a 47-year-old male and you can see he had problems on the right.

Here's enhancement of the third nerve in the cisternal segment on two views.

Another lesion that affects the cisternal segment would be the neurogenic tumor, typically the schwannoma.

And here we see a presumed schwannoma.

Notice how it's lifting up the posterior cerebral and sort of pushing down the superior cerebellar and it enhances on the post gadolinium axial image.

So we have lesions in the brainstem and the cistern if we look at more cisternal lesions.

Here's a patient with mantle cell lymphoma and you can see both third nerves are enhancing abnormally and on the axial images, the third nerves as they cross the cistern to enter into the cavernous sinus.

This patient obviously has neurofibromatosis type two, you see multiple neurofibromas.

And here you see one particularly affecting the oculomotor nerve.

Also in the cisternal segment there is an entity called the ophthalmoplegic migraine where patients get enhancement and enlargement of cranial nerve three in its cisternal segment.

Very unusual.

Can I tell you this is not a schwannoma?

Yes, because we imaged this lady sometime later after her migraines were gone and her third cranial nerve was actually normal.

So occasionally ophthalmoplegic migraine.

This is a very common lesion in the cisternal segment for a third nerve.

And you see that there is a posterior communicating artery aneurysm.

Cavernous Sinus Segment Pathologies

Now if we go to the cavernous sinus segment to have isolated third nerve diseases, distinctly uncommon because most cavernous sinus lesions give you 3, 4, 6 nv one nv two pathology.

But here notice the medial rectus muscle is small on the left compared to the counterpart on the right and there is a lesion in the cavernous sinus.

The cavernous sinus is full compared to the other side.

And this was a pathologically proven oculomotor schwannoma.

And then as I mentioned, other things that can involve the cavernous sinus may produce multiple cranial nerve palsies.

Here is just an MRA example of a fairly prominent carotid cavernous fistula.

You see the large draining superior ophthalmic vein or the arterialized vein.

Distal Segment Pathologies

Now if we go to the more distal segment, this is a patient who has pathologically proven single muscle graves disease.

And you can see this should not be superior oblique.

This is the superior rectus muscle, probably the superior oblique here.

This is a typographical error.

This is separate from the levator palpebrae.

So this is superior rectus and you see how large it is.

And this was biopsied because the appearance was so unusual and this was graves ophthalmopathy.

Cranial Nerve IV: Trochlear Nerve

Now if we move on to the fourth nerve, its nucleus is also in the midbrain but lower than that of the third nerve.

This one at the level of the inferior colliculus.

Remember the third nerve was at the level of the superior colliculus.

It exits the brainstem dorsally, it's the only cranial nerve that exits dorsally.

It goes around the brainstem in the cistern right under cranial nerve three.

So in a portion it's between the posterior cerebral and superior cerebellar artery vessels.

But it's very small and we don't really see this on our coronal images.

It also enters the cavernous sinus and traverses the superior orbital fissure and it innervates one muscle.

That's the superior oblique muscle.

So if we diagrammatically try to depict where the fourth nerve would go, it exits the brainstem dorsally and goes around through the cistern into the orbit.

On the axial image, the nucleus is on the opposite side.

These cross at the level of the superior medullary velum and exit on the contralateral side.

So lesions on the left right back here would actually produce pathology of the right superior oblique.

Now on the axial T1 images, occasionally we can see the fourth nerves in the cistern.

Very, very, very small lesions.

And if we look distally the normal superior oblique muscle here medially in the orbit here is the trochlea of the nerve and then the tendon inserting into the muscle inserting onto the globe.

So here is the anatomy of the superior oblique.

These are superior oblique muscles, very medially in the orbit you can see again the trochlea.

Now if you look here, the superior oblique on another level and then we actually get the medial rectus muscle on the same cut, but it lies lateral to the superior oblique.

And I notice a lot of times people will mistake on the axial image the superior oblique muscle for the medial rectus muscle.

