18 - CN IV and VI

Where is the CN IV (trochlear) nucleus located?

located at midbrain at level of inferior colliculus

What does the CN IV (trochlear) nucleus innervate?

contralateral SO

Where does CN IV (trochlear) exit the brainstem and where does it travel?

exits the midbrain dorsally and wraps around brainstem → travels in cavern sinus and superior orbital fissure

Why is CN IV (trochlear) consider the nerve of trauma?

longest intracranial course and most slender CN

What are the signs of a CN IV (trochlear) palsy?

1. ipsilateral (to nerve) hyperdeviation

2. deviation is worse with contralateral gaze and ipsilateral head tilt

3. may have contralateral head tilt, or may have ipsilateral head tilt (more rare)

4. cannot depress eye, especially if adducted

5. upshoot when adducted

Why does someone with a CN IV (trochlear) palsy have upshoot when adducted?

unopposed IO

Why would a patient with a CN IV (trochlear) palsy have contralateral head tilt?

puts paretic muscle at rest → decreases deviation

Why would a patient with a CN IV (trochlear) palsy have ipsilateral head tilt?

increases diplopia making it easier to suppress

What are the symptoms of a CN IV (trochlear) palsy?

1. vertical or oblique diplopia

2. sensation of torsion → world seems twisted

What are the common causes of a CN IV (trochlear) palsy?

1. congenital

2. head trauma

3. vascular

How should you evaluate a person with a CN IV (trochlear) palsy?

investigate for trauma

look for head tilt in old photos, evaluate vertical vergence ranges, and look for facial asymmetry due to head tilt to see if congenital

look to see if bottom ON is at higher level then midline macula → indicates extortion (normally at midline)

Maddox rod

What should be on your list of differentials fro CN IV palsy?

1. myasthenia gravis

2. partial CN III palsy (inferior division)

3. restrictive ophthalmopathy

4. skew deviation

What causes a skew deviation?

brainstem lesions that disrupt pre-nuclear pathways to CN III + IV nuclei

What are the main signs of a skew deviation that differentiate it from a CN IV palsy?

1. cannot isolate deviation to a single muscle

2. vertical deviation decreases in supine position

3. hypertrophic eye will be intorted

4. will have saccade/pursuit disorders, nystagmus, or other neuro abnormalities

What would be the presentation of a brainstem lesion causing a CN IV palsy?

ataxia or other neurological problems

What would be the presentation of a cavernous sinus lesion causing a CN IV (trochlear) palsy?

CN III, V, VI involvement

Horners

What would be the presentation of an orbital apex/posterior portion of orbit around SOF lesion causing a CN IV (trochlear) palsy?

ON dysfunction + other CN involvement

What would be the presentation of orbital disease causing a CN IV (trochlear) palsy?

proptosis

What is the management of a CN IV (trochlear) palsy if due to trauma?

observe

What is the management of a CN IV (trochlear) palsy if ischemic cause?

observe

MRI if no resolution in >3 months

What characteristics must be met to make a diagnosis of an ischemic CN IV (trochlear) palsy?

1. >50 years old

2. CV risk factors

3. no symptoms of GCA

4. no history of trauma

5. no increase vergence ranges

What is the management for a CN IV (trochlear) palsy that is not congenital, traumatic, and under 50?

MRI

What is the management for a CN IV (trochlear) palsy that is bilateral with no trauma? Why?

MRI

high likelihood of a pineal tumor

Where is the CN VI (abducens) nuclei located?

located at pons at level of facial colliculus

Where does CN VI (abducens) leave the brainstem and travel?

1. leaves brainstem at border of pons + medullary pyramids and travels superiorly

2. makes sharp turn over petrous portion of temporal bone + enters cavernous sinus

What does the CN VI (abducens) nuclei contain?

cell bodies for motor neurons that innervate ipsilateral LR

AND

interneurons that climb MLF to innervate contralateral MR subnucleus

What motor effect does CN VI nucleus have?

ipsilateral abduction and contralateral adduction

What is the most common EOM palsy?

CN VI

What are the symptoms of a CN VI (abducens) palsy?

diplopia that worsens on ipsilateral gaze and at distance

What are the signs of a CN VI (abducens) palsy?

1. esotropia in primary gaze that worsens when deviated eye is fixating

2. ipsilateral head turn

3. abduction deficit

What are the causes of a CN VI (abducens) palsy?

1. tumor

2. infarction of nerve trunk

3. trauma

4. MS

5. GCA

6. elevated intracranial pressure

7. infection

When is a CN VI (abducens) suggestive of a tumor being the cause?

if diplopia is slowly progressive and does not resolve over months

what is ischemic CN VI palsy typically associated with?

1. HTN

2. DM

What is the time course of an ischemic CN VI (abducens) palsy?

resolved in 3-6 months

What are the differentials for a CN VI (abducens) palsy?

1. TED

2. myasthenia graves

3. MR restriction

4. congenital Duane's

5. spasm of near reflex (if bilateral palsy)

How do you differentiate between a bilateral CN VI (abducens) palsy and a spasm of the near reflex?

pupils will be constricted if spasm of near reflex

What is Duane's retraction syndrome?

congenital CN VI dysfunction

What does Duane's retraction syndrome cause in all types?

co-contraction of ipsilateral medial and lateral rectus causing retraction on adduction

What are the different types of Duane's retraction syndrome and what are there presentations?

Type 1: impaired abduction, normal adduction

Type 2: normal abduction, impaired adduction

Type 3: impaired abduction + adduction

What is Foville Syndrome? What does its cause?

lesion at dorsal pons

causes ipsilateral CN VI palsy + CN VII palsy with contralateral hemiparesis + hemisensory loss

What is Millard-Gubler syndrome? What does it cause?

lesion at inferior medial pons

causes ipsilateral CN VI palsy (+ possibly CN VII) and contralateral hemiplegia

What is Moebius syndrome?

complete bilateral paralysis of CN VI and VII

Who gets Moebius syndrome?

kids

What is the presentation of Möbius syndrome?

1. strabismus

2. deafness

3. mask-like faces due to diplegia (i.e. face doesn't move a lot)

4. multiple systemic problems

What is the management of CN VI palsy in adults 15-50 years old?

refer for MRI → if normal, refer for neuro exam

consider lumbar puncture

if all normal → monitor 6 weeks, if worsening, re-eval

if no recovery in 6 months → re-eval

What is the management of CN VI palsy in a adults >50 years that meet ischemic cause criteria?

refer for full medical exam

if no recovery in 3 months → refer for MRI

What is the management of CN VI palsy in children (<15 years)?

consider Duanes or Moebius, exclude trauma

if none of above → refer for MRI

What is the management of a bilateral CN VI palsy with no trauma?

refer for MRI + LP

*should NOT be considered ischemic

What is the treatment for diplopia in a CN VI palsy?

1. MR botox

2. prism

3. surgery