CN IV Palsy Flashcards
What are the primary, secondary and tertiary actions of the superior oblique muscle?
Innervated by CN IV
- primary: intorsion
- Secondary: depression
- Tertiary: abduction
3 unique characteristics of CN IV
- longest intracranial course
- thinnest nerve (in terms of number of fibers)
- Only CN that decussates and exits at the dorsal aspect of the brainstem
Normally, when the head tilt, the eye on top extorts/intorts and the eye on the bottom extorts/intorts
top eye extorts; bottom eye intorts
extort: IO and IR laterally rotate away from note
intort: SO and SR laterally rotate toward nose
In a LEFT CN IV palsy, there will a be a RIGHT hyper/hypo tropia and extorsion/intorsion in primary gaze
hypertropia; extorsion
Vertical diplopia with a CN IV palsy is greater at near/distance
near
Because objects will appear tilted to someone with a CN IV palsy, they will develop a compensatory head tilt toward/ away from the affected side
away
Right CN IV palsy develops head tilt to the left
CN IV: TILT AWAY to relieve torsional diplopia
Park’s 3-Step test is useful to detect what?
A single paretic vertical muscle
SO
How is Park’s 3-Step done?
Perform ACT is primary gaze, right and left gaze, and with head tilted right and left
detects small deviations, tests for comitancy and quantifies devation
A patient with a RIGHT CN IV palsy will have hypertropia worse in which gaze/ head tilt?
Left gaze; right head tilt
What is a subjective measurement of the angle of excyclotorsion?
Bilateral Maddox Rod
What is an objective way to measure the angle of excyclotorsion?
Fundus photos
Normal Fundus: fovea slightly lower than optic disc; excyclotorsion: fovea will present as markedly lower
What does it mean if the objective measurement of the angle of excyclotorsion equals the subjective measurement?
Recent onset SO palsy
What does it mean if the objective measurement of the angle of excyclotorsion is greater than subjective?
Longstanding SO palsy
What will subjective and objective testing look like when the SO palsy is congenital?
Will only notice the objective measurement; patient will not report anything for subjective
3 most common etiologies of CN IV palsy?
congenital, traumatic, ischemic
3 causes of congenital CN IV Palsy?
- hypoplasia of trochlear nucleus
- anaomalies of the SO muscle
- Birth Trauma
What physical characteristics might someone with congenital CN IV palsy present with?
mild facial symmetry; long-standing head tilt
Vertical vergence ranges are small/ large in congenital CN IV Palsy
Large
10-15 PD
Why is CN IV vulnerable to trauma?
long course and surrounding structures
What can happen to CN IV at the free tentorial edge
compression
What can happen to CN IV at the ambient cistern?
Subarachnoid hemorrhage
What is the laterality of traumatic CN IV palsy?
unilateral or bilateral
What is the prognosis for traumatic CN IV palsy?
partial or complete resolution
What systemic diseases are often see with ischemic CN IV Palsy?
microvascular disease
HTN, DM, atherosclerosis, smoking
What is the onset of diplopia associated with ischemic CN IV Palsy?
Acute
no other CN involvement, neurologic signs or symptoms
What are the fusional ranges associated with ischemic CN IV Palsy?
Normal
How long does it take for ischemic CN IV Palsy to resolve?
3-4 months
What are the 5 syndromes of CN IV Palsies?
- Nuclear-fascicle syndrome
- subarachnoid space
- cavernous sinus syndrome
- orbital syndrome
- isolated CN IV palsy: acquired and congenital
What neurologic signs are associated with Nuclear-Fascicular CN IV palsy?
there are none
Is the CN IV palsy ipsilateral or contralateral to the lesion in nuclear-fascicular CN IV Palsy?
contralateral
fasicicles from nucleus decussate to innervate contralateral SO
Does Horner’s syndrome occur ipsilateral or contralateral to the lesion in nuclear-fascicular CN IV Palsy?
Ipsilateral
oculosympathetic pathways descend through the dorsolateral tegmentum of the midbrain adjacent to the trochlear fascicles
What is the most common cause for the bilateral CN IV palsy that occurs within the subarachnoid space?
Trauma
contracoup forces by the tentorial edge injur the nerves at this site
less frequent causes: subarachnoid hemorrhage, tumor and meningitis
Trauma is the most common cause of CN IV palsy in adults
If someone presents with bilateral CN IV Palsy, what else should we look for?
Dorsal Midbrain syndrome
What is the clinical picture of subarachnoid CN IV palsy?
- LND pupils
- Collier’s lid tuck in upgaze (lid retraction with limited upgaze)
- LHyper greater in left head tiltand right gaze
- RHyper greater in right head tilt and left gaze
- > 10 degrees of excyclotorsion
When is observation only acceptable in CN IV palsy?
unilateral cases: with established history of trauma or with increased vertical vergences
When does isolated, unilateral palsy withOUT trauma need to be worked up?
When there are no obvious microvascular ischemic or other risk factors
Work up: BP, Glucose tolerance test, CBC with diff, ESR/ CRP, RPR, FTA-Ab, ANA
When is neuroimaging ordered in CN IV Palsy in adults?
- bilateral
- evidence of dorsal midbrain syndrome
- involvement of other crainial nerves
- ischemic palsy suspected, but not resolving in 3-4 months
What is the most common cause of CN IV Palsy in Children?
Congenital
When are children with CN IV palsy observed only?
No workup ordered
- Unilateral with established history of trauma
- Unilateral with increased vertical vergences
When is neuroimaging ordered for children with CN IV palsy?
- bilateral
- evidence of dorsal midbrain syndrome
- other cranial nerves involved
When should caution be used with monocular occlusion as a management option for CN IV Palsy?
Children- may develop amblyopia
How can prism be used to manage CN IV palsy?
BD over the hyper (paretic) eye; can split prism between the two eyes
BD over hyper eye; BU over fellow eye
Which type of CN IV Palsy would benefit the most from surgery?
traumatic
Wait at least 6 months for spontaneous improvement
allow time to see if blood/ edema will clear; relieve symptoms with occlusion therapy or prism in meantime
