IV Nerve Palsy - Trochlear Flashcards
1
Q
Describe a IVth nerve palsy - which muscle is affected?
A
- IV CN Palsy causes a palsy of SO muscle
o 4th CN only supplies ONE MUSCLE - Purely a motor muscle
- Unilateral/bilateral
o More commonly bilateral - Congenital/acquired
o Can sometimes be congenital but not found until later teen or early adulthood
2
Q
What are the features of a IVth nerve palsy?
A
- Loss of depression so affected eye is sitting higher
o Deviation is a hyper deviation that may or may not be controlled – more eso than exo - Loss of incyclotorsion
- Loss of relative abduction
SO works at near – if issue with SO – will have bigger vertical & bigger ESO at near than at distance
Convergence should be completely fine
3
Q
Describe the anatomy of the IVth nerve?
A
- Dorsal midbrain at level of inferior colliculus ventral to cerebral aqueduct
- Decussation – R nucleus becomes L nerve, L nucleus becomes R nerve
- Moves posterior
- Fibres cross over
- Leaves midbrain
- Sweeps round midbrain
- Runs between posterior cerebral artery & superior cerebellar artery
- Enters cavernous sinus below IIIrd & ophthalmic division of Vth
- Enters Superior Orbital Fissure above annulus of Zinn
- Innervates SO
- SO is a complex muscle – lots can happen to it
4
Q
What is the aetiology of acquired IVth nerve palsy?
A
- Closed head trauma accounts for most acquired bilateral palsies & many unilateral
o Due to anatomy bashing head off floor, decelerating injury e.g. traffic accident (whiplash)
o In a child, trauma would be quite common
If have teenager w/ 4th nerve palsy – will not know if congenital or through childhood trauma
If adult develops it with no trauma then could be a vascular reason - Microvascular – hypertension, DM, high cholesterol
- Midbrain stroke
- Intracranial tumours – not common cause of 4th palsy (so not really looking for these pxs to be scanned unless other things ruled out)
- Myasthenia Gravis – can mimic anything – if px has this they will have other signs & symptoms too (ALWAYS WRITE THIS IN THE EXAM!!)
Think off aetiology in age groups – what could apply to this px?
5
Q
What is the aetiology of congenital IVth nerve palsy?
A
- 38.3% unilateral – 10% bilateral
- Anatomical anomaly of SO tendon, complete absence, abnormal insertion or excessively lax tendon
o If due to lax tendon then needs different management - Autosomal dominant form of inherited congenital SO palsy
o Can be familial
6
Q
Describe a congenital unilateral IVth nerve palsy?
A
- Px usually presents w/ an AHP (abnormal head position) in childhood but that can also be detected quite late in life
o AHP needs investigated, look at old photos - All children w/ an AHP should have a full orthoptic/ophthalmological examination to rule out an ocular cause
- AHP in unilateral form:
o Will tilt to unaffected side
o Vertical deviation: e.g R>L –> will always tilt to lower eye
o Head tilt to left – probably have a R 4th nerve palsy
7
Q
Describe a congenital bilateral IVth nerve palsy?
A
- Usually a V-pattern Esotropia with hyperdeviation of non-fixing eye
- Chin depression
- +ve BHTT on either side confirms a bilateral palsy
o Reversal of hypertropia on R & L tilt - No torsional symptoms but obvious torsion on fundoscopy
o No torsional symptoms since brain suppresses it
8
Q
Describe Abnormal Head Posture and facial asymmetry?
A
- Head tilt unaffected side
- Head turn to unaffected side
- Chin depression
- If acquired AHP then will have vertical diplopia
- Longstanding problems will have a compensatory head posture & new problems will not
Facial asymmetry – head tilt, chin depression – head tilt/head posture is what is allowing child to see clearly (not have diplopia) - Facial asymmetry is common in congenital palsies – it develops secondary to torticollis (shortening of neck) – facial asymmetry due to parts of face growing at different rates
- Reduction in distance between lateral canthus & corner of mouth on side of head posture
9
Q
What is intermittent diplopia? Where will the deviation in a IVth nerve palsy be larger? How will you see excylcotorsion deviation?
A
- Intermittent diplopia (at times can fuse, at other times cannot) can be 1st sign of decompensation as child ages – huge ability to have vertical fusion
- Large hyperphoria w/ AHP & larger hypertropia w/o AHP
- Deviation will usually be greater at near
- Horizontal deviation of 8Δ occurs in 10% of cases will be based on what they had before – more common is ESOphoria but if they already had an EXOphoria then they will still have this
- Excyclodeviation can be seen on fundoscopy – will see the discs is tilted in comparison to macula – will barely see this deviation on cover test
10
Q
Compare normal vertical fusion to IVth nerve palsy vertical fusion?
A
A normal px will have 3 dioptres of vertical fusion
Pxs w/ a longstanding or congenital 4th nerve palsy will often have increased vertical fusion (much more than 3 degrees)
Longstanding – could get this nerve palsy at 10 years old then have had it whole life
11
Q
Describe the Bielschowsky Head Tilt Test (BHHT) in IVth Nerve Palsy?
A
- Performed at 3 metres
o This is to not isolate any muscles – if at 6m then favouring distance, if do it a lot closer then favouring near - Target: kay picture or letter on logMAR chart
- Want know which direction the deviation is biggest in
- Head is tilted 30° to affected side & if hypertropia increases then a SO palsy is present
o If head tilted to affected side – eye shoots up – deviation gets bigger (SR now acting unopposed (do not have SO to keep eyes level) - Head tilt to unaffected side should show v little difference in deviation suggesting a contralateral SR under action
- +ve result should be minimum 5Δ difference from tilting right to left
o For it to be a +ve result then would have to measure with prism bars
12
Q
Describe Parks 3 Step Test?
A
- Cover test performed in primary position
- Alternate cover test performed on dextroversion (BEs to R) & laevoversion (BEs to L) to assess the greater vertical deviation – looking left & looking right to see if there is a vertical deviation
- BHHT is then performed tilting 30° right & left & noting the increase in hyperdeviation
13
Q
Describe acquired IVth nerve palsy?
A
- Recent onset of vertical diplopia
- No evidence of enlarged vertical fusion ranges
- Subjective awareness of AHP – px will know it
- BHHT will be +ve if px tilts to affected side
- History of trauma (most common aetiological factor)
14
Q
Describe unilateral IVth nerve palsy?
A
- Torsion is rarely complained of in unilateral palsies
- Examination is as before w/ a positive BHHT
- Hypertropia
- Excyclophoria/tropia
Can fuse ~3 degrees of excyclotorsion/incyclotorsion
Pxs do not know how to complain about torsion – often cannot tell if things are tilted or not
Cannot correct torsion optically – these pxs need surgery – REFER THE PX
15
Q
Describe a bilateral IVth nerve palsy?
A
- Torsional diplopia is main symptom – this prevents fusion
- Excyclodeviation may exceed 10° in PP
- Marked chin depression may be seen
o More likely to be ESO looking down - Reversal of hypertropia on R & L gaze – w/ a +ve BHHT
- V Eso pattern
o The more eso further down you get them to look because SO has no function on abduction anymore - Bilateral palsy biggest issue is the torsion
o Torsion cannot be relieved by prism – occlude one eye (to allow px to have comfortable viewing) – then consider surgery