So here's superior oblique.

Here is medial rectus and the cranial nerve four courses in the cavernous sinus wall.

Okay, the wall, not the sinus proper right under cranial nerve three, a very small nerve within the dural wall sleeves.

So if you look at this patient's superior oblique on the right, it's slightly diminutive compared to the one on the left.

Now if you look at this patient has a fourth nerve nucleus cavernoma.

Okay?

And in this patient clearly you see the right is diminutive compared to the left superior oblique.

And in this patient notice this small little area of encephalomalacia and on both the T1 and the T2 images.

And we presume that this is a very small vessel stroke.

Okay?

And his symptoms have been going on for five years and the nerve comes out of this side, crosses at the level of the velum, exits into the cistern and goes anterior to that right superior oblique muscle.

So these are some brainstem segment pathologies.

Cisternal Segment Pathologies

Now here's a cisternal segment pathology and again a very small superior oblique.

Here you see a regular superior oblique.

Now this is out in the cistern.

So this is presumably coming off the left coursing around.

This is a presumed trochlear nerve schwannoma.

They don't go in and actually biopsy or remove these lesions.

And here we saw I think it was Deb that showed a couple carcinoid lesions and they had that heterogeneous kind of with a cyst in the center sort of things.

This is my metastatic carcinoid tumor.

You can see the superior oblique is actually enlarged here on the right compared to its counterpart on the left.

The enhancement pattern is very strange and this happens to be metastatic carcinoid only to the superior oblique muscle.

Cranial Nerve V: Trigeminal Nerve

The trigeminal nerve is more interesting.

Its nuclei lie in the pontine tegmentum and the nerve exits the brainstem at the lateral pons, not the midline, the lateral pons and it traverses the cistern and enters the Meckel's cave.

Then it goes to the trigeminal ganglion and splits into V one, V two and V three branches.

But remember V one and V two go anterior into the cavernous sinus.

The motor root of V three comes down, bypasses the ganglion and it goes through the foramen ovale.

So if we look at the normal anatomy here, now remember this comes off the lateral pons.

So if you're looking for the nerve in the sagittal view, it will not be in the midline.

You have to go about three cuts off midline.

So here in fact is this cisternal segment of cranial nerve five exiting the lateral pons.

It almost looks like it's coming off the cerebellar hemisphere.

Here are the nerves in the cistern on the coronal view.

And here on the T1 imaging we can actually see fibers going anteriorly into the ganglion.

Ophthalmic Division (V1)

So if we start with the ophthalmic division, it's in the lateral wall of the cavernous sinus.

Larry Ginsburg just showed some nice imaging here.

This exit at the superior orbital fissure to go to the orbit divides into these branches and provide sensation to the nose, globe, forehead and scalp.

Where does it lie?

In the wall of the cavernous sinus here above the V two nerve.

Okay, so fairly large nerve again in the wall, not in the cavernous sinus proper.

So here we have a 12-year-old with esthesioneuroblastoma and you see a lesion in the superior aspect of the orbit.

Notice it's caused some thinning and it's gone through the orbital roof here, but it's compressing the extraocular muscles.

It's above the extraocular muscles where these branches of V one run.

This turned out to be a V one schwannoma.

Now here is another V one schwannoma, this one more posteriorly within the orbit.

Now he talked about some perineural tumor spread and for all I know this is one of his cases, but there's this little tumor here.

This was forehead squamous cell carcinoma and you have this abnormal soft tissue above the muscles.

And here you see enhancing tumor coming all the way back.

This is V one perineural tumor spread.

And here another example, this one from more of an inner canthus type lesion.

And you can see here that there is this abnormal enhancement again above and separate from the extraocular muscles that is V one perineural tumor spread.

Maxillary Division (V2)

Now if we go to V two, the maxillary nerve, it also runs in the cavernous sinus and this one exits the skull at the foramen rotundum goes through the inferior orbital fissure and becomes the infraorbital nerve.

