6th Nerve Palsy- MEH Flashcards
What is another name for the 6th cranial nerve?
Abducens nerve
Where is the 6th nerve nucleus found?
Base of the 4th ventricle in the pons (brainstem)
What two types of cells are found in the 6th nerve nucleus?
Motor neurones that innervate the ipsilateral lateral recuts
Inter-nuclear neurones that innervate the contralateral medial recuts via MFL
Explain the course that the 6th nerve takes to reach lateral recuts.
- Exits brainstem anteriorly
- Ascends the Clivus
- Passes over the apex of the temporal bone
- Goes through cavernous sinus
- It enters the orbit vis superior orbital fissure
- Terminates at the lateral recuts muscles
What is the function of the lateral recuts?
Inserts closest to the limbus and abducts
What is the lateral recti’s contralateral synergist?
Medial rectus
If there is a leison in the 6th nerve nucleus what issue will they have ?
Horizontal palsy on the same side
Fill in the gaps
Are congenital or acquired 6th nerve palsies more common?
Acquired
What is the cause of congenital 6th nerve palsies?
- Traumatic birth
- transient in newborns- this often resolves its self
What is the eight aetiologies of 6th nerve palsies in ADULTS?
- Microvascular (most common in older people)
- Vascular causes (aneurysms)
- Neoplasms (tumours)
- Trauma
- Neurological disorder (migraine, MS, raised inter cranial pressure)
- Iatrogenic
- Idiopathic
- Inflammatory
What is the aetiologies of 6th nerve palsies in children?
- Intracranial tumours (most common)
- Raised intracranial hypertension
- Idiopathic
- Trauma
- Inflammation
- Post viral
- Secondary to middle ear disease, drugs
What are some clinical features of unilateral 6th nerve palsy?
- Esotropia which is greater in the distance, px may be binocular at near with esophoria
- Limitation of abduction on affected side
- AHP- turned to affected side
- Field of BSV displaced to unaffected side
What you make sure you cover when taking a history for investigation 6th nerve palsy?
- Onset; is it recent? Or longstanding which could indicate complete palsy
- GH
- Age
- History of head injury
- Pre existing squint?
What tests would you carry out?
CT (with and without AHP)
OM
Hess chart to monitor progression
* looking for lateral face incomitances
What is the muscle sequelae you may see with a 6th nerve palsy px?
1) U/a affected LR
2) O/a contralateral synergist MR
3) O/a Ipsilateral synergist MR
4) U/a of contralateral rectus
In newly acquired 6th nerve palsies, which steps would you be likely to see?
1 & 2
Which steps of muscle sequelae can be seen here of a 6th nerve palsy?
1 &2
Which steps of muscle sequelae can be seen here of a 6th nerve palsy?
1 & 2 & 3
Which steps of muscle sequelae can be seen here of a 6th nerve palsy?
1,2,3,4
What is used to measure field of BSV?
An arc perimeter
Why is field of BSV useful to measure?
Helpful for planning surgery both post and pre op
What is a bilateral 6th nerve palsy?
Affects both LR—> bilateral abduction deficit which can be symmetrical or asymmetrical
*they may have AHP for BSV
How is 6th nerve palsy managed in children?
Sometimes the have spontaneous recovery
Encourage AHP, fresnel prism, BTXA to MR, occlusion for amb
Why must you refer to a neurologist for children with suspect 6th nerve palsy?
To establish the causes + get an MRI
How is 6th nerve palsy managed In adults with new onset?
Regularly monitored for spontaneous recovery (majority of micro vascular ones resolve with in 12 months)
Some do not though
What is the reason microvascular nerve palsies get better before they get worse (you should tell your px this) when receiving treatment?
As they have been seeing double, they may have have just been ignoring one. As they recover they images become closer= more noticeable to the px
What is conservative management for 6th nerve palsy?
- Occlusion for large angle SOT using a patch or bangerter foil
- Fresnel prism for smaller deviations
At what point would you incorporate a prism into someone’s rx for conservative management of 6th nerve palsy?
If they know the px will not recover & they are stable for 6th months with Fresnel prism
What is the aim of surgery for 6th nerve palsy?
Resolve dipl in PP + provide large area of BSV in PP and depression
What does type and degree of surgical management depend on?
- Uni or bi lateral palsy
- Degree of paresis of LR
- Size of deviation
For smaller deviations an reasonable abductions of a unilateral 6th nerve palsy, what surgery would be done?
MR recession and LR resection of affected eye
For a complete absence of abduction with a unilateral 6th nerve palsy, what surgery would be done?
BTXA to ipsilateral MR to asses abduction
With a unilateral 6th nerve palsy and no lateral rectus function what surgery would be carried out?
Transposition procedure: SR and IR transposed and sutured into LR
BTXA may be give to MR of affected eye too
For px with bilateral 6th nerve palsy, what surgery would be done?
Operate one eye at a time (3 mth gap), transposing procedure with BXTA to MR too
What are 8 differential diagnoses of 6th nerve palsy?
- Duanes retraction syndrome
- High myopia
- Graves Oribitopathy (thyroid eye disease)
- Orbital trauma
- Decompensating distance SOP
- Age-related distance esotropia
- Spasm of near reflex
- Myaesthenia Gravis (this is a DD for most conditions)
What would a px with age-related esotropia complain of?
Intermittent dipl in distance, and not sure of onset
What signs would you see with a px with age-related SOT?
No/ smaller esophoria deviation at near
Smaller/moderate esotropia at distance
No significant rx
Eye movements concomitant
What causes age-related esotorpia?
Inferior displacement of horizontal rectus muscle or atrophy on orbit leading to sagging LR
How is atrophy on orbit leading to sagging LR managed?
Incorporation of prism in glasses
Would you like some case scenarios?
Look at the slides at the end of the PP for a couple for them
