Cranial Nerve Lesion.. Which side?

[fuzzywuz]

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Hey all,

Maybe it's because I'm overthinking stuff, but I've managed to confused myself with CN lesions.

Do cranial nerves decussate? I thought only CN IV does that.

For example... if the R CN XII was lesioned, the tongue would point towards the side of the lesion. Meaning, the nerve on the right side was damaged. I can also further this by saying that the R hypoglossal nuclei is damaged right?

I'm using this example because in FA 2011...P418, it says "Decussates before medulla and synapse on contralateral hypoglossal nucleus." Not sure what that means?..

Thanks!

 

[coralis]

CN nerves do not decussate, thus if you have a CN lesion it'll always be IPSILATERAL to the lesion site, this is how you can figure out in .02 seconds which side a lesion is, even in those complicated artery obstruction cases/brainstem lesions, if they give you a CN sign... you'll know the side right away and from there just use a rule of thumb:

Midbrain 1-3
Pons 5-8
Medulla 9-12 +V3

Good luck

Oh and CN IV doesn't decussate it's just the only one that exits from the back of the pons and has to loop around but it stays on the same side

 

[mastamark]

Hey all,

Maybe it's because I'm overthinking stuff, but I've managed to confused myself with CN lesions.

Do cranial nerves decussate? I thought only CN IV does that.

For example... if the R CN XII was lesioned, the tongue would point towards the side of the lesion. Meaning, the nerve on the right side was damaged. I can also further this by saying that the R hypoglossal nuclei is damaged right?

I'm using this example because in FA 2011...P418, it says "Decussates before medulla and synapse on contralateral hypoglossal nucleus." Not sure what that means?..

Thanks!

Hypoglossal is one of those weird ones. As it leaves cortex it will decussate on contralateral XII nucleus for some reason, unlike the other CNs. So this is why if you have the tongue going away from lesion if it's UMN and if it goes toward lesion you know you're dealing with LMN lesion.

 

[fuzzywuz]

Awesome, thanks guys!

 

[Step1Hash]

CN nerves do not decussate, thus if you have a CN lesion it'll always be IPSILATERAL to the lesion site, this is how you can figure out in .02 seconds which side a lesion is, even in those complicated artery obstruction cases/brainstem lesions, if they give you a CN sign... you'll know the side right away and from there just use a rule of thumb:

Midbrain 1-3
Pons 5-8
Medulla 9-12 +V3

Good luck

Oh and CN IV doesn't decussate it's just the only one that exits from the back of the pons and has to loop around but it stays on the same side

Are you sure about this? I thought trochlear nerve lesions are ipsalateral but nuceli lesions are contralater bc the nerves cross after leaving the brainstem dorsally at the level of inferior colliculus.

 

[mastamark]

Awesome, thanks guys!

No prob. I just looked up what I wrote in fear I said something wrong. Had my finger on the edit button hehe, but yeah the corticobulbar fibers of XII cross right before hitting their nuclei on the contralateral side.

Here check this site out if you haven't already. I used it to help with first aid when something wasn't explained out well.

http://www.neuroanatomy.wisc.edu/virtualbrain/BrainStem/07CNXII.html

 

[Step1Hash]

No prob. I just looked up what I wrote in fear I said something wrong. Had my finger on the edit button hehe, but yeah the corticobulbar fibers of XII cross right before hitting their nuclei on the contralateral side.

Here check this site out if you haven't already. I used it to help with first aid when something wasn't explained out well.

http://www.neuroanatomy.wisc.edu/virtualbrain/BrainStem/07CNXII.html

thanks for this too...i would have had no idea if I didn't read this post haha.

 

[coralis]

[/B]

Are you sure about this? I thought trochlear nerve lesions are ipsalateral but nuceli lesions are contralater bc the nerves cross after leaving the brainstem dorsally at the level of inferior colliculus.

Oh, you're right, trochlear does arise from the contralateral nucleus... my apologies. I sometimes get carried away with the rule of thumb, yes CN IV is an exception for the decussation, ....

however the rule of thumb stands, CN lesion (LMNs) will be ipsilateral, no matter what nerve it is. Nuclear lesions will be more complicated because the CNS output UMNs will come into play.

 

[coralis]

No prob. I just looked up what I wrote in fear I said something wrong. Had my finger on the edit button hehe, but yeah the corticobulbar fibers of XII cross right before hitting their nuclei on the contralateral side.

Here check this site out if you haven't already. I used it to help with first aid when something wasn't explained out well.

http://www.neuroanatomy.wisc.edu/virtualbrain/BrainStem/07CNXII.html

The CN nerve itself does not cross, its UMN corticobulbar input does, so do others ex: facial has mainly contralateral but also some ipsilateral UMN input, hence why we can wrinkle the forehead if the lesion is UMN vs/ LMN; CN VI has contralateral input from CN III etc; BUT the CN nerves themselves are peripheral nerves (LMNs) stemming from the nucleus, the corticobulbar tracts are UMN fibers, thus technically not part of the nerve itself.

