Denervation Atrophy Patterns of Motor Cranial Nerves

Introduction

Hi, I'm Wendy Smoker. I'm back again.

This will be my last lecture of this two day course and I'm gonna talk about denervation atrophy patterns of motor cranial nerves.

Now of necessity, there is going to be some overlap with the diagrams in the anatomy that I showed you in cranial nerves three through six.

Again, I have no disclosures.

Denervation Atrophy Patterns

What's interesting about denervation atrophy is that now we can actually see stages of denervation.

The ability to visualize most cranial nerves. And as you've seen there exit foramina, we have to relearn cranial nerve anatomy.

The sequelae resulting from insults to cranial motor nerves is identifiable by denervation. Atrophic changes. When denervation is identified of the distal innervated muscle, you must totally trace the course of that cranial nerve back to its brainstem origin.

As I presented previously, you can have brainstem, cisternal segment, skull base, cavernous sinus, mele cave segments, and distal segment pathology.

When we look at denervated muscles, muscle enlargement and abnormal enhancement, acute denervated muscles are typically enlarged and enhanced. Abnormally do not mistake these muscles as harboring a neoplasm.

This is the most frequent error that I see made.

Muscle enlargement in acute denervation is thought to result from enlargement of extracellular spaces and increased tissue water and the abnormal enhancement may be due to increased blood flow in the denervated muscles and or the increased gadolinium contrast accumulation within the enlarged associated extracellular spaces.

Stages of Denervation

If you look at the stages of denervation, acute subacute and then early and late chronic, you can see muscle volume is only increased in acute. It's about the same in these two. And then in the late denervation it's decreased T two prolongation present in acute and subacute and then goes away.

Fatty infiltration not present in acute starts to show up in subacute and becomes very pronounced in chronic late denervation.

And the abnormal enhancement lags onto the subacute phase but is not present in the chronic stages.

You've seen this slide before, I'm not gonna spend any more time in it.

You do know the nerves innervated by this nerve are the levator pal pire, superior, rectus medial, and inferior rectus and inferior oblique. Virtually all of the extra cranial extraocular muscles except for superior oblique and lateral rectus.

And we've looked at these diagrams before.

Here's third cranial nerve between the PCA and SCA. Here it is on kiss and here it is on T two again between the posterior cerebral and superior cerebellar arteries.

Cranial Nerve III: Oculomotor Nerve

Now when patients have third nerve palsies notice in primary gaze there's posis of that particular eye. There's paralysis of upward gaze on the affected side, there is also paralysis of leftward gaze when looking to the right.

So if you look, when the patient looks to the left, you can see the eyes function normally 'cause the lateral rectus is working. But coming this way, you've got all of those other extraocular muscles out.

So this is a patient with right third nerve palsy. So this is normal. The third nerve nucleus is in the periaqueductal gray and here you see the gray on the axial image.

And here's that patient with the infarct in the third nerve nucleus with bilateral denervation of the medial rectus. The other muscles were also involved but you can't see them on this one image here is that patient with the cavernous malformation.

Here is a patient with a different cavernous malformation at the level of the superior colus.

Now here's a 25-year-old man with diplopia ptosis and dilated pupil. There's more images here than on the previous image. Here is that medial OID out.

But look here on the coronal image, the only extraocular muscles which are full and normal are the superior oblique and the lateral rectus. All of the other muscles innervated by the third nerve are markedly out if you see them at all.

And here is that oculomotor nerve schwannoma. You can see it here in the cavernous sinus on both the axial and post contrast coronal images.

Cranial Nerve IV: Trochlear Nerve

The trochlear nerve we've also covered, remember that innervates one muscle, the superior oblique.

These are the images that I showed you before crossing from one side to the other before exiting the brainstem and then the muscle just adjacent to the ethmoid air cells going to the trochlea. And finally the tendon.

Now when patients have fourth nerve palsies, these are difficult to diagnose clinically. This is a 65-year-old male with a six month history of vertical image separation.

You're supposed to notice that there's reduced downward and inward gaze of the right eye compared to the left, which I guess when you write it out this way you can probably appreciate.

But it's the most difficult, nerve palsy in the orbit to identify.

So here's an obstetrician who is all of a sudden having trouble catching babies, which is not a very good thing. And you notice that the left side is pretty normal. Excuse me, the right side is normal, but the left is very, very diminutive. All the other extraocular muscles are normal.

