Lecture 19 3rd nerve palsy Flashcards
- What is the 3rd nerve called?
- Where is it’s nucleus found?
- What path does it take?
- oculomotor nerve
- located in the midbrain of the brainstem, ventral to cerebral aqueduct
- Nerve emerges from anterior aspect of the midbrain passing inferiorly to the posterior cerebral artery and superiorly through the superior cerebellur artery.
*The nerve then pierces the jura matter and enters the lateral aspect of cavernous sinus.
*Within the cavernous sinus, it receives sympathetic branches from the internal carotid plexus. These fibres don’t combine with ocular motor nerve, only travel within its sheath.
*The nerve leaves cranial cavity via superior orbital fissure
What are the 2 branches of the 3rd nerve and what muscles do they innervate?
1.Superior division innervates:
-superior rectus
-levator muscles (LPS)
2.Inferior division innervates:
-medial rectus
-Inferior rectus
-Inferior oblique
-Branch of pupil sphincter
-Branch of ciliary muscles (supply’s pre-ganglionic parasympathetic fibres to ciliary ganglion which innervates sphincter pupillae and ciliary muscles)
What are the characteristics of a 3rd nerve palsy?
1.Exo and hypotropia
2.Limited motility (only LR and SO functioning)
3.Dilated pupil that doesn’t respond normally to light
4.Reduced or absent accommodation
3.ptosis
What is the aetiology of an acquired 3rd nerve palsy in adults?
- Aneurysms
*When pressure it put on the nerve or nerve doesn’t get enough blood, you can get 3rd nerve palsy
*Compression is a result of serious disorders such as a bulge or aneurysm in artery suppling the brain
*Most common cause is compression by posterior communicating artery (PCA) aneurysm.
*Signs may continue to evolve, and pupil may not be involved at first instance. This may not be fixed on first presentation.
*Urgent referral to HES REQUIRED as first presentation as can be life threatening.
2.Trauma
*Closed head injury, road traffic accidents, kick to the head from a horse
*Often has pupil involvement
3.Vascular
*Diabetic or hypertensive
*Often complete recovery
*50% undiagnosed cases
4.Undetermined
5.Direct damage from adjacent tumours
*Pituitary tumour (3% of cases)
6.Inflammation or infection
- recent vaccinations
- idiopathic
What can cause a congenital 3rd nerve palsy?
Isolated idiopathic
-no specific cause
-presumed developmental defect of nucleus or in the pathway
hereditary (autosomal recessive)
neurological defects
Closed head trauma (severe head injury)
Tumour/aneurysm (pituitary tumour)
Inflammation (meningitis)
Migraine (rare/transient, positive sickle cell trait)
How can you classify a 3rd nerve palsy?
complete: involves superior and posterior division
incomplete: superior OR posterior division. can be a single-muscle palsy. (IR SP MR IO)
- What is a child with congenital complete ptosis likely to have?
- What is a child with acquire complete ptosis likely to have?
- What is a child with congenital partial ptosis likely to have?
- What is a child with acquired partial ptosis likely to have?
- stimulus deprivation amblyopia and suppression
- no diplopia as ptosis obscures pupil
- strabismic amblyopia, AHP, some BSV
- diplopia
What cover test results can you expect in someone with a 3rd nerve palsy?
- Exotropia (crossed diplopia or suppression)
- Hypotropia
- Intorted
What pupil response will you expect in someone with 3rd nerve palsy?
-dilated, unreactive to light
1.What is pupil sparring?
2.What normally causes complete 3rd CNP with pupil sparring?
- where there is normal pupillary function but complete loss of eyelid and ocular motor functions of the 3rd nerve
- benign and secondary to avascular disease often associated with diabetes, hypertension, hyperlipidemia.
*Usually, 100% recovery within 6 months if avascular aetiology
What will you find on ocular motility with someone who has a 3rd CNP?
limited adduction, elevation and depression
- What causes aberrant regeneration?
- What is aberrant regeneration?
- When does aberrant regeneration not occur?
- most commonly occurs after aneurysm, trauma, tumour (rare), congenital (not common)
*Can primarily occur without any proceeding nerve disfunction - -Due to the miswiring which occurs as the damaged nerve regenerates. Results in bizarre eye movements which improve with time and can’t be corrected by surgery.
-Axons retract when damaged and grow forwards again. They enter the wrong myelin tube to supply inappropriate muscles e.g., IR to LPS - Does not occur in diabetic/hypertensive cases because structural framework of the nerve remains intact.
Why can a HESS chart not always be done for someone with 3rd CNP?
large deviation in pp
px may not be able to fix centrally
What is the onset of aberrant regeneration?
children: 5 weeks after onset of 3rd CNP
adults: 2-3 months after onset of 3rd CNP
What are the signs of aberrant regeneration?
*Elevation of the upper eyelid on attempted down gaze or adduction (pseudo-Von-Graefe phenomenon)
*Adduction of the eye on attempted up gaze
*Pupil constriction on attempted adduction or down gaze
*Retraction of globe on attempted elevation/depression due to Co-contraction of SR/IR