As we saw, this one has a lot of sensory branches and divides into a number of branches.

But the big one here is when the branches hit this pterygopalatine ganglion in the pterygopalatine fossa.

And that's where you have all of your branches may basically innervating the cheek lower and upper lid, upper teeth, et cetera.

So this is the V two coursing in the lateral wall of the cavernous sinus.

Now here are some unusual isolated V two lesions which are distinctly uncommon.

This is a neurofibroma and you can see widening of the pterygopalatine fossa here, thinning and bulging of the posterior wall, the maxillary sinus, and this basically non enhancing lesion that comes up through the fissure.

Okay, and goes posteriorly.

Here is an unusual V two schwannoma.

Now this one on MR notice, it's got this intra lesional necrosis if you will, but I would've a hard time calling this a V two schwannoma except for its location.

I mean you have some normal fat over here on the contralateral side, but this would be a very hard diagnosis for me anyway to make going forward.

This one is not hard because the imaging is so classic.

This happens to be an unusual pterygopalatine fossa dermoid tumor.

Notice the normal fat with the normal neurovascular structures on the right and this very bright T1 lesion, which on the fat suppressed T2 falls off in signal.

And here this turned out to be a chondromyxoid fibroma, okay?

As far as I'm concerned, that falls under the miscellaneous, who knows what it is lesion.

Would I ever, ever make that diagnosis on the basis of this imaging?

No I would not.

But I'm just showing you some of the different things that occur here.

Now don't forget things that affect the sensory component occur more distally.

Those were some pterygopalatine fossa lesions.

Don't forget your blowout fractures.

People come in with a numb face and that's because your infraorbital foramen and the floor of the orbit sort of is a path of weakness.

So a lot of the blue inferior blowout fractures will go through this foramen and can entrap fat and or muscle as you know.

Another lesion, this is a perineural tumor spread of a parotid adenoid cystic.

You can see it's probably coming around through the auriculotemporal nerve.

It's gotten onto V two and it's gone all the way forward to actually come out at the infraorbital foramen.

Here is enlargement of V two and you can nicely see it here on the coronal.

This is the pathologic V two compared to the normal V two on the contralateral side.

Now this is a case that Jenny lent me I believe.

And this patient has squamous cell carcinoma on the forehead and here's the area of the supraorbital nerve that has some pathologic signal on it.

Okay?

Shouldn't be anything above the muscles.

Then you come more forward.

This is in the region of the orbital apex, okay?

This is where V one would run.

Then you go further and you've got some stuff here in the lateral wall of the cavernous sinus V one and V two.

Then you come back and you look here and here is this enlarged enhancing foramen rotundum.

And you look back at the orbital ones and you see this mass hanging at the level of the floor.

This is enlargement of the infraorbital nerve coming forward.

So remember that Dr. Ginsburg said these things can go perineurally, retrograde and antegrade.

So here's one starting at the supraorbital nerve, gone back and run antegrade along the maxillary or V two nerve.

Mandibular Division (V3)

Now let's finally turn to V three here.

This exits the skull base through the foramen ovale and divides into two main nerves.

Here you see the foramen ovale and nice V threes coming down.

Notice the normal fat here below the foramen.

That should always be there.

Now we're not gonna talk about the masticator nerve so much but we'll talk about that in my last lecture.

But this nerve inferior alveolar provides sensation to lower face jaw teeth, tongue floor of mouth and even gives off a mylohyoid motor branch.

So if we look at this mandibular nerve, there's a couple small vessels that come off before it divides into its big terminal branches and those are branches to the tensor tympani and tensor veli palatini.

Then we have the masticator nerve that goes to the muscles of mastication and this inferior alveolar nerve that gives off a mylohyoid branch which is motor.

And I'll cover those more fully later.

So this person has trigeminal neuralgia.

So we're gonna look at the cisternal segment and here you see a branch of either the superior cerebellar most commonly or perhaps this could even be a vein crossing over the trigeminal nerve.