This person had a past medical history of sarcoidosis. No other lesion could be found. This was presumed involvement of the left fourth nerve.

Here's a patient again, diminutive on the right, normal on the left. And here we have a cavernous malformation in the tole nucleus and also notice the small DVA associated with this cavernoma.

Now here's a patient who had a right fourth for five years. Normal left very diminutive, superior oblique.

This is the patient who has that small presumed small vessel stroke as it's crossing over so that the opposite side is the side that is affected.

And here this is the patient who I believe has that trochlear nerve schwannoma in the cisterns and you can see coursing along the fourth nerve pathway.

Cranial Nerve V: Trigeminal Nerve (Motor Division V3)

Now we've looked at this particular diagram before and we're gonna be talking about V three, the motor division of V three.

So we mentioned the tenzer timi, I tensor palatini muscles. These are important. I'll show you where those are abnormal.

The masticator nerve coming down and supplying the four muscles of mastication. And then this mylohyoid nerve, which is a branch of the inferior alveolar nerve.

So here comes the inferior alveolar that's sort of motor and sensory coming out the mental foramen. But this branch actually comes off and provides motor innervation to the mylohyoid and anterior belly of the digastric.

Now when patients have a fifth nerve palsy notice, you can see here the normal temporal fossa. Notice how hollow it is on this side. The normal cheek kind of bulging out a little and very hollow on the other side.

And when the patient opens his or her mouth, the jaw deviates towards the side of the pathology 'cause it has unopposed muscle action from the muscles of mastication.

So this is a patient with right V three dysfunction.

This is a cadaver air study showing the nerves, remember exiting laterally here on the ponds not near the midline. And you see on the kiss image the fales going into the Mele cave.

And we've seen this normal cisternal segment almost looks like it's coming off of the cerebellum, bilateral nerves in the cisterns. And again here we see the nerves coming through foramen oval going into the high masticator space with fat just below the foramina oval.

Now this is what acute V three denervation looks like. Notice the muscle size increased muscle volume Of the oid musculature on the left compared to the right pathologic T two prolongation in that muscle.

Okay, this was misdiagnosis a tumor the person was sent in to have his tumor removed. Notice on the post contrast images, abnormal enhancement and enlargement of that lateral oid.

And here you see the causative lesion in this patient is a cavernous sinus or mecal cave lymphoma metastasis. That is the picture of acute denervation.

Here is a patient with subacute denervation. Notice the muscles have some fatty infiltration. They're slightly diminutive on the right compared to the left notice here.

All of this abnormal enhancement medial oid, lateral oid masseter, even the temporalis muscle up here in the temporal fossa and the causative lesion on this side. Another lymphoma metastasis, this one to Mecal cave and the cavernous sinus.

Here's early chronic denervation in a patient with breast carcinoma. Notice the normal medial oid but notice there's some fatty infiltration out here in the temporalis and in the masseter muscle.

And here we see that patient who had the breast carcinoma I showed you earlier here in Mele Cave here in Mele Cave and going down through a widen foramen oval to get into that masticator space.

So early chronic denervation. And then of course late chronic denervation. You just have fatty infiltration with very diminutive muscles.

As you can see here, the lateral parago very severely affected. Not so much the medial parago in this patient. Temporalis muscle, small TAUs tub. Darius notice that here's the normal size of the TAUs tub barus on the other side.

There's muscle in there that Taurus tube. Darius bump in the nasal pharynx is the covering of the levator veli palatini.

So when you've knocked out three, you knock out the tensor veli palini. So you may see this on coronal imaging. And here's the causative lesion, this trigeminal schwannoma.

Here's late denervation. Notice the fatty infiltration and the diminutive size of these muscles. This is the head of the temporalis muscle. You can't even see it in here.

And when we look up here, notice here's temporalis muscle coming up into the supra zygomatic masticator space. It's completely gone on this side. All fatty infiltration of the muscles.

But also notice here this is mylohyoid muscle. This is anterior digastric muscle. Those muscles are also supplied by that mylohyoid branch of the inferior alveolar nerve. They're really not even identifiable on the side where V three is obliterated.

So these muscles will also be involved. And the causative lesion here is a meningioma in the region of the mecal cave.

Cranial Nerve VI: Abducens Nerve

Sixth nerve. Remember innervates a single muscle, the lateral rectus muscle, the ci sternal segment going to doll's canal crossing over at the level of the baby's bum if you will.

