Lecture 9 4th nerve palsy Flashcards
1.Where do you find the 4th nerve?
2.What is unique about this nerve?
3.Describe the route this nerve takes?
- midbrain caudal to 3rd nerve nucleus
- only nerve to exit dorsally from the brainstem
- -passes laterally around the midbrain tectum
-crosses superior cerebellar artery and enters the dura at the free edge of the tentorium
-runs forwards into the cavernous sinus
-enters orbit via the Superior orbital fissure
-runs forqrd to the trochlear at the angle between the superior and medial wall
- What causes congenital 4th nerve palsy?
- What are some general features of congenital 4th nerve palsy?
1 *SO tendon being loose, absent or abnormally inserted onto globe
*The SO muscle being abnormally developed.
*Trochlea is abnormal or absent.
- SO interaction
-diagnosed from birth
-may have other health problems too
-WONT COMPLAIN of double vision
-may have head tilt or turn
-eye on the affected side may shoot upwards when child looks to opposite side
What are the causes of acquired 4th nerve palsy?
*Trauma (head injuries like road traffic accidents, sports)
*Vascular: result of poor blood supply to 4th nerve caused by HBP, DM or high cholesterol (microvascular palsies)
*Inflammation in the region of the nerve or direct pressure on the nerve
*80% of microvascular SO palsies will resolve in 3-6 months.
*Spontaneous recovery is less likely to occur if SO palsy caused by head trauma or tumour
How can you check 4th nerve function is still intact when 3rd nerve is damaged?
look for intorsion of affected eye as depression in abduction
What are the actions of the superior oblique muscle?
Primary action: INTORSION (maximum in depression and when globe is abducted)
secondary action: DEPRESSION (maximum when globe is adducted)
tertiary action: ABDUCTION (minor role)
How can you classify a 4th nerve palsy?
congenital
acquired
unilateral or bilateral
- What can you expect to see on cover test in someone who has a unilateral 4th nerve palsy?
- When is a person with 4th nerve palsy more likely to have diplopia?
- What are they likely to have problems doing?
- What AHP are they likely to have?
1.CT: hyper deviation in affected eye alongside possible Eso and extorsion)
*Likely to be great at near than distance.
*Deviation in PP may be latent or manifest.
*Angle of deviation will increase to the opposite side of the affected eye.
- acquired.
*Vertical diplopia is maximum on contralateral depression
*Torsional diplopia is maximum on ipsilateral depression
3*Problems with reading, eating, and going downstairs
- chin down, face turn and head tilt to opposite side
What is the muscle sequelae for superior oblique underaction?
- SO underaction of affected eye
- Contralateral IR overaction (non-affected eye)
- IO overaction of affected eye
- contralateral SR under action
- In bilateral 4th nerve palsy, how will you know if both eyes are equally affected?
- What OM results will you expect in bilateral 4th nerve palsy?
- What must you assume about all 4th nerve palsies?
- alternating hyper deviation
2.Hyper deviation will reverse in contralateral field (right to left on left gaze and left to right on right gaze)
*V pattern (equal to or more than 15D)
*Significant torsion in ACQUIRED palsy
*AHP (chin down)
- bilateral until proven otherwise. can be asymmetrical.
What signs will someone with congenital 4th nerve palsy present with?
*Well controlled with AHP but may decompensate in childhood or later life
*With AHP, they will have well controlled latent deviation and some BSV
*WITHOUT AHP: manifest deviation likely
*Rare to find no evidence of BSV
*Vertical fusion range of 6D may increase
*Will have stereopsis with AHP
*Ocular motility will show full muscle sequelae.
*Convergence may be reduced due to increasing hyper deviation as eyes converge
What are the symptoms of a decompensating congenital 4th nerve palsy?
- Asthenopia
- Blurred vision
- Possible diplopia but vague onset and duration
What are the symptoms of acquired 4th nerve palsy?
sudden onset vertical diplopia
ask specific questions about head trauma
What is a key feature to differentiate between congenital and acquired 4th nerve palsy?
congenital: sensory adaption to torsion. when viewing fundus with ophthalmoscope, macula will be considerably lower than optic disc to show extorted fundus. can also measure torsion with synoptophore in 9 positions of gaze.
acquired: will be symptomatic to torsion
What are the symptoms of acquired 4th nerve palsy?
*Will know exact onset of diplopia.
*May need prompting about GH (microvascular causes, head trauma)
*Troubled with cyclovertical diplopia.
*Bilateral 4th nerve palsy: torsion may prevent fusion in any position of gaze (10 degrees)
- What test can be used to confirm SO under action?
- How do you perform it?
- Bielschowsky head tilt test
2.*PCT is performed at 3 meters with px titling their head to the right side followed by left side.
*Based on righting reflexes (head tilt causes intorsion of ipsilateral eye and extortion of contralateral eye)
*In SO palsies, hyper deviation increases on head tilt to the affected side.