Here is the nerve on the contralateral side.

Here we see a V three schwannoma.

Again, it's sort of necrotic in the center.

This is a presumed lesion.

Notice how it's displacing the cisternal segment of that trigeminal nerve compared to the other side.

Here is that same patient with mantle cell lymphoma that we've seen who has infiltration of both trigeminal nerves in their cisternal segment.

And we see this really nicely on the parasagittal images as it's crossing over to go down through foramen ovale here a schwannoma that involves the cisternal segment and Meckel's cave segment here at the nerve exit zone crossing the cistern going into Meckel's cave.

Here is the normal fluid-filled Meckel's cave on the contralateral side.

Here is a patient with B-cell lymphoma.

Also notice the normal Meckel's cave on the left.

Notice this lesion on the right side cisternal as well as Meckel's cave segment and getting into the cavernous sinus.

Now here's an unusual Meckel's cave slash foramen ovale epidermoid lesion and it transcends, it goes through the foramen, which is absolutely enormous here.

And you can see it's clearly fat density on the CT exam and on the diffusion manifests the typical restricted diffusion of these large lesions.

And here is a woman unfortunately with supposedly a cured her breast metastases showed up with trigeminal symptomatology and you can see this soft tissue mass instead of the normal fluid in the Meckel's cave.

And here abnormal enhancement and a slightly enlarged foramen ovale as this tumor is into the upper masticator space, this is a distal segment schwannoma.

And you can see this is really it's medial masticator space and it's got the internal pockets of necrosis and you can see how it pushes the muscles away.

Here is a masticator space V three schwannoma.

And how do I know that?

Well, just looking at it, I don't, but I look here and I look at this inferior alveolar canal and it's absolutely enormous.

There's no normal fat.

It's supposed to be about that wide as its counterpart is.

Don't forget we've talked about perineural tumor spread a child with nasopharyngeal rhabdomyosarcoma.

Look at the size of this foramen ovale.

Now the nasopharynx has a mass in it but it's clearly broken through the fascia and gotten into the masticator space.

You can see here this very enlarged foramen ovale with tumor crawling through it.

And on the coronal and sagittal reformats we see this tumor crawling up into the Meckel's cave.

The primary site going across, invading that medial fascia of the masticator space, crawling onto V three and going intracranial.

Same thing in another child again, V three perineural tumor.

And then finally this parotid adenoid cystic carcinoma that has some direct extension here into the buccinator musculature.

It's actually destroyed mandible, it's gotten on V three.

Here's foramen ovale tumor and it's grown intracranial.

Here's another patient with nasopharyngeal carcinoma with both V two and V three 40-year-old female with numbness in these distributions.

Large foramen ovale obviously with enhancing tumor in it.

Notice the destruction of the lateral portion here of the base of the skull of the sphenoid.

And this is the normal Vidian canal you can imagine V2 is involved on that side.

We look here on the bone window CT very large foramen ovale.

Notice the normal Vidian canal with normal cortical bone around it.

And notice this Vidian canal is enlarged and the cortical bone surrounding it is destroyed.

And finally another case from Jenny.

This is thought to be trigeminal neuralgia for eight months.

Here is enhancement of the cisternal segment of five.

You come forward, there's abnormal enhancement in the Meckel's cave on that side.

You come further forward, it's going down through foramen ovale, you look further and here is the foramen rotundum with enhancing tumor and you look more anteriorly.

And here is tumor coming out the infraorbital nerve.

So this is V two and V three, no primary, we're not sure where this came from.

Cranial Nerve VI: Abducens Nerve

And we'll finish up with the abducens nerve.

This is cranial nerve six.

It's pretty easy.

Its nucleus is in the pontine tegmentum.

It crosses through the pons exits at the pontomedullary sulcus ascends along the clivus goes through Dorello's canal, the superior orbital fissure, the cavernous sinus of course, and ends up in one muscle, the lateral rectus muscle.