The floor of the fourth is where the sixth nerve nucleus lies or the level of the facial colliculus. And here the CSF following the nerves in Durrell's canal.

Now when patients have six nerve pri um, palsies in primary gaze, the left eye in this patient is wandering medially upward gaze, downward gaze, not so bad. Leftward gaze not so bad.

But here, when the patient looks to the left, excuse me, rightward gaze, you can see there's paralysis of gaze. This eyeball does not go that way. And so it's wandering here, it's not going there. This lateral rectus has to be out.

So this is a left sixth nerve palsy.

So here's a 19-year-old female. Here's a diminutive left lateral rectus compared to the right. And here's that patient who has that MS plaque. So this is brainstem.

Here is the 75-year-old who has a sixth nerve palsy. Notice this cavernoma with his DVA probably best seen here on the gradient or SWI, which is what we're using more commonly uh, in the so sternal segment here, a diminutive left lateral rectus compared to the, excuse me, right lateral rectus compared to the left.

This patient with a meningioma in the cisternal segment going forward, remember the sixth cranial nerve exits the brain stem at the ponto medullary junction and runs up along the clus.

So it's getting hit right here at the entrance to Dores Canal. Another skull base segment here, diminutive on the left. And this is the patient who has the big cholesterol granuloma as I mentioned, I have never seen this before as a causative lesion.

Cranial Nerve VII: Facial Nerve

Alright, a nerve we haven't discussed the facial nerve, its nucleus is in the pontine mentum. It enters also at the ponto medullary sulcus.

It has the circuitous course in the temporal bone and exit at the stylo mastoid foramen. Then it goes into the parotid gland and divides into its five terminal branches.

Now before it does that, it gives off a branch to the occipitals muscle and it gives off a branch to the stapedius muscle. So here is the branch to the stylo hyoid and posterior digastric.

Now we just saw the anterior digastric. It is supplied by branches of V three, but the posterior di gastric is fed by cranial nerve seven.

So stylo hyoid and posterior di gastric here in the parotid gland dividing to its five terminal branches to the muscles of facial expression.

But there's also a muscle to the bator muscle and the platysma muscle.

So when patients have seventh nerve palsy, it can be either central or peripheral. This is an example of a patient with peripheral seven. Notice that the forehead is involved, okay?

The eye is not, the eye is drooping. Okay? Isn't, I mean, excuse me, this one is not closing as it should because of the orbicularis oris muscle not working.

Also notice that there's drooping here of this portion of the mouth from the orbicularis orus orbicularis oculi and there's flattening of the nasal labial fold.

This one is a central per uh, seventh nerve because the forehead is spared. But notice here the drooping of the mouth, the loss of the nasal labial fold on this side, but the orbicularis oculi is working.

Okay, this is interesting. Here is a patient, oh, I wanted to show you the muscles that you can normally see innervated by seven. Most people don't go looking for them, but these are the posterior belly of the digastric muscles here.

The platysma muscles, those are all innervated by seven. Here are the facial muscles of mimetic facial muscles of expression.

These are probably zygomaticus major slash minor or portions of the levator labis superior aus. Also the bator muscle.

Okay, remember parotid gland pierce is the buccinator which hugs the um, maxilla. So these muscles are innervated by seven and you can't identify these.

So this person had a benign mixed tumor removal on the left. Notice here that the um, vaccinator muscle is slightly diminutive compared to the one on the right.

The muscles of facial expression may be a little bit down. But you look here and you see the platysma muscle is out on the left. This is the normal platysma muscle on the right.

So has some symptoms of facial weakness. Here is the same patient who has a diminutive posterior belly of the di gastric on both axial and coronal.

You see the normal posterior belly of the di gastric on the contralateral side. So the di posterior digastric stylo high are both out as is the platysma muscle.

Here is a partial peripheral seventh. This is a, a lesion that affects the mimetic facial muscles. These are normal on the left out here. I mean on the right.

But notice here on the left there's denervation of these muscles. You don't see the normal muscle bundles. And the causative lesion is this very small thing that was listed as high grade carcinoma not otherwise specified in a case from Christine Glastonbury.

Cranial Nerves IX and X: Glossopharyngeal and Vagus Nerves

Looking at cranial nerve nine now its nucleus is in Thera medulla and it exits between the olives and the peduncle. It exits in the pars nervosa segment of the jugular foramen and it goes in the high carotid space.