 

[mastamark]

The CN nerve itself does not cross, its UMN corticobulbar input does, so do others ex: facial has mainly contralateral but also some ipsilateral UMN input, hence why we can wrinkle the forehead if the lesion is UMN vs/ LMN; CN VI has contralateral input from CN III etc; BUT the CN nerves themselves are peripheral nerves (LMNs) stemming from the nucleus, the corticobulbar tracts are UMN fibers, thus technically not part of the nerve itself.

You are absolutely correct. Good catch!👍 There is contralateral cortical input but, not called "nerve" proper till it get's out of the nucleus. My bad to all.

Thank goodness they didn't ask something like that on my test, I would feel worse than I already do.

 

[coralis]

You are absolutely correct. Good catch!👍 There is contralateral cortical input but, not called "nerve" proper till it get's out of the nucleus. My bad to all.

Thank goodness they didn't ask something like that on my test, I would feel worse than I already do.

😉 that's why this forum is good and these discussions helpful!!! For these moments!

 

[monsoon338]

This issue is confusing.

Main question - does the entire cranial nerve pathway (the whole thing) have a contralateral effect? Example - Is the left eye movements controlled by the cranial nerve that originates on the right brain stem?

 

[cooldoc89]

So why is it that the Sternocleodomastoid deviates to opposite side when the CN 11 is lesion while traps deviate towards side of lesion, should they not be the same?

 

[Wolverines83]

So why is it that the Sternocleodomastoid deviates to opposite side when the CN 11 is lesion while traps deviate towards side of lesion, should they not be the same?

SCM contraction sidebends to the same side as the muscle and rotates the head away from the muscle (contract your left SCM now and you will have your left ear near your left clavicle while looking to the right).

lesioning left CN11 will paralyze shrugging of the left shoulder (left trap) and rotation of head to right (left SCM).

 

[Phloston]

Hey all,

Maybe it's because I'm overthinking stuff, but I've managed to confused myself with CN lesions.

Do cranial nerves decussate? I thought only CN IV does that.

For example... if the R CN XII was lesioned, the tongue would point towards the side of the lesion. Meaning, the nerve on the right side was damaged. I can also further this by saying that the R hypoglossal nuclei is damaged right?

I'm using this example because in FA 2011...P418, it says "Decussates before medulla and synapse on contralateral hypoglossal nucleus." Not sure what that means?..

Thanks!

If they show you a brainstem pic, your deficit is always ipsilateral to the lesion when selecting your answer.

 

[HSE21]

ALL Upper motor Neurons decussate just before synapsing with lower motor neurons in the motor nuclei in the brainstem.

Bilateral motor cortex innervation (i.e. UMN innervation) is seen in nerves innervating the muscles of the eye, eyelids and forehead e.g. CN III,IV,IV part of VII ( frontalis, orbicualris oculi). you could look at it from an evolutionary perspective to preserve the sense of sight.

So
UMN lesion --> Contralateral deficit
LMN lesion --> Ipsilateral deficit

 

[cooldoc89]

This issue is confusing.

Main question - does the entire cranial nerve pathway (the whole thing) have a contralateral effect? Example - Is the left eye movements controlled by the cranial nerve that originates on the right brain stem?

please answer this questions in a very simplified way bec i am still confused..

 

[Wolverines83]

please answer this questions in a very simplified way bec i am still confused..

here's the deal in general for the entire body:

UMN lesion = contralateral deficit. Remember right hemisphere controls left body
LMN lesion = ipsilateral deficit (in the spinal cord, for example)

****Cranial nerves are LMN****

LMN = ipsilateral

Cranial nerves = ipsilateral

 

[HSE21]

please answer this questions in a very simplified way bec i am still confused..

Entire cranial Nerve pathway ? .....
In the MOST basic way :
1- The motor pathway consists of 2 motor neurons, 1 UMN and 1 LMN.
2- say a Cell body of an upper motor neuron is in the motor cortex (cranial nerves motor fibres arise from the most lateral of the pre-central gyrus-head and neck areas-, just above the lateral fissure, supplied by the Middle cerebral artery, a stroke here will cause CONTRALATERAL).
- It passes through the corticobulbar tract in the genu of the internal capsule (which is supplied by the medial and lateral lenticulostriate arteries (MCA) and a stroke here causes CONTRALATERAL deficit) then fibres will decussate and synapse with the cell body of the lower motor neurons in the brainstem.
- The axons of LMNs will make the nerve which arises from the brainstem.
- The brain stem is supplied by the vertebrobasilar system and a stroke here will cause IPSILATERAL deficit.

Conclusion :
- If there is an UMN lesion in a bilaterally innervated neuron e.g. III,IV,VI there won't be a contralateral deficit.
- If there is an UMN lesion in the facial nerve (which has PARTIAL bilateral innervation --> to frontalis and Orbicularis oculi) there will be a deficit with sparing of these muscles.
- If there is a LMN lesion then it does not matter if the nerve was bilateral or trilateral UMN innervation, there will be ipsilateral deficit to the innervated region, because you have interrupted the innervation of the muscle.

if you still don't understand, please take the largest Neurology book you could find a read from it 🙂