Now here is the floor of the fourth, this is the sixth nucleus and this is the seventh nucleus and the fibers of seven go around the sixth nucleus causing these bumps in the floor of the fourth.

That's why this is called the facial colliculus and it shows you where sixth is.

Now show you here on the imaging studies.

Here is six crossing the cistern to Dorello's canal on the T1 imaging.

Again, MR here is six crossing the cistern.

Here is the facial colliculus.

I call this the baby's bum.

This looks like two cheeks with a crack in the middle.

That's how I know where the six nerve nucleus lies.

And here you can see fluid around the nerves within Dorello's canal.

The CSF, this particular nerve lies in the cavernous sinus proper.

The other nerves that we've discussed lie in the wall of the cavernous sinus and the dural reflection.

This is the only cranial nerve to lie inside the sinus proper.

Brainstem Pathologies

So here's a patient with relatively sudden right six nerve palsy.

You can see a small area of pathologic FLAIR signal, very small area of enhancement.

And here you see restricted diffusion with corresponding low ADC.

It's right where the sixth nerve nucleus belongs and this is a very small sixth nerve nucleus infarct.

Here's another patient with acute deviation of the right eye and also has some right seventh paresis.

And I think that this is a very nice example of a cavernoma which probably recently bled accounting for the acute symptoms and again at the level of the facial colliculus.

So both cranial nerves six and seven.

Here's a patient with a right six nerve palsy.

You can see this is more chronic.

The six nerve is small.

I mean the lateral rectus is smaller than the counterpart.

And you see this very small area of pathologic T2.

This turned out to be a multiple sclerosis plaque within the six nerve nucleus.

Here is another one a cavernoma.

This particular one associated with a fairly large developmental venous anomaly.

Cisternal Segment Pathologies

The cisternal segment can be affected by a number of things used, just a small meningioma and you can see it's isointense on T1 and T2 and enhances with some dural enhancement and it's right where the sixth nerve crosses in the cistern.

Skull Base Pathologies

Here's another lesion.

This patient had nasopharyngeal carcinoma that extensively went around the skull base.

I think you can see all of the abnormal enhancement and abnormal tissue and this is where the sixth nerve would cross.

So it's just hitting Dorello's canal in that skull base where the sixth nerve would be entering the base of the skull.

Another skull base lesion that is rarely associated with a nerve palsy is this cholesterol granuloma.

And this patient came in with a left six nerve palsy and has destruction here at the posterior margin of the central skull base.

And you can see the lesion right on T1, a little bit bright on T2 and it's right where Dorello's canal would be very unusual cause.

And another skull base lesion very unusual causes this huge sphenoid mucocele.

Notice the normal right six nerve.

Okay, abnormal, excuse me, here's the right six nerve.

This mucocele is cutting it and it is in Dorello's canal right where the six is trying to go.

Here is the normal six nerve on the contralateral side.

So a huge mucocele affecting that six nerve.

Here is a chordoma headache and left six nerve palsy.

You see this lesion central within the skull base right where the six nerve is crossing.

You can see that nicely And here where six would be crawling up the clivus.

Here's a lesion in the skull base but this is eccentric so it's slightly less likely to be a chordoma.

Remember if it's eccentric you must think of chondrosarcoma first.

And this was in fact a chondrosarcoma.

You can see right where six nerve would be crossing Dorello's canal here.

Distal Segment Pathologies

Now some of the distal things you might run into here is an orbital dermoid.

You can see the fat signal here, on CT fat density and notice how it's deforming and displacing this lateral rectus muscle.

Notice the optic nerve is moved over.

And finally this last case, acute bilateral diplopia.

This person had a very unusual pseudotumor infection sort of thing involving both lacrimal glands and presented with acute symptomatology.

So we've gone from Cambodia to the Galapagos Islands to Egypt.

I don't know where we're gonna go next, but thank you so much for your attention.