And we saw the images on the base of the skull in the carotid space previously.

I want you to know I have no lights up here so I don't know what time it's now.

If we look at this nerve, it innervates a single muscle, the stylo pharyngeal muscle to see denervation of this alone I have never seen.

But importantly, this nerve contributes to the pharyngeal plexus that innervates all of these muscles in combination with the contribution from cranial nerve 10 or the vagus nerve.

So we'll go ahead and look at the vagus nerve. Same kind of nucleus rostral medulla exits with nine between the olives and the inferior cerebellar peduncle.

This one exits in the pars VASIs, not the pars nervosa. Do I care? Not really, but they run together. They run in the high carotid space.

Okay, so you know where nine and 10 run together. Now if you look at the innovations from 10, it contributes to this pharyngeal plexus with nine and innervates all of those muscles we looked at.

It also has this superior laryngeal nerve that goes to the inferior constrictor and the crile thyroid muscle and the very important recurrent laryngeal nerve that goes to endo laryngeal muscles including the vocal or the thro retinoid muscle.

Now when we image this nerve, it's important to realize that the recurrent laryngeal nerve comes off of the vagus at different levels depending upon whether you're right or left.

And so on the left, on the right side it comes off the vagus and loops under the subclavian artery. But on the left side it comes off the vagus and it goes all the way down and goes under the aorta at the level of the aortal pulmonary window.

Then both of these asen to get up there in the tracheal esophageal groove.

So if you've got patient with vocal cord paralysis or you during next, you remember Dr. Hudgin was saying she always images to below the aorta. That's what you should always do.

Your imaging should always extend below the level of the AP window.

So here are the normal nerves. The nucleus ambiguous is down here in the medulla. The dorsal motor nucleus of 10 is right here in a pyramid median location.

Here you see 10 and perhaps nine going out to the level of the jugular foramen on these kiss images.

So when you examine someone who has paralysis of these nerves, you'll notice here you see normal tonsor pillars. These are the palatal glosses and palatal pharyngeal muscles innervated by that pharyngeal plexus.

Notice you don't see them on this side when you brush your teeth you can just open your mouth and you should see these things in the morning.

And when you say ah, your uvula should not deviate to the right side, it should just rise in the middle. This tells me the pharyngeal plexus is involved. This is a more proximal lesion.

Now if you just have distal vagal neuropathy, you will not affect the upper um, changes. So this is a left nine and 10 palsy.

Here we have the changes associated with vocal cord paralysis. Some of these cases you've seen, you have rotation and abnormal positioning of the arytenoid cartilage, a dilated ipsilateral piriform sinus.

You have medial positioning and thickening of the area epiglottic fold. Very common, very common, almost 78%.

And here on the coronal imaging you have dilatation of the ipsilateral laryngeal ventricle. You have this unusual fullness of the subglottic area here on that side.

And you have this weird pointing, this characteristic pointing of the thin vocal cords. These are the changes of VCP.

So here's a patient who had a thyroidectomy with voice problems, not a good thing. Notice the medialization here. Notice the enlargement of the piriform sinus.

Here you see that there is atrophy of the cricoarytenoid muscle here. It's full on the contralateral side. And um, so this is a um, vocal cord paralysis from the recurrent laryngeal nerve.

Now if you have proximal vagal neuropathy, you also have involvement of those upper muscles such as the pharyngeal constrictor muscles, in which case you'll have a dilatation of the oral pharynx because you've lost your pharyngeal constrictor muscle that contains the oral pharynx in a rigid fashion.

Um, this is a very old slide, it's the only one I have. But notice that this exhibits enhancement, these constrictor muscles up here, exhibit enhancement compared to the other side.

Now distally, okay, if you don't, if it's not a proximal lesion you just have vocal cord paralysis, which we see. But then we see this large lesion and this is in the posterior carotid space.

The common carotid is displaced anteriorly. You can see it goes all the way down into the mediastinum. And these were actually two separate lesions and when biopsy, these turned out to be malignant schwannomas or malignant peripheral nerve sheath tumors.

Here's a patient with hoarseness and a distal 10. Okay? And this person has left recurrent laryngeal parais, but the gag is intact so you know it's not high, it's low.

