4th nerve pasly Flashcards
(16 cards)
4th nerve pasly
IV cranial nerve pasly causing a pasly of the superior oblique muscles
purely a motor nerve
can be unilateral/bilateral/acquired/congenital.
features:-
1. loss of depression
2. loss of incyclotortion
3. loss of relative abduction
Pathway
Starts at trochlear nucleas in midbrain
Excits brainstem and crosses over to other side
Passes through the cavernous sinus alongside the sidewall
enters the orbit via the superior orbital fissure and innervates superior oblique
Aetiology acquired
Closed head trauma accounts for most acquired
bilateral palsies and many unilateral
Intracranial stroke
Microvascular
MG
Midbrain stroke
Aetiology congenital
38% unilateral and 10% bilateral
anotomical anomoly of superior oblique tendon,
complete absence, abnirmal insertion or excessive lax tendon.
Congenital unilateral IVN pasly
Patients usually presents with an AHP in choldhood but this can also be defected quiet late in life
All children with an AHP should have a full orthoptic exam to rule out an ocular cause
Beilschowsky’s head tilt exam
Performed at 3m
Head tilted to 30 degrees to affected side and if the hypermetropia increases then a SO pasly is present
Head tilt to unaffected side should show very little diff in the deviation suggesting a contralateral SR
possitive result should be minimum 5^ difference from tilting right to left
Parks 3 step
cover test performed in the primary position
Alternate covertest performed on dextroversion and laevoversion to assess the greater vertical deviations
BHHT is then performed tiklting 30 degrees right and left and noting down the increase in hyperdeviation
Explanation
RSO/LSO pasly
Tilt right - RE is intorted by the superior oblique and the superior rectus
The depressing action of the SO is balanced by the elevating action of the SR and the eye remains level
If a SO pasly, the elevating action of the SR us unopposed adn Hydev increased
This is a positive result
Congenital Bilaterlal IVN palsy
Usually a small v pattern esotropia with small hyperdeviations of the non-fixing eye
Chin depression
Possitive Bs on either side confirms a bilateral pasly, reverse on the hypermetropia on the R and L tilt
no tortion symptoms byt obvs on fundus
Acquired IVN pasly
Recent onset on vertical Diplopia
No evidence of enlarged vertical fusional ranges
Subject awareness of AHP
History of trauma
unilateral IVN pasly
Tortion is rarely complaioned in unilateral paslies
Examination is as before with a possitive BHHT
hypermetropia
cyclophoria / tropia
Bilateral IVN pasly
tortional diplopia is the main symptom, theefore preventing fusional reserves
Excyclodeviation may exceed 10 degrees in PP
Marked chin depression may be seen
reversal of the hypertropia or R and L gaze, with a possitive BHHT on either side.
V eso pattern
Investigations
Detailed history- microvascular causes
history of significant trauma- Skull, loss of consciousness, subdural heamotoma.
Full blood count, Bloo dsugar level and serum lipids.
Investigating Torsion
Can be measured sunjectivally and onjectivally
Double maddox rod, synoptophore, torsinometer, dully adapt on lees screen
synoptophore allows you to measure thr devation and torsion together in a position of gaze
cyclodeviations is worse on depression and a barrier to fusions
Muscle sequalae in 4th
Underaction of ipsialteral SO overreaction of contrralateral IR overaction of ipsilateral IO.
inhibition pasly of contralateral SR
Pattern
overrection of contralaterla synergist according to herings law of equal innervation- Immediately
overreaction of ipsilateral antagonist accorning to sherringtons law of reprocial innervation- TIme
Secondary inhibition of the contralateral antagonist with herrings law. this happens because the overreaction of the antagonist in the affected eye requires less innervation - More time