This was due from this small atherosclerotic aortic aneurysm right in the AP window where the left vagus goes underneath the aortic arch.

Cranial Nerve XI: Accessory Nerve

Moving to cranial nerve 11. Pretty easy. It innervates two main muscles, the sternal cla mastoid and trapezius muscle on physical exam at zero in neutral the shoulder droops.

You don't see the sternal cid mastoid muscle bundle here. And when you turn the head against resistance, if you remember your cranial nerve exam, this muscle shows up a little bit but not when you're turning it this way.

So you've got not apparent on turning to the right against force resistance.

So here's a 33-year-old with vocal cord paralysis and abnormal gag. That's nine and 10, but he also had a weak shoulder shrug. Notice normal sternal ma mastoid and trapezius muscles, they're completely out on this side.

So there's also 11. So where do you look? Well, you know, you have to look higher. Here's the vocal cord paralysis.

And you look up high and at the jugular foramen, right at the skull base there's a lesion. And this was a schwannoma here.

Another 36-year-old felt to be postviral and this was read as normal. Now I have to tell you, this just came across this last week.

Here's the changes of the vocal cord paralysis. There's the dilatation of the laryngeal ventricle and you look up here, I can't believe this was missed, but this was right at the top of a long neck study.

There is a lesion here in the jugular foramen don't see flow voids but favored pair glioma.

In addition to that, notice here the difference in size of the SCM. Here you see normal sternal collateral, mastoid, maybe diminutive.

When we look at further views here you see the trapezius muscle on one side, diminutive on the other. And maybe you can appreciate there is in fact enlargement of the levator scapula muscle.

This muscle takes over when eleven's been denervated or cut at surgery. And so here you see enlargement of that.

Now you look up here and you clearly see this lesion with flow voids appear glioma at the jugular foramen.

And I thought this was really cool. Here are those nerves crossing over nine, 10, and 11. And look here you can actually see the start of this jugular paraganglioma here on the cranial nerves in the so sternal segment as they go to the jugular foramen.

I've never encountered that where I actually see them on the cranial nerves.

Cranial Nerve XII: Hypoglossal Nerve

And then I'm gonna skip this and go on to cranial nerve 12 'cause I'm almost out of time. This innervates the intrinsic and extrinsic muscles of the tongue.

So here is a patient who sticks out their tongue and it deviates to the right side. That means her pathology is on the right, the tongue deviates towards the side of pathology.

This is what it might look like in the left tongue marked atrophy of the hemi tongue, longstanding denervation.

Here are the hypo. Here's the hypoglossal nucleus at the level of the medulla and the hypoglossal trigone okay is formed by the nucleus and denting it here you can actually maybe see the nerves crossing over, although sometimes they don't coalesce until you get into the hypoglossal canal.

Here is the typical well corticated hypoglossal canal at the skull base.

This patient is two weeks post tonsillectomy. Notice the hemi tongue is enlarged. That's abnormal.

Here is a patient that has, uh, subacute denervation two weeks out. So early fatty infiltration and hemi tongue enlargement. This one hasn't lost its size yet, but completely fatty infiltration without volume loss.

This is what chronic denervation looks like when the tongue is totally atrophic and prolapses into the oral pharynx.

This one we've seen before, this hemi tongue, um, early chronic or late subacute from this large pair glioma

Here is late tongue atrophy. Notice the hemi tongue very atrophic. Notice this lesion at the jugular, uh, excuse me, at the hypoglossal canal in the skull base.

And when you look at the MR images, we see this lesion right at the level of where the hypoglossal canal is. This was a hypoglossal schwan.

And finally this case, this is a 17-year-old trying to bulk up for the prom. He's a junior, senior girl invites him. So he decides he is going to go to the gym.

Well he is getting bigger and bigger on the right, but nothing's happening on the left. And now he just looks dorky.

So if you look at this, you see the sternal cla mastoid trapezius and crico fige muscle are a cricoarytenoid out here compared to the normal muscles on the other side.

You look higher, his tongue is out. Where do you have to look where they all run together At the high carotid space or skull base, we look up at the high carotid space, there is a lesion.

And on ct, you see this lesion is calcified. This makes it not a para glioma. This was a meningioma.

The good thing is we found his problem. The bad thing is he should stop exercising or he is gonna always look strange.

Conclusion

So anyway, it's been a pleasure being with you. That'll be it for me. And thank you so much for your attention.